TEXAS AGRICULTURAL EXPERIMENT STATION A. B. CONNER, Director College Station, Texas BULLETIN NO. 648 APRIL, 1944 CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST E. W. LYLE Division of Plant Pathology and Physiology - l»? iwas fiollegeStajjan, iexas ‘v ' AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS F. C. BOLTON, Acting President D-16-444-4M Fig. 1; Rose plants from commercial fields. ture; nondusted plant on right. On left, plant dusted with sulphnr-copper ~ w‘ Note the larger plant and more abundant foliage l ‘- a result of controllingthe black-spot disease. n’. .. . .-¢>@:4_J‘Q~@ ‘d..- . .._..~----~_- Premature defoliation of field-grown rose plants by the black- spot disease has been a major problem with commercial rose growers in East Texas. This loss of foliage has resulted in weak- ened bushes, die-back, low-grade market stock and poor growth or survival of the plants following transplanting. After several years of research on this disease, an effective sulphur-copper dust treatment has been developed at Substation No. 2, Tyler. In these experiments, the- most effective dusts have contained about 90 percent of an unconditioned 325-mesh sulphur and about l0 percent of an insoluble copper compound. Satis- factory control of black spot was obtained when the dust appli- cations were started at the first symptoms of the disease and continued at weekly intervals until July after which bi-weekly- dustings were made. From 1'5 to 25 pounds of dust per acre at each application has been found the most practical dosage. The use of this dust in the manner described has resulted in successful control of black spot, maintenance of abundant foliage on the plants throughout the growing season, and high quality plants that live and grow well following transplanting, shipment, or storage. CONTENTS Page Introduction ............................................................................................................... .. 5 Materials and Methods .......................................................................................... .. 8 Field Experiments with Sulphur-Copper Fungicides ...................................... .. 9 Comparison of a spray and dust treatment .............................................. .. 9 Sulphur-copper-lead arsenate dust compared With plain sulphur ........ ._ 9 Comparison of sulphur-copper-lead arsenate dust with sulphur-copper dust. ................................................................................ ..10 Tests of different proportions of sulphur and copper ......... ..' ............... ..10 Tests With conditioned and unconditioned sulphur, sticking agents, and various copper compounds ............................................. _.11 Comparisons of different grades of 325-mesh sulphur and various copper compounds ............................................................ ..13 Methods of Applying Dust Fungicides ............................................................... ..16 Dusting of plants from above as compared with dusting from below .................................................................................. ..16 Effects of varying the rate of dust application ...................................... ..16 Time, frequency, and amount of dust application .................................. ._18- Factors affecting primary infections and the need for beginning dust treatments .................................................................... ..21 Computed Profit from Dusting ............... ......... .. .. .................. ....................... ..23 Effects of Dust on the Soil .................................................................................. ..24 Recommendations ..................................................................................................... ..25 Summary .......................................................................... ....................................... .25 , Literature Cited ....................................................................................................... ..27 CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST‘ E. W. Lyle,’ Plant Pathologist Black spot is a fungous disease of the rose plant that attacks the leaves during rainy, humid weather (5). It is caused by the fungus, Diplocarpovz rosae. As the name of the disease implies, somewhat circular, black-colored spots (fig. 2) are formed usually on the upper leaf surface causing the leaf to become yellowish. Affected leaves usually are shed from the plant (fig. 1). This loss of foliage deprives the plant of much of its needed food materials that are synthesized in the leaves, resulting in the development of weak plants. Consequently, the younger twigs and terminal branches are unable to carry on their normal functions and a condition known as die-back (fig. 3) also occurs (10). Black-spot infec- tions are often found on the stems of rose plants and these cane lesions are believed (9) to be responsible for much of the carry-over of the fungus through the winter. Rose varieties show marked variations in resistance to black spot. Some hybrid tea roses such as Caledonia, Dame Edith Helen, Julien Potin, and others are very susceptible while varieties such as Radiance, Etoile de Hollande, and Edith Nellie Perkins are somewhat resistant. Most of the popular commercial varieties are sufficiently susceptible to black spot to require fungicidal treatments during the growing season, especial- ly when rains are likely to occur. The suggested use of spray materials to control black spot of roses probably began about 1888 when Scribner (15) recommended applications of Bordeaux mixture. Among the later more extensive experiments with fungicides to control this disease, were those under the direction of Massey at Cornell University in cooperation with the American Rose Society, con- ducted during the years 1929-1932. The conclusions of those investigations presented by Parsons and Massey (13) were that dusting was superior to spraying and that a mixture of dusting sulphur and lead arsenate was preferred to other fungicides tried. Early experiments in Texas on the control of black spot included spraying tests, especially with Bordeaux mixture (3), as well as dusting. Later, the spraying work was discon- tinued owing to the difficulties of hauling heavy sprayers through the light sandy soil, inadequate water supply near the fields, and the necessity of applying a fungicide quickly to extensive areas in critical periods. Good control of black spot was obtained experimentally by Boyd and Taubenhaus (3) as early as 1935 with a dust mixture of 10 parts sulphur, 1 part monohydrated copper sulphate, and 1 part Paris green. In 1936, it was reported (2) that sulphur used in combination with various insoluble copper compounds, or Bordeaux mixture plus wettable sulphur also gave good control of black spot in the field. At the same time, a combination lAcknowledgment is made of the cooperation of the Freeport Sulphur Company, the Texas Gulf Sulphur Company in this work and the rose growers in whose fields the investigations were conducted. iFoi-merly at Substation No. 2, Tyler; now at Substation No. 5, Temple, Texas. 6 BULLETIN ‘NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION of wettable sulphur and Cuprocide inhibited the germination of Diplo-c carpon spores, when used in suspension on glass slides in the laboratory, to a greater extent than either of the two materials used alone ( 1). Under conditions in Texas from the 1935 experiments up to the present time, the a a research data have shown a marked difference in favor of the mixture con- taining sulphur and a small amount of an insoluble copper fungicide. Em- phasis has been placed on such mixtures in these black-spot control ex- periments. Although mixtures of sulphur and copper constitute relatively newi i fungicidal materials, combinations of these substances have been used suc- cessfully in controlling plant diseases during the past ten years. As a g spray, Bordeaux mixture with wettable sulphur added was found effective I r .. 1;; eve-J‘, ‘i? "S? W Fig. 2. Black-spot lesions on rose leaflets. for Dothiorella rot of avocado in California (4), fig rust in Texas (14), and for early blight of celery in Florida (17). Used as dusts, sulphur-cop- per mixtures were reported to give practical and economical control of Cercospora leaf spot of peanuts in North Carolina (16). In Michigan (12), Cuprocide-sulphur-talc mixtures are reported to have given “superior con- trol” of early and late blights of celery. Preliminary reports of the effec- tiveness of sulphur-copper fungicides for controlling black spot of roses in Texas were published in 1939 (6), 1941 (7), and in 1942 (8). More re-l cently, those same materials have shown up well in tests on black-spot control in New York (11). 1 ’ x . S CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 7 Fig. 3. Die-back of rose stem on right; healthy stem on left. Defoliation of rose plants by lts in increased amounts of die-back, although the black-spot fungus black spot resu is not directly responsible for the dying-back of the stems. 8 BULLETIN NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION MATERIALS AND METHODS Many of the exper iments at Tyler were conducted in commercial rose fields while certain phases of the work that demanded closest attention . Care and management of the were conducted at the Experiment Station rose bushes in these nurseries were under the direction of the grower and were normal in all respects except for the dust treatments wh ich were ap- ing new fields, lv plied by the Station workers. Different experiments invo .w.00050050m00 .50 0505500005505 .0000 .00 00000050500 w000000mz0 50.0 000005050 m0 50000000500045 0.0000 .0505000M r5500 .50000|>0.50m 00000 0M .000Q0000000M :00 000M 0 500M .5508 .0000.505500 :00 505500 000005509. 550E .0000.505500 :00 000000 000005590. 0050M. 50005000 ..00 .5000 50005005 .02 6.05010 0m :00 0000000 0 0004. 5500050m 0000M. 5355M ..00 .5000 50.005050. 0050B .500m500.~. :00 .5000 50005005 .0 .70 .5300w0.5000>0 :00 05000000500 00005050090 5050000000 .0500000.>0 r00 .5000 30M 0050M. .500w50M :00 .5000 50w050uw .0. .2 0005M 0550M :00 .5000 5050000 NW .Z 60.50% 30Z...00 .5000 00.50500 .5 .2 c0505 3070 :00 000050050> .5. 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CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 9 different varieties and usually were conducted each year. In many cases the Caledonia variety was used because of its high degree of susceptibility to black spot. The location of the experiment, size of plots, and such other variables as types of dusts g used (table 1) and number of applications made are given separately in the presentation of work year by year. The number of replications de- pended on the size of the field and the number of bushes of a selected variety available. The various sulphur-copper mixtures were prepared at first through the cooperation of manufacturers of fungicides; later they were made at the Station with a Messinger dust mixer and hammermill. During 1941 and 1942 one commercially prepared dust was also used. In the early experiments on a small scale, the fungicidal dusts were applied Later a Root Model C2 “Challenge” hand-crank, rotary duster was used in large plots. Accu- rate records of the actual amounts of dust applied were kept by weighing the duster and fungicide before and after each treatment. In some cases the dust applications were made at definite, regular intervals. In other cases the applications were made with reference to local rainfall condi- tions, since infection was known to occur during wet weather (5). Counts of black-spot infection on individual leaflets were made in the field during the growing season. Final data as to the effectiveness of the treatments consisted of the weights of the bushes at digging time, usually in Decem- ber. FIELD EXPERIMENTS WITH SULPHUR-COPPER FUNGICIDES Comparison of a Spray and Dust Treatment Previous laboratory and field tests led in 1937 to field trials of a dust mixture containing sulphur, Cuprocide, and lead arsenate, and of a spray‘ material composed of Bordeaux and wettable sulphur. Both of these mix- tures were effective in reducing black spot and die-back. However, there was a slight burning of the foliage with both materials. Sulphur-Copper-Lead Arsenate Dust Compared with Plain‘ Sulphur In 1938, the sulphur-Cuprocide-lead arsenate mixture was compared with plain 325-mesh dusting sulphur on roses, variety Luxembourg, and was found to give better control of black spot and heavier bushes than plain sulphur. At three locations, the plants dusted with sulphur-Cupro- cide-lead arsenate outweighed those dusted with plain sulphur by 31, 21, and 6 percent. There was slight burning of the foliage from both treat- ments and it was suspected that lead arsenate was unnecessary for roses under these conditions. Although early in November the differences in amount of black spot were only 1, 2, and 3 percent less with the sulphur- Cuprocide-lead arsenate combination than with sulphur dust alone, the dif- ferences in black spot had been greater earlier in the season. Consequent- ly, the weight of bushes at the end of the season was considered the best measure of the accumulative effect in controlling the black-spot disease. somewhat different fungicidal materials‘ 10 BULLETIN NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION Comparison 0f Sulphur-Copper-Lead Arsenate Dust with Sulphur-Copper Dust In 1939 the fungicides tested included sulphur-Cuprocide (10:1) as? well as sulphur-Cuprocide-lead arsenate (10:1:1). In addition to the Cu-gi procide mixtures just named, mixtures of sulphur and “34” Copper Fungi- cide with and without the lead arsenate were also tried. These‘ were com- pared with six different brands of dusting sulphur. During this season“ the sulphur-copper and sulphur-copper-lead arsenate mixtures, in general, i A, 0 1 LAAHQQ ..._'.¢..2_;. J'_L2..//.(1AJL‘L4A¢. gave better control of black spot and larger bushes than dusting sulphur ‘- alone. Sulphur-copper mixtures Without the lead arsenate were practically as good as those with lead arsenate and the “34” Copper Fungicide ap- . peared to be as suitable and effective as the Cuprocide. The weather in 1939 was unfavorable for black-spot infection and only slight differences a were obtained in favor of the dusted plants. ‘Tests of Different Proportions of Sulphur and Copper The 1940 season was wetter than usual and an abnormal amount of black spot occurred. Various proportions of sulphur and copper materials were included in the field tests (table 2) at M. Balch’s Nursery, fourteen applications of the fungicides were made from May 8- to September 11, using a 2-quart plunger-type hand duster. There were 60 plants in each plot (3 rows wide by 20 plants long) and 4 plots of the same treatment were replicated systematically in each field. Data were taken from 10 consecutive plants located in the center row of each plot. Swan Brand sulphur was used and the treatments were begun only after black spot was seen in the field. Applications of fungicides were made at weekly in- tervals until July 1 and every two weeks thereafter until near the end of the growing season. (This schedule of applications was followed in subse- quent tests unless otherwise specified). As may be seen in table 2, the sulphur-copper mixtures were again superior to plain sulphur and the effectiveness of the mixtures tended t0 Table 2. Effects of dusting roses (var. Luxembourg) with various fungicidal materials in 1940; average of 4 replications. Leaflets with Wt. of 10 Increase . black spot bushes in weight Fungicide?‘ Oct. 22 Dec. 20 over check percent lb. percent None (check) 36.4 2.2 0 Sulphur:Cuprocide GA (99:1) 29.9 2.8 27 ” ” ” (96:41) 21.6 3.0 36 ” ” " (94 :6) 24.2 3.1 41 " " " (90 =10) 19.0 v 4.0 s2 Sulphur:“34” Copper Fungicide (99 :1) 22.9 3.0 36 " ” ” " (96 :4) 27.2 3.0 36 " " " " (90 =10) 24.6 3.6 e4 " " " " (85:15) 18.1 3.3 50 Sulphur :Grasse1li IN (90 :10) 27.4 3.7 68 Sulphur zBasi-Gop (90:10) 25.8 3.2 45 Sulphur 32.9 2.8 27 Sulphur zKMnOfi (97 :3) 24-8 3-0 36 C1ay:KMnO42:wheat flour (89:3:8) 28.7 2-1 -5 1A conditioned 325-mesh sulphur was used in each sulphur-containing dust. 2Potassium permanganate (200-mesh). O CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 11 increase in proportion to the concentration of copper. The dusts contain- ing the highest proportions of copper, in case of both Cuprocide and “34” Copper Fungicide, showed indications of injury to the leaves during mid- season so that the optimum concentration of the copper compound for field use was considered as 6 percent for Cuprocide and 10 percent for “34” Copper Fungicide. The other copper materials tested also appeared favor- able in mixtures with sulphur. Tests with Conditioned and Unconditioned Sulphur, Sticking Agents, and Various Copper Compounds Many brands of dusting sulphur are conditioned with a small per- centage of a material such as clay, magnesium carbonate, or tricalcium phosphate to make the sulphur flow more readily. Wet weather conditions in 1941 again favored black-spot development. In some cases, small plots, 3 rows wide by 3O feet long (table 3), were used to compare a wide va- riety of copper fungicides mixed with sulphur, in both conditioned and un- conditioned forms. These dusts were applied with the 2-quart plunger- type dusters. Black-spot leaf counts were made in October and weights of bushes were recorded at digging time in December. The results showed that several different materials could be used safely with sulphur as dust fungicides for roses. Little or no injury was apparent from any of the Table 3. Control of rose black spot with fungicidal dustsl as shown by leaflet infection and weight of bushes at harvest—Luxembourg variety—1941. Leaflets Condition with Wt. of black per 10 Fungicide dust spot bushes Sept. 17 Dec. 9 percent lb. Balch’s Nursery None (check) — 23 3.5 Sulphur:“34” Copper Fungicidezbentonite (80:10:10) Satisfactory 14 4.0 Sulphur:Tri-Basic Copper Sulphate (93.6:6.4) ” 16 4.0 Sulphur:“34” Copper Fungicide:flour (80:10:10) ” 18 3.8 SulphurzCuprocide (94:16) Became lumpy 8 3.7 SulphuxwGrasselli IN (90:10) satiSfflfimfy 17 3.6 Sulphur:Basi-Cop (90:10) Cltlgged duster 12 3.6 Sulphur:“34" Copper Fungicide (90:10) Satisfactory 11 3.5 Sulphur:Copper oxychloride sulphate (90:10) " 13 3.5 SulphurzSprayCop (90:10) ': 15 3-5 2Sulphur:“34" Copper Fungicide (90:10) ’ 13 3.4 SulphurzCuprocidezbentonite (84:6:l0) Became lumpy 9 3-3 zSulphurzCuprocide (94z6) Satisfacwry 15 3-0 SulphurzCupro-K (90:10) i’ 11 2-8 Pyrax:Cuprocide (9416) Drlfted 16 2-3 Ginn’s Nursery None (check) —- 28 2.8 SulphumZinc Coposilrbentonite (80:10:10) Satisfactory 21 3.2 p SulphurzDow Copper (90:10) ” 18 2.9 3SulphurzCopper Hydro 40 zbentonite (80:10:10) ” 19 2.9 Pyrax:Copper Hydro 40 :bentonite (80:10:10) Light, drifted 24 2.9 zsulphur Satisfactory 26 2.7 2Sulphurzbentonite (90:10) ” 20 2-5 lEleven applications were made from May 22 to Aug. 28. There were between 60 to 100 bushes per plot (3 rows wide and 30 feet long), and 6 plots of the same treatment were replicated in each field. Data were taken from 5 consecutive plants in the middle row of each plot for black-spot counts and from 10 plants for weights. 2Swan Brand (conditioned) sulphur; all other mixtures made with Owl Brand (uncondi- tioned). “Chipman Brand sulphur. 12 BULLETIN NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION fungicides during this season. In most cases an unconditioned 325-m sulphur (Owl Brand) was found as suitable for the sulphur-copper u .1 tures as the conditioned 325-mesh sulphur (Swan Brand). The benefit- bentonite and flour as sticking agents was questionable. Failure to a) good control of black spot was due to the infrequency of dust applicati" during the latter part of the season (bi-weekly treatment) when an a usually heavy amount of rainfall occurred. ’ Better results were obtained (table 4) from larger sized plots, 7 r0 wide and 272/3 or 55% feet long and where a rotary duster was used stead of the small plunger-type duster. These tests were devised mainly ( . ._». . e .~ _,_ ;.».;_. g- V Fig. 4. Control of black spot on the Caledonia variety in the field by us ing -wit su pa l copper fungicides. A, Bushes dusted after each rain; B, Dusted once a week; C, NI- dust applied; D, Field showing dusted areas at each end and a nondusted plot in the center. determine whether or not unconditioned sulphur would react as well as conditioned sulphur in the sulphur-basic copper sulphate mixture. Condi-i tioners serve to prevent lumping and to facilitate application with Inc-g chanical dusters, however, with copper materials added to the sulphur, it was thought the usual conditioner might be unnecessary. Another purpose was to test bentonite as a sticking agent in the sulphur-copper dust. The!‘ basic-copper-sulphate (“34” Copper Fungicide) was selected in preference to cuprous oxide (Cuprocide) because of its lower cost and because only questionable differences had occurred in the results comparing the two materials. Dusts were applied with rotary hand dusters in these tests. As usual, fungicidal treatments were withheld until black spot appeared, con- tinued regularly each week until July 1, and thereafter only once in two CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 13 weeks until near the end of the growing season. The weights of fungicidal materials used were calculated from those actually applied. An effort was made to apply the same amount of each of the different materials, how- ever, with differences in flowability through the dust gun, this was diffi- cult to accomplish. _ The data on the weights of bushes at harvest time show quite con- clusively the benefits from use of the sulphur-copper dust. There seemed to be no advantage in using a previously-conditioned sulphur in the mix- ture. Also the addition of bentonite to the fungicide as a sticking agent was not beneficial. The superiority of the sulphur-copper dust in com- parison with plain dusting sulphur was again demonstrated in 1941. Comparisons of Different Grades of 325-Mesh Sulphur and Various Copper Compounds The 1942 season also was favorable for the occurrence and spread of the black-spot disease. Benefits from use of fungicides similar to those in previous seasons were again obtained in most of the experiments. This year all dust materials were applied with rotary hand dusters. A comparison was made of the effects of two grades of 325-mesh sulphur in mixture with basic copper sulphate. One sulphur was ground to such fineness that at least 93 percent of the particles would pass through a sieve having 325 'ble 4. Comparison of sulphur and sulphur-copper mixtures for the control of black spot on several vari- eties of roses as shown by weight of bushes at harvest, 1941. Av. wt., pounds per 10 bushes. Unconditioned Conditioned Unconditioned ' Sulphl}? sulphur:“34” sulphur:“34” sulphur:“34” Location and variety Check Qwmi" Copper Fungi- Copper Fun- Copper Fungi- twneil) cide zbentonite gicide cide (50:10:10) (90:10) (90:10) Zorn Nursery1 alisman? 4.’) ".1 6.2 5.6 6.9 toile de Hollande 3.7 1.6 4.5 4.4 5.0 lumbia 4.1 4.0 4.4 5.1 5.5 . G. Hill 4.1 4.8 4.5 5.3 5.2 me. Edouard Her-riot . 3.5 3-9 4-4 4-5 5-0 resident Hoover: 4.7 5.8 6.5 6.0 7.0 v. increase over check~percent » ~ ~ 1'7 27 23 44 Whiteside Nursery‘ inrich Gaede ‘3-1 3-4 3-0 rs. Pierre S. du Pont 1-5 2-1 1-9 aledoniaz 1.6 2.7 2.1 aligman 3.5 4.6 5.3 toile de Hollande 3-2 4-3 5-6 v. increase over check-—percent —- 44 50 ounds of ) ust per Zorn’s 0 19.9 19.4 15.9 16.9 ere per ‘ pplica- ) Whiteside’s 0 26.4 22.7 ion 1In the Zorn Nursery the plots were 7 rows wide (1 row per variety except as noted) and 55% ft. long (0.04 acres, approximately 400 bushes per plot) and 3 plots of the same treatment (12 applications) per replication. In the Whiteside Nursery the plots were 7 rows wide (1 row per variety except as noted) and 27% ft. long (0.02 acres, approximately 200 bushes per plot) and 4 plots of the same treatment (14 applications) per replication. Data were taken from only 5 of the 7 rows, leaving two outside guard rows. 2Average from 2 rows of this variety. 14 BULLETIN NO. 64s, TEXAS AGRICULTURAL EXPERIMENT STATION meshes to the linear inch. The other was of such fineness that at least 98 percent of the particles would pass through a similar sieve. Both were unconditioned grades of sulphur (Owl Brand) and the latter (98 percent) was the same type as used in the 1941 experiments. As in previous years, dusting was withheld until black spot was observed and the applications were made at weekly intervals until July 1; thereafter applications were made every two weeks until the end of September. Other comparisons again were made of different copper materials in mixtures with the sulphur. In these tests, plots were two hundredths of an acre in size (7 rows wide by 27% feet long) with 150 to 200 bushes per plot. Data were taken from centrally located bushes in each plot. The results (table 5) showed only slight and probably insignificant differences between the two grades of sulphur in mixture with “34” Copper Fungicide. The cheaper grade (93 percent 325-mesh) was almost as good as the more expensive grade (98 percent 325-mesh). Among the different copper compounds, Copper Hydro 40, Dow copper, and Cupro-K provided the best black-spot control in that order and all of these were equal to or better than “34” Copper Fungicide. The cost of these materials would be the most important factor in choosing a copper fungicide for field utilization in a mixture with sulphur. Table 5. Results of various fungicidal dust treatments in 1942 for the control of rose black spot. Lbs. per Leaflets Wt. of Increase acre per with black 10 in wt. over Fungicide applica- spot bushes check tion percent lb. percent I Atkins’ Nurseryl I None (check) 0.0 I 48 2.3 —_ Sulphur (98% 325-mesh): Dow Copper (90 :10) . . .2 . . . . . . . . . . . . . . . . . . . . . . . . . 23.7 27 3.2 39 Sulphur (9870 325-mesh): “34" Copper Fungicide (90 :10) . . . . . . . . . . . . . . . . . . .. 26.1 21 3.1 35 Sulphur (93% 325-mesh): “34" Copper Fungicide (90:10) . . . . . . . . . . . . . . . . . .. 29.3 30 3.0 30 SulphurfiYellow Cuprocide (96:4) . . . . . . . . . . . . .. 26.7 23 2.8 22 Talc:“34” Copper Fungicide (90:10) . . . . . . . . . .. 21.9 I 35 2.5 9 Green's Nursery? I None (check) 0.0 I 19 4.8 — Sulphur (98% 325-mesh) :Copper I Hydro 40 (90:10) . . . . . . . . . . . . . . . . . . . . . . . . . .. 27.1 I 15 7.0 46 Sulphur (98% 325-mesh) :Cupro-K (90 :10) . . . .. 21.2 I 18 5.7 19 Sulphur (98% 325-mesh) :“34" Copper I Fungicide (90:10) . . . . . . . . . . . . . . . . . . . . . . . . . .. 24.0 ‘I 10 5.6 17 Wiley’s Nursery3 I None (check) 0.0 I 36 2.3 —— Sulphur (98% 325-mesh) :“34” I Copper Fungicide (90:10) . . . . . . . . . . . . . . . . . .. 30.0 I 23 2.8 22 Sulphur‘ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33.8 24 2.7 17 Sulphur:Copper (90:10)—General Chem. Co.... 33.1 I 21 I 2.4 4 Sulphur (98% 325-mesh) :Zinc Coposil (90:10).. 31.4 I 44 2.4 4 ‘Francis Scott Key variety, 15 applications (May 6-Sept. 23). Leaf counts were made Sept. 24. Bushes were weighed Dec. 1, 1942. Averages of five replications are given. zTalisman variety, 9 applications (June 7-Sept. 23). Leaf counts were made Sept. 25. Bushes were weighed Dec. 8, 1942. Averages of four replications are given . “Kaiserin Auguste Viktoria variety, 12 applications (May 27-Sept. 23). Leaf counts were made Oct. 1, 1942. Bushes were weighed Jan. 12, 1943. Averages of four replications are given. The sandy field, excessive pruning back of the young plants, and the variety used account for the small size of the bushes in this test. ‘Swan Brand sulphur; all other sulphur mentioned in this table was Owl Brand, with the exception of General Chemical Company's sulphur-copper dust. l CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 15 Another experiment in 1942 tested the effect of adding cotton seed oil (2 percent of the dust by weight) as a sticking agent in the sulphur- copper dust. An estimate of the amount of black spot on September 23 was less than 0.1 percent of the leaflets affected. However, on the basis of weight and grade of bushes, those dusted with the plain sulphur-copper mixture were somewhat better than those which received ‘the mixture plus the oil. Although no injury from the oil was apparent on the bushes, the oil interfered with the dusting process and made application of the dust more difficult. Fig. 5. Different metnous ot applying sulp ur-copper dust in tli‘ ield. Above, a rotary crank duster used in much of the experimental work. Below, a tractor-operated power duster commonly used in commercial rose fields. 16 BULLETIN NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION METHODS OF APPLYING DUST FUNGICIDES Dusting of Plants from Above as Compared with Dusting from Below ‘ An experiment was conducted with field-grown roses in 1938 in which) weekly applications of two fungicides were made with a Niagara plungeté. type 2-quart hand duster. In certain plots the nozzle of the duster Wallfi adjusted to project the dust upward underneath the foliage. In other cast the dust was forced down onto the upper surfaces of the leaves. The fungicides used were plain 325-mesh dusting sulphur (Swan Brand) and a; mixture of sulphur, Cuprocide, and lead arsenate (10:1:l). Single row plotsli with 15 plants per plot were utilized with untreated rows on each side o the test row and with 10 untreated plants between plots within the row‘? Treatments were begun April 20 and continued until October 26, making total of 28 applications. An average of 14 pounds of fungicide per acrd was applied at each dusting. Data were taken from 10 plants centrall. located in each plot (table 6). The results show that directing the dust downward was usually more effective than trying to direct it upward onto; the foliage. ' Effects of Varying the Rate of Dust Application In 1941 an experiment was conducted in W. B. McGinneysfIeld compare the effects of applying different quantities of fungicide on field- grown roses. The plots were 7 rows wide by 27% feet long (0.02 acres or 150 to 200 bushes each). The dust mixture used contained 90 parts Ow Brand sulphur and l0 parts “34” Copper Fungicide (90:10). This was ap-r Table 6. Control of rose black spot by dusting plants from above compared with forcing the} dust upwards from below, 1938. Direction of Leaflets with black Wt. of 10 l Treatment dusting spot Nov. 1-10 bushes percent lb. Pittnazln Field’ var. Luxembourg 1 (4 replications) __ None (check) W l2 as Sulphur Upward (3 5.9 i " Downward 6 4.0 2;; None (check) —~ 16 2.8 ~ S-C-LA‘ Upward 4 4.2 q i} " Downward 3 4.4 . - ' c‘. Shamburgei" Field—var. Luxembourg , £31,’; (3 replications) _ None (check) —— 25 4.5 Sulphur Upward 5 4.6 flip ” ‘ Downward 5 5.6 a None (check) -— 23 4.4 i S-C-LA1 Upward 5 5.5 . ” Downward 6 4.8 McGinney Field——var. Dame Edith Helen (4 replications) None (check) —— 24 3.3 Sulphur Upward 9 3.0 ” Downward 2.9 None (check) ~ —- 17 3.2 S-C-LA1 Upward '7 3-8 " Downward 8 5.5 A; lSulphumCuprocidezlead arsenate (10 :1 :1). CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 1'7 plied to the Mrs. Erskine Pembroke Thom variety at three rates of appli- cation averaging 13, 28, and 46 pounds per acre for each application. As in most other tests, treatments were withheld "until black spot was ob- served. They were made at weekly intervals until July 1, and once every two weeks thereafter until October 1. A total of 9 applications were made between June 19 and October 1. The results (table 7) show that larger bushes were obtained with the heavier applications of fungicides. Although foliage injury was anticipated from the heaviest applications, the season was such that no burnnig was Table 7. Effect of different amounts of sulphur-copper dust per appli- cation on the control of rose black spot, as shown by amount of foliage and weight of bushes, 1941. Av. of 5 replications. Amount of Number of Wt. of 10 Incr. in dust per leaflets per plants, wt. over application 5 plants Dec. 18 check Oct. 7 lb. lb. percent None (check) 210 _ 1 ~- 13 416 2.5 l9 28 421' 1.9 38 46 515 5.2 52 apparent. A graph of the results (fig. 6) shows that the heaviest applica- tion tested was possibly insufficient to cause the maximum increase in weight which could be derived, since each increase in amount of dust used U1 a 2 ‘f | | I I 0 10 2° 30 4U 5° Fungicide per Application per Acre - lb. Fig. 6. Graph showing relation of weight of rose bushes to amount of sulphur-copper dust used per acre per application. W1. l0 Bushes - lb. 18 BULLETIN NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION resulted in proportional increases in the weight of bushes. Although there was considerable variation in the number of leaves per plant on October 7, the percentage of leaves infected with black spot on that date did not differ significantly between the different treatments and the records of black-spot infection are omitted from the table. This experiment demonstrated the beneficial effect that the extremely heavy applications of the fungicide used might have on a variety known to be very liable to defoliation by black spot. In spite of the lack of in- jury from the heaviest treatment, however, such heavy amounts would not be recommended for practical purposes. Time, Frequency, and Amount of Dust Application Since it was known that black spot spread only during rainy periods, it was important to find out the effectiveness of a fungicide applied fol- lowing rains as compared with pre-rain applications and how long after a rain application could be made and still prevent black-spot infection. Greenhouse test. Potted bushes of the Caledonia variety were usei in a greenhouse experiment to determine the best time to apply the fungi- cide. Young plants with new, tender foliage were treated as shown in table 8. Inoculation was accomplished by atomizing the upper surface of the leaves with a suspension of conidia obtained from leaf lesions. Arti- ficial rainfall produced by means of a fine mist from a hose sprinkler, directed so that the drops of water fell on the leaves from above, was used in certain cases as noted. The period of sprinkling was two minutes. Table 8. Results of greenhouse tests with potted plants to ascertain the most effective time, in relation to occurrence of rain, for applying fungicides for black-spot control. Av. number of black- Treatment spot lesions per 100 leaflets Plants treated and inoculated April 25; data on May 5, 1942. Checkl 0 Artificial rain; inoculated; no dust 692 Dusted; artificial rain; then inoculated 222 Inoculated; dried for l hr.; then dusted 3 Dusted; then inoculated :2 Plants inoculated June 23; data on July 7, 1942. Check‘ 0 Inoculated; no dust 220 Inoculated; dusted immediately O Inoculated; dusted 4 hrs. later 0 Inoculated; dusted 8 hrs. later 4 Inoculated; dusted 12 hrs. later l Inoculated; dusted 24 hrs. later 0 Inoculated; dusted 36 hrs. later 40 Inoculated; dusted 48 hrs. later a 83 Inoculated; dusted 72 hrs. later 124 Inoculated; dusted 96 hrs. later 144 Plants inoculated July 8; data on July 21, 1942. i Check‘ 0 Inoculated; no dust 188 Dusted; artificial rain; then inoculated 106 Inoculated; dusted immediately 0 Inoculated; dusted 24 hrs. later 25 Inoculated; dusted 36 hrs. later 51 Inoculated; dusted 48 hrs. later 59 Inoculated; dusted 72 hrs. later 270 ‘Artificial rain for 2 minutes but‘ no inoculation or fungicide. CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 19 Fungicide applications were made with a two-quart plunger-type hand duster, using a light but thorough coverage with sulphur-copper dust (Owl sulphur: “34“ Copper Fungicide, 90:10). The plants were maintained over a pan of water in a shaded glass humidity chamber for 72 hours following the treatment indicated. Data on infection were obtained by counting the number of leaf spots which developed. It was found that the protective value of the fungicide was greatly lost if the foliage was sprinkled with water for only two minutes following dusting. The fungicide was most effective when ap- plied immediately after inoculation, but partial control of black spot was obtained even when application was delayed as long as two days after in- oculation. This experiment indicates that the best time to apply a dust fungicide under outdoor conditions would be as soon as possible after each rain. Field test. An experiment was conducted with Caledonia roses in the field to compare regular weekly dusting with dusting within 24 hours after each rain which was considered sufficient to spread the spores causing black spot. The amount of rain was not measured but was estimated to be 0.1 inch or more. The dimensions of the field were such that in replica- tions 1 and 2 the plots were each 6 rows wide and 27 feet long; in replica- tions 3 and 4 the plots were 5 rows wide and 31 feet long, making about 0.016 acre or approximately 200 bushes per plot. The dust used consisted of 90 parts Owl sulphur (98% 325-mesh) and 10 parts “34” Copper Fungi- cide. Treatments were made from May 4 to September 28 with 22 appli- cations for the weekly and 28 for the after-rain treatments. An average of 27 pounds of dust was used per acre at each application. This sea- son, no injury from the fungicide was apparent even with the large num- ber of applications. The data in table 9, taken from centrally located bushes in each plot (fig. 4) show only a slight difference between the dustings Within 24 hours after each rain and those made regularly once each week. However, for this particular season, with an abnormally high rainfall, the system of applying a fungicide within 24 hours after each rain required more ap- plications than the once-a-week treatment. Also, the total number of dust- ings required was greater than normal due to the early black-spot appear- ance in the field. (Methods to delay the development of black spot in fields are discussed under the next heading). With regard to the frequency of application and the amount of sul- phur-copper dust required, it would appear from experiments and obser- vations to date that fungicides should be withheld until black spot is seen in the field. The treatments should then be made at regular weekly in- tervals until about July 1. Thereafter the applications should depend on the season. If the weather is generally dry, the dust should be used only after rains and then as soon as possible after each rain that is heavy enough to wash the dust from the foliage. If the weather is generally rainy, then the frequency for economical field treatment should not be oftener than once a week. A normal average for the season would be be- tween 10 and 15 applications. The amount of dust to use depends on the method of applying. If a rotary hand duster (fig. 5) is used, the amount 20 BULLETIN NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION EDA.“ woaoaww ma»? mcmwwim we Ewowzw 2:8 d; owsfioowfi c313 0.53 wowmow was wEmEB we mwaooofi» .m~.. 3:». 531B wow», uuww uoaw-“AQANEN dvfiwwcmam uworfiwwasz we comofioommaw cmoiwcifl m5 .w::u wfivdw-im $2.5m wwwc» o». poiowcmlmnwxuo U Awewpmmw woo» wwocfiwo, Io? 63m 5T5 mowwaw saonv uwmcfi no mason“ 3 wanna mcofiw 80E no o>$|l§~ .oZ TUMEB no woman“ wH mwcwo mcofim 30E no oofifilé .02 "mwswso, wwou wo wowmuw ~NmOh®EEOo~ Nd Wm we E S. mm Wm pfi mm Exp Quin do: E =E£>> w; Wm we I cm 2.. 3 Em S >§$>> w; 9m m..." 3 w” 3 mam 3a o @215» ~26 oZ “Each...- E230 “Y1 62 m .o.Z muo-fiO fin dz fl .o.Z moans: 12$ 2 .32 x020 32 353-3 Gomunoflunu @..:|_m%3u @525? 12.22» m mo snow E :3? Imam; A15: mo we moswna 3 mo uswmokw moan-Z- mo ouawioonoh maoiawu mo 62 no 62 mofionuouh @9203. évm~|iwmua> amzowoiwOlloh-aou aoamionz E mmQGvZfi-ouwo o“ ma Ema :33 aouua iom-aoflnnm “m3. 15a uifimnw diomwnoflno.» v mo M7303 mo iomianfl-QO d Bash. w‘ .. F"77VP'VY"‘TV'Wl(l\' m, . .... . ,,_, . ,. CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 21 i should be between 20 and 25 pounds at each application. With a power ~or tractor duster (fig. 5), from 15 to 20 pounds are advised. The amount .would be less when the bushes are small and greatest when they reach mature size. Factors Affecting the Primary Infections of Black Spot in the Field and the Need for Beginning Dust Treatments Kind of understock. In one field experiment, black spot was observed very early in the season and because of this more dust applications than normal were required. The main reason for the early appearance of the disease in this case was due to the fact that in the same field another ex- periment was being conducted on the effect of different varieties of under- stock on the Caledonia scion and the reaction of both understock and scion to black spot. The varieties of understocks used were: Welch multi- flora (a recumbent type in general field use), Tate multiflora (an upright form used commercially to a small extent), Texas Wax (a semi-recumbent type in general use several years ago but almost completely replaced now), and Rosa. mawrtf'i (an upright form commonly used for greenhouse propa- gation but little used for outdoor roses). Of these four varieties the mul- tiflora types were observed to be highly resistant (possibly immune) to black spot. The Texas Wax was quite susceptible and the R. manctti was extremely susceptible. R. ma/netti was observed with black spot from the time the first leaves developed on the cuttings until the understock tops were cut off to force out the scion buds. With a great production of spores of the black-spot fungus coming from the understock, there was little chance of the scions escaping infection during their early development. Fig. 7. Close cutting of understock tops and scion t0 prevent carry-over of black-spot infec- tion. Left: Before pruning, showing scion (the thorny branch) prematurely forced. Right: Good development of lateral buds when scion was cut back close to under- stock. 22 BULLETIN NO. 648. TEXAS AGRICULTURAL EXPERIMENT STATION The occurrence of the disease was much earlier and more extensive o these plants than on scions of the same variety in other fields where th propagation was done on understocks which were resistant or immune to black spot. l Time of cutting of understocks. Another factor affecting the early j incidence of black spot on the scions was the date on which the under? stocks were cut off causing the scion buds to develop. Any delay in forcfi ing of the scions delays the initial infections of the scions. The extent to? which this could be accomplished would depend upon how late in the seaso the forcing could be done without interfering with the ultimate size and grade of bush at the end of the growing season. The time of cutting-off‘; the understock tops under average field conditions has been from February: 1 to April 1, under East Texas conditions. During the early months o the growing season the greatest number of rainy days occur, and thes frequent periods of rainfall are conducive to the spread of black spot. De»; lay in cutting off the understocks and forcing early growth of the scions‘; . therefore helps to delay the disease and the need for commencing fungi cidal dust treatments. .1 The question arises as to how late in the growing season the cutting- off can be postponed. Also there is the problem of what should be done‘; with the scions which have forced out before the understock tops are re moved (fig. 7). Field observations help to answer both questions. It was noted in 1940 that one of the nurserymen did not do the cutting-off ‘j of the understock tops in part of his field until April 22. Bushes which de- veloped from these plants were observed to be equal to or better than others grown that season. Considering the other question as to pruning of the scions which were already forced at the time of the cutting-off opera- tion, they normally were also cut back leaving a stub about two inches in‘ length extending from the bud union. Some scions were observed in fields which were cut back much closer. Due to the fact that cane lesions of black spot can also spread the disease as well as leaf spots, there should be 5 a distinct benefit from cutting back the forced scions as closely as pos- sible. ' In 1942 a test was made involving the points just mentioned. It was’ a nonreplicated trial with half of each row in part of the field forced out; 17 days later than the other part. Six varieties of roses were included in 1 the test. One date of cutting off the understock tops was March 24-25; ~ the other was delayed until April 11. At the time of cutting-off, all of the _ ' scions which had prematurely forced were cut back to within less than . half an inch from the bud union. The results were that black-spot wavél seen first on May 11 on a few of the plants which were forced earliest ’ i‘ while none was observed yet on those cut off last. No injurious effect was ‘ noted in those cut off last nor was there any injury apparent from cutting back the prematurely developed scions to less than half an inch in length. Lateral buds developed from the short scion stalk (fig. 7) and in most cases two or more branches grew from the bud unions to form well shaped ‘ .' bushes. The data in table 10 show no disadvantage from the later cutting- off, either in the grade or weight of bushes. The slight difference which did occur was in favor of the later cutting-off. Black spot was controlled with dusting (less than 0.1% of leaflet infection on September 23) and the l Hwy“ / CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 23 Table 10. Effect of time of cutting off understock tops on grade and weight of bushes—1942. Cut off early Cut off late (March 24-25) (April 11) Variety Grade‘ Number of Wt. of 10 Number of Wt. of 10 bushes in plants in bushes in plants in each grade each grade each grade each grade lb. lb. Rouge Mallerin 1 142 5.8 108 6.1 1% 147 4.2 205 4.6 others 27 2.4 16 1.9 Total3 316 4.8 329 5.0 1 50 7.4 50 7.7 Etoile de Hollande 1% 91 5.3 82 5.8 others 15 3.6 9 3.9 Total 156 5.8 141 6.4 1 117 1 8.5 1 163 1 8.3 Briarcliff 1% 221 1 5.9 1 202 5.8 others 44 1 4.0 1 56 3.8 Total 382 1 6.5 1 421 1 6.5 1 125 1 8.0 1 165 1 8.4 Cynthia 1% 245 1 5.8 1 190 1 5.8 others 86 1 3.6 1 61 1 3.1 Total 456 1 6.0 1 416 1 6.4 1 40 1 6.2 45 I 5.7 Francis Scott Key 1% 80 1 4.5 90 1 4.0 others 4d 1 2.7 1 11 1 2.5 Total 160 1 4.5 1 146 1 4.4 1 65 1 7.1 1 4U 1 8.9 Dainty Bess 1% 80 1 5.9 1 8O 6.2 others 30 I 4.7 1 23 - 4.8 Total 175 1 6.1 1 143 6.7 1 s39(ss%)* 1 v.17 | 571(se%)" I 7.52 Total of all 1% 864(52¢7U) 1 5.27 1 849 (537c) 1 5.37 varieties others 242(15°/0) 1 3.50 1 176(11”/0) 1 3.33 Total 1645 5.63 ‘I 1596 l1 5.91 ‘See footnote, Table 9. _ “Figures in parentheses represent percentage of total number of bushes. “Weighted mean in case of weights of plants. same amount and frequency of dusting was used for both parts of the field. The difference which occurred, therefore, was attributed to the fact that the earlier cutting-off produced plants which had to be topped back slightly, twice during May, to prevent wind damage and it is believed that the topping back process had a slight stunting effect which was greatest where it was done twice. Our observations indicate that cutting off the understock tops may be withheld until early in April. In order to state how much later it might be postponed without harmful effects, further ex- perimentation would be necessary. COMPUTED PROFIT FROM DUSTING It should be noted in a preceding experiment (table 9) that the fungi- cides not only controlled black spot, reduced defoliation, and produced heavier bushes, but also increased the number of high grade bushes (grades No. 1 and No. 1%). As compared with the nondusted plants the weight of the dusted bushes was 64 percent greater when dust was applied within 24 hours after rains and 57 percent greater when the applications were made once each week. The number of bushes grading No. 1 and No. 1% was increased by the fungicide treatment from 52 percent for the non- dusted plants to 86 percent in the case of the dusting within 24 hours after rains, and to 89 percent by dusting regularly once each week. On a 24 BULLETIN NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION _ 10,000 bushes per acre basis, the data would represent an average - i‘ increase of about $284.00 per acre from the use of the dust fungicide, e1 sidering only grades N0. 1 and No. 1% at 8 cents per bush and disca the inferior grades. The cost of dusting within 24 hours after each was estimated at $49.00 per acre for the season (the fungicide at $5.00 I 100 pounds and 40 cents per acre for labor and machine for each appliW tion). On this basis the net increase from dusting was $235.00 per . Actually, under commercial field conditions, the expense of fungicide =71 plication would be considerably less because the applications would be cof" menced later in the season, greater efficiency would be obtained fromi’. power duster, and there would be no nondusted check plots from which i spores would spread infection to the dusted plants. ._ Varietal differences in susceptibility to black spot and hardiness quite important from the standpoint of commercial methods and care the growing of roses. Whereas climbers, hybrid perpetuals, many spe roses and varieties of hybrid tea roses, such as the Radiance group, o 0f}, narily grow well and attain good size and grade without any fungici; treatment, most of the hybrid tea roses, which constitute the main cro~* require fungicidal treatment to insure good bushes as grown under con tions in East Texas. In this area, the rainfall is such that black spot factor in production at all times during the growing season. A 32-ye 5 record of weather at the Tyler substation shows an average of at least inch of rain on more than five days a month including the summer During the spring months the average is more than eight days per month??- Therefore, once the black-spot disease gets started in a field, fungicidaij protection should be given throughout the remainder of the growingxi season. ' ' It would appear advantageous to group the resistant types of together in one block and to have the others separate in order to conserve fungicide materials and facilitate the heavier treatment of types and va+ rieties which need protection the most. Many growers already are followiq ing this system. 7 The. benefit from the sulphur-copper fungicide has been reported to‘ extend into the storage of the bushes and also their subsequent planting.d_ In one case where the bushes were stored in a mid-western state preparaé", tory to distribution in the spring, there was little or no die-back in the storage of field-dusted bushes, whereas die-back developed in the non- dusted plants to varying degrees and even resulted in the complete loss of some bushes. In this case, mention was also made that storage molds were absent from those plants which had been field-dusted, while it occurred on undusted ones in different amounts. If the bushes are in good condition: when received for storage, it might not be necessary to spend large sums of money to keep them healthy during the storage period. EFFECTS OF DUST ON THE SOIL Where the sulphur-containing fungicide is used year after year on the same area, acidification of the soil may eventually occur to the extent that liming would be required. The soil should be tested for acidity from year to year and limed if the acidity is greater than pH 5-6, which can easily (D UlDllfDt-hu Lt LI‘ y g {F . l l 1 l CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER. DUST 25 be ascertained by a simple test. However, too high acidity of the soil would not be expected very soon in the normal production of roses because other crops not receiving the fungicide treatments would be used in rota- tion and the land would not be in roses more than once in three or four years. Rotation with crops other than roses would largely prevent an ac- cumulation of fungicidal chemicals in the soil. RECOMMENDATIONS Rose bushes should be dusted at the first appearance of black spot on the foliage. Dust the plants with a sulphur-copper mixture containing about 90 percent of unconditioned 325-mesh dusting sulphur and about 10 percent of an insoluble copper fungicide such as basic copper sulphate, “34” Copper Fungicide, Copper Hydro 40, Grasselli IN877A6, SprayCop, Copper Oxy- chloride-Sulphate, or Cupro-K. Certain sulphur-copper mixtures are now obtainable on the market ready for use. If cuprous oxide (Cuprocide) is used in the mixture, the sulphur should be conditioned. Repeat applications of the dust at weekly intervals until July (or until hot, dry weather begins), thereafter dust within 24 hours after each rain, but not more often than once a week, until growth of the plants is checked by cool weather. Use a sufficient amount of dust to cover the foliage lightly. This usually amounts to 15 to 25 pounds per acre at each application depending on the size of bushes and type of dusting machine used. SUMMARY An effective sulphur-copper dust fungicide for controlling the black- spot disease 0f roses has been developed in field tests at Substation No. 2, Tyler. This mixture gave better control of black spot than the pure dust- ing sulphur, formerly recommended. Various grades of 325-mesh dusting sulphur have been found satis- factory for mixing with certain insoluble copper compounds in forming the fungicidal dust mixture. Several copper compounds mostly sold under trade names were used in the sulphur mixture with good results in these experiments. Among the most effective mixtures were those containing about 9O percent 325-mesh dusting sulphur and 10 percent of a copper fungicide such as “34” Copper Fungicide, Copper Hydro 40, Cuprocide, Dow copper, Grasselli copper, SprayCop, Copper Oxychloride Sulphate, and Cupro-K. The addition of wheat flour, cotton seed oil, or bentonite to the sul- phur-copper mixture as sticking agents did not improve materially the de- gree of black-spot control obtained. Unconditioned sulphur was found as satisfactory as conditioned sulphur when used with certain of the copper compounds. Also, a 93 percent 325-mesh grade of sulphur was practically as good as a 98 percent 325-mesh brand for the dust fungicide. Greenhouse tests with potted roses showed that the sulphur-copper dust was removed from the foliage by a brief period of sprinkling and that the fungicide was most effective in controlling black spot when ap- 26 BULLETIN NO. 648, TEXAS AGRICULTURAL EXPERIMENT STATION plied immediately after inoculation. In corroborative field experiments the best results were also obtained when the fungicide was applied within 24 hours after each rain. This system required an extreme number of ap- a plications in certain seasons. The most economical and effective frequency _ of application appeared to be once regularly each week, following the ap- , pearance of black spot, until July 1 and then but not oftener than once a week for the remainder of the season. With a susceptible variety, Caledonia, the sulphur-copper applications not only reduced black spot and increased the weight of bushes at harvest- ing time, but also greatly increased the percentage of high grade bushes. Those grading No. 1 and No. 1% were increased from 52 percent for non- dusted bushes to more than 85 percent for those that had been dusted. The net increase in value from the fungicide treatments was figured at $235.00 per acre in that experiment with the inferior grades not included. A consideration was made of factors involved in the incidence of black spot in fields. Use of understock varieties which were resistant or . i immune to black spot delayed infection on the scions. Late cutting-off of within 24 hours after rains’ v s the understock tops and pruning back to less than half an inch all pre- ‘l maturely-formed scions resulted in later development of scions and a sub- sequent delay in the incidence of black spot. Any delay‘ in theoccurrence of black spot in a field lessened the amount of fungicidal treatment re- quired. Directing the dust downward onto the foliage gave as good or better i results than projecting it upward from below the leaves. About 20 to 25 pounds per acre of sulphur-copper dust at each application with a rotary hand duster, or 15 to 20 pounds per acre with a tractor power duster were found to give the most satisfactory black-spot control. Benefits from using the sulphur-copper dust on field roses were also obtained in storage. CONTROL OF BLACK SPOT OF ROSES WITH SULPHUR-COPPER DUST 27 LITERATURE CITED 1. Boyd, G. T. Effects of fungicides on germination of spores of the black-spot fungus (Diplocarpon rams). T921115 Agl‘. EXP. Sta. A1111. Rpt. 502 110. 1937. 2. Boyd, G. T. Control of black spot of roses. Texas Agr. Exp. Sta. Ann. Rpt. 49: 101. 1936. 3. Boyd, G. T., and J. J. Taubenhaus. Field control of die-back and black spot of roses. Texas Agr. Exp. Sta. Ann. Rpt. 48: 92. 1935. 4. Horne, W. T. and D. F. Palmer. The control of Dothiorella rot of avocado fruits. Calif. Agr. Exp. Sta. Bull. 594. 1935. 5. Lyle, E. W. The black-spot disease of roses, and its control under greenhouse conditions. N. Y. (Cornell) Agr. Exp. Sta. Bull. 690. 1938. 6. Lyle, E. W. Fungicides for black-spot disease control. Texas Agr. Exp. Sta. Ann. Rpt. 52: 149-150. 1939. 7. Lyle, E. W. Texas black-spot control work. Amer. Rose Ann. 26: 172-175. 1941. 8. Lyle, E. W. The sulphur-copper dust fungicide for roses. Texas Agr. Exp. Sta. Prog. Rpt. 778. 1942. 9. Lyle, E. W. Black-spot on rose canes. Amer. Rose Ann. 28: 155-156. 1943. 10. Lyle, E. W. and L. M. Massey Dieback of roses. Amer. Rose Ann. 26: 176-179. 1941. 11. Massey, L. M. The black-spot war situation. Amer. Rose Ann. 28: 141-154. 1943. 12. Nelson, Ray. Tests of new dust and liquid fungicides in 1938 for control of celery leaf blights. Mich. Agr. Exp. Sta. Quart. Bull. 21: 295-307. 1939. 13. Parsons, B. and L. M. Massey. Rose-disease investigations. Fourth Prog. Rpt. The Amer. Rose Ann. 18: 87-101. 1933. ' 14. Roney, J. N. and J. J. Taubenhaus. Control of fig diseases. Texas Agr. Exp. Sta. Ann. Rpt. 49: 106. 1936. l5. Scribner, F. L. Black-spot on rose leaves. In Report of the Section of Vegetable Pathol- ogy. Comm. Agr. (U.S.) Ann. Rpt. 1887: 366-369. 1888. l6. Shaw, Luther and T. T. Hebert. Copper-sulphur dusts and copper sprays give good con- trol of peanut leaf spot diseases. Phytopath. 31: 770. 19 . 1T. Townsend, G. R. Spraying and dusting for control of celery early blight in the Ever- glades. Fla. Agr. Exp. Sta. Bull. 366. 1942.