Soybean producers may be planting lower quality seed this spring. The main culprit responsible is Phomopsis seed decay, a fungal pathogen that developed on the plants during the wet, cool conditions that prevailed last fall. The cool, wet conditions also caused significant harvest delays extending the length of time that the seed was susceptible to infection and decay.
Another factor contributing to the lower seed quality is thin and fragile seed coats. The repeated wetting and drying cycles that the seed underwent last fall prior to harvest and the fact that much of the seed required drying with heated air are responsible for the thin and fragile seed coats. While much of the soybean seed sold in Michigan will have warm germination rates listed at 90 percent, some seed lots will be tagged at 80 or 85 percent and some may even be tagged at 75 percent where supplies are limited.
The warm germination percentage listed on the seed tag is guaranteed and it is always conservative.
Producers in southern Michigan that typically plant group III varieties may be the most likely to receive lower quality seed this spring as the germination scores for group III varieties have been lower than group II varieties.
Michigan State University Extension says the warm germination test is an excellent indicator of how the seed will germinate under ideal conditions. However, it does not predict how the seed will germinate and emerge in cool or stressful soil conditions. Some type of vigor test such as the cold germination or the accelerated aging test is required to determine this.
The vigor test results should not be used to estimate germination percentages of a given seed lot, but they can be used to compare and rank the ability of different seed lots to germinate and emerge under stressful soil conditions. Vigor test results are not typically provided to producers with the seed. The main reason for this is there is not an industry-wide standard for testing protocols and reporting results.
Submit samples from all seed lots having warm germination scores of 85 percent or less for vigor testing. This is important as seedling vigor deteriorates faster than warm germination. Samples can be submitted to the Michigan Crop Improvement Association in Okemos, Michigan. The cold germination test takes 14 days and costs $14 per sample. The accelerated aging test takes at least 10 days and costs $15 per sample.
Rank your seed lots by the germination score on the tag or vigor test results and consider this information along with maturity to determine your planting order. Always plant your highest quality seed first and your poorest quality seed last. Avoid planting low quality seed into cold, wet soils, poor seed beds or high residue conditions that may reduce seed-to-soil contact. Planting late-maturing varieties early will maximize yield potential while planting early-maturing varieties early will spread out your harvest window.
Fungicide seed treatments will help protect the seed from seed-borne and soil-borne pathogens and have been shown to increase warm germination scores by 10 to 15 percent when pathogens are present on the seed. Because most of the 2019 seed quality concerns are due to Phomopsis, consider having your seed treated with a fungicide that provides good control of this disease whenever the germination score is 85 percent or lower. A list of soybean seed treatments and the diseases they control is available at the MSU Field Crops Pathology website.
The warm germination score listed on the tag should always be used to adjust planting rates. A simple method for accomplishing this is to divide your desired harvest population by the warm germination score and then divide again by the warm germination score to estimate actual emerged seedlings. For example, if seed having a warm germination score of 85 percent will be planted and a harvest population of 100,000 plants per acre is desired, then 138,408 seeds per acre should be planted (100,000 ÷ 0.85 ÷ 0.85 = 138,408).
An excellent soybean seeding rate calculator developed at the University of Illinois will help you fine-tune your seeding rates to achieve your desired final plant stands.
You can reduce the potential for Phomopsis seed decay occurring in the future by using the following management practices:
- Planting seed-bean fields early.
- Planting on well-drained fields.
- Selecting varieties that will be ready to harvest before Oct. 1.
- Harvesting when the seed first dries to 13.5 percent moisture.
- Applying a foliar fungicide effective on the disease at R5.
While it is always important to handle soybean seed carefully, this becomes even more important when handling seed having thin, fragile seed coats or lower quality seed. Operate all equipment used to transport bulk seed slowly and keep augers as full as possible. Reduce the height that seed falls from augers and conveyors and never drop bagged seed from any height.