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Wheat Cereal Leaf Beetles and Disease Management
Warmer temperatures and some rainfall have wheat growing! Much of the crop is in Feekes 8 (flag leaf visible) to Feekes 10 (boot splitting) growth stages. To maintain potential yield, upper wheat leaves (particularly the flag leaf – the top leaf) need to be healthy. This includes minimal insect feeding and disease development. Weekly scouting is suggested through the grain fill hard dough stage. Powdery mildew was spotted last week in Duplin County.
Cereal Leaf Beetles
Cereal leaf beetle adults have metallic, bluish-black heads and wing covers. The legs and thorax front segment are rust-red. Adult beetles are 3/16-inch long. Adult beetle feeding is typically insignificant. Female cereal leaf beetle adults lay eggs singly or end-to-end in short chains on upper leaf surfaces (between and aligned with leaf veins). Females lay 100-400 eggs each. Eggs are elliptical, 1/32 of an inch long, and yellow/burnt orange in color. Eggs hatch into larvae in approximately 5 days. Larvae are slug-like with yellow bodies. Larvae yellow bodies are typically covered with black mucus/fecal matter, giving them a shiny black wet appearance. Larvae eat long strips of green tissue from between leaf veins and may skeletonize entire leaves. Severely damaged fields appear white/frosted when lots of green tissue are lost from upper leaves.
The cereal leaf beetle threshold is 25 eggs and/or larvae per 100 tillers. 50% of the threshold should consist of larvae. If threshold is met, low rates of several insecticides (such as Baythroid, Warrior, Karate Z and Mustang Max) will control this single generation pest.
Fungal diseases include powdery mildew, leaf rust and stripe rust. Powdery mildew lesions are first noticeable as white, powdery spots on lower leaves and stems. The disease may then progress up the plant. Powdery mildew variety resistance is the most economical control measure. Pay special attention to wheat fields planted to powdery mildew susceptible/moderately susceptible varieties. A fungicide should be applied if powdery mildew reaches 5-10% coverage of the upper leaves.
Leaf rust lesions are small/circular/brown and individually spaced. Stripe rust lesions are small/circular/yellow-orange and merge to form stripes. Leaf rust/stripe rust variety resistance is the most economical control measure. Pay special attention to wheat fields planted to leaf rust/stripe rust susceptible/moderately susceptible varieties. If the variety is rated susceptible/moderately susceptible and 1-3% of the leaf area is covered with lesions, a fungicide should be applied. If the variety is rated resistant or moderately resistant, it likely has adult-plant resistance meaning that although a few lesions will appear, it will not be profitable to apply a fungicide.
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