BOLO: Disease Pressure

Weather patterns are part of what dictates the possible pathogens to look for.

aspergillus crown rot
Aspergillus Crown Rot shows up as black sooty spores at the crown of dead plants.

Early hot, dry weather created conditions that favored both Aspergillus crown rot and lesser cornstalk borers says Clemson Extension peanut specialist Dan Anco.

Unfortunately, on the Aspergillus crown rot, the recommendations are to plant good quality, treated seed and include an in-furrow fungicide. After planting, and once dead plants are visible, it is too late to protect plants against this disease.

Maintain Sprays As Much As Possible

Growers should turn their attention now to the next problem diseases, such as white mold and leaf spot.

hopper burn
Hopperburn is the result of potato leafhoppers feeding on leaves and appears as v-shaped yellow areas at the leaf end.

Anco says white mold damage may not be visible until peanuts are inverted, or pulled out of the ground and flipped, so they can dry. However, using a 40- to 45-day application of the fungicide tebuconazole will help curb white mold growth.

He also says early leaf spot and late leaf spot have been found in a few places but are not out of control.

“The dry weather earlier gave us some latitude with starting fungicide programs maybe a little later,” Anco says. “Maintaining protection and making sure we don’t get behind now will keep things manageable as we get further into the season.”

Burn Injury: Phorate or Leafhoppers?

Growers also should look for burn injuries on their plants. Plant burn from the pesticide Thimet, also known as phorate burn, can show up as a variety of symptoms. These symptoms generally start at the tip of a leaf and can be chlorotic/yellow. Several small round brown/black lesions at the tip of leaves are common.

Thimet injury is more symmetrical and different leaflets are commonly affected at the same time. Symptoms can appear near the tips of leaves and can also have wedge or V-shaped appearances. The symmetry is caused by the different plants and leaflets being exposed to the phorate compound in the furrow at the same time.

White mold is difficult to spot and may not be visible until peanuts are inverted. Maintaining a spray schedule is the best way to protect against this disease.

“Thimet injury can at times look alarming, but it is nothing to worry about and is more of a sign that the Thimet is doing its job,” Anco says.

Thimet injury can look a little like hopperburn or leaf scorch.

Hopperburn is the result of potato leafhoppers feeding on leaves and appears as v-shaped yellow (no brown) areas on the leaf end. Treatment for hopperburn should begin when 15-20 percent of leaflets are affected. Hopperburn usually pops up around June or July and typically starts on field edges.

Protect Those Leaves

Leaf scorch disease commonly creates a small black lesion inside of the larger necrotic area on a leaf. This larger brown/necrotic spot of killed leaf tissue can take on a wedge shape. Anco says most fungicides regularly used for leaf spot control are likely also effective against leaf scorch.

If the weather pattern changes to rainy, but still warm, hopefully producers have a good start to their spray schedules to provide maximum protection against diseases that will favor these conditions.

Article by Denise Attaway, College of Agriculture, Forestry and Life Sciences; Public Service and Agriculture

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