What is in this article?:
- High-yield cotton at higher target spot risk in Alabama
- Yield losses seen from target spot
- Management options limited
- High-yield cotton is most at risk from target spot in Alabama.
- The disease usually shows up by the second, third or fourth week in July.
- Cotton varieties vary in their susceptibility to target spot.
- Late-planted cotton is less vulnerable to the disease.
PRODUCERS WHO ARE pushing for top cotton yields may be more susceptible to target spot, according to research in Alabama.
Management options limited
Management options currently are limited because cotton varieties tend to differ in their susceptibility to target spot, says Hagan. Phytogen 499 tended to have the greatest defoliation and the highest risk for a sizeable yield loss, he says.
“The flip side of that is that Phytogen 499 tends to be at the top of the yield list anyway, despite target spot sometimes. It may be a pretty good strategy to go ahead and spray if you’re planting this variety.”
Most DPL, Stoneville and Fibermax varieties are moderately susceptible and/or tolerant but can suffer sizable yield loss under ideal conditions, he says.
“We really don’t know what the yield loss might be on those varieties from target spot. In general, none of the varieties available today have a high level of resistance. They differ some in their sensitivity, but that’s about it.”
In some situations in the southern part of the state, one of the management options would be to grow a less-susceptible variety, says Hagan.
“On trials this past year, we applied Headline on half of the plot and left the other half unsprayed. Headline reduced the amount of disease in the field. It slows it down in many cases to get a yield gain, though it’s not significant. There were more bolls on the Headline-treated cotton than on the non-treated control. It looks as though the untreated plots have fewer bolls on the plants than the fungicide-treated plants. There’s no effect from this disease on cotton quality.”
A dryland grower on “thin” land that doesn’t tend to produce more than 1 ¼ bales per acre probably is not going to have a lot of target spot issues, he says.
“In dryland cotton, scout the fields, and if it has good yield potential that might be a situation where you’d want to spray. Consider variety selection, stand density, yield potential and location in treatment decisions.”
Growers are advised to monitor weather during bloom and boll set, and the more rain and heat they get, the higher the risk that the disease will defoliate cotton, says Hagan.
Fungicides haven’t changed, he says. “They are the same three products we’ve been looking at for the past two years – TwinLine, Headline and Quadris. You’re basically looking at two applications since it is recommended not to make more than two applications. These are all strobilurin fungicides.”
In trials at Fairhope, researchers tended to see more consistent yields with Headline at 9 fluid ounces per acre.
“The more gallons the better – it’s a real coverage issue with this disease. Use a minimum of 10 gallons of water per acre to insure coverage of the leaves in the lower and mid-canopy. Follow the first spray at first or second week of bloom with a second spray 14 days later. This is a preventative treatment. There’s some indication from our trials that rescue fungicide treatments may help protect yields. The most yield recovery you can expect is from 120 to 150 pounds of lint per acre. So if you’re losing 300 pounds, you can save half of it with a fungicide.
We are looking at newer products and chemistry on target spot. But honestly, they don’t look any better than what we already have.”
There are still a lot of issues left to be worked out with target spot control in cotton, says Hagan. “We’ll do a lot more work with it this year to see if we can fine-tune spray programs, look at application and seeding rates, planting dates – anything we can do to slow it down.”