Stalk and Root Rot Problems in Corn
Authors: Pierce Paul, Dennis Mills
The negative impact of the floods experienced about a month ago in some parts of the state and the drought experienced in other locations earlier in the season are now being seen as growers begin to harvest their corn fields. Reports of root, stalk, and ear rots are coming in from some fields that were under severe drought or flood conditions during the season. Flood deprives plant roots of oxygen, causing then to die prematurely, while drought and other stresses reduce the total photosynthetic capacity of the plant during ear development, resulting in inferior stalk and root quality. Weakened plants with poor root systems are predisposed to infection by stalk rot fungi. Even saprophytic organisms that would have otherwise not invaded plants with healthy, intact roots may contribute to stalk and root disintegration in flood-affected fields. In general, severely stressed plants are more greatly affected by stalk rot than stress-free plants
The greatest damage caused by stalk and root rot is stalk breakage or lodging. In addition, when plants lodge, ears in contact with the ground develop ear rot, leading to poor grain quality. Scout field for visual symptoms of stalk rot and test stalk integrity by squeezing the lower internodes between the thumb and forefinger. Stalks that are likely to lodge are easily compressed between the fingers. Since the level of stalk rot may vary from field to field and hybrids differ in their susceptibility to lodging, each field should be scouted separately. For more information on the different type of stalk rot and stalk rot management please refer to the OSU Plant Pathology web site "Ohio Field Crop Diseases" at: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/.
With ear rots come the additional concerns of kernel rot and mycotoxin accumulation in storage. In addition to the physical damage caused by ear rots, some ear rot fungi produce mycotoxins that reduce the quality and value of the grain. Storage temperatures above 40F and kernel moisture content of 22% and above are favorable for the growth of toxin-producing ear rot fungi (Fusarium species). Growers are advised to follow certain harvest and storage guidelines to minimize problems associated with kernel rots and mycotoxin contamination:
1. Harvest fields with stalk rot problems early to minimize lodging, and consequently, ear rot development.
2. Harvest at the correct moisture and adjust harvest equipment to minimize damage to kernels. Mold and mycotoxins tend to be higher in (machine or insect) damaged kernels.
3. Dry harvested grain to 15% moisture and below to prevent further mold development in storage.
4. Store dried grain at cool temperatures (36 to 44 F) in clean, dry bins. Moderate to high temperatures are favorable for fungal growth and toxin production.
5. Periodically check grain for mold, insects, and temperature.
6. If mold is found, send a grain sample for a mycotoxin analysis to determine if toxins are present and at what level. Toxins are harmful to humans and livestock. For more on moldy grain, mycotoxins, and mycotoxins sampling and analysis visit the following websites: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm .
Soybean Yellow Stem
Authors: Jim Beuerlein
Many soybean fields throughout the state have dry grain that is ready to harvest but the plants are holding onto some yellow petioles and leaves. This condition usually occurs as the result of poor pod set at some nodes and the fact that the grain was filled adequately without complete digesting of the leaf and petiole at those nodes. Inaccurate windshield observations of this condition may lead to delayed harvest and possibly reduced test weight. Maximum test weight occurs when the grain dries the first time to a moisture content of 13 to 17 percent which is also the moisture content where to least grain damage is inflicted by the harvest operation.
The low amount of moisture in yellow stems, petioles and leaves may be transferred to the surface of the seed while harvesting but should evaporate quickly and not increase the grain moisture content. Check the pods on yellow plants carefully. If the seed is loose inside the pod, and the pod will crack open, then harvest can begin regardless of the condition of the stems and leaves attached to the plant.
Nutrient Value of Corn Stover
Authors: Robert Mullen
Some animal operations are interested in corn stover as a feed leading many crop producers to ask - what is the nutrient value of my corn stover?
From a pure fertilizer value, corn stover contains a little phosphorus (P2O5) and moderate amounts of nitrogen (N) and potassium (K2O). The actual amounts of N, P2O5, and K2O contained in a ton of corn stover are 16, 6, and 25 pounds, respectively. A 160 bushel per acre corn crop will produce 4.5 tons of stover per acre removing 72 pounds of N, 25 pounds of P2O5, and 113 pounds of K2O. Thus stover does have some fertilizer value especially with regard to potassium that may require some additional fertilizer input in subsequent years, but soil testing should be conducted to validate the need for additional nutrients.
Corn stover also contains organic matter that when returned to the soil does have value, but it is difficult to put a dollar value on it. Continued removal of the above ground stover may have negative repercussions in the long-run in the form of decreased soil organic matter, especially if some organic residue is not returned to the soil.
Soybean Rust - It's Moving to the North
Authors: Anne Dorrance
Several more counties were turned red last week on the national soybean rust map (http://www.sbrusa.net) in Arkansas, Missouri, South Carolina, Illinois and Iowa. In Iowa, Illinois, Missouri, Kansas the incidence (number of leaves/plants in field) and the severity (number of pustules/leaf) is all very, very low. At this late in the season, this will have no impact on yield. But it does give us some data to see how this pathogen will move and what the incidence of disease is in some of these fields. The rains that fell at the end of the first week of September may have brought rust spores into these states. Interestingly, the rain trap data and the spore trapping data are all negative. Surveys of double crop fields in Ohio are negative so far. More will continue this next week.
State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Robert Mullen (Soil Fertility), Ron Hammond and Bruce Eisley (Entomology), and Jim Beuerlein (Small Grains). Extension Educators: Harold Watters (Champaign), Howard Siegrist (Licking), Jonah Johnson (Clark), Roger Bender (Shelby), Mike Gastier (Huron), Glen Arnold (Putnam), Ed Lentz (Seneca), Wes Haun (Logan), Steve Foster (Darke), Gary Wilson (Hancock), Alan Sundermeier (Wood), Todd Mangen (Mercer), and Curtis Young (Allen).