Compared to past years, we seem to be in a low cycle for many peanut pests. For example, not so many years ago it was pretty common to see rampant twospotted spider mite infestations turning large areas of peanut fields yellow, then brown. Dr. Rick Brandenburg at NCSU and I spent a lot of time in those years developing what at the time was the most effective management strategy: first miticide application at early detection followed by a second in 5-7 days. It took this two-spray system to break the mite egg-laying cycle and stop the infestation. Where have the mites gone? We see a few in fields every year but even in dry years we just do not encounter many really bad infestations. Let’s hope this holds because if we do start having problems, we have almost no control products available. The two general rule-of-thumb practices to lower risk to spider mites are 1) to use insecticides sparingly and only as needed, and 2) prevent mowing or burn down of weedy field edges during the high risk months of July and August.
Another pest that seems to be in a slack phase is the potato leafhopper. You can certainly find hoppers and some evidence of hopper burn in a lot of fields but it is pretty rare to see fields that are badly injured. During the heavy infestation years we ramped up field trials and were able to develop a decent plant injury threshold based on the relationship of percent of leaves showing hopper burn and pod yield. Results showed that yields began to be affected (reduced) when injury exceeded 20-25 percent of leaves. That is, some hopper burn is tolerable and will not cause any yield reduction, but there is turning point. Where are the badly injured hopper fields? Not easy to find these days and hopefully that will not change. Scout fields in July and August and tank mix an insecticide with a leafspot spray, but ONLY if plants are approaching the injury threshold and hoppers are active.
Southern corn rootworm (SCR) has received a lot of attention this summer because of the overall wet conditions that favor this soil pest. Many comments relating to SCR management were recently posted by Dr. Brandenburg and we are on the ‘same page’ so no need to restate. I do have a couple of additional observations. Even in recent moderately wet years we have not been seeing or hearing of much rootworm injury. And in general, we are not seeing as many of the adult cucumber beetles flying in and around peanut fields as we used to. During years with more consistent pressure, Dr. Brandenburg and I did a lot of work to establish the Southern Corn Rootworm Risk Index as a system to determine which fields are at risk. In normal rainfall years, it’s a pretty effective management system. Although we see some variability in its effectiveness, chlorpyrifos (Losrban) is still the only insecticide available if control is needed.
Corn earworm infestation intensity also varies from year to year with the general pattern of being worse in overall dry years and less of a problem in wet years. In my opinion however, corn earworm is only worth mentioning because many people spray for it, even though it is not an economic problem in peanuts. In the 25 years I have been working with the peanut crop, I can recall only ONE case where enough plant material was consumed by worms to result in a yield reduction—and that was in a dry year when the peanut plants had not developed a large canopy. In most years when worms move into fields with full-canopy, knee-high plants, they cannot eat enough leaf tissue to be a threat.
In summary, in general we seem to be in a ‘quiet’ period for peanut insect/mite pests. Pressure by mites, hoppers and rootworms has been generally low in recent years and so far, we have not experienced the burrowing bug or three-cornered alfalfa hopper problems that plague some Georgia and South Carolina growers. We have also been lucky with lesser cornstalk borers. Of course this could all change—in one year. So, feel lucky—but stay vigilant and question the need for each and every insecticide spray.
