FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
The strange bollworm moth, egg and caterpillar situation (generally late, light populations) continues in North Carolina. Light trap counts range from very low to moderate, on average two to three weeks behind last year's levels. Two-night light trap counts on August 6 in Lenoir, Sampson, Onslow and Craven counties were 110, 123, 183 and 224 bollworm moths, respectively. These levels are among our highest, and certainly can be considered moderate. Perhaps 50 percent or more of our light traps are presently showing less than 20 moths captured over two nights. Moderate levels of European corn borer moths are also being caught in a number of the light traps along with above average levels of stink bugs.
The number of cotton fields meeting the egg and/or larval threshold continues to spread northward into Edgecombe, Wilson and Nash counties and over to Martin, Washington, and Tyrrell counties. To this point, a number of producers and consultants who are carefully monitoring their fields have been able to save money by avoiding unneeded insecticide applications. Threshold levels in the Craven, Jones, Onslow, Scotland, Hoke and Robeson counties were reached (just barely in some cases) several weeks ago and have been treated with insecticide twice. Within the past few days, it seems that both egg thresholds in terminals (10 percent) and larval thresholds on fruit (3 percent) have been reached in about equal numbers. Therefore, in those areas which have not yet been treated, search both the squares and bolls for eggs and larvae.
Levels of moths, eggs, and larvae continues to vary greatly between
communities and even between nearby fields. Responding to
threshold levels of insects based upon sound scouting will continue
to be the best option. Some areas will likely experience very
little pressure and insecticide treatment this year, while others
have two to three more weeks of possible treatment. For producers
who have or will soon have their scouts leaving for school and will
be without scouting information, it would be best to err on the
side of protection (treatment) until four or less nodes are present
above the upper-most first position white flower. For twice per
week insect updates, call 1-800-662-7301; the cotton update is No.
11.
Remember that the cotton crop in North Carolina is still late and
susceptible, and many fields may remain vulnerable to bollworms,
European corn borers, fall armyworms and stink bugs until late
August, or even early September in some cases. A few fields have
been treated for stink bugs in the past week. One suggested stink
bug threshold which does not require a significant departure from
bollworm scouting is to treat with insecticide when stink bugs have
damaged 5 percent or more thumb-sized bolls. Be sure that internal
damage is confirmed before counting a boll as stink bug-damaged.
If a treatment threshold is close, with the late crop and
considering that pyrethroids do a fair to good job of preventing
European corn borers, fall armyworms and stink bugs from becoming
established, spraying may be indicated, especially where these
pests have been noted.
The bollworm moth flight started south of the Albemarle Sound during the last days of July and has slowly intensified to a moderate level at present. This week, between 125 to 150 moths per night were caught at a location with sandy soil and almost surrounded with corn. This is considered a very favorable location. Pheromone traps below the Albemarle Sound have also shown moderate catches, but high variation between traps. North of the Albemarle Sound moth numbers have also increased, but not to a peak level. Again there seems to be high variation in moth numbers across the landscape. During the week of August 4-7, egg thresholds were reached in many areas south of the Albemarle Sound, but only in scattered fields to the north. The moth flight is expected to peak in the next week, but emergence could be influenced by the continued dry weather. Moths have difficulty emerging from hard soil and often a flush of moths are noticed following rainfall. European corn borer moths are also present at moderate numbers. Early insecticide applications were made in many Washington, Tyrrell and Bertie county fields, southern Currituck County, in Bertie County along the Cashie River, and in Martin County around Jamesville. Currently, most fields have some low levels of eggs in the terminals. I have noticed a greater proclivity for eggs to be laid on the cotton plant stems below the terminal, especially in fields where plants have a lot of space between nodes in the upper plant and are moderately open-canopied. In some fields, egg thresholds could not be reached by examining only the uppermost portion of the terminal, but was exceeded if the main stem and leaf stems below the uppermost terminal were also examined.
Currently, all cotton fields have fruit that are almost totally susceptible to bollworms and European corn borers. Most fields have a good fruit set (squares, flowers, and bolls) between nodes 8 and 15, but the oldest bolls remain very soft and easily damaged by bollworms and other boll-feeding insects. This is due to the slow start the crop experienced earlier. Ordinarily, by mid-August early-planted cotton will have about 80 percent of its harvestable fruit too hard for a bollworm to penetrate. This year I suspect we will have only 25 to 40 percent hard fruit by this time. Therefore, an extended scouting and treatment effort may be necessary in 1997. Also, in a more typical year we get significant contribution to yield from nodes above number 14, but in 1997 there will be few fruit harvested above number 16 unless warm weather persists into the fall. I predict that plants will have a minimal ability to compensate for fruit loss to positions below approximately the number 14 node and believe that we should be vigorous in preserving all fruit set in the number 8 to number 14 zone. Ordinarily, most fruit are lost to bollworms and European corn borers because the grower: 1) delays the initial insecticide spray(s) so that an initial population of caterpillars have hatched and established prior to application; 2) allows a low population of caterpillars to accumulate and move into the lower plant areas before reapplication is made; or 3) is reluctant to make a final application and allows a low bollworm or European corn borer population to persist. All of these situations can be intensified by poor scouting and by having a low but persistent population of moths. Often, a low and variable moth flight and a late-maturing crop are prime ingredients for making bollworm treatment decisions difficult.
Soybeans are currently from the pre-bloom to full bloom stage and
are suitable for corn earworm infestation. However, during the
week I have seen few bollworm eggs and no larvae in soybeans.
Soybeans are currently full of insect predators which feed on eggs
and small larvae. I believe that we are likely to have a minimal
corn earworm problem in soybeans this year. Scouting will be
essential to pinpoint those fields requiring treatment.
Web page last updated on August 11, 1997 by Stephen J. Toth, Jr..
