What is in this article?:
- Thrips waiting to pounce on North Carolina cotton?
- Treatment threshold
• Thrips could very well become a problem during the third week in May for many North Carolina cotton producers when the residual effectiveness of the seed treatments begins to play out.
GOOD EARLY seed treatment activity (note expanded cotyledons), followed by subsequent loss of residual at 2.5 weeks (note ‘possum-eared’ next 4 true leaves). Seedlings approaching 5 true leaves are out of danger from additional damage.
Figure on a treatment threshold of approximately an average of 1 immature thrips per true leaf per plant (for example, 3 true leaf seedlings could tolerate up to 3 thrips per seedling).
Alternatively, one can use an average of 2 immature thrips per plant as justification for a foliar spray.
If one is scouting for a possible second application, for example in 2 to 4 leaf cotton, be sure to disregard leaves that may have been previously damaged. They’re not going to get better. Concentrate again for the presence of live thrips in the bud area and the newest unfolding leaf. If a foliar spray is needed, avoid pyrethroids.
One clue that seedlings are growing out of thrips damage is the presence of a smooth, shiny newest leaf in the bud area. With very few exceptions, cotton seedlings with 5 true leaves cannot be damaged by thrips, even if thrips are present.
In the photo, as one can see from the nicely expanded cotyledons, the seedlings got off to a good start following a seed treatment. However, with the residual for the seed treatment only lasting approximately 2.5 weeks, the next four true leaves are heavily damaged by thrips.
With the fifth true leaf just coming out, the seedling may be just getting to the point where a foliar spray is not needed because cotton at this stage can tolerate moderate thrips levels without further economic damage. A “revenge spray” at this point will not salvage the previously damaged leaves or plants.
Other seedling pests
So far we have had no reports of false chinch bugs, burrower bugs, vegetable weevils, sugarcane beetles, slugs or grasshoppers damaging cotton in North Carolina.
Because we are still on the front end of most possible insect problems, however, be sure to report signs of damage from the above or other pests to firstname.lastname@example.org so that we can pass this on to others in next week’s insect update.
Weekly cotton insect update tapes are also available each Wednesday at our Cotton Insect Corner web site.
(You might also be interested in Growers in 'thrips central' ready for 2012 battle).