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Goss's Wilt coming on strong

Corn prices are still pretty high, so it's putting a premium on raising a high-yielding, disease-free crop. But now, Goss's Wilt is threatening to pull those yields down.

"With grain prices so high, it’s difficult to watch a disease come in and rob yield. Not surprisingly, growers are looking for anything to protect yield potential," says Iowa State University Extension plant pathologist Alison Robertson.

Goss's Wilt, or Goss's leaf blight, causes linear lesions on corn leaves and can affect as much as 50% of the leaf surface. Look for "freckles" inside these lesions and "shiny patches of dried bacterial ooze," says University of Minnesota plant pathologist Dean Malvick.

Goss's Wilt typically thrives in wetter conditions. That's what makes this summer's outbreak so unusual, Robertson says. "Despite the hot, dry weather, the disease has progressed rapidly in the field," she says.

Robertson says 3 products are being discussed as potential control measures for Goss's Wilt. First, she says the bactericide and fungicide Procidic is effective. With citric acid as its active ingredient, she says the product has been shown to control other fungal pathogens in other crops, but has not yet been proven for Goss's Wilt in corn. Still, it's labeled for that crop and disease in Iowa.

Secondly, Robertson says DuPont's Kocide fungicide/bactericide has been suggested as a means for Goss's Wilt control. But, it's not labeled for the disease. Recent tests have shown little effect.

"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," she says. "On the resistant hybrid, no treatment differences were detected."

The third product Robertson says has been brought up as a potential Goss's Wilt stopper is a copper-based product called Intercept. It's been shown to control citrus canker -- another bacterial disease -- in Florida. But, at this point, Robertson's unsure whether or not Intercept can do much on Goss's Wilt.

"There were also some fields in Iowa that were sprayed with this product in 2010. There is no published information available on the efficacy of Intercept against Goss’s wilt or citrus canker," she says. "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."

If you confirm Goss's Wilt in your fields and you opt for one of these treatment means, make sure you get a clear picture of what your treatments are doing to your crops and don't forget that the management of a disease like this doesn't end with harvest this fall.

"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," Robertson says. "Recommended management practices include growing resistant hybrids, crop rotation and 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. Other factors include susceptible germplasm and stormy weather."

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