“What are you seeing?” is a question I have been getting and giving quite a bit the last couple weeks. The answer is a mixed bag of insects and a lot of variation in the level of pressure from field to field.
We have seen three cornered alfalfa hopper (TCAH) numbers increase over the last 14 days, and that comes with a lot of questions about if and when to treat for them. Though the adults are what we commonly see, it is the immature stages or nymphs that cause most of the stem girdling.
Can we treat the adults and prevent eggs from being laid? Maybe. The trouble is that TCAH adults are highly mobile, and if we make an insecticide spray today, there is no guarantee that more adults will not migrate into the field three days later. We expect eggs that are laid in mid-summer to hatch in about seven days. It will take nymphs 6 to 9 days to complete the first two stages of development. These early developmental stages are not known to girdle stems. It is the third through fifth instar (developmental stage) nymphs that are responsible for the bulk of stem girdling.
So what does all that mean? If a field is being scouted regularly, and the TCAH activity/population in that field is known, then you have some time from the initial increase in adult numbers until you would see an increase in stem girdling activity…at least two weeks to go from egg to third instar nymph.
Waiting to make an insecticide application could reduce the chances of needing to treat twice. If a field has not been scouted and/or the history of TCAH activity is unknown, making the decision to treat or wait will come down to a best guess. Keep in mind that we still do not have an economic threshold for TCAH.
There is quite a variety of caterpillars in our fields right now. I have seen a lot of loopers and good numbers of velvet bean caterpillars in several fields. Mixed in with them are corn earworm, cutworms, redneck peanut worm, and armyworms. We encourage growers to use the thresholds that exist for foliage feeding caterpillars and not spray fields just because the neighbors are spraying.
We continue to catch burrower bugs in light traps. We have nothing with which to compare 2015 light trap captures, so all we know is that the bugs are present. I am concerned about damage in dry areas…especially ones with a history of burrower bug damage. This is no different than any other year, but we do know that the insect is active.
Lesser cornstalk borers are present in some fields. Fields in dry areas are going to be at increased risk, but controlling the insect in dry weather is difficult at best. The spots in the fields that wilt first are likely areas to look for LCB larvae. In non-irrigated fields and dry corners of irrigated fields, growers who applied granular chlorpyrifos (Lorsban) for LCB or burrower bug should keep a close watch for early signs of spider mite infestation.