Seed is susceptible to disease before and during emergence, before the plant’s own defense mechanisms kick in when photosynthesis begins. Seed treatments effectively protect against seed and soil-borne fungus that cause disease during this sensitive time and even go beyond it to protect early leaves while they fully develop.
Below are three examples of seed and soil-borne fungus that affect cereals. These fungus names are often used interchangeably with the disease they cause. That’s why reading seed treatment labels can be confusing. For example, Fusarium spp. and Cochliobolus sativus (C. sativus) are different fungus that can cause the same diseases – seedling blight, root rot and seed rot.
Seed rot affects the seed and is the result of seed-borne infection. Root rot is the visible below ground portion of the disease and can be caused by both seed and soil-borne infection. Seedling blight is noticed above ground and can also be caused by both seed and soil-borne infection.
- Seed-borne fusarium graminearum and other seed and soil-borne Fusarium spp. Seed-borne fusarium graminearum doesn’t lead directly to that seed/plant having fusarium head blight (FHB) but is the result of it and is the same complex. For example, seeding of infected kernels causes seed rot, seedling blight, and root rot leading to reducing germination and emergence and can increase the inoculum in the soil that can cause FHB. Fusarium spp. can be seed or soil-borne and reduce germination, tillers, seeds per head and lead to pre-mature ripening in cereals. Fusarium spp. can be easily confused with C. sativus symptoms.
- Smut. There are three types of smut in barley – covered smut, false loose smut and true loose smut. Covered smut and false loose smut are externally seed-borne while true loose smut is internally seed-borne, because of this, true loose smut can be more difficult to protect against with a seed treatment. However, when applied correctly, they make a definite and highly visual difference when heading time comes. Regardless of the type, smut causes blackened spores at heading. Covered and false loose smut infect the seedlings as they germinate, whereas true loose smut can also be blown by wind and penetrate other embryos in developing seed. This makes seed testing especially important for true loose smut.
- Cochliobolus sativus: A seed and soil-borne disease that causes root rot and seedling blight. Symptoms include small brown spots on the crown roots, lower leaf sheath, and subcrown internode along with reduced germination and emergence. Under favourable disease conditions these will elongate and cause an extensive brown discoloration of the underground part of the plant. In comparison, if you dig up a healthy plant it will have white/cream coloured sheath, and the roots should be white after washed. In addition to reduced germination and emergence C. sativus can cause black point in kernels along with reduced tillering and pre-mature die down.
The graph below identifies soil-borne disease for all crops and the conditions that favor them. Often we’re led to believe that warm, dry soils don’t favour disease. In actuality, soil-borne disease is present regardless of the conditions, with the conditions just favouring one over another.
A seed test that can test for these and other fungal diseases should be done by an accredited lab. Regardless of the conditions, a seed treatment is your best insurance against reduced germination and emergence.