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In North Carolina, thrips
in most years ranks as the number two pest of cotton, second only to the cotton bollworm,
both in terms of control costs and in potential yield loss and maturity delays. In North
Carolina and Virginia, with their northern climate and resulting relatively short
production season, thrips control, along with other maturity-enhancing practices, has
become an important component of profitable cotton production. An early,vigorous cotton
crop helps set the stage for late-season management opportunities such as enhanced control
of bollworms and European corn borers, ease of defoliation and early harvest.
In cotton with conventional row-spacing (30 to 40 inches), the use
of an at-planting insecticide should be considered automatic. This is still true (or
perhaps especially true) in a year of low anticipated cotton prices. Untreated checks in
replicated university trials often loose 100 to 300 pounds of lint per acre to thrips
damage and maturity delays. In cases of limited at-planting insecticide persistence (for
example, sometimes seen with Gaucho-treated seed), high thrips populations, poor
insecticide uptake or slow grow off, foliar treatment(s) may be needed. Foliar
treatment(s) should be based on the finding of crinkled (or possum-eared) young leaves and
deformed or darkened buds along with 1-2 thrips per plant. In Roundup Ready cotton, this
application(s) can be very inexpensive if piggy-backed with Roundup Ultra, and often
coincides with a time of cotton plant vulnerability to thrips (1 to 4 true leaves). In a
typical year, approximately 25% of North Carolina's cotton acreage receives a foliar
treatment for thrips, although 60% of last year's cotton crop was treated.
Listed below are several at-planting insecticide options for thrips
control in conventional row cotton:
1. Temik 15G - Temik at the four to five pound
product rate generally provides good thrips control and suppression of early season cotton
aphids, and is generally considered a standard in North Carolina. Although not always
significant, Temik often provides earlier grow-off and fruit set, greater persistence,
earlier maturity and higher yields than other products. Due to a lack of safening from
Command-caused phytotoxicity, do not use Temik with this herbicide applied PPI or
pre-emergence unless a labeled rate of Di-Syston or Thimet is also used.
2. Di-Syston 15G and 8EC - In most
cases, this product provides acceptable thrips control without maturity delays,
particularly with later planting dates. Expect somewhat shorter residual activity,
however. Producers should be careful to avoid planting with Di-Syston under cool, wet
conditions, although leaving out the PPI or pre-plant herbicides, as is sometimes done
with Roundup Ready and Buctril systems, will lessen maturity delays. Di-Syston 8EC,
sprayed from a single nozzle directly into the open seed furrow, may provide more uniform
safening from Command injury than the granular formulation of this product, although this
application must be precise.
3. Thimet 20G - Due to Thimet's generally greater
adverse effect on maturity and yields, and less persistence for thrips control than Temik,
North Carolina producers are advised to use Thimet with caution. However, Thimet will do
an adequate job of thrips control without significant maturity delays and yield reductions
under most circumstances. Planting into warm soils is strongly advised. (Command comments
about Di-Syston also appropriate for Thimet.)
4. Gaucho Seed Treatment - This worker-safe
approach to early season thrips control more often than not looked impressive in all
parameters evaluated in 1995 through 1999 except one- persistence. Depending upon the
test, the Gaucho treatment sustained higher immature thrips levels than all of the above
options, in some cases supporting higher thrips populations than the untreated check.
However, maturity and yields have been very similar to Temik in many tests, although
Gaucho yields dropped off in moderate to heavy thrips pressure when conditions for
late-season plant compensation were poor. Do not depend on more that 3 weeks protection
from this seed treatment. Gaucho seed treatment, coupled with an early foliar treatment
such as Orthene, has performed well, and is very reasonable when the foliar product is
piggybacked with Roundup (or other glyphosates) or Buctril. This product would also likely
be an acceptable choice for cotton planted after about May 15.
5. Foliar Treatments - Automatic applications for
thrips (foliar treatments following or instead of an at-planting insecticide) are
generally to be avoided. Although inexpensive when applied in a band during a cultivation
or overtop herbicide trip, these products provide limited residual control and, can
contribute to secondary outbreaks of cotton aphids and budworms. However, well-timed,
need-based foliar treatment(s) can have a significant positive impact on early plant
growth, maturity and yields. Do not overlook the possibility of a very early
scouting-based treatment at the expanded cotyledon stage when the first true leaf is just
visable.
When the cotton plants have an average of approximately 5-6 true
leaves, thrips control should no longer be necessary if adequate moisture exists.
Although late planting of cotton is certainly recommended in North
Carolina, some individual fields or even areas are almost always planted to cotton after
mid May, or even into early June due primarily to various weather-related factors. If
cotton is planted after May 15, or thereabouts, 60% of the at-planting insecticide rate
(for example 3 lb. Temik 15G/acre) will probably offer enough thrips protection, given the
expected rapid grow off conditions. |
