Corn may need 'squeezed' before harvest

Farmers are concerned that their corn yields will be lower this year because of the extended dry weather. However, the dry weather may have also affected the stalk quality or the ability of the corn to stay upright until harvest time — generally referred to as lodging. There are two types of lodging — root and stalk. Root lodging generally occurs when the whole plant is still held by part of the root system but leans downward on the side with weaken roots. Roots are weakened or damaged by rootworms, planting too shallow, or by strong winds during the growing season. Generally, the plants will try to correct this situation by growing in a "gooseneck/curved" pattern. Depending on the time of year the root lodging occurred, the plants may still be viable since they are still connected to part of the root system but will not return to the original upright state. Since the stalks are curved, a farmer can generally get the snout of the combine under the stalk and cut the plants by harvesting at a slower speed. Stalk lodging, on the other hand, is a much more serious problem. The stalks will break or bend below the ear causing the ear attached to the stalk to lay flat on the soil surface making it difficult for the combine to pick it up. Also, an ear in contact with the soil for an extended time allows opportunity for the development of kernel diseases. The potential for stalk lodging occurs when corn has been exposed to an extended stress period, such droughty weather. This stress allows stalk rots to invade plants, which in turn destroys the structural tissue required for standing plants. Stalk lodging generally occurs after the plant has reached maturity and the farmer is waiting for the grain to dry to an acceptable harvest moisture. The rest of this article has Ohio State University specialists from the Extension Agronomic Crops Team discussing the interrelated factors that may make corn more vulnerable to stalk lodging. The actual disease, stalk rot, is caused by one or more of several fungi capable of colonizing and disintegrating of the inner tissues of the stalk. The most common members of the stalk rot complex are Gibberella zeae, Colletotrichum graminicola, Stenocarpella maydis and members of the genus Fusarium. The extent to which these fungi infect, and cause stalk rot depends on the health of the plant. In general, severely stressed plants are more affected by stalk rot relative to stress-free plants. When corn is subjected to stress (due to weather, especially drought, foliar diseases or insects) during grain fill, photosynthetic activity is reduced. As a result, the carbohydrate levels available for the developing ear are insufficient. The corn plant responds to this situation by removing carbohydrates from the leaves, stalk, and roots to the developing ear. While this "cannibalization" process ensures a supply of carbohydrates for the developing ear, the removal of carbohydrates results in premature death of pith cells in the stalk and root tissues, which predisposes plants to root and possibly stalk infection by fungi. The stalk rot fungi typically survive in corn residue on the soil surface and invade the base of the corn stalk either directly or through wounds made by corn borers, hail damage, or mechanical injury. Occasionally, fungal invasion occurs at nodes above ground or behind the leaf sheath. The plant tissue is usually resistant to fungal colonization up to silking, after which the fungus spreads from the roots to the stalks. When diseased stalks are split, the pith is usually discolored and shows signs of disintegration. As the pith disintegrates, it separates from the rind (part of stalk that is rich in fiber and lignin), and the stalk becomes a hollow tube-like structure. Destruction of the internal stalk tissue by fungi predisposes the plant to lodging. Nothing can be done about stalk quality at this stage; however, we can minimize yield and quality losses associated with lodging by harvesting fields with stalk problems as early as possible. We recommend to scout fields for visual symptoms of stalk issues and use the "squeeze test" to assess the potential for lodging. Since stalk rots and cannibalization affect stalk integrity, one or more of the inner nodes can easily be compressed when the stalk is squeezed between the thumb and the forefinger. The "push test" is another way to assess lodging risks. Push the stalks at the ear level; if the stalk breaks between the ear and the lowest node, stalk rot or cannibalization is usually present. To minimize further damage/losses, harvesting promptly after physiological maturity is recommended. Harvest delays will increase the risk of stalk lodging, grain yield losses, and slowdown the harvest process. The level of stalk standability issues vary from field to field and hybrids differ in their stalk strength and susceptibility to these factors, each field should be scouted separately. Although research has shown and we can expect better crop standability with new hybrids in the last decades due to breeding and crop protection advancements, lodging can still be a concern. Besides stalk rots and lodging, other issues to watch for include "droopy ears," which can occur for similar reasons that cause stalk lodging (e.g., late season drought stress, and cannibalization in the plant). This effect can lead to premature black layer and reduced yields. Finally, if crop stress is present, that will have effects on grain weight as well (test weight). Ears with low test weight reflect adverse conditions during the second half of the reproductive stages (R3-milk to R6-maturity). From R3 to R6, moisture in the grain is going down, while dry matter accumulation is going up. Approximately 40-45% of grain weight is gained during the first half of the dent stage (R5) alone. By physiological maturity (R6), kernels have no milk line and have reached maximum dry matter accumulation. We know that corn has been stressed by the abnormally dry weather this growing season, particularly in August and September. Farmers need to check fields for stalk integrity by using the squeeze or push test and determine which fields to harvest first because of stalk rots. Ed Lentz is agriculture and natural resources educator with Ohio State University Extension — Hancock County.