Ray Mueller
Correspondent
GREEN BAY
After a year in which white mold cropped up widely in Wisconsin’s soybeans, and plant diseases and hail affected a portion of the state’s corn crop, there still is no clear answer on how effective the application of fungicides is in combating those problems, Paul Esker, University of Wisconsin Extension Service field crop plant pathologist, indicated in presentations at the 2009 round of eight pest management updates.
A convergence of timing and weather conditions, such as record or near record low average temperatures in July and heavy morning dew on many days, led to the outbreak of white mold in many states, including for the first time in Kentucky, Esker reported. “It was the top disease problem in soybeans this year.”
Yield losses will run from 0.25 to 0.5 bushel per acre for every 1 percentage point of plant mortality due to white mold, Esker indicated. He pointed out that awareness of field history, crop rotations – more years between growing soybeans in the field, soybean variety and chemical or biological controls are ways to mitigate the incidence of the disease.
If nothing else, Esker observed, the past growing season provided researchers with lots of new data on white mold. He noted that the indeterminate growth of long-flowering varieties of soybeans enhances the possibility for the white mold infection, which occurs as soil-borne spores enter the flowers.
In Wisconsin trial plots that were harvested on Nov. 12, the incidence of plant mortality due to white mold ran from 1 to 35 percent in observations made on Sept. 9, Esker noted. He said no visual effect was detected from the application of several foliar fungicides but added that some benefit from fungicide was observed at trial plots in northern Illinois.
A product shown to be effective in killing sclerotia that house the white mold in the soil has been developed but its cost is a prohibitive $60 to $70 per acre, Esker remarked. He noted that the antidote organism, Coniothyrium minitans, must be tilled into the soil during the autumn.
With the 2009 corn crop, a host of diseases appeared because of the late maturity and poor drying conditions during the ordinary times for harvesting corn for grain, Esker continued. He said the effect on the storage and use of the corn grain is yet to be determined.
There are many questions pertaining to that point because of the widespread incidence of corn ear molds this year, but the first step to answering them is to identify the type of mold, Esker stressed. He added that having test results as a paper trail could help corn growers on crop insurance claims.
It is important to know what kind of mold is present because of the difference between the molds in the likelihood that they are an indication of mycotoxins, which are toxic to livestock, Esker explained. He noted that Fusarium and Gibberella are frequently linked with mycotoxins while Cladosporium mold is not.
Fusarium molds are the most common in Wisconsin this year, followed by Cladosporium, which appears as a dark or greenish powder on corn that was killed by the early freeze, Esker pointed out. He said only a minimal amount of Gibberella had been detected in Wisconsin by mid-November and that the state apparently didn’t have any of the Diplodia mold that was widespread in Illinois, Iowa and Indiana corn planted after mid-May.
But the bottom lines with molds and mycotoxins are that “mold doesn’t necessary mean mycotoxin” and “no mold doesn’t mean there is no mycotoxin,” Esker stated. For that reason, he advises resolving any doubt by sending corn grain samples for the 20-screen test at North Dakota State University for a fee of about $150.
In all cases with their 2009 corn, Esker tells growers to remove as many fines as possible in order to reduce the chances of mold in storage. He said the Extension Service hopes to be able to test about 100 grain samples gathered from around the state and promised that ethanol plants will test for mycotoxin before accepting shipments. Most of the samples tested so far have not had a dangerous level of mycotoxin, he added.
A localized phenomenon was hail damage to corn in July, including at the Extension Service’s trial plot in Lancaster in southwestern Wisconsin where fungicide was applied five days after the storm. Esker noted that on Sept. 9 the ear mold incidence was 3 to 13 percent, there was 8 to 20 percent plant top die off, lodging ranged from 20 to 58 percent and there was very little smut.
In the corn that reached blacklayer maturity by Oct. 7, there was no apparent benefit from the application of the Headline fungicide, the yield ran around 25 bushels per acre less than would have been likely without the hail damage, and the stalk health was good despite the amount of lodging, Esker indicated. He said the remaining parts of the study will focus on corn ear length and width and the presence of molds, including any sign of Trichoderma, which is a hail-induced mold that infects the whole ear.
With anthracnose, a common annual disease in corn, the research is also considering the possibility of infection through the roots in addition to the well-known infection by the spores from plant residue that are splashed onto young plants by raindrops, Esker remarked. He said the possible root connection is being studied because the leaf blight and plant top dieback are not directly linked to the stalk rot that often accompanies anthracnose.
To deal with anthracnose, Esker considers corn hybrid susceptibility to be the top factor for the onset of the plant disease. He commented that the hybrid’s susceptibility seems to override other possible variables such as crop rotation and tillage, but he acknowledged that moldboard plowing – to bury the infectious organisms – has not been part of his research on the subject.
With winter wheat, Esker pointed out that variety plays a crucial role in the vulnerability to diseases. He noted that Septoria leaf spot was the top winter wheat disease in Wisconsin this year, while pockets of powdery mildew, leaf and stem rust, and head scab appeared relatively late.
Know the susceptibility of wheat varieties to diseases and crop history in the growing area, look for consistency in choosing varieties and examine the Extension Service’s data that shows the link between diseases and the yields of particular wheat varieties, Esker stated.
Esker also commented briefly on alfalfa, noting that there appear to be multiple races of Aphanomyces – more than those for which quite a number of varieties have been bred for resistance.
