Hardlock continues to be a major problem for cotton producers throughout the most humid regions of the Cotton Belt. But researchers are beginning to make progress in identifying a cause of the problem and potential solutions, says David Wright, University of Florida Extension agronomist.
"In Florida, from 20 to 60 percent of the cotton is lost to hardlock, almost every year," says Wright. "When hardlock is only 20 percent, yields of 2-bale lint often are made. Yields often are reduced more by hardlock than any other factor, including drought. However, this is seldom reported since identification and means of control have not been developed."
Research into the problems of hardlock and boll rot have identified several different bacteria and fungi associated with symptoms, and the incidence appears to increase with rainfall, humidity, high nitrogen, plant size and density, says Wright.
Two thousand and two was one of the most severe growing seasons for hardlock in recent years in the humid areas of the Cotton Belt, he says, with yields in Florida averaging only 346 pounds per acre.
"Hardlock has been known to be a problem for years, with unknown etiology and without any apparent means of control. Symptoms do not appear until the boll opens and the locks of cotton look more like an orange slice than a fluffed-out boll of fiber," says Wright.
In many cases, he continues, the quality of the fiber isn’t severely affected, but yields have been known to be reduced by 50 percent or more in the lower Mississippi River Delta and in Louisiana, as well as other humid areas.
Conventional cotton pickers, explains Wright, either knock the hardlocks to the ground or do a poor job of picking them. Due to the common occurrence of hardlock along the Gulf Coast, there has been interest in strippers in ultra-narrow-row cotton that could harvest cotton regardless of hardlock.
"However, gin deductions, higher seed costs and poor stands in narrow rows — especially with reduced tillage — have led to less interest and the dilemma of how to harvest the cotton," he says.
Most of the U.S. cotton crop is harvested with spindle pickers, which require that cotton be fluffed out before it can be harvested.
As for boll rot, Wright says it has been mentioned in the literature since the early 1900s, and there are many different organisms associated with the problem.
Boll rot and hardlock have never been fully understood, he says. "Most disease information focuses on known seedling diseases that can be controlled by fungicides and seed treatments. Other information focuses on the different wilts which usually are controlled by plant resistance or by controlling nematodes."
Research from 1978 indicated that boll rots were more severe in wet years, he says, and that most boll rots or hardlock were caused by diplodia or fusarium in the humid, high-rainfall areas of the world.
Severe hardlock in Florida usually occurs when major storms or rainfall occurs during boll opening, says Wright. "But our data suggests that the infection may be set up during the day of bloom for each individual boll if weather conditions are conducive."
Research in 1981 suggested that insects can cause boll rot by creating wounds in the tissue and transmitting pathogens that cause boll rot. Florida data has shown that thrips can carry fusarium that may be transmitted during the day of pollination.
"It has been suggested that boll rot can be controlled by eliminating early season sources of inoculums with seed treatments and clean tillage. However, there is no data to support this since conservation-tillage has been shown to reduce diseases in crops such as peanuts."
Fungi such as fusarium are ubiquitous, says Wright, and may not be reduced by cultural practices. Likewise, research from McLean and Lawrence in 1998 indicated that young bolls generally are resistant to fungi except for phomopsis and diplodia which may attack flowers or young bolls and turn them black.
However, more recent research has shown that flowers can be infected by fusarium on the day of pollination, since the fungi has an open track into the flower for about 24 hours before the carpel seals over the area where the pollen tube went inside the boll, says Wright.
"The weather conditions on the day of bloom were highly correlated to the amount of hardlock, indicating infection through the bloom. Hardlock and boll rot normally occur on some of the most productive land in the field and in areas where plant growth can be excessive."
In Florida studies — where a stripper was used to harvest cotton and where hardlock occurs annually — yield increases were noted each year in the range of 300 to 400 pound per acre, depending on the treatment. There was an average of about 30 percent hardlock in each of the three years of the study.
"Cotton taken from four transgenic varieties that either was hardlocked or fluffed was sent to Cotton Incorporated to be ginned and graded. Even though cotton was hardlocked, grades were not much lower, and varieties made more of a difference than whether the bolls were fluffed or hardlocked. However, since ultra-narrow-row cotton has failed to be a mainstream production method with growers, our goal has been to find the cause of hardlock damage and develop a control strategy."
There have not been reports of hardlock in the arid regions of the Cotton Belt, even where crops are irrigated, says Wright. "Therefore, environmental factors are considered to be essential for the organisms to initiate infection resulting in hardlock. With diligence and cooperative research efforts, the problem of hardlock is being solved, and weather models may be used to predict when or if fungicides should be used to control fungi causing hardlock during the bloom period."