Biology, control and competition of spotted spurge Euphorbia Maculata L. in soybeans

Laboratory and greenhouse experiments to investigate factors affecting germination, dormancy, viability, and emergence of spotted spurge (E̲u̲ph̲o̲r̲b̲ia̲ m̲a̲c̲u̲la̲t̲a̲ L.) were done from 1978 to 1981. Optimum germination temperatures were 25 to 30 C. The optimum pH for germination was 7. Germination was not significantly different at seed moisture levels of 4 and 11% during storage. Storage of spotted spurge seed at an alternating temperature regime of 4/21 C for 2 to 8 weeks reduced dormancy when compared to storage at -9/21 C and constant temperature treatments of -9, 4 and 21 C. Gibberellic acid significantly increased germination of dormant seed compared to other treatments. Seed stored at 4 C maintained viability for 2 years but declined during the third year of storage. Emergence of spotted spurge seedlings decreased with increased depth of planting and no emergence occurred from depths greater than 4 cm. The preemergence and preplant-incorporated herbicides were applied to coincide with soybean planting dates at each location. The best and most long-lasting control of spotted spurge was with metribuzin [4-ainino-6-t̲e̲r̲t-butyl-3-(methylthio)-a̲s̲-triazin-5(4H̲)-one] and alachlor [2-chloro-2',6'-diethyl-N̲-(methoxymethyl) acetanilide] were applied preemergence, Linuron [3-(3,4-dichlorophenyl)-l-methoxy-lmethylurea] applied preemergence provided poor control. Alachlor and metribuzin gave the most complete and longest-lasting control. Vernolate [S̲-propyl, dipropylthiocarbamate], trifluralin [α, α, α-trifluoro-2, 6-dinitro-N̲,N̲-dipropyl-£-toluidine], and pendiraethalin [N̲-(1-ethyIpropyl)- 3,4-dimethyl-2.b-dinitrobenzeiieamine] applied pre-plant incorporated all gave good control of spotted spurge. Herbicides applied to the soil were more effective than those applied postemergence. Bentazon [3- isopropyl-lH̲-2,1,3-benzothiadiazin-(4)3H̲-one 2,2-dioxide] and naptalam [N̲-1-naphthylphthalamic acid] + dinoseb [2-s̲e̲c̲-butyl-4,6-dinitrophenol] applied postemergence provided poor control, but acifluorfen [sodium 5- [(2-chloro-4-trifluoromethyl)-phenoxy]-2-nitrobenzoate] gave fair control of spotted spurge. Competition studies were conducted to determine the influence of two spotted spurge populations and three spotted spurge removal dates on soybeans. The results indicate soybean seed yields may be reduced more by spotted spurge competition in dry conditions than when adequate moisture is available.