MSU Extension

The effect of seed treatments on a wide range of fungal diseases has made seed treatments indispensible for early season small grain establishment. Seed-borne smuts historically caused tremendous yield and quality reductions in grain-growing regions worldwide, but the use of effective seed treatments reduced the incidence and severity of many cereal smuts to the point that they are now rare. Smut problems could re­emerge if seed treatments were abandoned and many seed treatments now have a base requirement that they control smut, but may have additional active ingredients to control other pathogens.

Seed treatments control fungi inhabiting the surface of the seed (protectant) or are internal (systemic). In addition, seed treatments are also effective against soil borne pathogens that cause seed rots, root rots and damping off caused by Pythium. However, seed treatments generally do not control bacterial pathogens or control seed borne viruses. Several modern cereal seed treatments include insecticides to prevent damage caused to seed and seedlings by some soil dwelling insects and larvae. There are several new products with a varied range of activity, plus numerous products with combined active ingredients that are now available for use on small grains (Table 1). Seed treatments are very effective against a wide range of diseases and insects during the most vulnerable stage of the lifecycle of the cereal and are one of the least expensive and safest means of chemical pest control.

See Table 1 for the list of labeled uses for each of the registered fungicides. Seed treatments are an important pest management tool, but should only be used as part of an integrated pest management program. Such a program should include varieties with good general resistance to soil borne diseases, high quality certified seed, crop rotations that can potentially interrupt disease cycles, herbicide management of volunteer weeds and crops, adequate soil fertility, programmed application of other pesticides and, of course, the appropriate seed treatment based on knowledge of the pathological and entomological history of the location. Soil samples can also be submitted to MSU Diagnostic Services to determine the likely pest profile prior to selection of a seed treatment product.

Seed quality should be determined prior to seed treatment as treatment is no guarantee that it will improve seed germination or general performance. In fact, poor quality seed is more likely to be damaged by some seed treatments than high quality seed. Seed should be planted as soon as possible after treatment – like foliar treatments, the efficacy of seed applied pesticides decreases with time. Protectant seed treatments control pathogens on the surface of the seed whereas systemic seed treatments control internal pathogens; both types of pathogen can infect the seedling or the seed.

Diseases controlled

The three main types of disease controlled by seed treatments are the smuts and bunts, the seed and seedling diseases, and the root rots. The main smuts and bunts in Michigan include common bunt and dwarf bunt and are well controlled by Dividend products, Charter products, Raxil products, Ramona products and Vitavax. In dry years, if winter wheat is seeded into very dry soils, dry seed decay may occur. Symptoms include the growth of a blue-green mold (Penicillium) on the seed surface and can result in reduced germination.

Seed treatment with Vitavax or Raxil products and other listed products for general early season rots are effective. Fusarium seedling and seed rot is a common problem in small grain production in Michigan. Infections are rarely lethal, but can impact over winter survival. A range of species of Fusarium may cause seedling rot,but generally seed treatments, which control one species, are effective against the others. Vitavax and Maxim products provide excellent control of Fusarium species. Generally, seed treatments are ineffective against Fusariumhead blight developing later in the season.

Pythium is a soil­borne fungus that can cause pre­ or post­emergence damping­off of small grain seedlings. Symptoms include reduced plant establishment and pale-green stunted seedlings. Seedling roots may have water-soaked light to dark brown regions at the root tips. Pythium can be common in cool, wet periods after planting in Michigan, but the systemic seed treatments containing metalaxyl or mefenoxam (i.e., Apron, Belmont and Allegiance) can protect against Pythium damping­off. Since the activity of metalaxyl or mefenoxam products is limited to Pythium, they should always be used in combination with seed treatments effective against other pathogens.

Soil-borne diseases

Rhizoctonia solani can cause seedling blight and root rot in small grains. Symptoms occur during the early development of plants, causing them to become severely stunted and roots of infected plants have distinct sunken, brown lesions. The pathogen overwinters on plant debris and is most common in minimum­ and no­till systems. Maxim-based products and Dynasty are useful against Rhizoctonia, but should be mixed with broad-spectrum seed treatments.

Take­all is a destructive soil-borne disease of small grains that is extremely difficult to control. The disease develops through the season and after heading symptoms includes areas of bleached plants with unfilled heads. Plants have poor or rotted root systems with shiny, black roots. Take-all is favored by continuous wheat for two to five years, high alkalinity, low fertility (especially N and P), compaction, moderate temperatures (average daily 70^oF), and early­planted winter wheat. RTU-Baytan-Thiram is the only seed treatment registered in Michigan with Take-all listed as a suppressed disease.

Table 1. Small grain seed treatment products, common names and uses. View table as a pdf file.

^aGSR = General seed rots (such as those caused by Aspergillus and Penicillium).
FSR = Crown and foot rot caused by scabby seed and soil borne Fusarium
SR = Seed rot, damping off and seedling blight caused by Cochliobolus sativus.
ESR = Early Season Root Rot or bare patch (Rhizoctonia).
LS = Loose Smut (Ustilago tritici).
CB = Common bunt (Tilletia tritici; T. laevis)
TA = Take all (Gaeumannomyces graminis)
P = Pythium
ESF = early season foliar disease such as powdery mildew, common rust and Stagonospora leaf blotch
I = Insects

Dr. Kirk’s work is funded in part by MSU’s AgBioResearch.