Considerations When Deciding On Fungicide Seed Treatment Back »

Written collaboratively by Emmanuel Byamukama, Larry Osborne, Kay Ruden, Connie Strunk, and Bob Fanning (former SDSU Extension Plant Pathology Field Specialist).

Fungicide seed treatments protect seedlings from both seed-borne and soil-borne pathogens. Seed-borne pathogens can be those inhabiting the seed surface, such as Pythium spp, or those in the interior of the seed (for example loose smut of wheat). Soil-borne pathogens survive in the soil and when they come in contact with the seed or seedling and the conditions are conducive, the infection process is initiated.

Fungicide seed treatment costs can be high, therefore the decision to treat should hinge on whether the additional yield as a result of seed fungicide treatment can offset the cost of seed treatment.

Growers should ponder on the following scenarios when deciding on a fungicide seed treatment:

  1. What are the prevailing weather conditions? Wet and cool soils are favorable conditions for most seedling pathogens including Pythium spp. and Phytophthora spp. Cool soil conditions also reduce seedling growth rate, hence providing longer interaction time between the pathogen and the host.
  2. What is the history of seedling diseases in your field? For example if a field is known to have high population of the soybean cyst nematode (SCN), then seed treatment with a nematicide may be an option. Preliminary data show that the response to nematicide seed treatment is greater when there is a high population of SCN (>12,000 eggs per 100 cm3 of soil).
  3. Is the crop for seed production? Since grain for seed attracts higher prices, it may be beneficial to consider seed treatment in addition to other factors below. Fungicide seed treatments can also increase the likelihood of the seed being produced and offered for sale as disease free.
  4. Is the crop following the same crop as last season? Survival of seedling pathogens may be higher in non-rotated fields.
  5. Is the crop being planted in a till or no-till/minimum till field? No-till fields may have an increased risk of seedling diseases.
  6. When will you plant?  Planting early in the spring when the soil temperatures are low may increase the risk of seed/seedling infection.
  7. What is the disease rating for the cultivar to be planted? Seed companies provide disease rating for cultivars. For susceptible cultivars to seedling diseases, a seed treatment may be beneficial.
  8. What is the germination rate for the seed lot? For seed with a low germination percentage, seed treatment may protect young seedlings with marginal vigor and improve plant stands compared with untreated seed.
  9. How much stand reduction is acceptable? Some crops like soybean and wheat have a great potential for yield compensation. Therefore slightly reduced plant stand is not going to significantly impact yield.
  10. What is the desired plant population per acre? With increasing costs of seed, growers may be opting for lower plant population per acre, therefore to avoid further loss of plants; a fungicide seed treatment may be justified.
  11. What is the expected price per bushel. Higher prices per bushel would indicate that fewer additional bushels are needed to offset seed treatment costs.
  12. Is the seed for replanting?  If replanting because of stand establishment problems (especially in wet spots) is considered, using fungicide treated seeds may increase chances of survival of replanted seed.

Research conducted at South Dakota State University on fungicide seed treatments in corn, spring wheat, winter wheat, and soybean for the last 6 years indicate inconsistent yield increase as a result of fungicide seed treatments. For example 52% of soybean fungicide seed treatment trials had a yield difference between fungicide treated and non-treated seed of less than 3 bu/acre (Fig. 1). For full results of these field trials, see the following publications:

Plant Diseases & Fungicide Trials

Although the difference in yield was not correlated (P>0.1) with average soil temperature (April 15 through May 15), there appeared to be a general tendency for the difference in yield to decline with increase in temperature. This would indicate as soil temperature was increasing, there was minimum yield difference between fungicide treated and non-treated soybean.

Figure 1. Difference in yield (bu/ac) between fungicide seed treated and non treated soybean grown at Brookings (Br) and South East research farm, Beresford, South Dakota (SE) from 2006 through 2011. Fungicides used had either Trifloxystrobin(blue bars) or Mefenoxam (red bars) active ingredients. The broken line indicate the break-even point (3 bu/acre).

Similarly, other research results from various studies in the Midwest indicated that the probability of seeing an economic benefit from seed treatment depended on the environment and genetics of the cultivar used. If the environment favored high disease pressure (wet and cool soil temperature), and the cultivar planted was susceptible, then seed treatment was beneficial. That’s why it is important for growers to scout their fields and have an idea about the history of plant diseases in their fields.

If seed treatment is discerned to be the best way to go based on the above factors, there are a number of products registered for seed treatment for various crops. Fungicide products that contain the active ingredients metalaxyl or mefenoxam are effective against Oomycetes such as Pythium and Phytophthora spp., while active ingredients like captan, carboxin, thiram, fludioxonil, and PCNB are effective against Rhizoctonia, Fusarium and Phomopsis. Refer to the Managing Crop Diseases with Seed Treatments publication and 2013 South Dakota Crop Protection Guides, available at SDSU Regional Extension Centers or at the iGrow Store for a complete list of products and pathogens listed on the product label.

Fungicide seed treatment will not compensate for bad seed, e.g. shriveled, mechanical damaged or impure seed. It should be noted also that fungicide seed treatments are effective for up to 3 weeks, therefore, slowed seedling growth due to cool soil temperatures or favorable weather conditions for infection 3 weeks after planting may still pose a risk for potential seedling infections.

When treating the seed and generally when working with pesticides, care should be taken before, during, and after seed treatment. Questions including but not limited to: how to handle left-over seed, treated seed spill, protecting birds and other wild life from treated seeds should be addressed. The American Seed Trade Association (ASTA) and CropLife America (CLA) have published The Guide to Seed Treatment Stewardship that is freely available online and can be downloaded on smart phones and portable devices. Always read the product label for handling and application procedures of pesticides.

In the words of George Washington, “Bad seed is a robbery of the worst kind: for your pocketbook not only suffers by it, but your preparations are lost and a season passes away unimproved.” Starting with clean seed in a clean seedbed is a sure way of starting strong.

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