Three important aspects of a successful cotton harvest include monitoring the percentage of open bolls, timing defoliation appropriately, and being aware of future weather conditions.
Weather and timing
"There are two basic types of defoliation products, herbicidal and hormonal, and the goal is to remove the leaves and have more airflow through the canopy before harvest," said Brian Pieralisi, Mississippi State University assistant professor and Extension cotton specialist.
"This improves your harvest efficiency, and it can increase yield. If the harvest is too early or too late, it can negatively affect fiber quality, so timing is important. However, there's no real silver bullet approach to defoliation in terms of modes of action, especially since weather plays a big role in timing for defoliation."
The overall condition of the crop and the variety also factor into timing defoliation. An unusually dry or wet year plays into consideration, too. A drought-stressed plant tends to be harder to defoliate than a plant receiving an adequate amount of water.
"Another thing to consider is whether you are making one application or two to defoliate," he said. "Oftentimes, between applications, you can have some regrowth, which can be harder to remove.
"Hot weather can cause leaves to stick together with some herbicidal defoliant products, which makes picking less efficient, and it could affect your gin turnout. When it's hot, back down on your rates as well as your herbicidal defoliants."
The optimal time to harvest cotton is when the forecast calls for a stretch of several warm, sunny days in a row. However, sometimes the weather does not comply during harvesttime. A cool snap, wet weather, or a hurricane sends everything off course.
"If cool or rainy weather is in the forecast right at harvest, you might want to hold off harvesting because having leaves on the canopy often will help protect the crop," Pieralisi said. "If an application is made before a cool snap, I recommend upping your rates a little bit.
"Earlier is always better to harvest, in my opinion. Typically, the later you are harvesting the higher the risk of delays from wet weather, which means loss of lint and fiber quality."
Consider the capacity at which the cotton can be picked and defoliate a reasonable amount before defoliating more. Staging out the harvest will ensure the crop isn't all ready at once, so vulnerable cotton won't stay in the field for an extended period.
"You want to time it so you're finishing up one section of defoliation, and you have another section getting ready," he said. "It should also somewhat follow the order it was planted and the variety structure. Different varieties planted at different times will vary in maturity. Cotton will be ready for harvest 10 to 14 days after defoliant applications."
When to harvest
Three basic approaches help to determine when a cotton crop is ready to harvest: percent open boll, nodes above cracked boll, and the sharp knife technique.
"The first approach is the percent open boll method where you look for about 60% percent open bolls throughout a field," Pieralisi said. "Take a good percentage of the field or the area you want to defoliate to make sure you're not looking at the high end of the field or just the low end.
"If you're going to do the nodes above cracked boll technique, find the uppermost position of the first cracked boll toward the top. When there are no more than four nodes above the uppermost first position cracked boll, it's generally safe to defoliate.
"When using the sharp knife technique, gather a collection of bolls representative of the field, which will probably be on the top two nodes of the plant. Once the boll is cut with a sharp knife, if you see a well-defined, darker colored seed coat around the seeds on the inside of the boll, it's ready for defoliation."
It's best to try all three methods to get the most accurate representation of a crop to know whether it is time to defoliate.
"Ideally, when you're moving into late August and September and the cotton starts to open, you would like to see your canopy opening more and leaves falling off," he said. "Then you know you are getting ready for defoliation. You don't want any moisture under the canopy that could cause problems."
An efficient, effective, fast harvest is the name of the game.
"Changing weather may mean you have to change your defoliation strategy to be more aggressive or less aggressive, depending on if there is a sudden cold spell or if there is sudden hot weather," Pieralisi said.
"It's usually better to harvest a little early, but it depends on when you planted the crop. Earlier is better by the simple fact that the weather often changes for the worst the further into the harvesting months. However, there is no one right answer for when to defoliate. There are always a few factors that could cause you to adjust your strategy a little bit, so it is important to monitor the crop to know the right mode of action."