Cotton is going to be a valuable commodity this year and taking care to make optimum yields will be critical to overall profitability, which leads to an oft-asked question — do foliar-applied fungicides pay on cotton.

Tests across the Southeast have demonstrated that foliar applied fungicides effectively control a number of diseases that frequently hamper cotton plant development. Whether controlling theses diseases helps on the bottom line is another question.

The multi-state research project across the Cotton Belt recently took a look at the use of foliar fungicides. The results clearly changed some from state-to-state, but the general consensus was that fungicides do affect disease, but there was little correlation between disease management and yield.

Across the Southeast cotton acreage is up, but most of it was planted on the late side due to a lack of soil moisture at planting time. Pushing planting time back pushes bloom time back, affecting the timing of application of some foliar fungicides. Will the dryer conditions and later planting affect the need to use fungicides in cotton?

Virginia is expecting a 40-50 percent increase in cotton acreage this year and North Carolina 20-30 percent. Across much of the Carolina-Virginia Cotton Belt the increase in acreage will come from growers who haven’t grown cotton in a number of years or who have never grown it.

There is now a large body of research that indicates preventative fungicide treatments pay off consistently in wheat and in most years in corn and soybeans. In cotton, the benefits of using a fungicide as a preventative and yield enhancer are much less clear.

Growers new to cotton, or returning to cotton, may see the high value of the crop as a need to use foliar fungicides as part of their production program, but researchers across the Cotton Belt have not found evidence to support the need for preventative treatments.

Manufacturers claim boost

Fungicide manufacturers claim a significant yield boost from use of foliar-applied fungicides, applied at or near cotton bloom.

BASF, manufacturers of Headline fungicide contend in one season their product increased cotton yields in 77 on-farm trials by an average of 65 pounds of lint per acre with early or mid-bloom applications and 94 pounds of lint per acre with sequential bloom applications.

Quadris, another fungicide labeled for foliar application at or near cotton bloom has shown in research in Arizona to increase boll number on some nodes, but the increase did not affect cotton yield.

Researchers attributed the lack of yield increase to the long growing season in Arizona, which makes it possible for cotton plants to compensate minor changes in boll setting during the main fruiting cycle.

In Virginia and North Carolina a large part of the cotton crop was planted in cold, damp soil that went from nighttime temperatures for a couple of weeks after planting in the 40s to nighttime temperatures that remained in the 70s for a month after planting, combined with daytime temperatures pushing 100 degrees F.

There is some concern that slow developing and late-planted cotton in Virginia and the northern end of North Carolina may not have time to compensate for changes in boll set           

Despite a planting season and early growth period that seems ideal for stress, University of Tennessee Researcher Chris Main says there isn’t enough evidence of yield increase to advise cotton growers to use a foliar fungicide.

Later planting dates may not be the best solution to managing boll rot, which will be the primary disease concern for growers in the Southeast.    

The best way to manage boll rot is to prevent the plants from becoming rank by lowering nitrogen rates and correctly using plant growth regulators, he says.

“Since a late planted crop will have lower yield potential, resist the temptation to use products that are not proven effective in university trials to save on input costs helping improve your profitability at the end of the year,” Main advises.      

As part of a Beltwide fungicide test program, North Carolina State University Cotton Specialist Keith Edmisten conducted a series of tests in 2010 using Headline and Qaudris — two of the most commonly used fungicides labeled for use on cotton.                                   

“One of the first things we learned from these studies is that in North Carolina foliar diseases of cotton are frequently linked to potassium deficiency.

“Dry weather and other stresses may contribute to the potassium shortage, but most of the disease problems we’ve seen in the past few years were in some way associated with a lack of potassium or plant use of potassium,” he says.   

The need for K rises dramatically when bolls are set on plants, because developing bolls have a high K requirement. It is crucial that potassium be available when the plant is setting fruit on the first position of the first several branches, because 70 to 75 percent of the total yield occurs from first position bolls on the first 7 or 8 fruiting branches.          

Modern varieties different

Modern varieties are different from the older indeterminate cultivars that Southeast growers used a few years back. The length of the flowering period has been reduced in many of the newer varieties. Thus the current varieties produce a larger crop during a shorter period of time.  

The correlation between potassium deficiency and mid-season cotton diseases is well documented. Whether 2011 growing conditions will be dramatically different enough to create new stresses and give cotton diseases a better avenue to negatively impact cotton yields will up to Mother Nature.         

“In most cases both fungicides controlled diseases and in some cases reduced the amount of materials used to defoliate cotton. The link between fungicides and reduced defoliation has been a random occurrence,” Edmisten says.    

Fungicides have also been linked to reduced incidence of hard lock in cotton, but that didn’t happen in the North Carolina tests.   

Hard lock occurs when cotton fiber doesn’t fluff out, leaving the boll segments tightly packed together, much like the wedges of an orange.

Although the quality of the cotton fiber may not be severely affected, conventional spindle harvesting equipment is not able to capture the fiber and bring it into the harvester. The hard locked cotton is knocked from the plant and falls to the ground or is strung out of the boll giving the appearance of poor harvesting procedures.  

Hard lock is commonly associated with high nitrogen, high plant density, high temperature and high humidity, insect damage, and seed rot. In severe cases of hard lock in the Southeast, conventional cotton pickers can’t pick up the fibers and many times fields are abandoned.       

The North Carolina State researchers applied Quadris and Headline at 12 ounces per acre at early bloom on cotton. The same fungicides were applied in two six ounce applications, one at early bloom and one 21 days later. They also used both materials at 6 ounces per acre, applied at early bloom, followed by 12 ounces per acre applied 14-21 days later. 

None of the treatments produced a statistical yield difference, compared to check plots. The same lack of difference came up with fiber quality measurements like micronaire and fiber length. Again, no statistical difference, the North Carolina State researcher says.    

“Micronaire was the first place I looked for a difference and expected a difference. Keeping leaves healthier longer should have the most direct affect on micronaire, but we didn’t see any significant differences,” Edmisten concludes.

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