September 28, 2023
Hurricanes and tropical storms are a never-ending worry for North Carolina farmers come harvest time, which is why Extension recommends cotton farmers not to defoliate when a tropical event is on the way if some bolls are still closed at the time.
As North Carolina State University Extension Cotton Specialist Guy Collins points out, North Carolina is in a unique position among all of the cotton producing states because of its location along the Atlantic Coast. And while other Southeast cotton growing states do have to worry about hurricanes and tropical storms, North Carolina is a bit different because it protrudes out a little more than other Southeast cotton states.
“There is a lot of surface area with the North Carolina coast that makes us a little more vulnerable and that our cotton belt is positioned in the eastern part of the state predominantly to where this is something we can encounter in the fall, and it can be very damaging for us,” Collins said at the North Carolina Cotton Field Day Sept. 14 at the Upper Coastal Plain Research Station in Rocky Mount.
The importance of stormproof cotton
In addition to not defoliating before a tropical event is on the way, N.C. State University acknowledges that farmers can plant a stormproof variety among the varieties they plant to hedge risks against tropical storms and hurricanes.
“That is one reason that we tell you to spread your risk by planting multiple varieties, and stormproofness is just one of those characteristics that I think you need to use to spread your risk,” Collins advised.
“There does seem to be some value in having a stormproof variety, especially at higher wind speeds, but I’m not here to just sell you on a stormproof variety because you can encounter hard lock if conditions are conducive for it,” Collins said.
Collins said it is common when a hurricane or tropical storms threatens North Carolina for farmers to rush out and defoliate in fear of getting behind. He advises against it.
“They think if it’s going to come in here and drop a lot of rain on us then we’re going to get so far behind that we’re not going to be able to catch up. The point we try to make is that there is not much point to being on time if there is nothing left to harvest. A closed boll is a protected boll in a lot of regards, and our data supports that,” Collins said.
“It can still be vulnerable to rotting or hard lock if flooding or wet conditions persists after a storm, but in most cases, we have decent weather following a tropical event, therefore closed bolls are protected during a storm and they may comprise the majority of the only cotton we have left to harvest. When a storm is approaching, we try to tell growers not to defoliate if you have closed bolls. Wait it out and defoliate after the storm and hopefully losses will be minimal.”
Benefits of pre-storm defoliation delay
Research conducted by Collins and his colleagues confirms the benefits of delayed defoliating and inclusion of a storm proof variety. Collins presented highlights of the research at the field day. In a study conducted this year at the Coastal Plain Research Station, they simulated tropical winds and rains and their influence on cotton.
In the research, Collins and his team looked at two different varieties. They evaluated a stormproof variety that holds cotton a little tighter in the burr and is less likely to fall out of the burr and onto the ground but is also prone to hard lock issues. They also examined what Collins calls a “showy” variety that is a little looser in the burr so it’s a little bit more prone to weathering losses but is less likely to have hard lock issues.
In the study, the researchers examined two simulated wind speeds: 30 to 40 mph and 60 to 70 mph. They used a pressure washer to get the cotton completely soaked and then they used two different leaf blowers to implement the wind treatments.
“This was only done for five minutes in each plot. The losses could be far greater when you experience a true tropical event that lasts all day. Then we had two different levels of exposure. Half of this trial was done when only 15 to 20 % of the bolls were open. Then it was defoliated that afternoon. Then the second half of that trial, these treatments were implemented when it was essentially 100% open. We found that all of these variables are incredibly important,” Collins explained.
Collins said the research reveals that when there are only 20% open bolls and with 30 to 40 mph winds, there isn’t a big difference between the stormproof variety and the “showy” variety when it comes to percentage of bolls lost.
There is also no difference in terms of the percentage of bolls lost between the stormproof variety and “showy” variety in higher winds, 60 to 70 mph, when only a small fraction of the bolls are open at the time.
“However, when we have greater exposure, when it’s almost fully open, 90 to 100% open, still at 30 to 40 mph winds, there is no statistical difference between a stormproof and showy variety. But when we get up to those higher wind speeds we see a substantial difference in favor of a stormproof variety, so this illustrates that there is some value to having a stormproof variety in those ultra-high wind speeds when exposure is high, but not so much in these lower wind speeds,” Collins said.
When it comes to estimated yield loss, the research reveals that at wind speeds of 30 to 40 mph, the level of exposure didn’t matter too much for the stormproof variety. But when it comes to the “showy” variety that is a little looser in the burr, the 30 to 40 mph winds did significantly lower yields when more bolls were open and exposed.
In short, Collins said both the “showy” variety and stormproof variety did not fare well when 90% of the bolls were open and exposed to rain and 60 to 70 mph winds. He said the research clearly shows more yield is lost when more open cotton is exposed.
“This illustrates why we tell you not to defoliate when a tropical event is on the way,” Collins said.
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