Cool, Wet Conditions Favour Corn Diseases!

The somewhat cool but definitely wet conditions that has stalled over much of the province for the last week or so could lead to an increase in early season seedling diseases in corn and for early planted soybeans. If these conditions persist for any longer, corn germination or seedling development may be reduced or delayed. The result could be an increase in early season seed rots, seedling blights and/or root rots showing up in grower fields. Scout emerging corn fields for stand establishment problems (non-uniform emergence, gaps or missing plants) and for disease/insect damage.

The reason I say that corn germination or seedling development "may be" reduced or delayed is because corn is one of the few field crops where virtually 100% of the seed in the bag is treated with a fungicide. Fungicide seed treatments are one of the most economical and effective disease management tools available to producers. Growers can expect at least 2 -3 weeks of protection after planting under most conditions. As we have seen in warm, dry years good quality corn seed can stay in the ground up to a month. However, the wetter (saturated) the soil and the longer soil temperatures remain low the greater likelihood of diseased plants. It is unreasonable to expect any product to completely protect the seed and seedling under prolonged stressed conditions.

Start scouting the low-lying or poorly drained areas of the field since they often are the first to show disease problems. Seed rots and seedling blights are more severe in no-till or reduced tillage fields since heavy residue will keep soil temperatures cooler and wetter longer than conventional fields. Damping-off will occur in conventional fields when the crop is planted early into conditions that favour disease development or when environmental conditions cause the corn seed to sit in the ground for a prolonged period of time. Other factors that delay germination and emergence such as compaction, crusting, deep planting, etc. can also result in a poor stand. Plant vigour is often reduced in those plants that do survive. It is important to distinguish between seedling diseases and other potential problems such as insects, herbicide injury, soil compaction, etc.

When a stand establishment problem occurs look for any signs of insect feeding (holes, chewing, etc.) or abnormal plant growth which would indicate herbicide injury. Seedling diseases and insects often occur in patches and are most common under cool, wet conditions or in low or poorly drained parts of the field. Remember it is not uncommon to find an infected plant next to a healthy plant. This is another indication that a seedling disease or even an insect is the culprit. These are not typical patterns associated with herbicide injury.

Management of these early season diseases in corn is very limited and it basically comes down to whether to "replant" or "not" (next week).

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