Modeling the integrated management of
velvetleaf in a corn-soybean rotation

Alvin J. Bussan and Chris M. Boerboom

The objectives of this study were to model the influence of herbicides, wilt disease, and mechanical treatments on velvetleaf population dynamics, annualized net return (ANR), and economic optimum threshold (EOT) in a 20-yr rotation involving alternate years of corn and soybean. Mechanical treatments were interrow cultivation in corn and rotary hoeing in soybean. Herbicides at a quarter (1/4x) rate or lower did not reduce velvetleaf seed banks without mechanical treatments in the absence of wilt. Herbicides at full (1x) and half (1/2x) rates decreased velvetleaf seed banks 95% within 6 and 20 yr, respectively, when there was no wilt. Herbicides at 1/2x rates with mechanical treatments reduced the seed bank 95% in only 10 yr, but mechanical treatments did not increase the rate of seed bank decline with 1x rates. Wilt infection had to occur annually to reduce velvetleaf seed banks as effectively as herbicides at 1x rates alone. ANR was maximized with herbicides at reduced rates, even though they were not as effective at reducing seed banks as were 1x rates. The herbicide rate required to maximize ANR increased as the initial velvetleaf seed bank density increased. Mechanical treatments and wilt decreased the herbicide rate re­quired to maximize ANR. In fact, wilt infection increased the ANR of herbicides at reduced rates. The EOT was 0.55 and 0.4 seedlings m-2 when velvetleaf was man­aged with herbicides at 1x and 1/2x rates, respectively. Mechanical treatment had no effect on EOT, but wilt increased the EOT. Herbicides at reduced rates should only be used to manage velvetleaf in fields with a low seed bank density when integrated with mechanical treatments or when the field has a history of wilt. Her­bicides should be used at 1 x rates when fields have a large velvetleaf seed bank and when integrated management practices are not used.

Weed Science, 49:31-41. 2001