Scouting for Stalk Rot in Corn

Alyssa Koehler, Extension Field Crops Pathologist;

We are entering that time of year to begin scouting for stalk rots in corn. Stalk rot signs and symptoms do not appear until later in the season. After pollination, the ear becomes the major sink of sugars produced by the plant. If a stress event occurs, plants will divert or remobilize sugars from the stalk and roots to meet the needs of the developing ear. Often the pathogens that cause stalk rots are opportunistic and take advantage of plants that have been weakened by potential stress events (drought, flooding, hail, insect damage, foliar disease damage). It is also possible to have multiple stalk rot organisms in the same plant.

Yield losses occur when stalks become brittle and lodge close to harvest. Stalk rots can also result in premature plant senescence and reduced grain fill. When plants are a few weeks from physiological maturity (kernel black layer), stalk rots can be scouted by walking the field in a W pattern and randomly checking stalks with either the pinch or push test. (Aim to check 10-20 plants for every 10-20 acres). For the pinch test, pinch the stalk between the lowest two internodes to see if it can withstand the pressure, if the stalk collapses, it fails. To complete a push test, push the stalk 30 degrees from vertical (around 8 inches) and see how many spring back to upright or lodge. In cases where more than 10% of plants are lodging, you may want to consider harvesting at higher moisture and drying grain after harvest to avoid yield loss due to lodging.

Since stalk rots are linked to stress, the best management strategies are to reduce stress by planting optimal stand populations, irrigating when possible, managing insect pests and foliar diseases, and using a balanced nutritional program. Planting hybrids with some level of foliar disease resistance can also help to reduce plant stress and encourage strong stalk development.