1974 Soybean Herbicide Performance in Southeastern Kansas 1974 Soybean Herbicide Performance in Southeastern Kansas

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Louis J. Meyer, Agronomist Fred W& Boren, Station Superintenden t Thirty herbicide treatments were evaluated to determine: 1) how well they control weeds in soybeans, and 2) soybeans' tolerance of them. Nontreated, weed free, and cultivated plots were compared. The site was a Cherokee silt loam soil (1.4% organic matter). Herbicides were applied in 25 gallons of water per acre using a tractor-mount ed plot sprayer with 30 pounds pressure, and size 8003 nozzles. Plots were 10 feet wide (four 30-inch rows) and 30 feet long. Fertilizer was 15 pounds N, 50 pounds P 2 o 5 , and 50 pounds K 2 0 per acre. No rain fell the first two weeks after herbicides were applied June 19. July 4 it rained 0.21 inch, July 15, 0.61 inch.

Procedure
Preplant incorporated (PPI) herbicides were applied June 19 to cleantilled plots; then plots were tandem-disked once. Next, the plots were overseeded with a mixture of weed s eeds (containing primarily pigweed and crabgrass), springtoothed once, and drag harrowed once. Columbus soybeans were planted June 19 at 10 seeds per foot and covered 1.5 inches deep. Preemergent herbicides (PRE) were applied immediately after soybeans were planted. All plots were rotary hoed June 23. Cultivation-o nly plots were cultivated July 17 and August 1. Postemergent (POST) treatments were applied August l and August 27. The center two rows of each plot were harve sted October 24 by a self-propelle d plot combine.

Results
Lack of rainfall after planting resulted in poor weed emergence, but enough large crabgrass (Digitaria sanguinalis) emerged for July 25 control ratings. A second crabgrass germination flush followed late summer rains. On September 4 we evaluated control of late germinating crabgrass.
Soybean yields correla te well with early crabgrass control percentages, and demonstrate that controlling weeds increases soybean yields. No visual soybean injury occurred from any herbicide treatment tested.
Amiben, Treflan, and Lasso + Lorex were included as standards of comparison. For the July 25 date, Treflan controlled crabgrass best of those t hree and gave the highest soybean yield. No herbicide tested did b ette r . Several soybean herbicides give excellent grass control (even under droughty conditions as we experienced), but if large-seeded, broadl eaved weeds like velvetleaf, cockleburr, sunflower, jimsonweed, and morninglory are present, a herbicide effective against them should be used a l ong with a good grass herbicide.
FMC 25213 gave only partial crabgrass control early in the s eason, and apparently did not persist long enough to provide control late in the season. FMC 25213 in combinati on with Sencor controlled crabgrass better than either material. alone did.. . Mobil 8475 and Mobil 8479 both gave excellent control of early crabgrass, but only 8479 at 2 lbs. AI/a gave acceptable late season control. The 8475 + Modown combination gave excellent control the ·entire season.
CGA 24705 and CGA 17020 did not effectively control crabgrass early in the season. Late season control with 24705 was excellent. Rate of 17020 we used was too low for our soil. That was at least partially responsible for its relatively poor performance.
Velsicol 5052 did not effectively control crabgrass when used alone or in combination with Sencor.
Probe gave excellent full-season crabgrass control, but soybeans yielded more treated with other herbicides that controlled crabgrass. Probe may have injured the soybeans even though no injury was vi sible.
Soyex was highly effective when used in combination with Sencor, but used alone it gave only partial control of early season. crabgrass.
Bladex with Treflan was no better than Treflan alone. In combinati on with Lasso, Bladex was more effective on early season crabgrass than Lasso + Lorox; less effective on late season crabgrass.
Planavin + Sencor gave excellent control with shallow incorporation before planting except that control did not persist the entire growing season. Applied before soybeans emerged, the combination was only partially effective.
Amex 820 + Sencor provided excellent early season crabgrass control, but only partial control later in the season.
Basaqran + HOE 23408 are both postemergent herbicides. Because Basagran effectiveness on grassy weeds i s limited, results should primarily reflect HOE 23408 effectivene.ss. Crabgrass not germinating uniformly prevented properly timed applications and adversely affected performance. Crabgrass was too large (4-6 inches) for good control when HOE 23408 was applied August 1. However, excellent control of late season crabgrass indicates 23408 has some activity in the soil. The August 1 application was a few days before late season crabgrass emerged. August 27, early season crabgrass was too large to control; late season crabgrass (3-4 inches) was partially controlled. Rainfall totaling 1.55 inches the first 24 hours after August 27 applications probably reduced herbicide effectiveness.   • Means of three replications. Yields are at 12.5% moisture. \.1/hen t hese treatments were applied, they were not labeled for field use in Kansas, and may be used by growers only when approved. Some may be approved for field use in 1975.  Many herbicides or combinat ion of herbicides mentioned in this report are experimental and not approved for use on soybeanso They are not commercially available and may not be used until approvedo Rates of experimental herbicides used are not necessarily the rates that will be recommended when herbicides are approvedo Special thanks are due the following for support: