r r r Ap T -P C A* R r a 4 4VA Y1 p a0 % w < I1 tar 9 g t a * ",S CONTENTS Page INTRODUCTION __ ...------------------------------------------------- 3.. Weed-Crop Competition Principles Row Spacing------EXPERIMENTAL PROCEDURE 4 5---------------------5------------------7---------------7-------------------12 Weed-Crop Competition Experiments Experiments on the Quantitative Effects of Florida Beggarweed and Sicklepod on Peanuts Row-Spacing Experiments Row-Pattern Experiments --------------------RESULTS AND DISCUSSION -----Research on Weed-Crop Competition Research on Row Spacing SUMMARY AND CONCLUSIONS .. LITERATURE CITED ACKNOWLEDGMENTS ------------------------ 12 ----------------------12 23 ............................ 33 ---------------------------------....---------------------------------------------- 35 35 FIRST PRINTING 4M, NOVEMBER 1982 Information contained herein is available to all persons without regard to race, color, sex, or national origin. Production of Peanuts as Affected by Weed Competition and Row Spacing' Ellis Hauser and Gale A. Buchanan 2 INTRODUCTION Weed-Crop Competition Principles AN UNDERSTANDING of some principles involved in competition among plants provides an increased perspective of competition between weeds and peanuts. The first principle involves the competitive effects between plants. These effects depend upon the relative ability of the two plants to utilize growth factors in the environment. Similarities in foliar and root characteristics and methods of reproduction contribute to competitive relationships between weed and crop plants. The closer the similarity of plants, whether between or within species, the more they will compete with each other - this is one reason why the legumes Florida beggarweed [Desmodium tortuosum (Sw.) DC.], peanuts (Arachis hypogaea L.), and sicklepod (Cassia obtusifolia L.) are so competitive with each other. The second principle is that the species which first occupies a given space has an advantage over later invading species. These late emerging weeds are less competitive. However, the degree of this competition varies with the crop and weed species. Therefore, growers should concentrate weed control efforts during the early part of the spring season. The third principle of weed competition is that weed species vary in competitive effects on a given crop. For example, Texas panicum (Panicum texanum Buckl.) undoubtedly competes better sanguinalis(L.) Scop.]. with peanuts than does crabgrass [Digitaria 'Cooperative investigation of the Alabama and the Georgia Agricultural Experiment Stations and the U. S. Department of Agriculture. 2Respectively, Research Agronomist, U. S. Department of Agriculture, Coastal Plain Station, Tifton, Georgia 31793; and Dean and Director, Alabama Agricultural Experiment Station, Auburn University, Alabama 36849. 4 ALABAMA AGRICULTURAL EXPERIMENT STATION Two of the most troublesome weeds in peanuts grown in the southeastern Coastal Plain of the United States are Florida beggarweed and sicklepod. Both of these weeds compete vigorously with peanuts. An understanding of competition dynamics for these broadleaf weeds is especially important, because the nature of the developing peanut foliage precludes the use of directed postemergence application of herbicides. Information is needed as to when these weeds emerge and compete most severely with the peanut crop. Unsuppressed broadleaf weeds and some grass weeds such as Texas panicum may tower 4 to 8 feet over peanuts at harvest, interfering with the harvest and also damaging the harvesting equipment. Knowledge of weed-crop competition will enable farmers to use herbicides, cultivation, and other weed control practices much more effectively. Row Spacing Studies of the effect of row spacing on the growth and yield of peanuts began in the 1890's (1) and since that time have continued on a limited basis. Early investigators emphasized the difficulty in cultivating peanuts in narrow-row plantings. Beattie et al. (2) pointed out that "in commercial practice the intervals between rows vary from a width sufficient for the passage of a mule to as much as 4 feet". Later, Parham (8) found that yields of Spanish peanuts were higher in 18-inch rows than in 24-, 30-, 36-, or 42-inch rows. However, alluding to the difficulty of cultivating narrow rows and to the large quantities of seed needed for planting, he suggested 26- to 30-inch row spacings as the most practical. In more recent studies, Duke and Alexander (4) found that, in 2 out of 3 years, yields of large-seeded Virginia bunch-type peanuts were higher in close rows than in standard-width, 36-inch rows. Within the close-row patterns, yields were similar with either 12or 18-inch rows. They further observed that peanuts planted in conventionally spaced rows produced more extra large kernels than did those planted in close rows. In contrast, row spacing did not significantly affect runner-type peanuts. In other research, Norden and Lipscomb (7) reported a significant 16 percent yield increase of 'bunch' lines of peanuts planted in 18-inch rows as compared to 36-inch rows. The 5 percent yield increase of runner lines was not statistically significant. They used an in-row seeding PRODUCTION OF PEANUTS 5 rate that resulted in equal plant populations in each of the row spacings employed. Cox and Reid (3) conducted many spacing experiments in North Carolina. They reported that increasing peanut plant populations, either by higher seeding rate in the row, or by decreasing row widths, led to higher yields of peanuts. Decreasing row widths was generally the more effective and consistent means of increasing yields. In Alabama, Mixon (6) failed to show a yield advantage when runner-type peanuts were planted in 12- and 18-inch rows as compared to 36-inch row spacing. He did suggest other possible advantages of close-row peanuts such as better opportunities for control of weeds and diseases with pesticides. Mixon's research did not include Florunner since this variety was not available at the time. -Much of the research conducted prior to 1950 was neither conclusive nor statistically analyzed. Most early investigators, however, did emphasize the difficulty of cultivating narrow-row plantings. With the precision cultivating equipment and herbicides that are available today, difficulty in cultivation is no longer a compelling reason for the use of conventional row spacing. Statistically significant increases in yields from "close-rows" of runner-type peanuts have not been reported. Furthermore, no publications were found describing the effect of row spacing on Florunner, the most widely grown cultivar in the United States. The objectives of these studies, conducted from 1971 to 1981, were to determine (a) the effects of different periods of weed-free maintenance or weed competition on the yield of peanuts, (b) emergence dates of the weeds that are severe problems at harvest, (c) the effects of row spacing on yields of peanuts, and (d) the influence of row spacing on the weed-crop competitive relationships involved in growing Florunner peanuts. EXPERIMENTAL PROCEDURE Weed-Crop Competition Experiments Experiments with sicklepod were conducted from 1971 to 1973 at Headland (Dothan loamy sand), and at Plains, Georgia (Greenville sandy clay loam). Studies with Florida beggarweed were conducted at Tifton, Georgia (Tifton loamy sand). Unless otherwise stated, all other experiments described were conducted at Headland and Plains. 6 ALABAMA AGRICULTURAL EXPERIMENT STATION In one experiment conducted at both locations, peanuts were maintained weed-free by hand-weeding for various periods of time, table 1, after peanuts cracked through the soil surface. At the end of the weed-free maintenance periods, weeds were allowed to emerge and remained undisturbed. In the other experiment, weeds were allowed to compete with the peanuts for specified periods of time after the peanuts cracked through the soil surface. At the end of each period of competition, the weeds were removed by hand and the peanuts were maintained weed-free until harvest. In the combination competition-cultivation experiments, sweeps were set flat to cultivate shallow 4 weeks after the peanuts emerged. Stands of Florida beggarweed were erratic at Tifton because the planted seed did not emerge. To establish treatments without peanuts at Headland, the emerged peanut seedlings were removed by hand-hoeing shortly after emergence. At Plains and Tifton, peanuts were not planted in the no-peanut treatments. The whole plots were "weeks of weed-free maintenance" while the split and split-split plots were (a) peanuts versus none and (b) cultivation versus none, respectively. At the end of each period of weed-free maintenance or competition, weeds were counted, harvested, and weighed. After the respective weed-free maintenance periods, the dates of newly emerging weeds were recorded by placing labels near the seedling weeds. Thus, the dates of emergence of weeds which eventually overtopped the peanuts could be identified. Peanuts were harvested by combine in August or September and the pod weights were recorded. Samples were taken from each plot for use in determining market value. In all competition experiments sicklepod was planted to supplement the natural stands at Headland and Plains. Florida beggarweed stands were erratic at Tifton because of poor emergence. Other weeds were controlled with benefin (N-butyl-N- ethyla,a,a-trifluoro-2,6-dinitro-p-toluidine) at 1.5 pounds per acre incorporated 3 inches deep before planting at all locations. In addition, vernolate (S-propyl dypropylthiocarbamate) at 2.5 pounds per acre was injected for the control of nutsedge when the peanuts were planted at Tifton. Unwanted escaped weeds were hand-weeded shortly after they emerged. Treatments were arranged in a randomized complete-block design with four replications for the weed-free maintenance experiments and in a split, split-split plot design for the competition- PRODUCTION OF PEANUTS 7 cultivation experiments. Individual plots consisted of four rows each 25 feet long (with the two center rows for harvest) at Headland and two rows (each 25 feet long) at Plains and Tifton. A check (two-row plot) containing the weed under study, but also planted to peanuts, was left between each treated plot at Plains and Tifton. Row width at Headland was 36 inches. At Plains and Tifton, a modified two-row pattern accommodated flat-bed culture with two rows 28 inches apart on the bed, with 36 inches between the rows on adjacent beds. 'Florunner' peanuts were planted at Headland, and 'Tifspan' at Plains and Tifton. Recommendations of the Alabama and Georgia Cooperative Extension Services were used to control insects and diseases in all studies. Analyses of variance and Duncan's multiple range test were run on all data. Experiments on the Quantitative Effects of Florida Beggarweed and Sicklepod on Peanuts Immediately after planting Florunner peanuts at Headland at 100 pounds per acre, sufficient seeds of Florida beggarweed and sicklepod were sowed, with a hand-pushed planter to give 130 to 200 seedlings per 3 feet of row. The weed seedlings were thinned to 0, 0.5, 1.0, 3.0, 6.0, and 36.0 plants per yard of row after they grew to 1 inch and then again at 3 to 4 inches. All weeds except Florida beggarweed or sicklepod were removed by hand. Fresh weight of weeds, cut at the ground level, was determined about 2 weeks prior to peanut harvest. The in-shell peanuts were harvested, dried, and weighed. Independent experiments were conducted with each weed species in randomized complete-block designs with four replications. The experimental design was based on an additive crop-weed interaction model, wherein the yields obtained from growing a crop at a constant population were affected by changes in weed and, therefore, total plant population density. Since the experimental variables were quantitative, regressions were determined for the effects of Florida beggarweed and sicklepod populations and fresh weights on peanut yields. Since the regression coefficients for the several years for each species were not homogeneous, the results are presented on an annual basis. Row-Spacing Experiments Experiments were conducted from 1974 to 1977. Both sickle- 8 ALABAMA AGRICULTURAL EXPERIMENT STATION pod and Florida beggarweed were included in Alabama experiments, but only sicklepod was stulied in Georgia. The experimental design w.as a split plot with four replications. Whole plots were dates of wa eed emergenc e. These included: (a) 0 weeks of weed-free maintenanc e, that is, weeds emerge with peanuts; (b) 2 weeks of w eed-free maintenance, that is, weeds allowed to emerge about 2 weeks after the peanuts; (c) 5 weeks of weed-free maintenance, that is, weeds allowed to emerge about 5 weeks alter the peanuts; and (d) season-long weed-free maintenance, that is, peanuts maintained free of weeds for the entire season. Florunner peanuts were planted in all experiments. Split plots were row spacing of 32, 16, and 8 inches. The rows spaced 8 and 16 inches apart are referred to as "close-row" spacings. On the Greenville soil, the peanuts were planted on b)eds which measured 62 inches between the tractor wheel centers and about 50 inches from shoulder-to-shoulder of the bed. Two rows, 32 inches in width; 3 rows, 16 inches in width, and 5 rows, 8 inches in width were centered on each bed. On the Dothan soil, 2, 4, and 7 rows of peanuts were planted to give 32-, 16-, and 8-inch row spacings, respectively. The number of peanut seed planted per 3 feet of row was constant, 10 to 12 per 3 feet regardless of row spacing. In later research , other row patterns were used without the variable of weed-free naintenance intervals (1979 and 1980) and with "normalized" seeding rates (1977 'K -ai~srM h_ .aa a. :! P- 9~.. 01, , PRODUCTION OF PEANUTS 9 a <7 SW S 9, 'K -'-A b a - NC -. - ~ 3/ a' * a 0 - - *fl ~ ~,rs% Z-~n 'ag ~ ,MA - f -4 aw + Peanuts planted in (1) 32-inch, (2) 16-inch, and (3) 8-inch rows waon after emergence of uicklepod plant in rows, Wiregrass Substation, 10 ALABAMA AGRICULTURAL EXPERIMENT STATION Sickiepod and Florida lbeggarweedl wetre plantedi with either hand-pushed or tractor-mounted pilnters to gix c ab~out 30) plants per 3 feet of row of we eds. Seeds that had bteen appi op)riately scarifiedl to ensur e high gcirmtination wetre plantedl as follows: four rowas of weeds per ro of' peanuts in peanut r ows spaced 32 inchles apart; tw~o row~s of Na ee(Is per tow of pecanults ini peanutt rows s paced 16 inches apar t; andI one tow of weeds per row of peanuts in peanut rows sSpac ed 8 inches apart. In order to establish cornpar able borde (et ffects, weed1 seeds wer e alwax s planted approximately 4 inches ftr0m the cr op row. Dates of weed emergence (weeks of weed-lice maintenance) treatment were established by band-hoeing anid p)ulling for the specified times. For planted stanlds, weeds were planlted near the end of tihe weed-free maintenance period. For "natural" stands, weed seed already in the soil wxetc simlply al low ed to getinate after the weed-free maintenance periods were completed. If rain had not occurred within 5 days after tihe imlplemlentationl of a weed treatment, the entire experimental atea was itrigated using a sprinkler system. Recommended insect and disease control plractices were used. The entire experimental area was treated with benefin (Balan) applied as a preplant-incorporated treatment to control grasses and small-seeded b~roadleaf weeds. Undesirable escape weeds wvere renioved by hand Wallinl