Effect of dicamba on soybean yields

Yangzhou pioneer chemical CO.,LTD

by Bob Hartzler

The widespread use of dicamba in corn, combined with the high sensitivity of soybeans to this herbicide, results in numerous cases of soybean injury each year.　 The tendency of soybeans to develop symptoms characteristic of dicamba in the apparent absence of the herbicide has complicated diagnosing this problem (see related article).　 When dicamba injury occurs, whether from spray drift, volatilization or sprayer contamination, the common question is "How much will yields be affected?".　As with any source of crop stress, it is impossible to accurately predict yield loss potential from dicamba injury that happens early in the growing season.　This article will summarize results of controlled studies on the effect of dicamba on soybean yields to help evaluate situations that occur in the field.
One of the best studies was conducted by Behrens and Leushen at the University of Minnesota (Behrens, R. and W.E. Lueshcen.　 1979.　Dicamba volatility.　Weed Sci.　27:486-493.)　 They reported that significant injury to soybean due to volatilization from corn fields could occur up to three days after application.　In one out of five experiments they observed minor injury due to volatilization on the fourth day after application.　 Rainfall events after application greatly reduced vapor movement of  dicamba.　
The researchers reported that low levels of foliar injury (leaf cupping) did not influence yield potential (Table 1).　Soybean injury was evaluated three weeks after dicamba drift using　a scale of 0 (no injury) to 100 (complete kill).　 Slight leaf malformations (injury rating of 10) were observed up to 200 ft downwind of treated corn.　More severe injury was observed closer to the corn (injury ratings of 60-70), with terminal bud kill and axillary bud release resulting in short, bushy beans and delayed maturity.　Significant yield losses were not observed unless severe early-season injury was observed.