Stability of corn (Zea mays)-foxtail (Setaria spp.) interference relationships

Variation in interference relationships have been shown for a number of cro p-weed associations and may have an important effect on the implementation of decision support systems for weed management. Multiyear field experiment s were conducted at eight locations to determine the stability of corn-foxt ail interference relationships across years and locations. Two coefficients (I and A) of a rectangular hyperbola equation were estimated for each data sec using nonlinear regression procedures. The I and A coefficients repres ent percent corn yield loss as foxtail density approaches zero and maximum percent corn yield loss, respectively. The coefficient I was stable across years at two locations and varied across years at four locations. Maximum y ield loss (A) varied between years at one location. Both coefficients varie d among locations. Although 3 to 4 foxtail plants m(-1) row was a conservat ive estimate of the single-year economic threshold (T-e) of foxtail density , variation in I and A resulted in a large variation in T-e. Therefore, the utility of using common coefficient estimates to predict future crop yield loss from foxtail interference between years or among locations within a r egion is limited.