August 28, 2019
Dr. Darrin Dodds, Mississippi State University Extension cotton specialist and department head for Plant and Soil Sciences, says the state’s cotton farmers face unique challenges as they prepare to harvest the 2019 crop.
Recently Dodds fielded questions about cotton defoliation for this year’s crop.
How will the unusually wet planting season affect harvest?
“Probably, the biggest way the wet planting season will affect harvest is the planting delay. Approximately 70 percent of our crop went in the ground after May 20.
“Typically, by the time we get to that third week in May, we’re trying to finish up planting or hope to be well over halfway done. The weather this year did not allow that to happen. Over the last six to seven years, the weather throughout the spring has not allowed us to do a tremendous amount of planting in April, what I call the early window.
“Historically, if the weather got warm enough, you got to start planting cotton around the third week of April. In the last few years, the weather hasn’t allowed early planting, so there is a valid concern about how the wet planting season may affect yields.
“However, planting late will not always hurt our yields, and I’ll use 2013 as a reference. In 2013, almost 75 percent of our cotton was planted after May 20, and we averaged over 1,200 pounds per acre, the second highest yield ever recorded as a state.
“So, just because we were late planting does not inherently mean that yields are going to be bad. Certainly, we need good weather in the next several weeks. The biggest way, though, that the wet weather will affect harvest is that it will push harvest later into the fall.”
Will harvest be spread out longer than usual?
“It will, potentially, mainly because 70 percent was planted after May 20, so 30 percent was planted before, during some drier weather. A portion of our crop probably will be ready the third or fourth weeks of September, and the crops planted after May 20 will be ready to harvest mid-October, depending on the weather. However, if it stays hot as it did in 2016, it could speed the maturity of the crop, but if it starts to cool off, that late-planted crop may be stretched even later into November.
“Cotton harvest is lengthy by nature, but because of that split planting window, harvesting will probably stretch out even longer. I don’t think that it’s going to extend it for an inordinate amount of time since some will come in earlier. A lot will come in later, and the key there will be getting out of the field as quickly as we can.”
How will cotton defoliation be affected in fields with non-uniform stands, where some areas were replanted?
“That is certainly a concern. We typically defoliate cotton at 60 percent open. If you’ve got cotton that’s at two, three, four, even five nodes of growth difference just because of emergence or replanting and if you defoliate the bulk of the crop, you will more than likely penalize that crop that emerged late.
“It’s a balancing act, but I encourage farmers to consider how that uneven emergence will affect yield on a field by field basis. If it’s a very small percentage of the field, I would defoliate when the vast majority was 60 percent open because you don’t want to sacrifice 95 percent for 5 percent of it. If you have half a field in one stage of growth and the other half in another, you have to wait for your crop’s latest maturing point to defoliate, and then do it all at once. When you are split down the middle in terms of a crop maturing and you pull the trigger too early, potential yield ramifications could be quite negative.
“The key will be balancing how much of the field has variable emergence on it, and then managing it as late as you possibly can.”
Any change in the harvest aid chemicals farmers might want to consider?
“Typically, as the weather cools, we tend to adjust rates of a given product, but at some point, we must start selecting different products and not just adjusting the rates of the ones we were using.
“For example, thidiazuron is the most commonly used harvest aid for taking leaves off in Mississippi. Once we start averaging 65 degrees, activity from this product slows greatly and will eventually become ineffective. Therefore, when lower temperatures occur, we start changing the materials we’re using. As an example, if we get to the first of October and we’re still getting leaves off the crop and it turns cool early, we will have to adjust defoliation programs to account for that.
“If we don’t — as the old saying goes — the most expensive application is the one that doesn’t work. If we make an application and it doesn’t work, we run the risk of suddenly having to make another application. While we often do a two-pass defoliation program anyway, you still need to clean up the leaves if you make another application, which adds expense.
“Defoliation is such a dynamic thing in cotton you have to continue to make adjustments according to the weather to get the optimal performance.”
What is your best recommendation for chemicals and timing?
“It’s a little complicated on the chemistry side. If the temperatures are warm, from an efficacy and a cost standpoint, it’s hard to beat an application of thidiazuron. It’s cost-effective and works well when it’s warm.
“If the temperatures go under 65 degrees, we start moving away from thidiazuron and start looking at other products. Honestly, that’s when defoliation becomes a little bit more complicated.
“As far as timing goes, the standard is to wait until 60 percent of your bolls are open, and then take the leaves off. When variable emergence occurs, younger cotton may be 30 percent open while the rest of the crop might be 70, 80, 90 percent open. If it’s a good portion of a field, you don’t want to take the leaves off too early and not get that top part of the crop open because that could have a negative impact on your yield.”
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