In 2002, the SCB was an unexpected, major problem in the lower Delta parishes of the northeast part of Louisiana. This year, SCB field infestations have been relatively low, but there is some evidence that this pest may have expanded its presence even further north. SWCB field infestations were relatively light this year in May, but pheromone trap counts were unseasonably high at some locations in northern parishes such as Franklin and Richland.
These trap counts suggest that heavy SWCB infestations are likely to occur in some fields during early to mid-June. Another indicator for the next generation of stalk borers is the relative age of first generation borers in the field. Field samples from splitting stalks in late May and early June revealed mainly large larvae and some pupae, thus suggesting a moth flight by mid-June.
Although SWCB pheromone traps are a good indicator for this pest in early summer, there is no pheromone available for the SCB. Therefore, treatment decisions should not be made on moth counts alone. The worst-case scenario would be low SWCB moth counts in the pheromone trap, but heavy SCB infestations in the field. Although field scouting for either pest is difficult and tedious, it is still necessary in order to time insecticide applications properly. Treatments applied too soon may not give sufficient residual control, and treatments applied too late cannot control larvae that have already bored into the stalk. Therefore, it is necessary to detect early activity of borer moths, eggs and/or newly hatched larvae on the front end of the second field generation. If a heavy moth flight is in progress, moth activity in fields can be observed during the late evening before sundown.
Because of complications with field scouting, the treatment threshold for borers has been lowered to 5 percent of the plants with egg masses, newly hatched larvae or freshly bored holes. Although egg masses can be deposited anywhere on the plant, eggs and small larvae are normally found in the middle of the plant, in the vicinity of the primary ear. If bored holes are used as a measurement to determine treatment, it will be necessary to differentiate between new holes with small larvae and bored holes from old damage in May.
The LSU AgCenter recommends the following insecticides for stalk borer control in corn: Capture, Furadan 4F, Baythroid, Asana XL, Ambush, Pounce, Warrior T, Intrepid and Fury. All of these products can provide effective control, if application is properly timed. Intrepid, a new recommendation, provides some additional advantage because of its extended residual activity. High volume aerial application (5 gallons of water per acre) and the addition of a wetter/binder are recommended when using Intrepid. This will ensure thorough coverage and maximize its residual effectiveness. High volume aerial application would probably be beneficial for all recommended insecticides.
Jack Baldwin is Extension entomologist for grains and soybeans with the LSU AgCenter.