In some years, spring stand establishment problems can be severe due to saturated soils, cold soil temperatures, frost injury, herbicide injury, nitrogen deficiencies, seed decay and seedling blights. In some instances seed decay and seedling blight may progress into crown decay resulting in even more severe stunting and yellowing of plants.
Conditions which delay seedling development and emergence give seed decay and seedling blight fungi more of an opportunity to attack developing corn seedlings. Seed decay and seedling blights of corn are generally caused by soil-inhabiting fungi species such as Pythium, Fusarium, Diplodia, Rhizoctonia and Penicillium. These fungi may rot the seed prior to germination or cause pre-emergence or post-emergence seedling blight.
Affected seeds are usually discoloured and soft and may be overgrown with fungi. Rotted seed may be difficult to find because they decompose very rapidly and soil adheres fairly tightly to the decomposing seed. With pre-emergence seedling blights, the seed germinates but the seedlings are killed before they emerge from the soil. The coleoptile and primary roots are usually discoloured and have a wet, rotted appearance.
Most of the fungi which cause seed decay and seedling blight of corn may also contribute to decay of the permanent root system and crown rot of young plants. Tips of the permanent root system may be water soaked and discoloured with the outer layers sloughing off.
The Pythium, Fusarium, Diplodia, Rhizoctonia and Penicillium species are the primary cause of seed decay, seedling blight and crown decay. If conditions are favourable for germination and emergence, these fungi may not have the opportunity to invade seed, germinating seed or young seedlings so seed decay, seedling blights and crown rot will not be significant problems.
On the other hand, conditions that are not favourable for germination and emergence, give these soil fungi more time to attack the seed and developing plants. Numerous other factors also contribute to early season corn establishment problems. Insect damage, nutrient imbalances, herbicide injury, soil conditions and environmental factors, especially saturated soil conditions and oxygen deprivation, may also cause or contribute to early season corn establishment problems.
Corn seedling blights are more severe in wet soils, from post plant irrigation or in soils that have been compacted or remain wet for an extended period of time. If soil temperatures are below 12°C the wet soil conditions favour Pythium seed decay and seedling blight.
Disease severity is also affected by planting depth, soil type, seed quality, mechanical injury to seed, soil crusting, herbicide injury or other factors which delay germination and emergence of corn. Planting high quality seed into a good seedbed when soil temperatures are above 12°C and rising will help minimise the potential for early season problems.
Virtually all field corn seed comes with a fungicide seed treatment. When evaluating corn stands this season, it is important to check several plants to determine the extent of damage to the initial root systems, the mesocotyls and the permanent root systems.