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Keep An Eye Open For Stalk Rots

Oct 09, 2017
By Rebecca Vittetoe 
Field Agronomist 
Over the past couple of weeks we’ve been doing stalk rot assessments at several of the ISU Research Farms including the Southeast Research and Demonstration Farm, the McNay Research Farm, and the Ames Farm. While the plants seemed to be standing well, minus where the raccoons had fun in one of the trials, it was not uncommon to find stalk rots in the plants we sliced open to evaluate.
This is a good reminder that initial symptoms of stalk rots are not easily observed. Unfortunately we typically don’t notice stalk rots until either the exterior stalk tissue is affected or lodging or snapping has occurred.
We encourage you to get out and take some time to evaluate your fields for stalk rots. Check stalk firmness by pinching the lower internodes (“pinch test”). If the stalk crushes easily by hand then the integrity has been reduced by stalk rot and the risk of lodging goes up.
An alternative to the pinch test is the push test. With the push test, push the plant tops approximately 30 degrees from vertical. If the plant fails to snap back to vertical, the stalk has been compromised by stalk rot. Either method works fine.
With both tests randomly select a minimum of 100 plants in the field. We suggest while walking through the field, stop at five different spots and evaluate 20 plants. You want to get a good representation of the field.  If more than 10 percent of plants in a field exhibit stalk rot symptoms, that field should be one of the first or next fields harvested to reduce the potential for plant lodging and for yield loss.
The shiny black blotches on this stalk rind are very characteristic of Anthracnose stalk rot. Photo taken 9/22/17 at the Southeast Research and Demonstration Farm. 
Discoloration and a rotting pith caused by a stalk rot. Photo taken 9/22/17 at the Southeast Research and Demonstration Farm.