Here is a disease and mite update from Clemson Peanut Specialist Jay Chapin.
Pretty simple: We need water not just to fill pods, but also to suppress mites, lesser cornstalk borer, and burrower bugs. All of our most serious peanut insect pests can be controlled with adequate soil moisture.
Time to Check for Disease.
The first week of August is always a threshold to begin checking how well our disease prevention program is working. That’s roughly when late leaf spot or white mold and CBR symptoms start to show up in the field.
We have significant white mold in at least a few fields of dryland 09Bs. Several growers producing runners for the first time have reported white mold on 09B in fields that never had any white mold when planted to Bailey in previous rotations. Bailey is certainly far superior to the runners we have for white mold protection, but the fact that we got such high temperatures so early in the season is probably a factor too. White mold is driven by heat more so than by moisture.
Our worst white mold issues often occur under drought stress when the disease is driven underground.
Responding to White Mold
It’s important to be sure white mold is the primary problem. Dead areas with the root rotted are often CBR with possibly white mold colonizing dead tissue. CBR kills the root first, white mold plants have an intact, flexible root for a long time.
Keep in mind that although we have some highly effective fungicides, there are no sure things when it comes to white mold control. Under heavy disease pressure they all have disease “hits” and none of them work without rain to move them onto the soil surface.
We can make peanuts in fields with white mold hits. We can’t cure the infected row lengths, but we can limit spread down the row from plant-to-plant.
In previous white mold “rescue” tests, Convoy, Provost, and tebuconazole have been the more effective than the strobilurin products (Headline, Abound).
Our standard recommendation for white mold rescue has been Convoy or Provost, usually adding 7.2 oz tebuconazole to Convoy because the tebuconazole is cheap and is still effective against white mold.
We have never had Fontelis or Priaxor in a white mold rescue test, but Fontelis has been as good as the standards on white mold in our preventative tests, and Priaxor was excellent in Dr. Brenneman’s preventative test at Tifton.
Ideally for a rescue treatment, any of these products would be applied immediately before a rain or irrigation, or even in the rain when it’s hard to come by.
Late Leaf Spot
We found a few late leaf spot lesions down in the bottom of the canopy – mostly but not all on rank growing irrigated Bailey.
Responding to Late Leaf Spot
Let’s say late leaf spot lesions are found in the bottom of a dense canopy at about 90 DAP. Depending on variety and how good a pod crop has been set, we have to keep the leaves on the plant for at least 40 – 60 days. It’s hard to get any coverage to the source of infection down in the bottom of the canopy .
I would recommend an immediate application of a systemic fungicide + 1.5 pt Bravo, then come back in 10 days with 1.5 pt Bravo + 10 oz Topsin + tebuconazole (for white mold). Previously we have recommended Headline because it was clearly the most effective against late leaf spot, but in the past two years, Headline performance has slipped significantly in rescue tests. Therefore, the current go-to material for systemic rescue treatment of leaf spot is Provost because it has been most consistent in our rescue tests. Priaxor may ultimately prove to be even better; we will know more after this year.
It’s only a matter of time until spider mite hits get noticed in severely stressed fields in this weather. They often get overlooked in wilted peanuts until a rain greens up the plants and makes damage more visible. Look for yellow areas on the topmost leaves near field borders. Flip the leaves over and you can see the mites crawling on the underside (they’re small but you can see them move). Mites are almost never a problem under irrigation or with near normal soil moisture.
The unfortunate truth is we don’t have good control options labeled on peanut. Comite (2-2.25 pt depending on formulation) is the best choice but you have to catch them early, use 20 gal/ac, and retreat in 7-10 days to get the hatched eggs. There are some highly effective and cheaper options on cotton that we hope will get a peanut label.