By Travis Faske, Extension plant pathologist
Sclerotinia blight of peanut is a cool season fungal disease that was first reported in 2014 in Arkansas. Earlier this week it was reported in two NEW commercial peanut fields in Lawrence and Randolph counties. This is a challenging disease to manage because host resistance is moderate at best, fungicides are few and expensive, and finally, once the disease has been detected in the field there is no way to eradicate the pathogen. Preventing the spread of the pathogen is the best way to keep fields free of Sclerotinia blight. The pathogen can be transported in soil or peanut vines that hitch a ride on cultivation or harvesting equipment, so with peanut harvest on the horizon and current conditions favoring disease development, now is a good time to review symptoms and the necessary steps to take if Sclerotinia blight is suspected.
Sclerotinia blight is caused by Sclerotinia minor and S. sclerotiorum in Arkansas, but S. minor is the greater of the two evils. Here are a few tips when scouting for Sclerotinia blight. Typically this disease begins in mid- to late-September, but with cooler temperatures in August it is developing earlier than normal and symptoms are more severe.
- The first symptom is the “flagging” or wilting of infected branch tips and petioles (Fig. 1). With Sclerotinia blight the leaves are curled rather than clasped together as with southern blight.
- With a closer inspection, the infected stems are often bleached with white fluffy hyphae surrounding the infested stem. Hyphae often become matted around the stem later in the afternoon, when conditions are warmer (Fig. 1 and 2).
- Black sclerotia can be found on and inside infected stems (Fig. 3). These range in size from no. 8 to no. 4 lead shot and often misshapen like very coarse ground black pepper.
What to do if Sclerotinia blight is suspected?
- Confirm that the disease is Sclerotinia blight and document locations in the field where confirmed.
- Consider harvesting non-infested or non-diseased fields before harvesting diseased fields.
- Always power wash equipment (tractor tires, tillage and harvesting equipment) by removing as much soil as possible and all peanut stems before moving from infested or diseased fields to non-infested fields. Thrashing equipment is difficult to clean, hence point no. 2.
- Develop a long ration program. It is best to keep the field out of peanut for at least two years, longer is better because sclerotia (“seed of fungi”) can remain viable for several years.
*Attend winter peanut production meetings organized by University of Arkansas. Management decisions for this disease are different from those of southern blight (syn: white mold, southern stem rot). For example, fungicides that control southern blight do little or nothing to control Sclerotinia blight.