Hill and Furrow

Stalk rots increase lodging potential, which can decrease harvest-able yield, literally leaving much of your yield on the ground. Corn plants are top-heavy and stalk rots increase the chances that plants will fall over (lodge) due to either gravity or wind and weather events. Many of the fungi that cause common stalk rots in Illinois survive in corn residue. Agricultural practices such as continuously planting corn and conservation tillage increase the amount of residue on the soil surface, increasing the risk of stalk rot. High nitrogen and low potassium soils also increase the risk of disease.

The 2012 growing season has been ideal for the development of stalk rots. Mid-season conditions that favored kernel set followed by conditions that favored plant stress increase the risk of disease. At the Northwestern Illinois Agricultural Research and Demonstration Center (NWIARDC), North of Monmouth, early planting, residual soil moisture, and a 2 inch rain on June 30^th resulted in successful and the potential for large ears. After pollination, however, plants received only 0.09 inches of rain during the entire month of July. This, along with high temperatures 5.6 degrees above normal, led to water and heat-stressed plants.

Kernels place a very high demand on the plant for sugars. Stress reduces the rate of photosynthesis, thereby reducing the amount of sugars that the plant is able to produce. If the plant is unable to keep up with kernel sugar demand, the plant can rob sugars from stalk tissue, predisposing it to stalk rots. Many different stresses can reduce the rate of photosynthesis in your crop: too much or too little moisture; nutrient imbalances; and plant injury (ex.: hail, insects, diseases); excessive plant populations; and even long-periods of cloudy weather.

Symptoms

Symptoms of Anthracnose stalk rot were observed at the NWIARDC, both in- and out-side stalks. External symptoms included shiny, black discoloration of the rind (Figure). External symptoms don't tell us what is happening inside the plant as plants with rind symptoms may or may not have internal symptoms, and some plants without any external symptoms can be severely diseased inside. Internal symptoms include blackened and discolored tissue that can be easily crushed.

Stalks were rated on July 31^st and on August 14^th and what a difference 2 weeks makes! Whereas there were no stalk rot symptoms on July 31^st, stalk rots were common on August 14^th. Many stalks had just the beginning symptoms of stalk rot with discoloration at the outer margin of lower nodes (Figure). Fewer exhibited the more severe symptoms of shredded pith tissue (Figure).

If you have stalk rot, there is nothing you can do this year to get rid of it. There are, however, several things that you can do to both minimize your risk of stalk rots in future growing years and reduce your risk of literally leaving your yields on the ground this year.

Future years. Many hybrids carry some level of resistance to stalk rot. Look into purchasing seed with good 'stalk rot', 'lodging', and/or 'standability' ratings. Crop rotation and best management practices such as balancing soil fertility, planting recommended populations, and scouting and treating for insects and diseases that have reached economic thresholds are important ways to reduce your risk of disease.

This year. Scouting for stalk rots is essential to minimize harvest losses. Begin scouting your fields just before physiological maturity (when a black layer forms between the kernel and cob) when grain moisture is between 30 and 40%. Scout each field in one of two ways, by pinching or pushing plants. Regardless of the way you plan to scout, walk each field in a zig-zag pattern, checking 20 random plants from 5 spots in the field. For the pinch test, pinch stalks toward the bottom, below the lowest node, checking for firmness. For the push test, hold your arm up at a 45 degree angle from your body and push the plant to see if the stalk breaks. With either test, there is a significant lodging potential if 10 to 15% of the plants fail your particular test. Harvesting fields with the greatest lodging potential first minimizes your chances of having to harvest lodged corn. If you do have to harvest lodged corn, remember to drive slowly and harvest against the grain.

I wish you all a save a safe and prosperous harvest!