WOOSTER, Ohio -- Despite recent rain from the remnants of Fay, parts of Ohio remain abnormally dry, and the drought-like conditions may cause stalk rot and lodging problems in corn.
Pierce Paul, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that dry conditions experienced during grain fill often increase the potential for stalk rot and lodging problems, which can have a significant impact on harvest losses.
"Since the dry spell occurred during grain fill, the damage, unfortunately, has already been done," said Paul, who also holds an Ohio State University Extension appointment. "Any rain in corn production is useful, but it may be a little too late for some of the corn in the state."
Stalk rot and lodging may occur when stalks are weakened as a result of drought or any other stress that negatively affects the photosynthetic efficiency of the plant. Under drought stress conditions, leaves roll up to reduce water loss and as such intercept less light for photosynthesis. The corn plant responds by "cannibalizing" the leaves, stalks and roots in favor of ear development. While the process ensures a supply of carbohydrates for the ear, the removal of carbohydrates results in premature death of the stalk and root tissues, predisposing the plant to fungal infections and, consequently, stalk rot and lodging.
"The presence of stalk rots in corn may not always result in stalk lodging, especially if the affected crop is harvested promptly. Many hybrids have excellent rind strength, which contributes to plant standability even when the internal plant tissue has rotted or started to rot," said Peter Thomison, an OSU Extension agronomist. "However, strong rinds will not prevent lodging if harvest is delayed and the crop is subjected to weathering."
Thomison said that growers can assess the potential for stalk lodging by squeezing the stalk between the thumb and finger.
"A common symptom of stalk rot is the deterioration of the inner stalk tissues so that one or more of the inner nodes can be easily compressed when squeezed," said Thomison.
The "push" test is another way to predict lodging.
"Push the stalks at the ear level, six to eight inches from the vertical. If the stalk breaks between the ear and the lowest node, stalk rot is usually present," said Thomison. "To minimize stalk rot damage, harvest promptly after physiological maturity (about 30 percent grain moisture). Harvest delays will increase the risk of stalk lodging and grain yield losses, and slow the harvest operation."
Drought-stressed corn also faces the potential for mycotoxin development and nitrate problems.
Mycotoxins, especially aflatoxins, are produced by Aspergillus flavus, an ear mold fungus, and drought-stressed corn is most susceptible to infection. Mycotoxins can cause animal and human health problems.
"As the corn dries down and we get closer to harvest, producers should start checking for ear molds by stripping back the husks and examining the ears of 80-100 plants sampled from across the entire field," said Paul. "Since not all ear molds are associated with mycotoxin contamination, it is important to properly identify ear molds before harvest in order to determine if mycotoxin will be a concern and to make adequate marketing and storage decisions."
For more on ear molds and mycotoxins, including sampling and testing for toxins, log on to http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm, or http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/mycotoxin%20text2.htm.
Dry conditions can also lead to the development of toxic levels of nitrates in corn harvested for silage, which can be harmful to livestock. Nitrates are major constituents of fertilizers, and when processed properly by the plant, are converted to harmless proteins. During times of dry weather, plants are unable to convert nitrates into proteins and the nitrates accumulate in the stalks and stems. Research has shown that the lower one-third of a corn stalk can have a nitrate concentration of as much as 5,000 parts per million. By comparison, the leaves accumulate less than 20 parts per million in nitrates.
Thomison said that the best recommendation growers can follow to minimize nitrate toxicity is to delay harvest, especially if drought-stressed corn is suddenly subjected to rainfall.
"You don't want to harvest right after a rainfall," said Thomison. "If growers can wait, say two or three weeks after rainfall before harvesting to allow that nitrogen to be metabolized into amino acids and proteins, then that's the safest for the animal."
For information on testing and feeding corn with varying nitrate-nitrogen levels, check out the following publication: Nitrates in Dairy Rations, available at http://ohioline.ag.ohio-state.edu/as-fact/0003.html.
According to the Ohio Agricultural Statistics Service, 3 percent of Ohio corn has been harvested for silage so far. Despite dry conditions, especially in the northwest region of the state, the corn crop remains 80 percent in fair to excellent condition.