I recently posted on the ineffective management tactic of aerial insecticide sprays for stink bugs in corn (link to previous post). For the past two years, I have tracked the movement of brown stink bugs from wheat to corn, with work continuing this year. Last year, I documented significant densities of stink bug nymphs moving from wheat stubble into corn. So this year, with the support of the Corn Growers Association of North Carolina, I sprayed a pyrethroid on wheat stubble located directly adjacent to corn after wheat harvest. Here are the results two days after treatment:
Live stink bugs: wheat stubble sprayed, 1.33 per square meter, wheat stubble unsprayed, 0.58 stink bugs per square meter- no significant difference.
Dead stink bugs: wheat stubble sprayed, 0.33 per square meter, wheat stubble unsprayed, 0.42 stink bugs per square meter- no significant difference.
Stink bugs in weeds along the ditch bank separating wheat and corn: wheat stubble sprayed, 0.68 stink bugs per sweep, wheat stubble unsprayed, 0.98 stink bugs per sweep- no significant difference.
Stink bugs in corn: wheat stubble sprayed, 0.05 stink bugs per plant, wheat stubble unsprayed, 0.03 stink bugs per plant- no significant difference.
Clearly many stink bugs are in the weeds along the ditches. I expect these stink bugs to move into the adjacent corn within the week. Although I will continue to monitor the population, I do not think that spraying wheat stubble had or will have any impact on movement into adjacent corn.
Other management options might be to spray the ditches. However, the ditch in this study was filled with water. Spraying a pyrethroid over water is a definite no-no- a ten foot buffer between water and the spray-zone is specified on pyrethroid labels. Furthermore, these labels carry a 30-day pre-harvest interval restriction for use in wheat. So stink bugs in wheat that might move into corn must be targeted with an insecticide once they move into corn. Right now, our only effective option for stink bug management in corn is to use ground-applied sprays (link to previous post for recommendations). The future of insecticide management for stink bugs in corn looks bleak given our current options.