Early Season Diseases

The May forecast by Environment Canada is for normal to slightly cooler temperatures with a likelihood of above average precipitation for most of Ontario. Cool, wet conditions can favour many early season soil pathogens. Some of the most common culprits in corn and soybeans are Pythium, Fusarium, Rhizoctonia as well as Phytophthora in just soybeans. There are a number of factors other then weather which is important in disease development.

We often recommend the best way to minimize the impact of these pathogens is to plant when soil temperatures are close to optimum which increases seed germination and growth. Although this is ideal in some years it is difficult to get the crop planted in a timely fashion.

There are a number of things that you can do to reduce your risk to these early season diseases. First - Begin with a fungicide seed treatments which is still one of the most economical and effective disease management tools available to producers. Seed treatments are most beneficial under the following conditions: early planting (cool temperatures), fields with a lot of residue (no-till), planting in wet soil conditions, deep planting depth, field with a history of disease problems, are using low quality seed, and have a poor rotation.

Don't forget to take into account the general disease package of the variety. Although there is some degree of tolerance to some early season diseases, there is very little genetic resistance available in most corn hybrids or soybean varieties. Thus, the need for seed treatments will provide added protection under these conditions. One of the best examples of resistance and tolerance is Phytopthora root rot in soybeans.

Other factors that you need to consider is the history of the field, soil type and tillage. Although most early season diseases are caused by organisms that survive in the soil for along time, the better the crop rotation the less build-up of these organsims. The same goes for soil type. Some organisms such as Phytopthora and Pythium love wet saturated soils and therefore, are often found on clay soils or fields with drainage problems. Crop residues are great at minimizing erosion concerns but they can increase early disease problems by keeping soil conditions cooler and
wetter so don't rush these fields.

Keep in mind though the benefits from seed treatments often go beyond just stand count. An increase in seedling establishment and early season plant health can reduce later season plant stresses that can increase yield, quality and reduce diseases.

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