FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina
and may not apply in other areas.
The major corn earworm (bollworm) moth flight began on July 16 in
southern Scotland and Robeson Counties, North Carolina. The light
trap count near Rowland (southern Robeson County) jumped to 214
bollworm moths for a single night (from only 15 moths six days
earlier). The light trap in Johns (southern Scotland County)
increased to a two-night count of 226 moths, compared to only 17
moths two days earlier. Additionally, moderate numbers of
recently-emerged, fresh bollworm moths were noted by Area Cotton
Agent David Morrison, and some fields in this area had just over 30
percent eggs in the terminals. The above counts and observations
confirm that the flight is underway in the southern part of the
state. At this point, the flight is somewhat later than in 1994
and a little earlier than in 1995. It is too early to speculate on
the size of the flight. I expect these flights to possibly extend
into central North Carolina (Wayne, Sampson, Greene, and Lenoir
Counties) by the weekend (with some isolated pockets occurring
earlier) and into the remainder of the state July 22-29.
This would be a good time to intensify scouting for insects in cotton -- two times per week would be optimal prior to initiation of insecticide treatments and every 4 to 6 days thereafter. In most cases, a response to this flight will be the cotton producer's first insecticide application, as only a limited amount of the cotton acreage has been treated for early budworms. Because a high percentage of the state's cotton has good to excellent moisture levels at this point, most of the eggs deposited by bollworm adults will be found in the terminals. In the cotton damaged by the hurricane (blown over exposing more of the fruit), some eggs have already been found on the fruit. In this situation, the protective threshold of 2 percent eggs on fruit may be appropriate (assuming the major flight is underway in that area). Although the focus is on eggs at flight initiation, remember that 3 percent or more larvae on squares or bolls also triggers treatment with insecticide at this time.
Cotton producers and scouts with Bollgard (B.t.) cotton are
reminded that they will be responding to 3 percent larvae (1/8 inch
or larger) or 6 percent economically-damaged squares. Bollgard
cotton should be scouted at least as intensively as standard cotton
(see pages 11-13 in the Cotton Insect Scouting Guide for details
on scouting). Although tobacco budworms and European corn borers
will not cause a yield loss in Bollgard cotton, bollworms will
likely reach threshold in some fields and require treatment with
insecticide.
When the moth flight has arrived and the egg threshold met,
treatment with insecticide is strongly advised. The first 2 or 3
weeks of the flight are typically when the most costly mistakes in
treatment are made (often underestimating the serious fruit damage
which bollworms can inflict and getting a slow start). When
treating at the egg threshold, two pyrethroid applications at the
industry rate five days apart or a single treatment at a high
labeled rate will provide a very clean start. Producers with
ground application equipment that requires more than 5 or 6 days to
cover their cotton acreage are advised to use the high rates of
pyrethroids to extend the application interval. Post-egg threshold
application(s) should be based upon reaching a 3 percent larval
threshold on squares or bolls, along with a consideration of the
susceptibility of the particular field and perhaps egg levels.
Expect a wide variation in the attractiveness and vulnerability of
the cotton crop from area to area and from field to field as the
season progresses. Cotton planted from mid May through early June
can be expected to remain attractive to bollworms and European corn
borers until late August if moisture levels remain adequate.
Aphids levels have been increasing in cotton during the past week,
but remain at generally low to moderate levels.
Fall and beet
armyworms are only occasional pests of cotton in North Carolina and
so far have been at either low or manageable levels in states to
the south.
Recent rains have given the peanut crop a real boost and helped it outgrow modest insect pressure. The few isolated locations with lesser cornstalk borers should be of little consequence at this time. Spider mites have received a serious setback, although I saw spider mites still active in watermelon. Remember that there is still time for spider mites to build to damaging populations during August. Potato leafhoppers are causing some yellowing of plants in a few isolated fields. Generally heavy rains help, but it can not be guaranteed to correct this problem. Remember that applications of insecticides for control of rootworms are generally effective in controlling leafhoppers.
The recent rains have created a favorable environment for southern
corn rootworms in peanuts. If you have high risk fields that
suffer from rootworm problems, it would be advisable to treat these
fields with insecticide since many rootworm beetles were observed
in peanuts this week and, at least at this time, soil moisture is
very favorable for egg and larval survival. Soon it will be time
for corn earworms and fall armyworms in peanuts. Scouting and
using thresholds often helps us avoid unnecessary insecticide
applications. Be sure and begin scouting your fields in the next
few weeks to keep track of the caterpillar populations. In many
years, the abundance of these caterpillars never exceeds the 4 per
row foot threshold. Do not treat with insecticide unless
necessary. Not only a dollar saved is a dollar earned, the
avoidance of unnecessary pesticide use in peanuts may also help
reduce the risk of spider mite problems later in the season.
In the second week of July, weather conditions became favorable for sclerotinia blight. Sclerotinia was observed on July 17 in several northern North Carolina counties. While temperatures have been and will continue to be rather warm, wet conditions will keep this disease brewing in peanut fields. Growers can expect a significant increase in the disease as soon as temperatures cool down, if conditions remain wet. While most peanut plants are still fairly small in size, growth is very rapid. Thicker vines are more prone to sclerotinia blight.
Most growers have sprayed fungicide for peanut leafspot. The first spray advisories were issued around June 20 in most peanut counties in the state. The recent wet and warm weather is very favorable for leafspot as well as southern stem rot and rhizoctonia. This is a good time for growers to use Folicur or Bravo/Moncut to protect peanuts against foliar and soil-borne diseases, especially in fields with a history of significant problems with these diseases.
Tomato spotted wilt has been observed in a number of North Carolina
counties. Care should be taken to distinguish between this disease
and CBR. Recent research indicates that both Folicur and benomyl
have suppressive activity against CBR.
Web page last updated on 22 July 1996 by Stephen J. Toth, Jr..
