July may be a challenging month for insect control in Alabama cotton. Multiple pests will likely have to be dealt with. These include plant bugs, aphids, spider mites, stink bugs and escape bollworms on 2-gene Bt cotton varieties. On top of that we have cotton of all ages, sometimes even in the same field.
Growers, scouts, agri-fieldmen, and other decision makers need to be on high alert and listen out for rapidly changing insect management situations and recommendations. In this inaugural newsletter, I will hit only the high points for each pest. Call the Pest Patrol Report (First text “PESTPAT11 to 97063”. Then reply “Y” to confirm that you would like to receive text alerts or call Ron Smith directly at 334-332-9501) for more details on insect control and management as conditions may change rapidly.
Aphids have been increasing since mid-late June. Parasites, predators, and a naturally occurring fungus will eventually take out the population. Controls have been applied to many fields due to the young age of the cotton or the fact that it is behind in maturity.
Spider mites are also present in many fields. Populations will increase under hot and dry conditions. Treat when they are found over most of a field and the weather outlook is hot and dry for the next 5 to 7 days.
Adult plant bugs moved to cotton in June, fed on pinhead squares, and deposited eggs. The eggs will be hatching as nymphs or appear as immature plant bugs during July. These nymphs will no longer feed on pinhead squares in the terminal but instead on older squares just before bloom. Survey for immatures with a drop cloth. Treatment threshold is 3 per 5 row feet. If left untreated they will eventually reach adult stage and can be observed in white blooms.
Stink bugs overwinter in high numbers and have been very abundant in corn this season. They were in pre-bloom cotton in June but do not feed on squares. They prefer 10-day old bolls (quarter in diameter) but will feed on small bolls as soon as the bloom drops off. Therefore, we need all stink bugs out of cotton by the second week of bloom. 2019 will likely be a three treatment (application) season for stink bug control on cotton for central and south Alabama.
Three species of stink bugs — southern green, brown, and the new brown marmorated — are present in many fields. Examine quarter diameter bolls for internal stink bug damage. Ten percent damage is a treatment threshold from the 2nd to 6th week of bloom. We will discuss more about late season stink bug control in an August newsletter.
In 2017, escaped bollworms in Alabama cotton were making it through 2-gene Bt cotton (Bollgard II, WideStrike, and Twinlink). Although there weren’t as many issues in 2018, we think problem fields will exist in 2019.
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We’ve observed bollworm in 2-gene Bt corn (the same genes in cotton) throughout mid to late June, which indicates we are on schedule to see bollworm infestations in cotton around July 10 to 15 in the South, July 20th in Central AL, and late July to early August in North AL. Use these dates as a basic guide, but also understand that bollworms are attracted to fruiting cotton.
We don’t need to get behind an infestation. This requires frequent monitoring and a good scout. Flights will generally last from 7 to10 days, and bollworms will lay eggs throughout this period. Scouting is essential to maximize efficacy of treatments. If day-old larvae or eggs are observed at threshold, an application of a diamide such as Prevathon or Besiege will provide control throughout the rest of a single, typical flight.
Pyrethroids remain somewhat effective in Alabama but provide very little residual control, and a second application could be necessary if incorrectly timed.
There are two things to consider when you are scouting and making decisions for bollworm.
- Are you better at looking for day-old larvae, eggs, or damage?
- What Bt technology do you have in the field?
If you have 2-gene Bt cotton (Bollgard II, WideStrike, or Twinlink), then you should treat when you find eggs or day-old larvae on 25 percent of plants checked or 5 percent damaged fruit observed. We’d recommend looking in blooms for eggs or day-old larvae. Pesticide efficacy is going to decrease if you are trying to target bigger worms that have made it inside fruiting structures.
If you have 3-gene Bt cotton (Bollgard 3, WideStrike 3, or Twinlink Plus), don’t treat until you observe 5 percent fruit damage. Presence of eggs or day-old larvae in 3-gene cotton does not necessarily mean damage will occur – these technologies are still controlling bollworm. We think we still have a few years before the 3rd gene loses any efficacy, so 5 percent damage will be exceedingly rare in 3 gene cotton.