As cotton enters the blooming period, we should begin transitioning from plant bug management strategies to protect squares–to stink bug management strategies to protect developing bolls. Stink bug populations seem to be on the rise and we are already hearing of a few fields with upwards of 30% internal boll damage.
In Virginia we are faced with a large variation in the maturity stage of cotton fields. Early planted fields (end of April to 1st week of May) have been blooming for 3 weeks or so with a few of the oldest bolls almost at the stink-bug-safe stage (25 days or older, 1.25 inch-diameter or larger). The majority of their bolls are still stink-bug-susceptible (5-24 days old, 0.5-1.24 inch-diameter). Later planted fields (2nd and 3rd weeks of May) are just beginning to bloom. This means that no single recommendation can cover all cases, except that we are firm in the belief that when making stink bug control decisions, following the new Dynamic Threshold will fit. Basically, with this new threshold the allowable percent of bolls with internal stink bug damage changes with crop age. This threshold is based on two concepts: that cotton plants can compensate for relatively high levels of early season boll damage, and that the number of stink bug susceptible bolls changes as plants mature. These concepts were thoroughly evaluated in a cooperative multiple-state project (VA, NC, SC, GA, AL) resulting in the development of the Dynamic Threshold (1st week of bloom-50%; 2nd week-30%; 3rd, 4th and 5th weeks-10%; 6th week-20%; 7th week-30%; 8th week-50%). The many field evaluations also showed that applying the new threshold consistently resulted in higher profit ($) per acre.
If an insecticide treatment is needed for controlling stink bugs, there is a lot of misinformation being passed around as to the best choices. Although the neonicotinoid insecticides are effective against plant bugs, they are not as effective against stink bugs as products like Bidrin or high rates of the pyrethroids. Green stink bugs are easily controlled with most any pyrethroid. Brown stink bugs, if the dominant species in the field, are a bit more difficult to control and products containing bifenthrin seem to have a better track record. Another misconception is that a single treatment will provide ‘weeks of residual control’. Not so. Although they provide a good kill of existing adults and nymphs, none provide residual control against newly invading adult stink bugs. If they do continue to invade fields, especially if they invade several days to weeks after initial sprays, additional treatments would be needed. This has not been common in Virginia, but each year is different so the best defense is careful and consistent crop scouting and applying the threshold until all ‘harvestable’ bolls are safe from bug damage.
