When it comes to corn diseases, early detection and treatment are key. But what’s even more important is preventing the disease in the first place. Here are a few typical early-season diseases, advice on how to spot them, and strategies for reducing your susceptibility and maintaining your yields:
Anthracnose Leaf Blight
What causes it: The fungal pathogen Colletotrichum graminocola, typically combined with moderate temperatures and wet weather. It often shows up in corn-on-corn situations, thanks to the fungus overwintering in corn residue.
When it shows up: Anthracnose leaf blight presents itself around V1 to V3 in corn.
How to recognize it: Lesions first appear on lower leaves and show up as tan to dark brown, oval or spindle-shaped, and with wavy edges. They can be up to one inch long and a half-inch wide. Lesions can also grow together into large areas that may turn yellow and wither.
Tips to reduce susceptibility: While Anthracnose Leaf Blight might make young corn plants look troubled, the disease rarely causes yield loss. However, certain fungicides specifically target anthracnose leaf blight, and some hybrids offer higher resistance levels. Tillage and crop rotation can also reduce the level of fungus that overwinters and survives into next season.
Physoderma Brown Spot
What causes it: The chytridiomycota Physoderma maydis. Wind and splashing water move sporangia into young plants’ whorls. When those whorls fill up with rain or irrigation water for an extended period, the sporangia germinate and produce tailed zoospores, which swim in the water and infect plant tissue.
When it shows up: Usually around V5 to V9.
How to recognize it: Yellowish or brown round-to-oval spots in bands across the leaves and purplish to brown spots on the midrib. Lesions can also be found on stalks, leaf sheaths, and husks. Node 6-7 infection can lead to brittle stalk rot that will snap easily with just a gentle push.
Tips to reduce susceptibility: Choose a hybrid that offers a strong defense the next time corn is planted in that particular field. Physoderma maydis can survive 2-7 years in the soil and crop debris, so growers need to put a plan in place as soon as it starts affecting yield. Crop rotation can also help, as well as many fungicides.
Gray Leaf Spot
What causes it: The fungus Cercospora zeae-maydis. It attacks lower leaves early in the year during prolonged warm periods (75-85 F) and humid (90%+) weather.
When it shows up: In the V6 to V12 timeframe.
How to recognize it: Lesions first appear as small, hard-to-see pinpoints, but eventually the pinpoints mature into longer, more rectangular gray to brown spots. They expand parallel to major leaf veins and can be up to two inches long. Leaf tissue infection reduces a plant’s photosynthetic area, leading to lower carbohydrate production meant for grain fill, then more stalk rot and lower yields.
Tips to reduce susceptibility: Select more resistant hybrids (ask your local AgriGold agronomy expert), try out fungicides, and manage residue with tillage or crop rotation to enhance breakdown. Growers should also keep plants clean from ear leaf up.
If you’re looking for more tools to defend against these diseases ask your local AgriGold agronomy expert which hybrids could offer the most resistance.
Crop Production Network. 2022. Anthracnose Leaf Blight of Corn. https://cropprotectionnetwork.org/resources/articles/diseases/anthracnose-leaf-blight-of-corn
Iowa State University Extension and Outreach. 2015. Physoderma Brown Spot and Stalk Rot. https://crop.extension.iastate.edu/cropnews/2015/07/physoderma-brown-spot-and-stalk-rot
Wise, Kiersten. 2010. Diseases of Corn Gray Leaf Spot. https://extension.purdue.edu/extmedia/bp/bp-56-w.pdf