What is in this article?:
- 2012 was a big year for target spot in Southeast cotton
- Looking at time frame
- Did get defoliation reduction
• While target spot is found in dryland cotton, heaviest leaf spotting and defoliation has been seen in irrigated cotton, particularly when strip- or conservation-tilled.
• In 2012, disease outbreaks were observed in cotton in the Florida Panhandle, South Carolina, North Carolina and Virginia.
TARGET SPOT IN cotton continues to spread throughout the Southeast and has caused yield loss in some fields.
Did get defoliation reduction
“We did get a reduction in defoliation with Headline and Twinline. But we need something else in the mix other than strobilurin fungicides and we don’t have it, at least not a really good one.
This year, we’re going to try a five or seven-spray program on cotton with Bravo, just to see if it works. We may at some point need a broad-spectrum fungicide for this disease.”
Based on research thus far, the recoverable yield or what you can protect in cotton probably will be in the range of 100 to 200 pounds of lint per acre if you use a fungicide, says Hagan.
“You’re limited to two applications of whatever is on the market, because there isn’t an option with the chemistry. If we overuse them, they may not work at all.
“We may already have tolerance or resistance to strobilurin fungicides, and there’s nothing in the pipeline for the next couple of years. Work is being done on a cotton registration package for Fontelis, but those take awhile.”
In 2012, Alabama researchers had five rotation patterns at the Wiregrass Substation that included cotton for 10 or 15 continuous years, says Hagan, and there was no cotton cropping frequency impact on the incidence of target spot, at least in small plots.
“In our variety trials on the Gulf Coast, we were planting cotton for the third consecutive year in one plot, and the other plot was planted in cotton for the first time in several years. The amount of disease was the same in both areas.”
Target spot is moisture-driven — the wetter it is, the worst it will be, particularly when you start at flowering or at pinhead square and go through the end of the season with such conditions, says Hagan.
It may attack seedling cotton, but it won’t make much difference, he adds.
“What are the management options? At least in dryland, you might plant one of the varieties that is a little less sensitive to target spot. You might sacrifice on the yield side, but you could have less disease. If it’s irrigated cotton, where you’re talking about a high yield potential, that’s where I might use a fungicide.”
Looking at fungicide use on dryland cotton, Hagan says he would scout at first bloom and apply at the first sign of disease. If there’s heavy defoliation, there’s probably not a reason to treat late, he says.
“It might help to have a very dense wheat or rye cover, roll it down, and then strip-till into that cover. The heavy leaf cover from a small grain probably will interfere with the splash dispersal of the fungus.”
The question remains, says Hagan, as to whether the use of strobilurin in soybeans has contributed to the poor fungicide performance in cotton. Or, whether or not it’s a coverage problem.
“Do we need to put drop nozzles in the middle of the row and spray into the lower canopy to get Headline down into the bottom of the plants? We were spraying over-the-top this past year. We’ll continue to look at this.”
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