Date of Graduation

5-2019

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

Roberts, Trenton L.

Second Committee Member

Gbur, Edward E. Jr.

Third Committee Member

Barber, L. Tom

Keywords

atrazine; metribuzin; photosystem II inhibitor; weed control

Abstract

Atrazine is a foundational herbicide for weed control in both corn (Zea mays L.) and grain sorghum [Sorghum bicolor (L.) Moench] production. However, studies have shown that while atrazine may be an effective herbicide for preemergence and postemergence control of weeds, it also has risks. The low Koc of atrazine as well as its extensive use over the past 50 years have led it to become the most common groundwater contaminant near agricultural soils. Given these findings, atrazine has faced severe scrutiny while under consideration for reregistration. In the event that atrazine is not reregistered, corn and grain sorghum producers will be forced to seek alternative herbicides for weed control. Therefore, research was conducted in 2017 and 2018 to test the tolerance of corn and grain sorghum to other photosystem II-inhibiting herbicides in combination with other herbicides and also to test weed control with and without atrazine in corn production systems. When applied preemergence in grain sorghum, all PSII herbicides tested reduced grain sorghum yield compared to atrazine treatments. However, when applied postemergence, diuron, fluometuron, linuron, metribuzin, prometryn, propazine, and simazine did not cause grain sorghum to suffer yield loss when compared to atrazine-containing treatments. When applied preemergence in corn, diuron, linuron, metribuzin, and simazine did not cause yield loss to corn when compared to atrazine. However, when applied postemergence in corn, only corn treated with metribuzin and simazine yielded comparable to corn treated with atrazine. Weed control studies displayed that Palmer amaranth (Amaranthus palmeri S. Wats), pitted morningglory (Ipomoea lacunosa L.), and broadleaf signalgrass [Echinochloa crus-galli (L.) P. Beauv.] can all be controlled without atrazine; however, weed density was low in these studies. This research demonstrates some potential PSII-inhibiting herbicides should be further evaluated to assist corn and grain sorghum producers in controlling weeds if atrazine is not reregistered or its use is severely limited.

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