Soil Moisture and Effectiveness of Preemergence Herbicides

The relation between soil moisture and the effectiveness of preemergence herbicides for control of giant foxtail ( Setaria faberii Herrm.) was studied under greenhouse conditions using surface soil from Drummer silty clay loam with 25, 31, and 37% moisture. Herbicides used were 2-chloro-4-ethylamino-6-isopropylamino- s -triazine (atrazine), ethyl N,N -dipropylthiocarbamate (EPTC), 3-amino-2,5-dichlorobenzoic acid (amiben), α,α,α-trifluoro-2,6-dinitro- N,N -dipropyl- p -toluidine (trifluralin), 2-chloro- N -isopropylacetanilide (propachlor), and 2-chloro- N -(methoxymethyl)-2',6'-diethyl-acetanilide (hereinafter referred to as CP 50144). The effectiveness of atrazine and EPTC was increased when soil moisture was raised from 25 to 31%, but no further increase was obtained at 37% moisture. Response to amiben increased linearly and response to trifluralin decreased linearly with increasing moisture. Increasing moisture within this range had little effect on propachlor or CP 50144.