Following are ‘collaborative’ comments by Rick Brandenburg, David Jordan (NC State) and me regarding the insect/mite situation on peanuts.
Rootworm: July is the month when we think about spider mites and southern corn rootworm. The two are quite different in that spider mites do best under dry conditions and rootworms do best under wet conditions. Add to that the fact that rootworms must be treated preventively and that if it turns dry, not only will you not have rootworms, you will encourage spider mites with the rootworm application. This situation creates lots of unknowns for growers. Make sure you use the southern corn rootworm advisory to make decisions about rootworm treatments. Light, sandy soils will rarely see rootworm problems but are most prone to spider mite outbreaks. Heavier soils retain soil moisture and are more likely to suffer rootworm infestations. July is the key month to treat for rootworms as we have seen poor performance form rootworm insecticides applied in August.
Spider mites: Keep an eye on the weather. Hot and dry will always equal a threat from spider mites. Also, be very careful with ‘automatic’ pyrethroid applications as these can flare mites. If mites become a problem, there are only three products registered for use in peanuts that provide spider mite control: Comite, Danitol and Brigade. Of these, Comite provides the best control and if applied early in the infestation cycle and has often worked with a single application. But in recent years Comite has become difficult for grower to find, and has no activity on worms. Products like Danitol or products with bifenthrin (e.g., Brigade) should be considered if worms and mites are both present. Both can provide decent worm control and at higher rates can provide mite suppression. But sometimes one application of Danitol (or Brigade) might not be completely effective as they knock down adult and larval mites but not eggs. Last year fields were overwhelmed in some areas and a single application wasn’t enough due to the life cycle and high populations. Two applications spaced 5 days apart may have paid dividends under 2010 pressure.
Corn earworm: We are approaching ‘worm season’ in peanuts. We are in the process of doing our annual field corn survey for corn earworm to determine the extent of that population, as it is a good predictor of what is to come in peanuts, cotton and soybean. Preliminary results are showing a moderate to large population in corn, and one that is a bit ahead of schedule. Moth counts in black light traps are still very low which indicates that adults are not moving out of corn yet. We expect to see this picking up in 7 to 10 days. More will be provided when the survey is completed next week. The latest corn earworm pyrethroid resistance monitoring results from Virginia did not show a large jump in resistance level over the past few weeks, but we are continually monitoring and will keep you updated.

The peanut crop has responded to the recent rains and in some fields rows are already nearly ‘touching the middles’. The ‘old-timers’ used to say that the best yields occurred in years when plants ‘shook hands’ by the 4th of July. In that regard, things look very promising. We are seeing an increase in potato leafhopper populations with untreated fields reaching 5-10% hopper burned leaves. Our recommendations for hopper management are to scout field prior to any planned fungicide applications (e.g., for leaf spot) and tank mix an insecticide if plants are approaching 25% hopper burn and hoppers are still active. Automatic sprays may or may not have value. It is easy to check fields for hopper and make those tank mix applications IF NEEDED. Unnecessary insecticide applications are never good, as they waste money and kill beneficial insects that can help suppress future pests by eating their eggs and immatures (e.g., corn earworm). We are also getting some calls about the need for Lorsban 15G applications for soil insects, especially southern corn rootworm. Wet years favor rootworm populations, as the eggs and larvae require high levels of soil moisture to survive. But even in a wetter summer, we have seen little value for Lorsban applications in the sandiest fields. We recommend confining Lorsban to fields with heavier soils and those with a history of rootworm damage.

With the dry weather, spider mites are already showing up in many crops and weedy field edges. Once established, mites are tough to control in peanuts. One of the most risky options is the application of Lorsban 15G under dry conditions. Lorsban can contribute to mite flares in peanuts and it is our experience that Lorsban flared mite populations are especially hard to get under control. Lorsban may be needed for rootworm control at some point in the season, but if fields remain dry, rootworms will not survive in the soil and will not be a threat. Lorsban would be safe if the crop is under irrigation, otherwise, I would recommend holding off for another week or so to see what the weather is going to do. There will still be time to apply Lorsban (through July) if the weather turns and we start getting consistent rains. We are also beginning to see some potato leafhopper damage in peanuts. Lorsban will provide good leafhopper control for a few weeks, but the risk of flaring mites offsets that advantage. A better option would be to apply Danitol at the 6 oz/acre rate which will control leafhoppers, and will suppress the mite population.

It is worth noting that potato leafhoppers are active in some peanut fields. In some of our plots, especially those that were not treated with in-furrow insecticides for thrips, we are approaching threshold levels of damage. Our recommendation is to treat fields if 20-25% of leaves show typical hopper burn leaf damage symptoms (the yellow V-shaped pattern on the leaflet tips) and hoppers are still present in the field. It is important to determine if leafhoppers are still present because we have found that they typically migrate into and back out of peanut fields throughout the season, and may not actually be present even when leaf damage symptoms are obvious. Mid July is a fairly common time to begin seeing thresholds, if they are going to occur. We recommend checking fields just prior to making other sprays (example, leafspot) so insecticides can be tank mixed if a threshold for leafhoppers is detected. Several pyrethroid insecticides are listed for potato leafhopper control. Also, Lorsban 15G will provide some control, if applied for soil insect control.

The attached Word document contains data tables summarizing Dr. Herbert’s 2009 thrips research in peanut. Trials are still in progress. Additional information: peanutthrips-doc