Early August is the time of year we commonly see populations of corn earworms and other caterpillars in peanuts in Virginia and North Carolina. Recent light trap catches would indicate we should see some worms in peanut over the next couple of weeks. Two very appropriate questions have been asked in recent weeks and a quick review of possible answers to these questions is in order.

The first question focuses on the issue of insecticide resistance in corn earworm populations in peanuts. There is some indication that pyrethroid resistance among corn earworms, including the ones we find in peanut fields, is a real concern. However, the pyrethroids cost less than other options and for many growers are the preferred means of control. In addition, pyrethroids are not the best choice for controlling tobacco budworms or fall armyworms in peanuts and control is often less than satisfactory against these pests. The second question focuses on which product to select if the field is also infested with spider mites.

In our opinion, 100% control should not be an overriding goal when treating for caterpillars in peanuts. Good control of corn earworm can still be obtained in most situations with the high rate of pyrethroids. Guidelines for helping determine which type of product to select in peanuts this year might include the following:

1.Very high populations of worms. If populations exceed 8-10 worms per row foot, then the use of a non-pyrethroid insecticide might be a better choice.

2.If populations of tobacco budworm or fall armyworm make up more than 25% of the population, then the use of a non-pyrethroid insecticide might be a better choice.

3.If you understand that you do not need to obtain 100% control of caterpillars to preserve yield, then the use of a non-pyrethroid insecticide might be a better choice.

4.If spider mites are present, then Danitol or Brigade should be used for caterpillar control.

Guidelines are subject to specific local conditions, but in general we believe that pyrethroids still hold value for caterpillar control in peanuts this year. The recent rains certainly helped with the spider mite situation, but temperatures this week will drive populations back up. If caterpillar and/or spider mite populations increase in the coming weeks, we will update you on any changes in our recommendations.

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.