July Peanut Pointers Peanut Notes No. 81 2019
The following is a regular column for Peanut Grower magazine in July
With early season issues addressed, in July and August and into early September growers focus on controlling weed escapes (in particular annual grasses but also broadleaf weeds,) foliar-feeding insects (armyworms, tobacco budworms and corn earworms), and foliar and soil-borne pathogens. Controlling escaped grasses almost always pays for itself because of pod loss during digging. Many broadleaf weeds may be well past the size they can be controlled with herbicides, and pulling up those escapes can help not only this year but equally as important in years to come. Pay particular attention to common ragweed and Palmer amaranth. Escapes of both of these species need to be addressed, especially if you have an intense PPO herbicide regime. We don’t need biotypes of these weeds to get entrenched in fields.
In North Carolina, the threshold for foliar-feeding insects has been increased from 4 per foot of row to 8 per foot of row in July, and from 8 to 12 in August. With the presence of pyrethroid resistance and tobacco budworms, when you need to treat the more expensive yet more effective insecticides are often the best bet for complete control. Leaf spot and stem rot are key issues in the Virginia-Carolina (and elsewhere) and a well-timed, diverse fungicide program with no gaps in protection when pathogens are active is important. Healthy plants in the fall provide the greatest flexibility in digging and give us room to dig at optimum maturity. We had a hot and dry May and that always brings concerns about spider mites. Keep an eye on fields for pockets that may develop and address those areas in a timely manner. Avoid mowing areas around fields in order to minimize movement of mites into peanut fields from weeds. Conversely, if we have significant rain, leading to robust plant growth, the plant growth regulator prohexadione calcium can be an effective option to keep excessive vine growth at bay. While expensive, in surveys of the Virginia-Carolina region about half of the farmers make at least one application of prohexadione calcium during the growing season. Apply at 50% row closure (when half of the vines from two adjacent rows touching) and repeat the application 2-3 weeks later if peanuts begin to have new growth. It is best to error on the side of being late rather than early with the first application: we don’t need to keep peanuts from lapping rows. Always include a nitrogen solution or ammonium sulfate with this plant growth regular.