Goss’s wilt on corn: Get the facts
Consider 115 bushels per acre — no matter what price that corn is sold at, that is a ton of money. And 115 bushels per acre was the yield difference reported between two hybrids in a split-planter field this year. The primary yield difference factor? Goss’s wilt.
While this field may have been at the extreme end of the yield loss spectrum, Goss’s wilt hit most of Iowa pretty hard in 2011, and 30- to 50-bushel-per-acre yield losses were not uncommon. No matter what corn price we got, that hurts.
Historically, Goss’s wilt was primarily a concern for corn in western Nebraska and eastern Colorado under irrigation. However, in 2008 we confirmed this foliar corn disease in eight counties in Iowa, and its prevalence has increased each year.
The bacterium that causes Goss’s wilt survives in infested crop residue. Research has shown that the bacteria can survive on surface residue for at least 10 months. The disease cycle and plant infection is still being studied and is relatively complex, but I’ll take a shot at a simple explanation.
Good reason for concern
Overwintering bacterium are splashed up onto young corn plants during rainstorms and can enter plants through wounds caused by rain, hail, wind and associated sand blasting; leaves whipping each other; and other types of physical damage. Couple the ability of bacterial diseases to ramp up quickly with Goss’s overwintering capacity and you can see how a nearly imperceptible Goss’s infection in your fields in 2010 may have blown up into a yield robber in 2011.
With Goss’s so widespread in 2011, we all have good reason to be concerned about Goss’s in 2012. I was always told if I was going to come to the table with problems, I better bring some proposed solutions along with me. As you will read, solutions for Goss’s are a work in progress, but here is what we have for now.
Being a bacterial disease, fungicides won’t prevent or cure Goss’s. Bactericides are commonly used in high value crops like citrus and vegetables, but rarely in corn. Let’s take a quick look at a few products that we get asked about a lot. Keep in mind that the very recent emergence of Goss’s as a major Corn Belt disease means that research from chemical companies and universities is just getting rolling.
Research is seeking answers
Procidic is advertised as a broad-spectrum fungicide and bactericide with citric acid as an active ingredient. Research we are familiar with reports on the effect of citric acid on fungal pathogens of horticultural crops, but no reports of results against bacterial diseases, and no reports on corn. Procidic is labeled for use in Iowa to control Goss’s wilt, and Iowa State University plant pathologist Alison Robertson is in the process of evaluating it in depth for Goss’s management.
Another product that has been suggested for use to manage Goss’s wilt is Kocide. Since this product isn’t labeled for use on corn to manage Goss’s yet, it should not be used. Since it may be labeled in the future, several Midwest universities are looking at it. Preliminary work from University of Nebraska was inconclusive.
A third product we are often asked about is 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, which is caused by a bacterium. But there is no published information on the efficacy of Intercept against Goss’s wilt or citrus canker. Research will likely be done on this product as well.
As we look at how similar products are used in citrus and vegetable crops, it becomes evident that it will be challenging to find the right fit for products like these against Goss’s. These products don’t “cure” bacterial diseases; rather, they are more effective as preventatives with some suppressive capabilities. A proposed spray schedule for Goss’s wilt would be four applications from emergence to silking. You got it — the ground rigs and aerial applicators will be real busy.
How can you control Goss’s?
Without pesticides as a viable option yet, we have to concentrate on other strategies. So what can you do?
• Economics aside, rotating to soybeans is a good agronomic option since Goss’s doesn’t affect them. Rotating away from corn in 2012 could also greatly reduce the risk of Goss’s for those fields in 2013 given the reduction in host corn residue.
• Burying corn residue with tillage can limit Goss’s survival. But tillage has many other risks. You will have to balance the potential soil erosion, organic matter reduction and loss of soil structure against the risk of Goss’s wilt. Fuel, equipment, labor and the time costs of tillage will figure in there somewhere as well.
• To quote ISU’s Alison Robertson, “Hybrid selection is the key right now.” While there isn’t true resistance to this disease in today’s corn hybrids, there is a wide range of tolerance among hybrids from very tolerant to very susceptible. Talk to neighbors and agronomists to see which hybrids performed well in your area in 2011 in the presence of Goss’s wilt.
Lets hope that Goss’s wilt goes the way of a few other crop issues we have dealt with before; we see them ramp up, we react and prepare to fight — and they don’t show up the next season.
McGrath is partnership program manager of ISU’s Corn and Soybean Initiative.
This article published in the January, 2012 edition of WALLACES FARMER.