Ryan Wolf

Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Plant Science


Herbicides from the irnidazolinone and sulfonyl urea families both inhibit acetolactase synthase (ALS) and became a popular choice for many wheat (Triticum spp.) and soybean (Glycine max (L.) Merill) growers in the late 1980's and early l 990's to control eastern blacknightshade (Solanum ptycanthum Dun. ex DC.), kochia (Kochia scoparia (L.) Schrad ). and wild buckwheat (Polygon11m convolvu/11s L ) Multiple year use of the same chemical mode of action has led to performance problems with kochia when ALS-inhibitor herbicides were used as little as three continuous years in South Dakota Kochia problems have rapidly spread within and between fields due in part to the tumbleweed nature of the mature plant. Today, growers want to continue ALS herbicide use because of the excellent control of problem weeds, but need treatments to control ALS-resistant kochia. Field experiments were conducted to determine control of ALS-resistant kochia using several herbicide strategies. Plots were established in cooperators' fields near Groton and Britton, SD in 1996 and Bath and Verdon, SD in 1997. Postemerge herbicide treatments were applied to wheat and included 2,4-D, dicamba, bromoxynil, MCPA, and Harmony Extra. Soybean treatments were applied at both pre and post emergence timings. Soybean treatments included stand alone treatments and mixtures of imazethapyr, pendimethalin, metribuzin, acifluorfen, bentazon, and lactofen. In wheat, kochia density, kochia biomass, wheat height, wheat density, and wheat biomass were measured 14, 28, 38, and 67 days after herbicide treatment (d.a.t.) and at harvest. Yield, test weight, grain protein concentration, and 1000-kemel weights also were measured in wheat. In soybeans, kochia density, weed biomass, soybean density, and soybean height was measured at 50% bloom and 50% pod. Yield, test weight, protein and oil content also were measured on the soybean grain. Wheat treatments of 2,4-D + dicamba and bromoxynil + MCPA in both years had the best control of ALS-resistant koch.ia with kochia densities of 99 and 90 plants m-2, respectively, at 28 d.a.t.. The untreated check, averaged 600 plant and the Harmony Extra (a mixture of thifensulfuron and tribenuron) treatment averaged 470 plants m-2. Yields from the 2, 4-D + dicamba and bromoxynil + MCP A treatments were 10 to 31% greater than most other treatments in both years of the study. The cost of these two treatments according to the average herbicide prices for South Dakota in 1997 were $6.67 ha-1 and $22.24 ha-1, respectively. However, the bromoxynil + MCPA treatment consistently out yielded the 2,4-D + dicamba treatment by 3 to 21 % over both years and resulted in a higher crop value minus herbicide cost per hectare. In soybeans the pre-emergent plus postemergence treatment of pendimethalin (pre) plus lactofen + bentazon + imazethapyr (post) yielded 3088 and 2786 kg ha-1 in 1996 and 1997, respectively, the greatest in both years. The greatest crop value minus herbicide cost was obtained with this four herbicide treatment combination. Using only a postemergence lactofen treatment had the lowest yield with 2212 and 2178 kg ha-1 in 1996 and 1997, respectively, and the lowest net profit return both years. The results of the wheat experiment indicated that cost effectiveness of using an ALS-inhibitor herbicide in combination with a non-ALS herbicide was poor. Due to the lack of kochia control with ALS-herbicides in these fields, it appears that growers should treat suspected ALS-resistant kochia fields as if the total population is resistant. The results of the soybean experiment indicated that an application of a pre-emerge and post emerge herbicide gave greater control of ALS-resistant kochia than a post emerge herbicide alone.

Library of Congress Subject Headings

Kochia -- Control
Wheat -- Weed control
Soybean -- Weed control
Acetolactate synthase



Number of Pages



South Dakota State University