What is in this article?:
- 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.
If you’re the kind of cotton producer who’s always pushing for top yields, then good for you. Just know that you’re at a higher risk for target spot.
“The guys who are pushing the yield envelope on cotton are the ones who are most likely to have problems with this disease,” says Austin Hagan, Auburn University Extension plant pathologist.
If you’re growing irrigated cotton – especially in the southern half of Alabama – you might want to spray a fungicide, particularly if you’re eyeing 3 to 3 ½ bale potential,” he advises.
With such a yield potential at stake, growers should consider spraying regardless of the variety planted, said Hagan, speaking recently to a group of crop consultants meeting on the Auburn University campus.
Target spot (Corynespora leaf spot), he says, starts out as a grayish, water-soaked lesion on the leaves in the lower mid-canopy. “Usually, you’ll start to see it in the second, third or fourth week in July in Alabama. It progresses to a number of leaf spots on the leaves, then a little coalescence of the lesions, and finally the leaves fall off. It’s not uncommon on some varieties to see 75-percent defoliation by Sept. 15. It can really knock the leaves off of cotton,” he says.
This past year, researchers started looking for disease in cotton around the third or fifth leaf stage in early to mid-June, says Hagan.
“We saw some leaf-spotting out there in central and north Alabama and down in Fairhope, and we thought target spot might already be in the cotton. It turned out it was actually Aschochyta leaf spot which is known to be an early season leaf spot disease on cotton and usually doesn’t cause a problem. But, we had a lot of rain this (past year) in May and June. If you stand there and look at it without a microscope, you’d have a hard time telling a difference between the two of them.
“And down in Fairhope, there was another leaf spot – Myrothecium – which is identical in appearance target spot. This never has really developed into a problem. It’s just an occasional spot out there. This was in early cotton, sometime in June. Target spot took off at mid to late summer, so we know it’s a mid to late-season disease in cotton. It’s not showing up – so far – on seedling cotton.”
In 2012, target spot symptoms started showing up the last week in July on Phytogen 499 and DPL 1050, and the disease progressed until the middle of September, with 80-percent defoliation on the cotton, says Hagan. This past year, the progression was pretty much the same on Phytogen 499 and DPL 1252. Growers probably won’t really notice the disease until sometime around the first part of August, he adds.