In some areas of the Corn Belt, Goss’s wilt has re-emerged as an economically important corn disease the past few years. In Iowa, it was the clear winner as “Disease of the Year” in 2011, prevailing throughout much of the state. In some of the hardest-hit fields, yield losses of more than 100 bushels per acre were reported.
Goss’s wilt is a foliar disease, showing up as large, gray to reddish cigar-shaped spots, which usually start on the upper corn leaves. Spraying corn with fungicides won’t control it, as Goss’s wilt is caused by a bacterium, not a fungus. “It’s difficult to say exactly why Goss’s wilt was so severe last year. There is still so much we don’t know about this disease,” says Alison Robertson, Iowa State University Extension plant pathologist. “There are several factors involved, and farmers need to keep in mind this isn’t going to be an easy disease to manage.”
• Goss’s wilt has re-emerged as an economically important disease of corn.
• Management starts with growing resistant or highly tolerant corn hybrids.
• Foliar-applied product has been approved by EPA to control Goss’s wilt in corn.
Widespread planting of corn hybrids that are susceptible to the disease is a prime factor. Unfortunately, hybrids with the greatest yield potential are often the most susceptible to Goss’s. Current crop production practices are another reason the disease is showing up. There’s more corn following corn, which favors a pathogen that survives in crop residue.
Looking ahead to 2012, Robertson recommends planting corn hybrids that have resistance to Goss’s wilt, using crop rotation such as corn-soybean instead of continuous corn, and using crop residue management.
These are the best bets to reduce the risk of Goss’s wilt. However, she also understands that with strong grain prices and the fact that some farmers need more corn for livestock feed, continuous corn is going to be grown. And with soil erosion a concern, you have to be careful with tillage if you try to manage this disease by burying crop residue.
Planting resistant hybrids
Robertson advises farmers when they’re making seed choices to weigh the risks of high yield potential versus a field being hit hard by Goss’s wilt. Numerous corn hybrids are tolerant to Goss’s wilt. Such hybrids should be planted on fields that had Goss’s wilt in 2010 or 2011.
In 2012, however, corn acreage is increasing considerably, and your first choice in corn hybrids may not be available. “The problem this year is while there is enough seed to plant all the corn acres, some of the hybrids are susceptible to Goss’s wilt and need to be strategically placed,” says Robertson. She advises farmers plant the susceptible hybrids on fields that are at lower risk for Goss’s wilt, such as corn following soybeans, or fields with minimal amounts of crop residue. Lower-lying fields that are less prone to wind damage are also less susceptible.
Everyone is looking for a silver bullet to stop Goss’s wilt. Robertson is often asked if any foliar-applied products are available to manage Goss’s wilt. While fungicides don’t provide control of bacterial diseases, there is a product on the market named Procidic, a broad-spectrum fungicide and bactericide combination. It’s the only product labeled to control Goss’s wilt registered for use throughout the Corn Belt.
Still a lot more to learn
Robertson and her ISU team are conducting greenhouse trials on Procidic and other products to assess their effectiveness. The trials are ongoing. In the first trial completed earlier this year, Procidic was applied to corn seedlings at V3 stage of growth. The trial is being repeated to gather more data. Results from the second test should be available soon.
“Even so, farmers don’t grow corn in greenhouses,” notes Robertson. There could be something to Procidic, and it may end up working on corn to control Goss’s wilt. But it needs more scientific testing, and Robertson wants to see field results in various weather and growing conditions. She also says, “There is so much we don’t know about the disease itself. For example, when does infection actually occur? What’s the inoculum threshold? Which infections are economically important?”
Procidic costs about $33 per acre, applied at a 14-ounce rate. At an 8-ounce rate applied preventively to young, growing corn plants, the cost would be more in line with fungicide applications. Robertson doesn’t believe there would be any need to apply Procidic on a corn hybrid that’s resistant or tolerant to Goss’s wilt.
New broad-spectrum product
A flexible product, Procidic can be applied as a preventive treatment or as a curative, says Steve Knauss, of Greenspire Global Inc., which markets Procidic. Knauss, based in Des Moines, says the combination fungicide/bactericide contains all natural ingredients and doesn’t cause stress to plants. There’s no maximum number of applications and no rate restrictions on the amount that can be applied per year.
If you use the product to control fungal diseases along with bacterial diseases such as Goss’s wilt, you could start with 2 ounces applied in-furrow. Or a 6-ounce rate sprayed on the corn at V3 to V5 growth stage, followed by a second application prior to tassel at the 8-ounce rate. In a worst-case scenario, if you haven’t used Procidic and you find Goss’s in a field, then you have to use a higher rate, up to 14 ounces per acre. “Using Procidic this way, as a curative or rescue treatment, we’re trying to prevent losing any more bushels, trying to save yield,” says Knauss.
If Procidic is applied at a 14-ounce rate for $33 per acre and corn price is $6 per bushel, and if you gain 5 to 6 bushels per acre by controlling the disease, that’s the breakeven. “Anything above a 5- to 6-bushel-per-acre return would add to profitability by protecting your crop,” says Knauss. “A key benefit of Procidic is you are buying one product for the price of two. It’s a fungicide as well as a bactericide; it controls other corn diseases in addition to Goss’s wilt.” The label says Procidic controls anthracnose, southern and northern corn leaf blight, fusarium wilt, gray leaf spot and others. It also controls diseases of soybeans, alfalfa, wheat and rice.
Procidic works on contact and is rapidly absorbed into the plant to work systemically, too, says Knauss. When disease pressure is present, you have to use a higher rate and shorter interval between spraying. Rates and instructions for use depend on timing of application. “Recommended application rates vary whether you use Procidic preharvest, after tasseling or after harvest,” he says. “An added benefit to consider is Procidic has no harsh chemicals to pollute the soil, and there’s no re-entry waiting period required.”
Check out www.greenspireglobal.com.