Date of Graduation

8-2013

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Norsworthy, Jason K.

Committee Member

Scott, Robert C.

Second Committee Member

Mauromoustakos, Andronikos T.

Third Committee Member

Slaton, Nathan A.

Keywords

Biological sciences; Carryover; Halosulfuron; Imazosulfuron; Soybean; Sulfonylurea herbicides

Abstract

In the Midsouth, soybean is often grown in close proximity to rice or in rotation with rice. Herbicides used in rice can injure soybean via drift or carryover. Consequently, field trials were conducted to determine the response of soybean (cv. AG 4703) to imazosulfuron drift and carryover (at Fayetteville, Marianna, Keiser and Pine Tree, AR) from rice. To assess the potential for carryover, soybean was planted into rice fields treated the previous year with imazosulfuron (rotation study). To evaluate in-season sensitivity of soybean to imazosulfuron (tolerance study) relative to halosulfuron, a common sulfonylurea herbicide applied to rice, both imazosulfuron and halosulfuron were applied preemergence (PRE) at varying rates and soybean was immediately seeded into treated plots. For the drift study, imazosulfuron was applied at the VC, V2, V6, and R2 growth stages of soybean at 1/256 to 1/4 times (X) the labeled rate of imazosulfuron (336 g ai ha-1). To evaluate carryover potential, imazosulfuron was applied PRE to rice at 112 to 672 g ha-1for the rotation study; whereas for the tolerance study, imazosulfuron and halosulfuron were applied at 1/256 to 1/4X the labeled rate of imazosulfuron and halosulfuron (52 g ha-1). Soybean was highly sensitive to imazosulfuron drift, with injury (stunting and purple veins, typical of acetolactate synthase-inhibiting herbicides) resulting at all rates and application timings. At 2 weeks after treatment (2 WAT), topical application of the highest (1/4X) rate of imazosulfuron caused more than 73% injury at the VC application timing. Soybean recovered from the injury, with little to no injury observed from the lowest four rates of imazosulfuron applied at the VC and V2 growth stages by the end of the growing season. For the carryover trial at 2 weeks after planting (2 WAP), soybean exhibited 3 and 13% injury at Keiser and Pine Tree, respectively, when imazosulfuron was applied to rice the previous year at 672 g ha-1, a 2X rate. Injury to soybean was transient and not apparent by the end of the growing season. For the tolerance study, sulfonylurea-tolerant (STS) soybean was not injured. Moreover, no injury was observed on non-STS soybean by PRE-applied imazosulfuron or halosulfuron regardless of herbicide rate, and yield was comparable to the non-treated control. Results of this research indicate that imazosulfuron should be applied with extreme caution to rice as off-target movement will likely cause injury to non-STS soybean (cv. AG 4703) in adjacent fields and applications of imazosulfuron may carryover to non-STS (cv. AG 4703) soybean on silt loam soils having low organic matter and a high soil pH, especially in fields where overlap of an imazosulfuron spray occurred in the preceding rice crop. Under conditions conducive for imazosulfuron to injure soybean via off-target movement or carryover, planting of STS soybean is recommended to avoid possible risks of soybean injury.

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