Our pest pressure in cotton is starting to wind down some as the bolls harden. We still need to watch out for stink bugs for a little bit longer, but the bollworm pressure has dropped off.
We are approaching harvest for cotton, and with that comes the consideration for harvest aids. Timing of harvest aid application is important, we want to strike a balance between keeping up the lint quality in older open bolls, but also allowing younger bolls to mature. Applying to early can halt green boll maturation, but applying late can have a negative impact on lint quality of the older bolls. Most product labels recommend application between 50% to 70% open boll, but research has shown that optimal application timing can be anywhere from 42% to 81% open boll, depending on the distribution of fruit on the plant. Cutting a cross section of a boll is another way to determine maturity. Mature bolls are more difficult to cut, and contain dark seeds, not soft seeds with a jelly like inside. Nodes above cracked boll (NACB) can also be used to determine maturity. Research has shown that harvest aids applied at three NACB will not result in lint weight loss, while applications at greater than 4 NACB can result in yield loss.
Environmental conditions can have a large impact on how well a harvest aid will work. Ideal conditions are warm, sunny, with low soil moisture, without excessive soil nitrogen, and plants that have reached maturity and are not actively producing leaves. Nozzles should provide uniform coverage with small droplets. Spray volume should be 15 GPA for ground applications and 5 GPA applied aerially. A combination of defoliants and desiccants is often used to finish cotton out. Defoliants are broken into two categories, hormonal and herbicidal. Hormonal defoliants include thiaiazuron, and herbicidal defoliants include tribufos and PPO inhibitors. Too high a rate of defoliants can cause leaves to stick to the plant rather than falling off. Boll openers can also be used, their active ingredient is usually ethephon, which is converted in the plant to etheylene. Etheylene causes fruit to ripen, so causes bolls to open more rapidly. It causes them to open, but it does not cause any increase in maturity, only an increase in opening.
Check out Josh McGinty's publication for more info: http://agrilife.org/texasrowcrops/2015/08/03/preparing-for-the-2015-south-texas-cotton-harvest/
Good luck harvesting, everyone. We have rain in the forecast, and I hope everyone gets their crop out in a timely fashion. Let me know if you have any questions or concerns, or find anything weird in the fields.