American Germander (Teucrium canadense) Control in Corn (Zea mays)

Experiments were conducted to develop systems for control of American germander [Teucrium canadenseL. var.virginicum(L.) Eat.] in corn (Zea maysL. ‘Trojan TXS 105A’). Soil-incorporated, preemergence, and postemergence herbicide treatments were evaluated in greenhouse studies. Soil incorporated applications of EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide), atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] effectively reduced its growth. Preemergence applications of alachlor and atrazine did not control American germander. Postemergence applications of the dimethylamine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] the butoxyethanol ester of 2,4-D and dicamba (3,6-dichoro-o-anisic acid) gave 20 to 41% control. Atrazine + crop oil gave 76 to 84% control. Soil-incorporated treatments of atrazine or EPTC + R-25788 controlled American germander better than alchlor when the rhizomes were planted at depths of 2.5 and 10 cm in greenhouse studies. In field trials American germander was a severe competitor in corn, especially when soil moisture was limited, and had the capability of substantially reducing corn yields when not controlled. EPTC + R-25788 and atrazine applied alone or in combinations as preplant incorporated treatments increased yield significantly and controlled 85 to 99% of the American germander 72 weeks after planting. Atrazine + oil was the only effective postemergence treatment.