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Soybean
Seedling Blights
Compliments of
Agronomy Services Department
This is a very common problem in soybeans
planted early into cool soils. In understanding Seedling Blights and
diseases it is important to know the effect of planting date, soybean
varieties and field drainage.
Early planted soybeans can increase yields
but can also create added stress on soybean seedlings. Soils should be
planted between 50 to 55 degrees F for the seed to germinate. Planting in
soils below these temperatures causes slow emergence and enlarged
hypocotyls. If there is a herbicide in the soil the seedling will be
absorbing it while it lays in this unfavorable condition. These swollen
hypocotyls are more vulnerable to seedling blight, Rhizoctonia, and
Fusarium root rot.
Some of the symptoms of Seedling Blight
(damping off) are; roots turn brown with a soft texture, seeds become
covered with mycelium and is creamy to the touch, and seedlings wilt as
the roots turn brown and eventually die. Some look-alike symptoms from
flooding, dinitroaniline and triazine carryover may be wrongly suspected.
There are several herbicides that could show similar symptoms, so know
what was put on last year as well as the current year.
Soils can "crust" over when
intense rains fall on heavily tilled soils. Seedlings can become deformed
and spend their energy reserves in their attempt to emerge. The best
management tool for this situation is a rotary hoe to loosen the soil and
help the seedlings emerge. Compacted soils with "hard pans" can
cause the seedlings to have distorted root systems and result in abnormal
growth.
Fertilizer "burn" can occur when
occur when salts come in contact with developing seedlings and is more
common when banded applications of nitrogen and potash are used. It would
be a better recommendation to use a very low N and P starter fertilizer,
such as, 10 � 34 � 0 for seedling safety. Symptoms can be leaf
necrosis, bluish appearance, stunting, and sudden wilting of the seedling.
Solutions to Seedling Blights are
management related. Plant seed in well drained soils when soil
temperatures are consistently 55 degrees F or above. Use planter box seed
treatments to help protect seed in cooler soils. Plant varieties that are
rated good to excellent for emergence. The affect on yield is dependent on
evenness of the final stand, variety planted, planting population, and
growing conditions the remainder of the season. Those varieties with the
ability to branch can compensate for stand loss.
For more agronomic information, go to our
web site at: www.mycogen.com
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