FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
As of May 15, I have not seen or heard of significant damage caused by thrips to this year's cotton crop. Our crop and insects in general are again off to a late start. High thrips levels have been reported in Georgia, mostly in very dry areas where significant migration from wild hosts has begun. Predictions of considerably warmer, drier weather over North Carolina for the next five days should initiate the drying of wild hosts, resulting in a sharp increase in thrips levels.
Scouting for thrips should now have been started in all cotton approaching the expanded cotyledon stage. Much of our cotton is just coming into the thrips-vulnerable, expanded-cotyledon stage. Although thrips are not problematic so far, migrating adult thrips populations can increase rather dramatically over a short period of time. This was certainly the case in 1997. Although at this time of year the insecticide rate can be cut by 40 percent due to the shorter anticipated time in which the seedling must be protected from thrips damage (quicker plant grow-off as the weather warms and typically declining thrips populations in early June), this at- planting insecticide treatment should not abandoned.
Continue scouting for thrips on a weekly basis for live thrips and
their damage until cotton reaches the less vulnerable 5-6 true leaf
stage. Walk fields and inspect plants for crinkled or possum-
eared leaves or deformed buds; plants with these symptoms should
be inspected for immature thrips. The presence of immature thrips
should be confirmed prior to insecticide treatment. In the initial
inspections, pay particular attention to the youngest leaves and
buds. Older leaves tell little about the present situation.
Magnification via a 15 to 30x hand lens may be required to find the
tiny, wingless immature thrips. Several seedlings may carefully
picked and rapped sharply against either a white or a dark flat
surface (an index card or a shallow box will work). A treatment
threshold of 2 immature thrips per plant is suggested.
At present, no reports of significant or even moderate insect
problems on cotton in North Carolina have been brought to my
attention. Plant bug, aphid and spider mite levels were several
times higher in 1997 than in previous years -- the next three weeks
will tell if we are heading that direction in 1998. Georgia is
reporting fall armyworms on corn in the past few days, very unusual
this early in the season.
Variable planting times and growing conditions will result in a
high potential for inconsistent thrips control. If peanuts have
cracked it is important to check them for thrips and thrips injury.
Early-planted peanuts have a greater likelihood of receiving a
serious infestation of thrips than often seen in late-planted
peanuts. Cool, cloudy conditions may have also resulted in poor
uptake of in-furrow insecticides. The onset of warm temperatures
in association with good soil moisture often corrects this
situation. The uncertainty associated with thrips in this year's
crop make scouting more important than ever, regardless of which
thrips control option chosen.
Web page last updated on May 18, 1998 by Stephen J. Toth, Jr..
