FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina
and may not apply in other areas.
Cotton fields with a high square retention rate do not require further sampling for plant bugs because a square retention rate of 80 percent or greater in a cotton field indicates a crop with a healthy fruit set and plant bugs (Lygus) primarily feed upon these small squares. However, tobacco budworms are now present in a number of cotton fields at various levels and are responsible for some lost fruiting positions. If fields are showing low square retention rates, the actual presence of threshold numbers of plant bugs should be confirmed prior to treatment. Following the thresholds listed below will result in a correct decision on whether or not to use insecticide in a very high proportion of the cases, primarily because the overwhelming majority of North Carolina cotton fields are far below threshold.
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NUMBER OF PLANT BUGS
PHENOLOGICAL STAGE PER 100 SWEEPS
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First Two Weeks of Squaring 7.5
Second Week Until Bloom 15.0
After Bloom 30.0
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Note that the suggested threshold doubles at the onset of the
second week of squaring, and doubles again at the beginning of
blooming. Many fields have now started to bloom. These thresholds
may be modified downwards (more protective) slightly in the case of
delayed fruiting (for example, 50 percent or less square retention,
or if cotton has begun to square on the eighth or higher node).
Tobacco budworm levels in terminals and on squares are generally higher than at this time last year, with cotton fields ranging from 0 to over 15 percent budworms in terminals, with some establishment on squares. Higher establishment of budworms is generally more common in the southern counties of North Carolina, though most fields throughout the state are showing low budworm levels. In many fields not treated for thrips with a foliar insecticide or treated more than 10 days ago, beneficial insect levels are moderate to high. Big-eyed bugs (Geocoris) and damsel bugs (Nabis), both small, active predators of budworm and bollworm eggs and small larvae, are plentiful in a number of fields. As a result, a low percentage of fields scouted on a regular basis have been at threshold for second generation budworms so far. Scouting in the late afternoon or evening may result in lower tobacco budworm levels due to daytime mortality. Also, it is not unusual to find a number of budworm-damaged terminals and very few live budworms. Do not treat on the basis of this damage.
Utilize the higher budworm/bollworm thresholds of 8 percent larvae
in terminals or 6 percent in squares prior to bloom. Remember
these June to early July thresholds are probably very protective
(i.e., cotton plants at this stage of development can easily
compensate for the amount of fruit loss caused by this level of
infestation).
Outside of those fields reaching the thresholds for budworms and
plant bugs (in a few scattered cases) over the next few weeks, the
vast majority of producers should not experience significant insect
problems until our mid to late July bollworm and
European corn
borer moth flights. The size and timing of the major moth flights
are difficult to predict at this point. Field corn (especially now
when much of it is silking) is for the most part still green and
attractive to bollworm (corn earworm) and European corn borer
moths. Although bollworm and European corn borer moths and
caterpillars may be scarce in cotton during the next few weeks,
they can build to high levels in our untreated field corn acreage.
This next generation can emerge as moths from drying corn fields in
large numbers, despite being virtually non-existent in cotton now.
In a few weeks, we can begin to estimate the potential size of the
upcoming bollworm moth flights by getting assessing the percentage
of earworm-infested ears in different areas.
Until the major bollworm moth flight, Bollgard cotton can be scouted for insects essentially the same as conventional cotton, except that tobacco budworms can essentially be disregarded on Bollgard cotton due to its extremely high toxicity to this species of insect.
The following cotton scouting schools have been scheduled for mid-July:
Lenoir-Greene-Craven-Jones-Onslow County area. July 16, 1996 at 7:00 p.m. King's Restaurant, Kinston. Contact either Curtis Fountain (919-633-1477) or Alan Harper (919-527-2191) for information.
Union-Stanley-Anson-Montgomery area. July 17, 1996 at 9:00 a.m. Contact Tom Pegram (919-704-3801) or Jim Monroe (704-983-3987) for information.
Northampton County. July 18, 1996 at 9:30 a.m. Northampton County Administration Building, Jackson. Contact David Fogarty (919-534- 2711) for information.
Halifax County. July 18, 1996 at 1:30 p.m. Halifax County Agricultural Building, Halifax. Contact Arthur Whitehead (919-583- 5161) for information.
Edgecombe County. July 19, 1996 at 9:30 a.m. Edgecombe County Administration Building, Tarboro. Contact Joe Dickens (919-641- 7815) for information.
Both indoor and field instruction are planned for each scouting
school. John Van Duyn, Extension Entomologist, Vernon G. James
Center, Plymouth, North Carolina, has arranged a series of similar
schools for the northeastern North Carolina cotton counties.
Scouting for bollworms, European corn borers, armyworms and stink
bugs in conventional and B.t. (Bollgard) cotton will be emphasized.
The new scouting guides will be distributed at the schools. The
Cotton Insect Scouting Guide is also available on the Internet.
Presently the cotton crop is progressing well. In general, fruit
retention is very high and insect populations have been light.
Northeastern North Carolina is now experiencing the first flight of
tobacco budworm and corn earworm moths into cotton. On June 27 I
observed newly laid eggs, darkened eggs, and a few small larvae in
cotton terminals in Chowan, Washington, and Bertie Counties. The
highest count of eggs was about 32 eggs per 100 terminals in
individual samples, but field values averaged below this level. I
do not suggest treatment based on egg counts. Egg counts were
highest in early planted, larger cotton. Scouting for larva in the
terminals and/or on squares should commence. Thresholds are 8
larva per 100 fruit or 6 larva per 100 squares.
This has been good year for brown stink bugs. There was a surprising amount of brown stink bug injury in seedling corn, particularly no-tillage corn, and, in some situations, Penncap M was used to control this insect in small corn. In addition to early infestation in corn, wheat fields usually contained a lot of adult stink bugs. This was often noted by farmers when the harvested grain was augered into trucks from the combine and the bugs climbed up the walls of the truck bed. Now that most of the wheat has been harvested, the bugs have moved to greener pastures. In particular, corn fields are very attractive to the bugs, but cotton will also become infested. Currently there are a lot of stink bugs in corn fields, especially beside harvested wheat fields. The bugs like to feed at the ear site and into the developing grain, even before pollination. Grains on which the stinks bugs feed often abort and leave blank spots on the grain rows. Typically stink bugs prefer to feed on the outer side of the ear (away from the stalk) and ears that have many grains aborted will crook downward due to the lack of full elongation on the outer ear. I suspect that county extension agents will see this later this year.
Regarding insecticide treatment for brown stink bug in full stature
corn, this is an unusual situation for which we are poorly
prepared. There is no threshold and we do not understand the
relationship of numbers of bugs and yield loss. Also, it is very
difficult to get insecticide coverage of large corn plants by
aircraft and the brown stink bug is relatively hard to kill, all
factors which affect the success of an insecticide treatment. This
week I did suggest insecticide treatment to one farmer who reported
about two bugs per ear on headland areas of fields adjacent to
newly-harvested wheat fields. In this case, the headland of
adjacent corn fields (two aircraft passes) was to be treated with
Penncap M at a rate of 3 pints per acre.
Peanut plants are outgrowing feeding injury by thrips in most
locations in North Carolina. There are a few exceptions, where
peanuts are still quite small, have a lot of thrips injury, and the
soil is dry. There is little indication that 1996 will be a year
for early season (July) spider mite problems, but some areas have
become dry over the past two weeks and a few mites are on the
increase in field corn. I will try to monitor this situation
closely and keep you updated.
Web page last updated on 1 July 1996 by Stephen J. Toth, Jr..
