The following update was prepared by Clemson Peanut Specialist Dan Anco.
We are still in the first week of June, and while most of the planting is complete, the growing season is just getting started. We often talk about the benefits of a good and long rotation cycle in between peanut crops, and SC as a whole is very good at this. As we also know, an important part of maintaining a good rotation cycle of intentionally planted crops is dealing with the unintentionally planted crops, AKA volunteers. Volunteers can be a wrench in the gears of an otherwise healthy rotation, since the presence of that crop (even though in much lower numbers than when the entire field is planted with it) can serve as a food supply for diseases and insects to feed on while they wait/fast for the next round of susceptible host crops. Attached are pictures of late leaf spot lesions and spores from volunteer peanuts in one of the fields at Edisto in Blackville.
When examined directly under the microscope from the field, the lesions did not yet show active spore production. Putting the leaves in a moist chamber overnight produced the characteristic spores in one of the pictures.
We received about an inch and a half of rain last night in Blackville, and with the overcast skies the field is now a bit similar to a moist chamber. Typically we don’t start seeing late leaf spot lesions this early (late July into August is more common), and so far late leaf spot hasn’t started showing up within our planted tests. However, we can see how the fields near these volunteers will be at a higher risk of late leaf spot than fields free from volunteers. Scouting is the best way to ensure fields are free from volunteers. If volunteers are found in a field of a Liberty-link variety (resistant to Liberty), Liberty is an excellent way to lethally manage peanuts. As we start making fungicide applications, volunteer peanuts nearby is another factor that increases our risk of late leaf spot and motivates the use of more premium products.