Thursday, May 22, 2014

Estimating Hail Injury to Soybeans

Hail injury can vary among fields, so each soybean field will need to be evaluated separately.  Most soybeans now are early in their development, so the first step will be to determine growth stage, leaf loss, growing point, and axillary buds.  If there is more than one leaf cotyledon or leaf tissue present, there is hope, because soybeans will be able to regrow. However, keep in mind, that if one or both of the cotyledons are lost, early in the growth of the soybean, the growth rate will be reduced.  Leaf loss means that the cotyledon leaves are absent or brown in color.

The soybean growing point is located between the 2 cotyledon leaves (when the soybean first emerges - VE or VC growth stage).  If the growing point becomes injured, the axillary buds will come out of dormancy and develop near the stem, above the leaf petioles (where the leaf meets the stem).  If the plant gets cut or snapped off below the cotyledons, the plant will die.

The growing point will next produce 2 unifoliate leaves (V2 growth stage), above the cotyledons, and these unifoliate leaves also posses auxillary buds above their leaf petiole, where it meets the stem.  Again, these axillary buds are dormant, until an injury occurs to the growing point, and then, these axillary buds become activated to produce soybean growth.

This picture provided by Hans Kandel, NDSU, is a great visual to help in field evaluation and more on soybean growth and development can be found at:
Next, take stand counts (1/1000th of an acre) throughout the field (not just one area of the field) to get an idea of the injury.  Do not count soybeans that are missing leaf tissue, have brown leaf tissue, or are cut below the cotyledons.  The hula hoop method can be used, or you can measure off 17.5 feet within 30 inch rows, and count each uninjured plant to get an average plant population.  If you have 15 inch rows, you can still measure off 17.5 feet, but be sure to count plants on each side for the average plant population.

Remember that soybeans can tolerate low populations and may only have a small amount of yield loss, with a wide amount of plant loss. Populations of 100,000 have the potential to produce maximum yields and populations around 80,000 could potentially produce 90 percent of the maximum yields.  However, the maximum yield potential may be reduced if there are gaps or gaping holes within your field.  You quickly start to lose your maximum yield potential as the plant population average across the field is below 50,000.

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