Stalk rot is present in almost all Iowa cornfields to some degree each year, as the pathogens that move in are common and opportunistic, attacking corn as it starts to mature. Fortunately for farmers, in many years stalk rot diseases set in relatively late and don't have much impact on yield, drydown and ease of harvest. However, when plants are stressed from a wide range of factors (nutrient deficiencies, soil compaction, shortage of soil moisture or excess of soil moisture, hail damage, root damage, not enough sunshine, excess heat, etc.) stalk rot can set in earlier and have more impact on yield, drydown and standability.
"This year we have had it all in Iowa, so stalk rot is something we will really want to scout for as we prepare for harvest," says Clarke McGrath, an Iowa State University Extension field agronomist at Harlan in western Iowa. McGrath writes the monthly "Corn and Soybean Insight" column each month in Wallaces Farmer magazine.
Determining stalk quality now will help you prioritize fields that should be in the first half of your harvesting schedule
Most of the more severe stalk rot infections result in deterioration of the inner "pith" tissue inside the cornstalk, notes McGrath, leaving plants much more prone to falling over in storms or even moderate winds.
* Do you need to identify the particular pathogen? For example, is it anthracnose stalk rot, diplodia stalk rot, gibberella stalk rot, pythium stalk rot or maybe a bacterial stalk rot? "I see long articles written that drill down into each of the pathogens and give great descriptions, but often the identity of the pathogen isn't that easy to do nor is it relevant," says McGrath. "Once we get to the point we are seeing stalk rot issues in a cornfield, usually multiple pathogens are present and deciding which one was the initial culprit is tough to do."~~~PAGE_BREAK_HERE~~~
Most stalk rot diseases are caused by fungal organisms, and behave by primarily infecting injured, stressed or maturing plants. Typically, multiple stalk rot organisms are present at initial infections, and then a particular disease is favored by a certain set of environmental conditions.
* What can you do to reduce the incidence of stalk rot in future years? Management to reduce stalk rots for future years is pretty consistent among pathogens; with a few of them you can reduce the pressure by "burying" crop residue, but that can create other issues if soil structure and health is compromised. "In some regions and fields in Iowa tillage is a good option, but I rarely recommend doing that in most of Iowa with our slopes and erosion challenges," says McGrath.
Management suggestions to reduce or avoid stalk rot problems in future years. McGrath lists the following considerations and recommendations:
* Plant corn hybrids with the genetics that have good stalk strength ratings.
* Also, look for hybrids with resistance to leaf diseases; consider applying foliar fungicides if necessary.
* Rotating crops will help a lot. If you must plant corn on corn, talk to your seed dealer about rotating genetic packages.
* Sample your soil and have it tested to ensure soil fertility is optimum.
* If your field tends to be wet, consider drainage management.
* Fine-tune your management to optimize soil structure and planting depth; be sure that corn rootworm and stalk pests such as corn borers are controlled.
Now is time to scout for stalk rot and decide which fields are priorities for harvest
McGrath recommends the following procedure to assess your fields prior to harvest: If you are scouting for stalk rot, look for lower stalk discoloration, and check stalk firmness by pinching the lower internodes. Healthy stalks are firm and won't compress easily; if a node can be "squished" or if it otherwise feels soft, stalk rot has set in and risk of lodging goes up. Check at least 100 plants per field. Try to sample the different "management areas" you have in a field, sample them separately -- various tillage systems, crop rotations, hybrids, drainage issues and fertility histories. Prioritize scouting towards fields that showed stress first. In the droughty areas of Iowa, of course, that was all of them this season!