Look for potential corn seedling diseases
May 9, 2019
Symptoms of Stewart’s wilt (left) and symptomless corn plant (right). (Photo: JK Pataky, Universitiy of Illinois)
The spring of 2019 has been one of the coolest and wettest springs in most of the Midwest. Planting in most of the Corn Belt has been delayed. Hopefully, there will be fewer seedling diseases due to later plantings and warmer soils. However, farmers still need to be on the look-out for potential corn seedling diseases as corn seedling blights can still cause problems and affect plant stands. The cool and wet conditions are ideal for fungal seedling blights. Corn that was planted earlier in some areas or in no-till ground is more susceptible to these diseases. Recent cool and wet periods were ideal for the disease organisms that cause seedling blights.
The pathogens that infect corn seedlings are species of Pythium, Fusarium and Rhizoctonia. These fungi over-winter in the soil or plant debris and infect a substantial portion of the developing root system, including the mesocotyl which attaches the primary roots of the seed to the developing seedling, or the seminal roots.
Roots appear brown and become soft, rotted and water-soaked. The outer tissue of the infected roots may peel off. Yellowing and stunting of the plants may occur.
The sprouted seeds of the infected plants start rotting and become mushy and the seedlings become a brownish color. Survival of the seedlings depends on healthy germinating seeds which should remain firm and mesocotyl should be white.
Stewart’s bacterial wilt can also affect seedlings. It is caused by the bacteria Erwinia stewartii which is injected into the plants when the flea beetles feed on them and leave streaks on the leaves. If the plants survive, this pathogen can cause bacterial leaf blight. If there are tiny black flea beetles at the seedling stage, control them by spraying an insecticide. Fungicides don’t control bacterial diseases.
For the future, crop rotation may be helpful in reducing inoculum levels, but some fungi can affect both corn and soybeans. Use of the best seed treatments available is strongly recommended.