C.O.R.N. Newsletter 2006-36

Dates Covered: 
October 24, 2006 - October 30, 2006
Editor: 
Curtis E. Young

Be on the Lookout for Ear Molds

Authors: Pierce Paul, Dennis Mills

Due to poor field conditions resulting from recent rains, more that 50% of Ohio's corn is still out in the field waiting to be harvested. As a result, some growers are concerned about mold development and poor quality of the grain harvested from these fields. Ear molds are most problematic when cool, wet conditions occur during silking and early grain development, when the ears are most susceptible to infection. Most ear mold-causing fungi (Diplodia, Gibberella, and Fusarium) survive in corn residue left on the soil surface, and as such, ear molds are generally more severe in continuous corn fields.

DIPLODIA EAR ROT. Wet weather from mid-June through mid-July initiates the development of spores and heavy rain showers just prior to tasseling deliver the spores to the susceptible parts of the plants. Continuous rain in July favors infection and disease development. Diplodia causes a thick white mass of mold to grow on the ear, usually initiating from the base of the ear and growing toward the ear tip. Eventually the white mold changes to a grayish-brown growth and infected kernels appear glued to the husk. Infected ears are usually lightweight and of poor nutritional value. When infections occur early, the entire ear may become moldy. When infections occur late, only a fine web of fungal growth appears on the kernels.

GIBBERELLA EAR ROT. Like Diplodia ear rot, Gibberella ear rot is generally most severe when rain and wet weather occur during the 7-10 days after silking. The fungus enters the ear tips through the silk channel. Optimum temperatures for disease development are 65-70 F. Ears with visible white to pink mold covering the ear tip or more of the ears are characteristic of Gibberella.

FUSARIUM EAR ROT. Fusarium ear rot is especially common in fields with bird or insect damage to the ears. Affected ears usually have infected kernels scattered over the ear among healthy appearing kernels or are confined to kernels that are damaged. The fungus appears as a white mold and infected kernels sometimes develop a brown discoloration with light colored streaks.

Although condition during silking and early grain development were unfavorable for mold development (warn and dry), molds may still develop and reach fairly high levels when ears are exposed to persistent wet weather during harvest. This may certainly be the case this year. Late-season infections generally occur at the base of the ear where the fungi penetrate the husk, and are especially severe when ears do not turn down and water collects at the base of the ear between the husks and the kernel. With ear molds 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. There have been no reports of Diplodia producing mycotoxins under field conditions, however, Gibberella and Fusarium species are know toxin producers. Gibberella zeae (which causes Gibberella ear rot and stalk rot of corn and wheat scab) produces several different mycotoxins that are harmful to livestock. Deoxynivalenol (DON or vomitoxin) and Zearalenone are the two most common mycotoxins found in Gibberella-infected kernels. Hogs are particularly sensitive to these toxins. DON can cause feed refusal at concentrations in grain at around 1 ppm. Therefore the FDA advisory level for DON in corn to be fed to hogs is 5 ppm and this is not to exceed 20% of the diet. Zearalenone is an estrogenic factor causing infertility and abortions in hogs and other animals. In general ration with over 0.5 ppm zearalenone should not be fed to swine. As a general rule do not feed grain with 5% or more Gibberella moldy kernels. Several different Fusarium species are involved with Fusarium ear rot. One common species produces a toxin called Fumonisin. Horses are particularly sensitive to Fumonisin, but cattle and sheep are relatively insensitive.

Hybrids differ in their susceptibility to ear rots, so hybrid selection is very important for managing this disease. In addition, destroying corn residues after harvest and crop rotation also contribute to reduced ear mold problems.

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 first to minimize lodging, and consequently, ear rot development.

2. 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. For long-term storage, dry grain to 13-14% moisture.

4. Store dried grain at cool temperatures (36-44 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/wheat/mycotoxin%20text2.htm
http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm

"Goosed-necked" Corn

Authors: Ron Hammond, Bruce Eisley

We are receiving reports of producers finding down (goose-necked) corn in a few fields as these fields are being harvested. These fields are located primarily in the western part of the state. There are a couple of reasons for goose-necked corn including poor root systems due to environmental conditions and because of rootworm larval feeding injury in August. However, it is extremely difficult to determine what caused the poor root systems at this time of year because of natural decay of the roots. Our best suggestion at this time is to look at the roots and see if rootworm feeding injury is apparent. However, it may be impossible to state for certain at this time that the damage was caused by rootworm. This is the primary reason why we recommend digging roots and checking for rootworm injury in early July, soon after the majority of rootworm feeding occurs.

Odds and Ends on Fall Herbicide Treatments

Authors: Mark Loux

This article contains reminders about fall herbicide treatments for several different situations. Fall treatments can be invaluable for control of a number of weeds, including dandelion, poison hemlock, wild carrot, and dense stands of winter annual weeds.

1) In any wheat field that has not yet been planted or where the wheat has not yet emerged, an application of glyphosate is the most effective treatment for control of dandelions and winter annuals. This is a far more effective tool for management of dandelion than any of the herbicides that can be applied to emerged wheat. Application of glyphosate at this time will typically result in wheat that is free of winter weeds next spring. As a result, spring herbicide treatments, where needed, can be timed for best control of early-emerging summer annuals such as giant ragweed, marestail, and lambsquarters.

2) Where glyphosate was not applied prior to emergence, it is possible to apply other herbicides to emerged wheat yet this fall for control of winter annuals. Broadleaf herbicides labeled for application in the fall to emerged wheat include Harmony Extra, bromoxynil, dicamba, Peak, and Sencor. Of these herbicides, Harmony Extra provides the broadest spectrum of control of winter annual weeds. There are also four herbicides labeled for fall application to emerged wheat for control of winter annual grasses: including Axial (annual ryegrass); Maverick (downy brome and cheat); Olympus (downy brome and cheat); and Osprey (annual bluegrass and annual ryegrass).

3) We spend a lot of time discussing fall treatments for corn and soybeans, but they can be an effective tool for control of certain weeds in pastures and hayfields. The biennial weeds that are common in pastures, such as bull thistle, burdock, and poison hemlock, can be effectively controlled at this time of the year. This is also the best time of the year to apply herbicides for control of Canada thistle. Unfortunately, all of the herbicides that control these weeds will also injure or kill any desirable legumes in the pasture. See the "Pasture" section of the "Weed Control Guide for Ohio and Indiana" for more information on herbicide effectiveness on specific weeds.

4) Late-summer seedings of alfalfa often become infested with winter annual weeds, such as chickweed, mustards, field pennycress, wild turnip, and wild radish. These weeds can compete with the alfalfa in the fall and early spring, reducing the health of the stand and the quality of the first cutting next spring. Wild radish and wild turnip can be extremely difficult to control in the spring, because overwintering plants already have a well-developed, large root by the time herbicides can be applied. Fall herbicide treatments provide the most effective control of these two weeds. We have somewhat limited research on the control of wild radish and wild turnip, but results so far show that Butyrac (2 qts/A) or Pursuit plus Butyrac (1.44 oz + 1 qt/A) is among the most effective treatments. Pursuit will injure any grasses in the field, especially in new seedings. In Roundup Ready alfalfa, fall application of glyphosate (0.75 lb ae/A) should also control most winter annual weeds and dandelions.

5) We have heard from many growers over the years who manage to treat some portion of their acreage with fall treatments, and would have treated more but ran out of time or favorable field conditions. Not all fields require or benefit from fall herbicide treatments, but the benefits of fall treatment are substantial in fields with dense populations of winter weeds. We seem to be having a long harvest season due to wet weather, and it is possible that fall herbicide treatments will move to the bottom of the "to do" list as a result. Should this be the case, consider arranging for custom application of herbicide in those fields where fall treatments are needed.

Fall Slug Sampling

Authors: Ron Hammond, Bruce Eisley

The next month is the time period when slugs should scouted for potential problems next year. Sampling is easiest following harvest. While we do not have thresholds, sampling will indicate whether a field has a small or large slug population.

There are a number of ways to sample for slugs. The main technique is placing wood boards or roofing shingles on the ground across the field and checking them by counting the number of adult slugs underneath the traps. It is best to count the slugs in the morning. Ten traps in a field would be a good number to use. Other ways of determining if fields have a lot of slugs is by visiting the fields in late evening before dusk or early in the morning during periods of heavy dew or fog for slugs crawling on the plant residue. Growers are also advised to look underneath the leaves of larger weeds that are covering the ground.

To repeat, although no thresholds are available, fields with large numbers of slugs should be monitored more closely next spring. Fields with low numbers, while still needing sampling next spring, can be a lower priority.

Soil Compaction Concerns from Grain Harvest

Authors: Randall Reeder

For many Ohio farmers, this is the wettest fall since 2003. Wet soil compacts easily and that can lead to problems next spring.

Here are some tips to help reduce compaction, ranging from quick and cheap, to things that work long term:

1) Run tires at the correct pressure for the load. Many farm tires are over-inflated which reduces the tire footprint, increasing compaction. Over-inflation also reduces traction.

2) Remove excess weights. For a tractor used to pull gravity bed wagons, remove weights that are only necessary for tillage operations.

3) Don't fill the grain cart to capacity. On wet soil, plan to empty the grain cart when it's half to three-quarters full. The grain cart is usually the heaviest piece of equipment in the field, followed by the combine and tractors.

4) Try to empty the combine before the grain tank is full. Of course this may reduce field efficiency a bit during harvest, but could pay off in less compaction.

5) When you make several trips across a field, try to run in the same path, rather than making a new track with each pass.

6) Add more tires, or switch to bigger tires or rubber tracks. More rubber in contact with the ground for the same total axle load means tire inflation pressure can be lower, reducing pressure on the soil.

7) Practice controlled traffic. Wet soils show the value of a system where all traffic is confined to specific paths year after year. With auto-steering systems more available today, the opportunities for controlled traffic are much greater than a few years ago.

8) Use permanent no-till, perhaps with strip-till for corn. Soil that is tilled every other year does not develop a good structure that can support heavy loads as well as long term no-till.

Archive Issue Contributors: 

Pierce Paul and Dennis Mills (Plant Pathology), Mark Loux (Weed Science), Randall Reeder (Agricultural Engineer), Ron Hammond and Bruce Eisley (Entomology). Extension Educators: Roger Bender (Shelby), Todd Mangen (Mercer), Howard Siegrist (Licking), Gary Wilson (Hancock), Harold Watters (Champaign), Bruce Clevenger (Defiance), Curtis Young (Allen), Glen Arnold (Putnam), Ed Lentz (Seneca), Steve Foster (Darke), Keith Diedrick (Wayne) and Greg LaBarge (Fulton).

About the C.O.R.N. Newsletter

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.