FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina
and may not apply in other areas.
Judging from how thrips have
worked over some untreated cotton
(primarily where a tube was blocked and the at-planting insecticide
was not delivered) in the past few days, some cotton is still at
risk from thrips injury. Remember to consider only the uppermost
two true leaves to determine whether further sampling for thrips is
needed. Do not be influenced by the lower leaves, even though
battered lower leaves are common in a number of fields (they
provide little information about present or recent thrips damage).
With the June tobacco budworm flights approaching, be extra careful
to base treatments on threshold levels of thrips (an average of
about 2 per plant). Again, plants which have 6 or 7 true leaves
can usually be considered out of danger from thrips damage.
As cotton seedlings begin squaring, routine checking for small
square retention is suggested as the first step in assessing
potential damage from plant bugs. The monitoring of terminal
square retention will be the initial, and easiest, step in
determining the need for further, more comprehensive sampling for
plant bugs. The terminal area of the plant will also be the focal
point of initial tobacco budworm activity. Under most
circumstances, the early terminal and lateral square retention
percentage should be in the low to upper 90's. Unless square
retention drops below 80 percent, further sweeping for plant bugs
is not needed. If sweeping for plants bugs is needed, 25
individual sweeps in 10 randomly-selected representative areas of
the field is suggested, counting both adults and large nymphs. Do
not mistake beneficial insects, such as ambush or big-eyed bugs,
for plant bugs. During the past 3 years, approximately 1 of 100
fields has reached the treatment threshold for plant bugs. For more
detail on scouting and thresholds, see pages 145-155 in 1996
Cotton Information or pages 14-16 in the new Cotton Insect Scouting Guide.
Although a few tobacco budworms may arrive on cotton about any time now, the earliest treatable populations of budworms on cotton that I can recall have arrived around June 8 or 9 in the most southern and southeastern counties of North Carolina. So far, based upon populations on tobacco, this year's flights will occur on time, or perhaps a little late. Population levels on tobacco have been variable, but generally moderate to high like last year.
Most of the scout's attention should be directed to cotton
terminals, with the primary emphasis being placed on finding tiny
larvae in the terminals and/or on squares, either in the terminals
or on lateral branches. Do not recommend treatment based upon
damaged terminals; most of these small tobacco budworms are killed
by beneficial insects before they get out of the terminal area even
though the evidence of feeding remains. Emphasize the use of the
higher thresholds for this June generation (8 percent live budworms
in terminals or 6 percent on or in squares). Because the budworms
eggs are deposited at night and much of the egg predation occurs
during the day, it may be advisable to scout for budworms in the
late afternoon after most of the mortality has taken place. Also,
it should be emphasized that the treatment thresholds are very
protective. Approximately 4 percent of our state's cotton acreage
was treated for early generation budworms in 1995. B.t. or
Bollgard cotton will not be adversely effected by June tobacco
budworms.
Three of our earliest cotton scouting schools have now been scheduled and are listed below. Producers, scouts, consultants and industry personnel are invited to any of the schools. Additional sessions will be scheduled and announced later. John Van Duyn arrange cotton scouting schools for Northeastern North Carolina.
Jones County Area: June 6 at 6:30 p.m. at the Civic Center. Contact Curtis Fountain, Craven/Jones/Onslow Cotton Agent at (910) 633-1477.
Robeson County Area: June 14 at 10:00 a.m. at the O. P. Owens Agricultural Center, Lumberton. Contact David Morrison, Scotland/Robeson Area Cotton Agent at (910) 277-2422.
Sampson County Area: June 18 at 9:30 a.m. at Fann's Restaurant, 6
miles west of Spivey's Corner on Highway 13. Contact Bill Ellers,
Sampson Agricultural Agent at (910) 592-7161.
For cereal leaf beetles in small grains, this year has been severe, and populations of adult insects are beginning to move into corn. Although leaf feeding damage in corn is largely cosmetic, the unusual nature of this year gives us reason to be cautious. Following is some information and a table for decision making.
Cereal leaf beetle is mostly a pest of wheat, oats, and other small grains. Larvae build up in small grains in early spring and change to adults in late May. Adults emerge as the small grain crop is drying and migrate to other areas to find suitable food. Often, corn fields close to fields of small grains are attractive to the migrating beetles, especially along the edges nearest small grain fields. Cereal leaf beetles eat the leaf surface tissue on whorl- stage corn plants; narrow streaks are eaten between the leaf veins (usually on the surface but sometimes completely through the leaf). If beetle populations are very high, defoliation can reduce yield, but leaf feeding is usually cosmetic. Damage is often alarming to farmers even if it poses no economic threat. Beetles do not reproduce or remain for a very long time in corn fields and, therefore, damage is a single, short-term event that rapidly developing corn plants soon outgrow.
Insecticides are occasionally necessary to prevent serious defoliation to corn fields or portions of fields. Evaluation of the need for insecticide treatment includes: 1) assessing the percent defoliation; and 2) determining if beetles are still present at high numbers in the field (is the defoliation going to get worse?). Estimates of defoliation should be used in Table 1 to determine potential yield loss. A 5 percent potential yield loss and a large beetle population will justify insecticide treatment. If treatment is necessary, consult a current edition of the North Carolina Agricultural Chemicals Manual for suggested insecticides to use on corn.
Table 1. Estimated corn yield loss (bushels per acre) due to defoliation by leaf feeding insects.
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PERCENT OF LEAF AREA DESTROYED
LEAF ***********************************************************
STAGE 10 20 30 40 50 60 70 80 90 100
********************************************************************
7 0 0 0 1 2 4 5 6 8 9
8 0 0 0 1 3 5 6 7 9 11
9 0 0 1 2 4 6 7 9 11 13
10 0 0 2 4 6 8 9 11 14 16
11 0 1 2 5 7 9 11 14 18 22
12 0 1 3 5 9 11 15 18 23 28
13 0 1 3 6 10 13 17 22 28 34
14 0 2 4 8 13 17 22 28 36 44
15 1 2 5 9 15 20 26 34 42 51
16 1 3 6 11 18 23 31 40 49 61
17 2 4 7 12 20 27 35 45 56 69
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In general, corn in Northeastern North Carolina looks good. Old billbug feeding remains apparent in many fields and a few fields have been plowed due to severe infestation and damage. In these areas, growers generally failed to properly identify the problem before planting and did not have a focused, integrated approach to billbug control. Several insecticide options for billbug (e.g., Furadan 15G, rates of carbofuran above ca. 1 pound of active ingredient per acre, and Counter 15G) have been lost and blasting billbugs with insecticide is not a successful approach to management. An integrated approach includes: 1) a solid rotation plan with maximum isolation from last year's corn; 2) proper pH and fertility management; 3) a vigorous corn hybrid; 4) early seeding; 5) seeding at a high rate; 6) the use of starter or pop-up fertilizers; 7) application of an at-planting insecticide at a high rate; 8) scouting; and 9) post-emergence insecticide use. These options focus on reducing carry-over populations through rotation and effective management in the previous year, promoting early growth so that seedlings gain stem diameter as early as possible (hopefully, before billbugs emerge in force), detecting above- threshold populations, and treating populations over threshold. The goal is to get through the early seedling period with a full plant stand.
Cereal leaf beetles are now entering corn fields as they emerge
from the ground in infested wheat. The small, slender steel-blue
and rust-orange beetles like to feed on corn foliage and will
undoubtedly be the cause of many calls to county extension agents.
These beetles do not lay eggs in corn and there is no possibility
of a second generation (in corn). Adults will feed for a week or
more and then move from the field. Feeding appears as very narrow,
short streaks of leaf tissue removed from the upper blade surface.
In corn bordering small grains, the beetles will accumulate and may
cause defoliation above the threshold. This generally does not
include the entire field, but the 12 to 24 rows adjacent to the
grain. Thresholds are presented in Corn Insect Note #1 and the
recent insect note on cereal leaf beetle sent to county extension
agents (the one with the big color pictures). Most defoliation is
cosmetic, but insecticide treatment is sometimes required (usually
spot treatment). Often growers do not notice the damage until the
beetles have mostly left the field.
Thrips populations are now in the expansion phase and fields without effective systemic control will likely begin to look thripy; they may already be that way. Thrips counts from several counties show many small immature forms infesting untreated plants. Counts from previous weeks did not show many immatures, but adults were present, sometimes in high numbers. Therefore, it appears that the current generation is beginning to hit the peak larval population. The immature thrips are the primary cause of cotton seedling damage.
Slugs have been detected in no-till cotton in Virginia (several
weeks earlier), and in Hyde County, North Carolina (this week).
These non-insect pests have cause a lot of excitement and a
scramble to find a remedial treatment. There are no pesticide
products labeled for slug control in cotton. In Hyde County, the
slugs were confined to no-till fields with a lot of mulch (cotton
following no-till soybeans in wheat stubble), but populations were
not high in areas with little mulch (cotton following cotton).
Most damage observed was old and it appeared that feeding was
confined to the cotyledon leaves and during the time of seedling
emergence or immediately prior to this. There was no feeding on
true leaves. Cotyledon leaves often showed paper doll hole
patterns, signifying feeding prior to the leaves unfolding. Damage
averaged about 15 to 20 percent defoliation of the cotyledon leaf
surface and probably had no effect on plant performance. Possible
treatments include a urea foliar treatment (diluted urea spray
applied in the evening or at night).
Variable growing conditions have resulted in rather severe thrips damage in some peanuts in North Carolina. Currently, it does not appear that thrips populations are abnormally high, but cool days and nights have slowed peanut growth and reduced insecticide uptake, resulting in some rather severe thrips injury. Warmer temperatures and plenty of soil moisture are predicted in many places which should maximize the potential of at-plant, in-furrow insecticides. When considering a foliar spray, be sure to give the preventive insecticide (if used) a chance. Make sure active thrips are still present in unopened leaflets and do not treat unless more than 25 percent of the newly-opened leaflets have thrips damage. Treating beyond 6 weeks after planting usually does not provide much benefit.
Reports of the loss of propargite (Comite) for use on peanuts to
manage spider mites are incorrect. Uniroyal, the manufacturer of
propargite, has dropped a number of uses from the product label,
but at this time Comite will still be available to manage spider
mites on peanuts.
Blue mold is still contained in Kentucky (where it is spreading)
and in Florida. This is a good time to regularly check the blue mold
forecasting system on the World Wide Web. The blue mold forecast has become one of the most frequently used resources by off-campus users.
Granville wilt has occurred early in several fields. Warm soil temperatures (a couple of weeks ago) with sufficient soil moisture is to blame. The more recent cooler temperatures may delay symptoms in other fields. Black shank has also been confirmed on tobacco not yet laid by.
When either of these diseases occur this early, the fields are
usually a total or near total loss. Growers in fields with
histories of these diseases are advised to cultivate shallow to
avoid root damage. Black shank fields will usually benefit from a
layby application of Ridomil (1 to 2 quarts) or Ridomil Gold (0.5
to 1 pint) used pre-plant. There are no other recommendations for
fields with Granville wilt at this point.
Budworm infestations are spotty, but heavy in some areas. Some fields in the Coastal Plain of North Carolina are reported well above the threshold of 10 percent of plants infested. As usual, growers are reporting difficulty in controlling this pest.
Whitefringed beetle problems continue to occur. Plants damaged by this pest may be severely stunted. Check underground stems and roots for signs of feeding. This damage looks a bit like wireworm feeding, but is much more pronounced and with more root pruning and less tunneling. By digging carefully and looking through the soil, the white, compact, legless grubs can usually be found near damaged plants.
Alan Harper, Agricultural Extension Agent, Lenoir County, North
Carolina, has reported an increase in hornworm moths in light
traps, and a few larvae have been found in test plots. Growers
should be looking for small hornworms over the next week. The
threshold for hornworms is 1 large (over 1 inch) larva for each 10
plants checked. Large numbers of smaller larvae should be watched
daily to determine whether beneficial insects and other factors
will reduce their numbers.
Web page last updated on 3 June 1996 by Stephen J. Toth, Jr..