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Scout for These 4 Corn Diseases

13:00PM Jun 27, 2016

As corn is at or near pollination across much of the corn growing states, it’s important to keep your crop focus on pollinating kernels. Scout for these four corn diseases to take action when possible and protect your bottom line.

Northern Corn Leaf Blight

Northern corn leaf blight favors mild temperatures from 65° F to 89° F. Fungal spores overwinter in corn residue. Next year, select resistant hybrids to reduce the likelihood of developing this disease.

Northern corn leaf blight has spread from Minnesota to Tennessee and is one of the most common corn diseases.

Warning signs and management tips:

  • Corn on corn fields and no-till with a history of the disease are more likely to develop the disease again this year
  • Cigar-shaped tan to gray lesions start on lower leaves and work their way to the top leaves
  • If resistant plants show infection they lesions will appear with yellow, transparent, irregular borders and fewer spores
  • Scout at or after silking during warm, wet conditions
  • Fungicides can slow the infection

Gray Leaf Spot

From corn silking to maturity watch for warm, humid weather to encourage gray leaf spot. The disease overwinters in corn residue, but fungicide can slow the disease.

Gray leaf spot not only limits the plant’s ability to photosynthesize, it also opens it up for more fungus and disease to enter the plant. Scout to catch this disease early.

Warning signs and management tips:

  • Early symptoms show small yellow or tan spots with halos
  • Symptoms later appear as gray rectangular-shaped lesions up to 4” long and 1/8” wide with parallel edges
  • Lesions might appear in early July on lower leaves, but the disease is much stronger and spreads faster in late July and August
  • Use resistant hybrids, tillage and rotation to minimize disease since its soil-borne

Goss’s Bacterial Wilt and Leaf Blight

Goss’s wilt thrives in warm, humid conditions. If you’ve had Goss’s wilt in a field before, you might see it again this year from overwintered spores. Consider resistant hybrids next year.

Fields will be more susceptible if corn has undergone stress from wind, hail, machinery damage or has infection from other diseases that open it up for Goss’s wilt.

Warning signs and management tips:

  • Lesions appear gray, yellow or red striped with wavy margins following leaf veins that might contain dark, watery spots
  • After splitting the stalk you might see orange to brown bundles visible in vascular tissue which can cause stalk degradation
  • There is no in-season fungicide or other treatment available for Goss’s wilt
  • Look for damage near corn silking, but it can appear anytime from May to September

Antracnose Leaf Blight and Stalk Rot

Watch for this disease during warm, wet summers. Since it can infect both the leaves and the stalk make sure you’re scouting early for stressors such as insect, disease, high populations or nitrogen loss. Leaf symptoms appear in late April through July, and stalk rot appears from August to late October.

Warning signs and management tips:

  • The disease overwinters in corn residue, select resistant hybrids to mitigate risk
  • Leaf blight shows ¼” to ½” round or oval lesions that might have small black specks in the center of the lesions; when humid, disease starts on lower leaves and works up to the top leaves
  • Dark brown to black stalk lesions go through the rind
  • After tasseling, infection might cause the top leave the corn plants to die prematurely