TEXAS AGRICULTURAL EXPERIMENT STATION R. D. Lewis, Director College Station, Texas BULLETIN 699 JULY 1948 A Control of Cotton Root Rot by Sweetclover in Rotation E. W. LYLE, A. A. DUNLAP, H. O. HILL and B. D. HARGROVE 1,. AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS c.1131? GILCHRIST, P-esident J55-748-6M-L1 80 [Blank Page in Original Bulletin] Preface It has been shown frequently that the plowing under of legumes increases both the nitrogen content and the organic matter of the soil. Experiences of some farmers, soil-fertility demonstrations and pre- liminary experiments have indicated that losses from root rot may be- reduced following rotation of cotton with certain legume crops. The use of replicated plots in a 5-year study (1943-47) at the Blackland Experiment Station (Substation No. at Temple has proved the value of sweetclover in the control of cotton root rot and in the increase of cotton yields. Sweetclovers best adapted to growing conditions in the central Blacklands of Texas (the Temple area) are indica (Melilotus indica) and hubam (Melilotus alba var. amzua). Both were used in the rota- tion experiments reported in this bulletin as winter and winter- summer crops. Rotation with hubam that is grown to maturity at‘ least once every third or fourth year was found to offer the best means yet known for the control of cotton root rot in the central Blacklands. In addition to a larger yield of cotton through disease control and increased soil fertility, the hubam crop provides additional farm income when used as pasture for livestock or when harvested as hay or seed. Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . f: CONTENTS Introduction u u u Q ¢ - Q ¢ . . o a . ¢ | . - - ¢ - - - - - - - - - ¢ o u o ¢ - Q | o o o Q | - ¢ - - | o - o ¢ n u n a Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- . . . . . . . . . . . . . . . . . . . . . . . . . . ‘Residual Elfects of ‘Sweetclover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - Root-rot Infection of Non-wilted Plants . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4'- ' Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BULLETIN 699 JULY 1948 Control of Cotton Root Rot by Sweetclover in Rotation E. W. LYLE, formerly Plant Pathologist, Substation No. 5, Temple, Texas A. A. DUN LAP, Head, Department of Plant Physiology and Pathology H. 0. HILL1, Superintendent, Bluebonnet Farm, McGregor, Texas B. D. HARGROVEZ, Agronomist, Bluebonnet Farm, McGregor, Texas Cotton root rot h.as persisted as one 0f the most bafiling problems in Texas agriculture. It has been the object of much research in the last half century, particularly in regard t0 studies 0f the causal organism (P/tymatotflchum omnivorum (Shear) Duggar), resistant crops and crop rotation. Root-rot-resistant varieties of cotton have not been found. Consequently, rotation with immune plants such as corn, oats, sorghums or grasses have in the past constituted the most frequent recommendations for partial control of this disease. The sclerotia (Figure I) of the causal fungus—sma1l seed-like resting bodies that remain alive for many years——have been found from six inches to eight feet in the soil (20). Since these seed-like bodies keep the disease active from year to year, methods have been sought for producing cotton even in the presence of the fungus. A step in this direction was the development of rotations with resistant crops. These practices were suggested for root-rot control as early as 1888 by Pammel (18) and a survey of the literature on this subject has been made by Rea (I9). Another attack on the root-rot problem involved the use of organic manures. This method of control was also suggested by Pammel in the following state- ment written over 6o years ago: “Near Brenham, on Post Oak land, a field was found, two acres of which received a heavy dressing of stable manure two years previous. Here very little dead cotton was found. The soil adjoining this patch was identically the same, so far as one could tell from a superficial examination, yet nearly one-third of the cotton was dead. Mr. Peters pointed out to me a similar case near Calvert.” More recently, King and Loomis (I2) have found soil amendments of barnyard and green manures to give excellent control of root rot under irrigated experimental con- ditions in Arizona. The addition of organic material was found by Jordan at al. (7) to increase the effectiveness of deep-tillage prac- tices for cotton root-rot control. In other experiments, Jordan, Nelson and Adams (9) showed that smaller percentages of cotton died from root rot where sorghum residues were turned under than in plots of continuous cotton. Experiments by Scofield (21), and Taubenhaus 1 zFormerly superintendent and agronomist, respectively, at Substation No. 5, Temple, Texas. 6 BULLETIN 699, TEXAS AGRICULTURAL EXPERIMENT STATION Figure 1. Sclerotia (resting bodies) of the cotton root-rot fungus, about one-half natural size.'On left, sclerotia as they are found in the soil; on": right, germinating sclerotia with thread-like mycelium. These seed-lik l, bodies remain alive in the soil for many years. 5' and Killough (24), however, showed little effect from manure} It is of interest to note that Collins at al. (6) found higher contents} of organic carbon and total nitrogen and wider carbon-nitrogen‘ ratios in areas of non-infested Texas Blackland soil than in spotsfl; where thedisease occurred. ' The most recent development in the control of cotton root rotl involves the use of legumes. One of the first reports of this method, was made by Rogers (20) in a 2-year rotation experiment con ducted at the Blackland Experiment Station (Substation No. 5)‘. in 1940 and 1941. Rogers found ‘that plots of cotton following hubam (M elilotus alba var. anmm) had much less root rot than com-‘ parable plots where cotton had been grown for several years, and. the yields of cotton were about twice as large. Some of the sweet-if clover in this experiment was cut for hay and some was harvested‘ for seed. The crop residues were then plowed in late summer. Asi pointed out by Rogers, hubam may be severely attacked by the root-f rot fungus when the plants are allowed to stand in the field until late summer for seed. Even though the hubam was attacked, thereto. was a marked reduction in root rot in the succeeding crop of cottonfll 3These experiments have been continued separate from the experiments; reported herein and the data on root-rot incidence and cotton yields have been assembled by Superintendent J. R. Johnston for the years 1941-47.. Although only a few (2 or 4) replications were used these data may be Sig; nificant. At least they show the same general trend as the results from al larger number of replications reported in this bulletin. The average for» the 7 years shows a yield of 390 pounds of seed cotton per acre from the continuous cotton plots, 475 pounds from the cotton-corn rotation, 6277 pounds after hubam for hay and 737 pounds after hubam for seed. The number of plants killed by root rot in August in these same treatments on a 7-year average was 28, 19, 5 and 3 percent, respectively. 1 CdNTRdL OF‘ COlTTON ROOT ROT BY SWEETCLOVER IN ROTATION l7 Figure 2. Fall-planted sweetclover showing desired amount of growth at time of plowing under for green manure in late winter or early spring. ' ~- Figure 3. Fall-planted hubam showing height and‘ denselstand (at time of cutting for hay in early summer. ~ 8 _ BULLETIN 699, TEXAS AGRICULTURAL EXPERIMENT STATION During the past five years 1943-47, three progress reports ha been issued by the Texas Station on the value of sweetclover n‘ in reducing the losses from cotton root rot. The first of these L Hill, Lyle and Johnston (Io) showed the results with cotton" a 2-year rotation with hubam which was harvested as hay (Figure v or for seed. The second by Lyle and Hill (r5) gave results n experiments with hubam and annual yellow-blossom sweetclo (Melilotus indica, commonly called indica) as winter "cover cro' only. These two reports involved data taken during the first 2 yea, of the study reported in this bulletin. Brooks (4) issued a repo“ in 1947 of similar studies at Substation No. 16, Iowa Park. Following suggestions from the Extension Service and the ...~. Conservation Service, Texas farmers in areas where cotton root r, is prevalent have used legume crops for several years to impro 3 cotton yields and lessen the damage from root rot. The experienl of farmers in the Blackland area has tended in most instances substantiate these recommendations. Additional information on t,’ effect of a legume crop on ‘root-rot control is provided by Bark“, and Blank In their survey of cotton fields in the Pecos Valle? of Texas and New Mexico, it was noted that alfalfa was commonl I used in rotation with cotton and that losses from root rot wer slight, particularly during the first 3 or 4 years following the plow ing under of alfalfa. Two theories have been mentioned as the possible explanation o the effectiveness of legume crops in cotton root-rot control. Th effects of additional nitrogen in the soil offer one possible answe since nitrogen or ammonium fertilizers have shown beneficial elfecfi against the disease in several instances (I, 3, 6, 7, 8, 9, 23). other theory is that changes in the microfloral populations of the are responsible for the control of the disease through antibioti effects of other soil organisms on P/zymatotric/Lum omnivorum. Ac cording to King (14): “The root rot fungus does not thrive in th presence of great activity on the part of saprophytic organisms, the cotton plants frequently escape infection.” King and Loom' (II) had reported earlier that apparently healthy cotton plants i? manured plots were occasionally found to have infected roots - they suggested that “the plants may be better equipped to avoif, or withstand the disease under the modified soil conditions. Mitchell, Hooton and Clark (I7), and Clark (5) have shown th; a both the mycelium and sclerotia of P. omnivorum are destroyed Q non-sterile soils with added organic matter. Increases in the popul; tions of such soil organisms as bacteria, actinomyces and certas‘ fungi have been noted by. King, Hope and Eaton (I3), and t} Mitchell, Adams and Thom (16) in soils which had received organ materials. a CONTROL OF COTTON ROOT ROT BY SWEETCLOVER IN ROTATION 9 Experimental Procedure Three acres of fairly level and uniform land of Houston Black clay soil were set aside in 1942 at the Blackland Experiment Station for these cotton root-rot control experiments. The experimental area was in cotton the previous year and in miscellaneous non-legume crops prior to that time. Crop rotations with hubam and indica were started. The plots were 18 feet wide and "158 feet longfwith a 6-foot interval between plots kept clean. The cotton was in 3-foot i rows and data were taken from 132 feet of the four center rows. There were four treatments in each of six randomized blocks. These treatments were continuous cotton, cotton each year following hubam green manure (winter cover), cotton each year following indica (winter cover), and 2-year rotations of cotton with hubam (grown to maturity for seed). Record of the cotton plants killed by root rot was taken at least twice each year, early in August and Sep- tember. The taproots and large lateral roots of the non-wilted cotton plants in the various plots were examined in 1946 for signs of root-rot infection. Hubam was tested as a winter cover crop and also in a z-year rotation with cotton. Indica was used as a winter green manure crop. It is better adapted to warm winter climates and makes more winter growth than hubam in locations where it survives. The vicinity of Temple is about the northern limit for fall planting of indica. This study was conducted as originally designed for 2 years. It was then desired to alter the design slightly and to obtain informa- tion concerning the residual effect of the hubam on root rot. The hubam planted for green manure was allowed to mature in 1945. This area in 1946 provided information for 1 year in cotton after hubam, and in I947 for 2 years in cotton after hubam. By allowing the hubam to mature for harvest, information was made available for studying the amount of root rot in cotton 1, 2 and 3 years after a crop of hubam was harvested for seed (Table 4). -The sweetclover seed were inoculated and planted each year in the fall (early October). Hubam and indica were drilled at the rate of about 10-15 pounds per acre. The top growth of the sweetclovers was sampled just before bedding under about March 15 when used as green manure, and just before seed harvest when the hubam was grown to maturity. The plots with hubam grown for seed were flat broken after seed harvest, and then bedded and rebedded before planting cotton the next year. The Roldo Rowden cottonseed was Kemgas delinted, treated with New Improved Ceresan, and planted with a hill-drop tractor planter about the middle of April. the seed crop is nearly ready for harvest and therefore causes no 10 BULLETIN 699, TEXAS AGRICULTURAL EXPERIMENT STATION . rdotww . p V_ .| _ . . ._ Results A temperature of 17° F. on December 15, I943, plus about five additional days of freezing weather“ totally killed ‘the indica but~ caused only about‘ 5 percent loss in" the “hubam. After replanting» the indica, another freeze (January 9-15) killed about 50 percent) of the top growth with scarcely any further damage to the hubam. i The amount of legume growth turned under before the planting of cotton is shown by the dry weights of samples cut, from each l.“ plot (Table I). Although the winter cover was small (from 48 to 450 pounds dry weight per acre) in each case, the indica gave more i winter growth than the hubam except where the former was frozen a out. The hubam made rapid growth in the spring (Figure 2) and by seed harvest time had developed a top growth of from 6,400 to 9,400 pounds dry weight per acre (Figure 6). Although the legumef crops aided inrdelaying or preventing root rot in the cotton whiclrf followed, they were not resistant to the disease themselves. Root rot does not occur in the winter but it may develop on hubam grown for seed. The disease, moreover, does not appear on hubam until . 4 economic loss. The effect of legumes in rotation on the amount of root rot or delay in dying of cotton is shown in Table 2 together with the _ yields of seed cotton from these plots. The winter legume green i manure (Figure 2) reduced the kill from root rot from 34 to I7 a percent (August data) and increased the yield of cotton about 25 percent (Figure 5). The 2-year rotation of hubam was far more effective than the winter green manures in its action to reduce root 1 rot and increase the yield of cotton (Figures 4 and 6). Four years’ a results, 1944-47, show that the disease was reduced from 29 to 5 percent with a yield increase of about 56 percent (Tables 2 and 3). ' The effect of hubam in rotation was studied further (Table 3), and will be described later. The difference between August and September records for root_- I rot kill proved that the legumes delayed the incidence of the disease. q Later observations showed that although the disease did spread, r it did not attack as large a number of plants in the rotation plots r as it did in the checks. There was partial control as well as delay I of the disease, particularly with the 2-year rotation. There was prac- tically no difference in effect between the two legumes used as winter is‘ green manure crops. The yield of cotton was related inversely to I the amount of root-rot kill; the less root rot the more cotton pro-a duced. The August record of root rot was more nearly a correct measure of the loss in yield than the September record. “ Table 1. Dry weight of sweetclover (tops) when plowed under and yield of hubam seed in 2-year rotation Location Dry weight, pounds per acre Yield of seed, pounds per acre Rotation acre and plot 1943 1944 1945 1946 1943 1 1944 [ 1945 ‘ 1946 1947 Hubam as green E7—5 549 348 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . manure (winter E7—8 589 339 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cover) F7—1 311 149 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F7-—9 318 626 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G7-5 516 253 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G7—8 288 354 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Average.. . . . . . . . . . . . . . . . 427 345 48 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indica as green E7—1 585 179 290 322 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . manure E7—7 508 185 145 290 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (winter cover) F7—4 375 163 290 209 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F7—10 502 158 97 354 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G7—2 362 132 145 322 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G7—6 381 124 242 258 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Average . . . . . . . . . . . . . . . . . . . 452 157 202 292 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ’Hubam as a seed E7—4, 3* 5920 9502 8809 2320 1452 1636 1452 213 568 crop in a 2-year E7—6, 9 8440 10293 8518 2620 1815 1694 1016 227 805 rotation F7—5, 2 7135 8652 7889 2180 1936 1752 968 227 610 F7—8, 6 5920 9716 7986 2660 1573 1844 1065 257 610 G7—1, 4 4980 8200 6292 2240 1694 1452 678 281 422 G7—9, 10 6102 10502 8470 2500 1573 2120 1258 294 647 Average . . . . . . . . . . . . _ . . . . . . . 6416 9478 8023 2420 1674 1750 1073 250 610 *Plots E7—4, E7—6, F7—5, F7—8, G7—1, and G7—9 were in hubam during even years; E7—3, E7—9, F7—2, F7—6, G7—4, and G7—10 were in hubam during odd years. I II NOLLVLOH NI HEIAOTOLEIEIMS LEI LOH LOOH NOLLOO JO TOH-LNOO A Table 2. Root rot and yield of cotton in rotations with indica. and hubam '0 Percent of plants killed by root rot Location Yield, seed cotton, Rotation acrel and 1943 1944 1945 pounds per acre p 0t Aug. 2 Sept. 7 Aug. 2 Sept. 1 Aug. 1 Sept. 3 1943 1944 1945 Continuous cotton E7—2 34 98 5 8 28 58 522 504 371 (check) E7-—10 13 26 23 27 46 81 962 457 280 F7—3 50 95 5 5 26 71 371 425 366 F7—7 74 96 7 8 46 83 275 412 319 G7—3 52 99 28 32 43 86 344 404 176 G7~7 31 71 47 60 60 86 605 237 250 Average . . . . . . . . . . . . . . . . . . . 42 p81 19 23 42 78 513 406 294 Indica as green E7—1 8 74 3 4 11 41 742 547 613 manure (winter) E7—7 41 88 22 28 46 57 578 440 280 followed by F7—4 35 89 1 3 4 19 468 492 624 cotton (1 year F7—10 23 77 9 16 18 48 660 371 476 rotation) G7—2 16 80 9 13 14 71 688 503 437 G7—6 25 69 21 26 47 ' 71 715 363 286 Average . . . . . . . . . . . . . . . . . . . 25 80 11 15 22 51 642 453 453 Difference from check . . . . . . . . . . . . . . . . . . . . . . . ——17 —1 -—8 ——8 —20 —27 +25% +12% +54% Hubam as green E7—5 20 70 5 9 16 35 742 463 566 manure- (winter) E7—8 11 83 4 7 19 51 550 499 335 followed by F7—1 17 67 21 33 20 68 990 550 330 cotton (1 year F7—9 28 95 2 4 14 28 550 502 547 rotation) G7—5 33 80 8 9 41 80 701 429 292 G7—8 12 82 9 12 5 8 550 400 544 Average . . . . . . . . . . . . . . . . . . 20 80 8 12 19 45 680 474 436 nouvms mnawnmaxa "xvzmmnonxov svxm. ‘s69 nrmzwnna ZI nqvvfr““uw>-»yvpinflvl~.r .,._....,._ w,‘ v 7.1.7.7.". ,.. Difference from check . . . . . . . . . . . . . Hubam for seed, 1 year; cotton next year (2 year rotation) Average . . . . . . . . . Difference from check —22 ———1 ——11 —-11 ——23 —33 +33% +17% +48% ** ** 17 25 12 25 ** 430 646 . . . . . . . . . . . . . . .. 4 6 14 28 496 542 . . . . . . . . . . . . . . .. 7 12 7 16 446 490 . . . . . . . . . . . . . . .. 7 9 5 10 468 688 . . . . . . . . . . . . . . .. 4 7 1 7 489 707 . . . . . . . . . . . . . . .. 5 8 1 5 564 490 . . . . . . . . . . . . . . .. 7 11 7 15 482 594 . . . . . . . . . . . . . . .. ——12 ———2 —36 —63 ........ +19% +1029} *P1ots E7—4, E7—6, F7—5, F7—8, G7—1, and G7—9 were in cotton during 1943 and 1945; E7-3, E7—9, F7-2, F7—6, G7—4, and G7—-10 were in cotton during 1944. **First year of test, in hubam,-no Z-yearrotation results. SI NOLLVILOH NI HEIAOTCLLEIHMS L?! LOIIXLOOH NOLLOO e10 TOILLNOO 14 _BULLETIN_ 699, TEXAS AGRICULTURAL EXPERIMENT STATIOII Table 3. Root rot and yield of cotton after hubam 1946 1947 Location Percent root rot i Seed cotton Percent ' Seed cotton acre and pounds root rot pounds plot Aug. 1 Sept. 1 | per acre Aug. 1* per acre Continuous cotton (check) Continuous cotton (check) E7—2 15 63 187 4 685 E7—10 45 79 165 14 421 F7—3 28 68 190 3 536 F7—7 42 80 138 3 347 G7—3 34 75 151 - 9 490 G7—7 67 89 58 7 433 Average. . . . 39 u 76 4 14s 7 485 2 years in cotton after 1 year 3 years in cotton after 1 hubamT year hubam E7—4 22 43 275 1 564 E7—6 38 72 154 3 531 F7—5 26 57 162 6 487 F7—-8 20 56 305 5 509 G7—1 16 54 278 2 663 G7—9 8 22 316 tr.T 583 Average. . . . 22 U 49 ‘ 24s 3 55s 1 year in cotton after 1 year 2 years in cotton after 1 hubam year hubami E7-3 7 11 289 1 690 E7—9 7 16 553 1 633 F7—2 11 20 308 4 699 F7—6 5 16 358 2 589 G7—4 8 21 371 9 514 G7—10 2 2 390 tr. 540 Average.. . . 7 14 378 3 611 Cotton after hubam (winter) Hubam this year ' L E7—1 12 27 368 . . . . . . . . . . . . . . . . . . . . . . . . E7—7 7 13 443 . . . . . . . . . . . . . . . . . . . . . . . . F7—4 11 23 346 . . . . . . . . . . . . . . . . . . . . . . . . F7—10 11 _ 26 a 330 . . . . . . . . . . . . . . . . . . . . . . . . G7—2 12 30 324 . . . . . . . . . . . . . . . . . . . . . . . . G7—6 30 68 226 . . . . . . . . . . . . . . . . . . . . . . . . Average. . . . 14 31 340 CONTRO_L OF COTTON ROOT ROT__I3_Y_ SWEETOLOYER IN ROTATION 15 Table 3. Root rot and yiéld of cotton after hubam-Continued i ’ 1946 ' 1947 {Location Percent root rot l Seed cotton Percent Seed cotton acre and ‘——-—— ——————t pounds root rot pounds ' plot i Aug. 1 i Sept. 1 I per acre Aug. 1* per acre ‘ l Hubam for seedthis year 1 year cotton after 1 _ year hubam I i - ; I . . i ' E7—5 y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 677 E7—8 » . . . . . . . . ..i . . . . . . . . . . . . . . . . . . ‘ " 0 503 F7—1 I . . . . . . . . . . . . . . . . . . . .4 . . . . . . . . . . . . y tr. 652 F7—9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 641 G7—5 1 . . . . . . . . . . . . . . . . . . . . l . . . . . . . . . . . . tr. 556 G7—8 l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 666 Average. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . tr. 616 l I *Owing to the dry season in 1947, root rot developed but little after August 1 and no readings were taken in September of that year. T1 year in hubam for seed, 1944. I2 years in hubam for seed, 1943 and 1945. TTrace——less than 1 percent. There was a great variation in results, both in replications of the same treatments and in different years. This is a characteristic of the disease more than with most other plant pathological problems. Residual Effects of Sweetclover It was decided in the fall of I945 to use the winter green manure plots to determine the lasting effects of a mature hubam crop on root-rot occurrence and on the yield of cotton. This would indicate how often the hubam would need to be grown in a given area to give the most economical control of root rot. The I945 cotton plots in the 2-year rotation were planted to cotton again in I946 to give results on the second year of cotton after hubam. These plots would be third-year and fourth-year cotton in I947 and I948, respectively. The plots planted to hubam in the fall of I946 were allowed to mature for seed in I947. As may be seen in Table 4, there were marked increases in yields of seed cotton in the second year after hubam, both in I946 fland I947. The I947 data also show an increase for the third year after _hubam, although the difference in this case was not as great as in the caseof the first and second years after the mature hubam. Root-rot Infection of Non-wilted Plants All cotton plants in the two border rows in each plot which seemed to be healthy from above-ground appearance were pulled in Sep- 16 BULLETIN 699, TEXAS AGRICULTURAL EXPERIMENT STATION tember 1946 and the roots examined for infection by the cotton- root-rot fungus. This examination was made following a rain which loosened the soil .to that the cotton roots could be easily removed. It was expected that many living cotton plants would be found in the 2-year hubam rotations which had been attacked by the fungus and had recovered through the maintenance of one or more healthy lateral roots. This was not found to be the case. Although a large percentage of the plants in the check plots had roots that showed varying amounts of infection on the root system, those in the 2-year hubam rotations showed much less infection. It was noticed that long lateral roots often became infected by the root-rot fungus when they entered the fallow areas between the plots. Discussion The average yield of cotton following the various rotation and green-manure treatments for each of the 5 years of experimental work is given in Table 4 which summarizes the data in Tables 2 and 3. As may be seen in this table, all of the treatments resulted in increases in the average yield of the six plots in all years. These differences were not statistically significant in 1943 and 1944, however, the treated plots had a higher yield than the continuous cotton. During the years, 1945-47, ‘on the other hand, nearly all of the treatments were significantly different from the checks. The significant differences occurred mainly between the continuous cotton and the treatments as a whole. There were no marked differences between the various sweetclover treatments. A tendency can be seen for the effectiveness of the mature-hubam treatment to diminish in successive years, and eventually the cotton in the I-year hubam plots probably would have yields and root-rot losses comparable Table 4. Summary of average yields of cotton following the various treat- ments for the 5-year period; Seed cotton, pounds per acre Treatment 1943 1944 1945 1946 1947 Continuous cotton (check) . . . . . . . . . . . . . . 513 406 294 148 484 1st year after hubam for seed . . . . . . . . . . . . . . . . . 482 594 378 616 2nd year after hubam for seed. . . . . . . . . . . . . . .’ . . . . . . . . . . . . . 248 611 3rd year after hubam for seed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 556 Winter hubam (green manure) . . . . . . . . . . 680 474 436 339 . . . . . . Winter indica (green manure) . . . . . . . . . . . 642 453 453 . . . . . . . . . . . . CONTROL OF COTTON ROOT ROT .BY SWEETCLOVER IN ROTATION 17 with the continuous cotton plots. For best results, therefore, it would appear desirable to grow a crop of mature hubam in the rotation every 2 or 3 years. In comparison with other recommendations for the control of cotton root rot, the sweetclover-rotation method offers the best control measure yet devised for holding the disease in check (Figures 4, 5 and 6) and at the same time increasing the yield of cotton. Aside from root-rot control, the maintenance of soil fertility through the beneficial fixation of nitrogen by the legume and the addition of organic material to the soil are in keeping with the best agronomic practices. Although early flat-breaking alone may result in considerable control of cotton root rot (7, 22), this cultural practice is not always effective (7). Sweetclover residues plowed under in late summer or early fall give a higher degree of root-rot control as well as increased yields, when compared with early plowing. The apparent decrease in activity of the root-rot fungus on cotton in the 2-year hubam rotations may indicate an additional effect of the decomposed hubam residue in the soil. Examination of the data shows a correla- tion between the yield of cotton and the percentage of living plants at the time of the first count of dead cotton. This would indicate a direct effect of root-rot control on yield increases in the cotton in addition to the increased soil fertility provided by the legume. Figure 4. Experimental plots showing excellent control of cotton root rot where hubam was grown to maturity the preceding year (H2 on left, 1st-year cotton after hubam for seed). The check plot on the right (CK) shows a high percentage of root rot. 81 NOLLVLS LNEIWIHEIdXH TX/HILLTIIOIHDV SVXELL ‘669 NLLEFYIHEI Figure 5. Good control of cotton root rot was obtained in the 2-year hubam-cotton rotation (H2) on left. More root - rot occurred in the center plot (winter indica, MW) and in the check plot (CK) on the right. The yield of cotton was higher ‘in the ceter plot than in the rot ‘following fl3vm check plot due to delay in appearance of root Awinter cover crops, The pic¢ w Figure 6. Heavy loss from root rot is shown in the check cotton plot (left center, Q - - in which hubam was harvested for seed the previous year is practically free from dead clggéoxltlllfz;ch?rfigofiu%grghfiegiggg after harvest for seed and ready to be turned under for experimental root-rot control ' may be seen on the extreme left. 6T NOLLVLOH NI HEIAOTOJHHAAS LEI LOH LOOH NOLLOO cIO TQZLLNOC) 20 BULLETIN 699. TEXAS AGRICULTURAL EXPERIMENT STATION Acknowledgment Special acknowledgment is made to R. C. Henderson for his. assistance in collecting field data, and to Dr. j. R. Johnston, present”; superintendent of Substation No. 5, for consummation of these‘ studies. \ Summary This bulletin presents the results of a 5-year study at the Black-l land Experiment Station on the effectiveness of winter and winter-i summer crops of M elilotus indica (referred to as indica) and flileli- ; lotus alba var. annua (hubam) in rotation with cotton for the control of root rot. When sweetclovers were used as green-manure crops (plowed under» in early spring) and followed by "cotton the same year, cotton root.‘ rot was delayed and decreased and increases in yield were found, in most cases. _ " Delay and marked reduction in cotton root rot and the highest yields of cotton were found in the plots in which hubam had been’ grown’ to maturity the previous year. Outstanding yield increases in cotton were obtained during the first 2 years following the rota- tion with mature hubam and there was also an apparent increase in ' the third-year cotton after hubam. A The degree of root-rot control, as shown by the increased yield? of cotton in plots following mature hubam the previous year, is; proportional to the reduction in number of» cotton plants killed early in the season by root rot. Late-season root rot has less effect on yield.- The beneficial effects of the hubam in rotation appeared to diminish with successive plantings of cotton, making the plowing; under of the mature hubam crop necessary about every third qr? fourth year for best results. i Literature Cited 1. Adams, j. E., R. C. Wilson, L. E. Hessler and D. R. Ergle. Chemis and growth of cotton in relation to soil fertility and root-rot. Proc. So' Sci. Soc. 4: 329-332. 1939. i 2. Barker, H. D. and L. M. Blank. Some notes and observations on "of totrichum root rot in the irrigated regions of Western Texas and Easte g New Mexico. August 1o to August 18, 1940. Unpublished manuscrip 3. Blank, Lester M. Effect of nitrogen and phosphorus on the yield u? root rot responses of early and late varieties of cotton. jour. Amer. r Agron. 36: 875-888. 1944. ‘ 4. Brooks, L. E. Hubam clover as a cash and soil-improving crop for if Wichita Valley. Tex. Agr. Exp. Sta. Prog. Rpt. 1069. 1947. IO. II. I2. 13. 14. 15. I6. .17. 18. 19. 20. 2I. 22. 23. 24. CONTROL OF COTTON ROOT ROT BY SWEETCLOVER IN ROTATION 21 Clark, Francis E. Experiments toward the control of the take all disease of wheat and the Phymatotrichum root rot of cotton. U.S.D.A. Tech. Bull. 835. 1942. Collins, E. R., W. V. Black, D. R. Ergle and P. R. Dawson. Root-rot occurrence in relation to chemical characteristics of soils. In report of the Fifth Annual Cotton-Root-Rot Conference. Phytopath. 22: 988-989. 1932. Jordan, Howard V., James E. Adams, Dalton R. Hooton, Dow W. Porter, Lester M. Blank, Eldon W. Lyle and C. H. Rogers. Cultural practices as related to incidence of cotton root rot in Texas. U.S.D.A. Tech. Bull. 948. 1947. Jordan, H. V., P. R. Dawson, J. J. Skinner and J. H. Hunter. The relation of fertilizers to the control of cotton root rot in Texas. U.S.D.A. Tech Bull. 426. 1934. Jordan, H. V., H. A. Nelson and J. E. Adams. Relation of fertilizers, _crop residues, and tillage to yields of cotton and incidence of root rot. Proc. Soil Sci. Soc. Amer. 4: 325-328. Hill, H. 0., E. W. Lyle and J. R. Johnston. Hubam clover in rotations causes higher yields and less root rot. Tex. Agr. Exp. Sta. Prog. Rpt. 868. 1943. King, C. J. and H. F. Loomis. Experiments on the control of cotton root rot in Arizona. Jour. Agr. Res. 32: 297-310. 1926. King, C. J. and H. F. Loomis. Cotton root-rot investigations in Arizona. Jour. Agr. Res. 39: 199-221. 1929. King, C. J., Claude Hope and E. D. Eaton. Some microbiological ac- tivities affected in manurial control of cotton root rot. Jour. Agr. Res. 49: 1093-1107. 1934. King, C. J. A method for the control of cotton root rot in the irrigated Southwest. U.S.D.A. Circ. 425. 1937. Lyle, E. W. and H. O. Hill. Winter legumes reduce root rot and increase yield of cotton. Tex. Agr. Exp. Sta. Prog. Rpt. 871. 1943. Mitchell, Roland B., James E. Adams and Charles Thom. Microbial responses to organic amendments in Houston black clay. Jour. Agr. Res. 6s: 527-534- I941- Mitchell, Roland B., Dalton R. Hooton and Francis E. Clark. Soil bac- teriological studies on the control of the Phymatotrichum root rot of cotton. Jour. Agr. Res. 63: 535-547. 1941. Pammel, L. H. Root rot of cotton, or “Cotton Blight”. Tex. Agr. Exp. Sta. 1st Ann. Rpt. pp. 50-65. 1888. Rea, H. E. The control of cotton root rot in the blackland region of Texas. Tex. Agr. Exp. Sta. Bull. 573. 1939. Rogers, C. H. Cotton root rot ‘studies with special reference to sclerotia, cover crops, rotations, tillage, seeding rates, soil fungicides, and effects on seed quality. Tex. Agr. Exp. Sta. Bull. 614. 1942. Scofield, C. S. Cotton root rot in the San Antonio rotations. Jour. Agr. Res. 21: 117-125. I921. Shear, C. L. and George F. Miles. Texas root rot of cotton: Field experiments in I907. U.S.D.A. Bur. Plt. Ind. Circ. 9. I908. Streets, R. B. Phymatotrichum (cotton or Texas) root rot of cotton in Arizona. Univ. Ariz. Tech. Bull. 71. I937. Taubenhaus, J. J. and D. T. Killough. Texas root rot of cotton and methods of its control. Tex. Agr. Exp. Sta. Bull. 307. 1923.