Some cotton has reached cutout this week (5 nodes above highest white bloom). Many producers are still applying plant growth regulators (Pix) due to the heavy and consistent rains we’ve had over the past two months.
Producers are still watching for bollworms. Reports from the southern Blacklands and College Station area indicate that many fields have been treated, but infestations appear to be spotty/hit-or-miss. Keep in mind that very heavy bollworm pressure can break through any Bt technology.
The threshold for Bt cotton is 5-6% square damage with 8-12 large worms (over ¼ inch) in 100 plants. A spray could also be warranted in a field with high square damage and high egg lay, which indicates that small worms are lasting long enough to damage the fruit and more are on the way.
Once cotton has accumulated 350 DD60s (heat units) past cutout, it is safe from yield loss from small bollworms. You can calculate DD60s in a day with this formula:
(Max temp + Min temp)/2 – 60
So, if your plants reached cutout last week (let’s say Wednesday), currently they have accumulated 239 DD60s. If the temperatures remain fairly constant, your field in this example should be relatively safe after the 19th (next Wednesday).
If you want help calculating heat units for your cotton feel free to give me a call.