Posts Tagged ‘fusarium ear rot of corn’

Dealing With Corn Ear Rot Infected Grain

Friday, September 23rd, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

We continue to get samples of stalk rot, and now ear rots in field corn. More samples of Fusarium ear rot caused by Fusarium moniliforme also known as Fusarium verticillioides have been received in the diagnostic lab this week. Hybrids that have been holding their ears vertical and have poor ear cover can be more susceptible to ear rots that benefit from moisture trapped in the ears. Ears that have been damaged by insects, particularly corn earworm, can also have more ear rot fungal infections. Fusarium moniliforme can produce mycotoxins called fumonisins.(see below), but not all isolates of the fungus produce fumonisins. Infected grain should be dried to 15% or below to prevent mold growth in storage.

When evaluating an ear rot problem, remember that certain ear rots are a warning sign to suspect toxins, but ear rots do not always lead to toxin problems. When potentially toxigenic ear rots are noticed in the field, grain can be managed to minimize toxin development. If more than 10% of ears have a significant amount of mold (25% of the ear or more), these fields should be harvested and the corn dried as soon as possible. The combine will remove some of the moldiest kernels.

Fusarium ear rot caused by Fusarium moniliforme

The best option for moldy grain is to feed it or sell it instead of storing it. However, it should be tested for toxins before feeding. Testing for mycotoxins can be done before putting the grain in storage. The best sampling method is to take a composite sample of at least 10 pounds from a moving grain stream, or to take multiple probes in a grain cart or truck for a composite 10-pound sample. If toxins are present, it is possible that it can be fed to a less sensitive livestock species, such as beef cattle (depending on the specific toxin and its concentration). A veterinarian or extension specialist can help with these decisions. If the grain is sold, there may be a reduced price due to mold damage.

Cleaning the grain removes fine particles that are usually the moldiest and most susceptible to further mold development. Good storage conditions (proper temperature and moisture content, aeration, insect control, clean bins) and regular inspection are essential in preventing mold and toxin development in any stored corn. G. Munkvold (Iowa State Univ. Ext.)

Corn and Soybean Disease Update – August 12, 2011

Friday, August 12th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Corn
Gray leaf spot is increasing in irrigated corn but it is too late to affect yield. This late in the season we often see an increase in gray leaf spot as well as Northern corn leaf blight.

We have seen several samples of ears with the milk line half-way up the kernels with random discolored kernels. This is Fusarium ear rot caused by Fusarium moniliforme. The fungus travels down the silks and infects the individual kernels. Often white fungal growth can be seen as well. Hybrids vary in their susceptibility and infection is favored by hot, dry weather. When severe the whole ear can be whitish. Often most of the fungus growth is limited to the tips of the ears. If grain is to be stored it is important to dry it sufficiently to prevent growth of the fungus to prohibit growth of the mycotoxin, fumonisin.

Individual random kernels and some tip infection by Fusarium moniliforme.

Soybeans
Despite the hot, dry weather downy mildew is showing up in full season irrigated soybeans now. Varieties vary in their resistance, but this fungus disease has never been yield limiting or damaging here. The disease produces numerous small yellow spots on the upper leaf surface and a tuft of grayish fungal growth on the corresponding lower leaf surface.

Downy mildew on the upper leaf surface of soybean caused by Peronospora manshurica.

Grayish tufts of the downy mildew fungus on the lower leaf surface.

Plan Ahead to Deal with Corn Stalk Rots, Ear Rots and Toxins in Grain

Friday, August 20th, 2010

Arvydas (Arv) Grybauskas, Extension Plant Pathologist, University of Maryland; arvydas@umd.edu

Corn harvest will begin earlier this season due to the high average temperatures increasing the speed with which growing degree-days (GDD) have accumulated. Typically in seasons characterized by high temperatures and droughty conditions there is an increase in stalk rots and certain ear rots. Most notably two fungal ear rots that can produce toxins in the grain, Aspergillus and Fusarium ear rot, are favored by these conditions. The more dangerous of the two is Aspergillus. Aspergillus infected kernels can contain the carcinogenic toxins known as aflatoxins.

Aspergillus is a fungus that is highly tolerant of high temperatures. Because of its high temperature tolerance it is the most prevalent ear-infecting fungus during hot dry conditions. The fungus survives is soil and crop debris and is spread to silks by wind and insects. The use of certain types of BT corn have helped reduce the incidence of Aspergillus infection by reducing the insect-associated infections but direct infections are still possible. Stressed corn appears to be more susceptible to infection. Typically only a few kernels near the tip are infected by Aspergillus, but tolerance levels for aflatoxin are in parts per billion (e.g. 20 ppb for human consumption). A blacklight is commonly employed as a quick preliminary test for aflatoxin contamination. A sample of cracked or coarsely ground kernels is illuminated with a blacklight and viewed for a yellow-green fluorescence. It is important to know that the fluorescing material is not aflatoxin itself but often is an indicator of (correlated with) aflatoxin. Other material will fluoresce under blacklight like corn glumes (a.k.a. beeswings), certain weed seeds, and uninfected kernel tips, so that false positives are possible. Since the advisory limits are at ppb levels false negatives are also possible with the blacklight test. There are commercially available rapid test kits that provide better and in many cases quantitative detection, as well as commercial labs that will test for toxins.

Similarly, Fusarium ear and kernel rot is favored by high temperatures and droughty conditions especially when they occur near flowering. There are several species of Fusarium that are involved but generally are different from the primary species that cause scab in wheat. Fusarium ear and kernel rot is important because of a production of a class of toxins known as Fumonisins. Fumonisins are known to cause equine leukoencephalomalacia, “blind staggers” in horses and pulmonary edema in swine, and have been linked to human cancers in other parts of the world. Different tests are required to detect Fumonisins.

Stalk rots caused by fungi leading to premature lodging are also generally favored by stressful growing seasons. In general any stress on the corn plant can lead to insufficient capacity of the plant to provide photosynthate to the developing ear. When the capacity is exceeded the plant mobilizes stored carbohydrates from the stalks to fill the demand. This leads to premature senescence of stalk tissue and predisposes the plant to colonization by any number of opportunistic stalk rotting fungi.

Regardless of the stalk rot or ear rot, there are a few things that can be done to minimize losses and improve the harvestablity. First, harvest the corn at high grain moisture (25 to 27%), and make sure the combine is adjusted properly to minimize cracking. Harvesting as early as practical reduces the time that the damaging fungi have at colonizing the tissue. This reduces lodging due to stalk rots, kernel infection and toxin development. Cracked kernels are more susceptible to post-harvest colonization and toxin development. You can also use simple pre-harvest stalk testing to determine which fields are at greater risk for lodging to schedule harvest accordingly. You can pinch stalk internodes to determine a percentage that are soft and likely to lodge if left in the field, or you can use the push test. The push test is simply pushing corn stalks at arms length and determining the percentage that break. In both cases the greater the number of plants and sites scouted the better the information. A rule of thumb I like is 10 stalks in 10 sites for every 10 acres. It is also important to note that fungicides used near tassel will not have a direct effect on stalk rotting. If there was a foliar disease then fungicides reduce the stress associated with the foliar disease and this indirectly reduces stalk rotting. There is no fungicide residue available by the time stalks are predisposed to stalk rotting fungi to directly affect the colonization by these fungal organisms.

Secondly, to reduce the damage from ear rots and in particular to keep toxin development to a minimum, after harvesting corn at high moisture with careful attention to reduce cracking, dry the corn as soon as possible (within a day or two) to 15.5% moisture or lower. The ear rotting fungi continue to grow in high moisture corn in the bin. Controlling moisture and temperature of harvested corn is the most cost-effective method of preventing spoilage.

Figure 1. Healthy stalk (left), stalk rot (right).

Figure 2. Fusarium ear rot.

Agronomic Crop Diseases

Friday, September 19th, 2008

 Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Small Grains
Be sure that you plant wheat varieties with high levels of disease resistance. Select varieties with high levels of resistance to powdery mildew, leaf rust and stripe rust. Seed should be treated with Baytan, Raxil or Dividend to protect plants from loose smut and common bunt. Varieties that are susceptible to powdery mildew should be treated with Baytan, Dividend or other seed treatment that will protect them from early infection.

Soybeans
Do not ignore soybean cyst nematode. Soil sampling after harvest before any fall tillage is recommended for fields to be planted next season to soybeans following this year’s crop. Do not plant SCN susceptible varieties without soil testing first. Soil sample bags are available from the county Extension offices for $10/sample bag.

Septoria brown spot and downy mildew are still evident on some late beans. Most levels that I have seen should not limit yield in any way.

Charcoal rot was diagnosed this week on a Group IV soybean in Sussex County. The irregular spots of dead and dying soybeans at first observation looked as if they were maturing due to the drought but upon closer observation of the roots and stems that it was charcoal rot. This soilborn fungus infects soybeans early in the season and if stress conditions persist, infection results in lower stem decay and prematurely dead plants. The spots were not that large and the plants did set some pods but it would have been easy to just think it was the drought. Rotation and planting later maturing varieties in areas where charcoal rot has been a problem in the past is the best control program.

 

Charcoal rot on split soybean stem. Note the powdered charcoal appearance of the microsclerotia imbedded in the stem tissue and scattered in the pith.

Corn
Corn harvest is underway so be sure to check corn fields for lodging potential by squeezing the lower nodes or pushing on the stalks. A simple way to do this is to walk through the field and, keeping your hands at chest height, push stalks 8-10 inches from vertical. If 10-15% of the stalks lodge, schedule the field for early harvest before a strong wind results in severe lodging.

Fusarium ear rot caused by Fusarium moniliforme also know as Fusarium verticillioides has been seen this week in several locations. Hybrids that have been holding their ears vertical and have poor ear cover can be more susceptible to ear rots that benefit from moisture trapped in the ears. Ears that have been damaged by insects, particularly corn earworm, can also have more ear rot fungal infections. Fusarium moniliforme can produce mycotoxins called fumonisins (see below), but not all isolates of the fungus produce fumonisins. Infected grain should be dried to 15% or below to prevent mold growth in storage.

When evaluating an ear rot problem, remember that certain ear rots are a warning sign to suspect toxins, but ear rots do not always lead to toxin problems. When potentially toxigenic ear rots are noticed in the field, grain can be managed to minimize toxin development. If more than 10 percent of ears have a significant amount of mold (25 percent of the ear or more), these fields should be harvested and the corn dried as soon as possible. The combine will remove some of the moldiest kernels.

The best option for moldy grain is to feed it or sell it instead of storing it. However, it should be tested for toxins before feeding. Testing for mycotoxins can be done before putting the grain in storage. The best sampling method is to take a composite sample of at least 10 pounds from a moving grain stream, or to take multiple probes in a grain cart or truck for a composite 10-pound sample. If toxins are present, it is possible that it can be fed to a less sensitive livestock species, such as beef cattle (depending on the specific toxin and its concentration). A veterinarian or extension specialist can help with these decisions. If the grain is sold, there may be a reduced price due to mold damage.

Cleaning the grain removes fine particles that are usually the moldiest and most susceptible to further mold development. “Good storage conditions (proper temperature and moisture content, aeration, insect control, clean bins) and regular inspection are essential in preventing mold and toxin development in any stored corn.” G. Munkvold (Iowa State Univ. Ext.)

 

Fusarium ear rot caused by Fusarium moniliforme