Reports of Goss's wilt have been coming in hard and fast this past week. This corn disease appears to be widespread north of I-80 in Iowa this year. Despite the hot, dry weather, the disease has progressed rapidly in the field.
"We have been visiting a field near Gilbert regularly and collecting data on the disease," says Alison Robertson, an Iowa State University Extension plant pathologist. "The photos below show the severity of the disease when we first visited the field on July 21 and on a return visit on August 2.
These photos were taken in approximately the same place in the field."
Across the majority of the field (approximately 95%), every corn plant shows characteristic leaf blight symptoms of the disease. In the headlands, which are bordered by trees, incidence of the disease (percent of plants with symptoms) is as low as 10%. Scattered throughout the field are isolated wilted dead plants (less than 1% incidence). "We will continue to monitor the disease progress in this field and continue to collect data to calculate the yield loss estimates," says Robertson.
With high grain prices, it's hard to watch disease come in and rob yield
With grain prices so high these days, it's difficult to watch a disease come in and rob yield. Not surprisingly, growers are looking for anything they can do to protect yield potential. "I am aware of three products that growers are trying in Iowa, and they have had questions regarding the efficacy of these products against Goss's wilt," says Robertson.
Procidic is advertised as a broad spectrum fungicide and bactericide. The active ingredient is citric acid. Robertson notes that "There is no published data that I am aware for Procidic. Plant Disease Management Reports contains reports on the effect of citric acid on fungal pathogens of horticultural crops, but has no reports of results against bacterial diseases, and no reports on corn. Procidic is labeled for use in Iowa to control Goss's wilt. The field we are monitoring in Gilbert has had an application of Procidic, as well as an earlier application of Stratego YLD. We plan to monitor the effect of both products on Goss's wilt disease development and general plant health of the corn."
Another product has been tested but is not labeled for use on corn
Another product that has been suggested for use to manage Goss's wilt is Kocide. "Since this product is not labeled for use on corn to manage Goss's wilt, it should not be used," says Robertson.
A team of researchers (Korus et al. reported in 2010) evaluated Kocide 3000 and Headline for Goss's wilt control on two corn hybrids (one susceptible and one resistant) in Nebraska in 2009. The trial was inoculated with the Goss's wilt bacterium at growth stage V6/V7. Treatments were applied six days before inoculation, four hours after inoculation and 24 hours after inoculation. Goss's wilt disease was slightly reduced on a susceptible hybrid with an application of Kocide 24 hours after inoculation, but no differences in yield were detected between this treatment and the untreated, inoculated control. On the resistant hybrid, no treatment differences were detected.
If you are trying any of these products, be sure to leave check strips
A third product Robertson has heard about that some growers are trying is also a copper-based product called Intercept. There is very little information available on this product. Apparently it has been used successfully to control citrus canker in Florida. Citrus canker is also caused by a bacterium. "There were also some fields in Iowa that were sprayed with this product in 2010," she says. "There is no published information available on the efficacy of Intercept against Goss's wilt or citrus canker. I am aware of a couple of fields that have been sprayed in Iowa, and I will be evaluating those fields for the product's efficacy."
Roberson adds, "I encourage anyone who tries either of these products to leave one, preferably more, unsprayed strips in the field and meticulously monitor disease development and collect yield data. The check strips should be left in areas of the field that are representative of the entire field."
What should you do to help manage Goss's wilt in 2012?
The bacterium that causes Goss's wilt, Clavibacter michiganensis subsp. nebraskensis, survives in infested crop residue, explains Robertson. Therefore, recommended management practices include growing resistant corn hybrids, using crop rotation and crop residue management. "Continuous corn production together with minimum tillage practices have in part contributed to the epidemic of Goss's wilt we are witnessing in 2011," she says. "Other factors include susceptible germplasm and stormy weather."