Urbana, Illinois
April 4, 2008
University
of Illinois Extension
The
Bulletin No. 2 Article 6 / April 4, 2008
Soybean seed with lower-than-normal
germination, especially in certain maturity groups, is very common this
year. This low germination is apparently due to thin seed coats, which
make seeds more prone to mechanical damage. I have received a few
questions about how fungicide seed treatments may impact germination on
these seeds. Fungicides will not increase germination of poor-quality
seeds when the poor quality is due to mechanical damage. If it is due to
fungal infection, fungicide seed treatments could increase germination
in some cases.
Increased risk of seedling blight could be associated with planting
seeds with damaged seed coats. Research conducted in the 1970s at Ohio
State University indicated that the quality of soybean seedlings that
emerged from seeds with cracked or scarified seed coats was poorer than
of seedlings that emerged from seeds with intact seed coats. Exudation
of nutrients from seed with damaged seed coats can be greater than from
seed with intact seed coats. This nutrient exudation can stimulate
Pythium, a soilborne pathogen that can cause seedling blight of soybean.
For this reason, treatment with a fungicide of seed with damaged seed
coats could provide some protection against Pythium and other soilborne
pathogens that can cause seedling blight.
A confounding factor is planting date. When planting into cool soils,
fungicide seed treatments may have a bigger impact than when planting
into warmer soils. Under cool soil conditions, seeds germinate more
slowly and may be more at risk to some Pythium species that do well in
low temperatures. With soils presently saturated across the state and
forecasts for additional rain, it is unlikely that much "early" planting
will occur. Later-planted fields will likely mean planting into warmer
soils, where fungicide seed treatments may not provide a benefit.
Some seed companies have recommended not treating the "poor germination"
soybean seed this year because of fear of increasing mechanical damage
that could happen in the treating process. In these cases, a planter box
treatment could be used. If the decision is made to treat soybean seeds
or to use a planter box treatment, it is important to use a product that
contains either mefenoxam or metalaxyl, both of which provide specific
protection against Pythium. In addition, the product should contain at
least one other active ingredient (fludioxonil, trifloxystrobin,
carboxin, and others) that will provide protection against other
pathogens.
by Carl A. Bradley |
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