2012 Mid-South Cotton Defoliation Guide

Cotton harvest aid applications are beginning to go out on some of the earliest planted and/or burnt up cotton in several areas throughout the state.  As most know, there are several methods that can be used to time defoliation applications; however, keep in mind that no single method is perfect and that several techniques should be used in order to defoliate the crop and open bolls at the proper time.  Using percent open boll as a method for timing defoliation has been the standard for many years.  This is a good method given that an accurate assessment of percent open bolls is obtained.  Often times when estimating percent open bolls from the truck, we tend to under estimate the percent of open bolls present.  For example, it is not uncommon for a crop to be called 40% open from the truck that may actually by 60% open and ready to defoliate.  In contrast, when estimated leaf defoliation (such as from worms is soybeans), we tend to overestimate the amount of defoliation present.  For example, often times leaves are called 25% defoliated that may actually be 10% defoliated.  The point of this is that there is no one perfect method.  If using 60% open as a guide, also use the sharp knife technique.  Select the uppermost harvestable boll (generally 4 to 5 nodes down from the top) and cut the boll in cross section.  If the seed coats have a dark appearance and the cotyledons are well formed within the seed coats, the crop is ready to defoliate.

Some also like to use nodes above cracked boll as a guide for defoliation.  For this method, find the uppermost first position cracked boll and count upwards on the plant to the uppermost harvestable boll.  Generally, if you have a count of 4 nodes or less above cracked boll, the crop is ready to defoliate.  If you have a crop that has a high number of fruit set on vegetative branches and/or on outer fruiting positions, waiting until you have three nodes above cracked boll may be a more cautious approach.

Given that several fields throughout the state have a fruiting gap in the middle, timing a defoliation application can be somewhat challenging.  If using 60% open as a guide and the gap is in the upper portion of the plant (this has not been the case in most fields I have seen this year), you may be prone to defoliate prior to upper fruit being fully mature.  The lower portion may be fully open whereas the top may not be.    In addition when using the nodes above cracked boll method, if the fruiting gap is large, you may have the boll just under the gap cracked but none above it.  This may lead to an inflated node above cracked boll number and a delay in defoliation application.  With either of these methods, cutting the uppermost harvestable boll with a knife and looking for darkened seed coats and formed cotyledons should guide you in the right direction.

My colleagues in Arkansas and Tennessee as well as myself developed a defoliation guide in 2011.  We have updated this publication this year and it is available through the link below.

2012 Mid-South Defoliation Guide