What is in this article?:
- Target spot severity varies among cotton varieties
- First seen at top of plant
- Some question about seriousness
• Little is known about the impact of the fungal disease on yield and quality, but recent research indicates there may be significant differences among varieties.
NORTH CAROLINA STATE Cotton Specialist Keith Edmisten says growers should make some careful evaluations before spraying fungicides for target spot.
First seen at top of plant
“These diseases are normally seen first on the top of the plant, compared to target leaf spot which tends to start on the lower portion of the plant,” Edmisten says.
“Typically, North Carolina growers don’t spray fungicides to manage these diseases, because there hasn’t been any documented proof that they can increase yields,” he adds.
Target spot has been more of a problem in the Lower Southeast, since it first began to show up in yield-damaging levels in 2010 and again in 2011.
Though it’s not a welcome visitor to cotton fields, on some varieties this disease will actually aid in defoliation, whereas fungicide applications may make defoliation more difficult.
As in the Carolinas, target spot’s arrival in Virginia created great concern among cotton growers, but how much real damage it caused to cotton is not clear.
If target spot defoliates mostly bottom limbs of cotton plants, it could have a positive effect by creating better air movement and lowering the incidence of boll rot.
However, if the upper leaves of the cotton plant are defoliated, it seems more likely that a significant yield loss would be possible if the disease reaches the mid-canopy level prior to 10 to 20 percent of plants with open bolls.
If the disease defoliates the cotton prematurely, then reduced micronaire and yields should be expected.
How widespread the disease will be in 2013 is hard to predict.
History from other cotton growing states indicates it won’t likely go away. However, it is highly dependent on extended periods of warm, wet weather to form.
Unlike most common cotton fungal diseases, target spot takes 24-48 hours to infect cotton roots — more than twice as long as other fungal diseases on cotton.
The most likely targets for the disease is cotton that is irrigated. The second most likely is cotton that is in a no-till or minimum-till situation, and in areas with conducive weather patterns.
Spores for the disease are more likely to be moved by seed than by air currents. The spores are too large to move great distances in the air, though tropical storm systems could increase the distance they move to some extent.
Research in the Lower Southeast indicates the disease causing fungi do survive in crop residue. So cotton following cotton or in rotation with grain crops and grown in minimum-tillage production may be at higher risk to the disease.
Since target spot has been more prominent in the Lower Southeast, most of the research on fungal disease has been done there.