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 bollworm is now occurring throughout North Carolina, with light trap captures quite variable. Despite counts in a number of traps dropping significantly in the past week, the bollworm flight peaks have not necessarily been reached, as evidenced by a few counties where counts dropped but resurged. For example, light trap counts in Northampton and Halifax Counties had increased modestly on August 2 to the 12 to 87 range for a two night catch, while the Sampson County trap count increased from a July 31 low of 300 bollworm moths to the alarming count of 2,325 moths on August 2. Egg counts in a number of areas across the state are very high; 50 to 100 or even 200 bollworm eggs (primarily bollworm, but also some budworm) per 100 terminals are common. Many cotton fields in need of treatment with insecticide are presently impossible to negotiate with ground equipment.
This is still in a critical time period for protecting the cotton
crop. A high pyrethroid rate is probably warranted in areas where:
1) treatment delays have or will occur; 2) large numbers of eggs
are present prior to the first application; 3) larval thresholds
are exceeded 1.5 to 2-fold after the initial application(s); 4)
cotton is rank/lush; or 5) 6 or 7
days are required to cover a
producer's acreage. As we enter the month of August, cotton fields
will begin to vary increasingly in their attractiveness and
susceptibility to bollworms and European corn borers. This means
that cotton crop maturity will become as or more important than the
numbers of moths. Nevertheless, black light and pheromone trap
catches will continue to provide at least a rough gauge of the
flight intensity in local areas, particularly if a number of traps
have similar results. Additionally, some the bollworm complex
adults observed this past week were the harder-to-kill budworm
species, which are poorly attracted to black light traps. Most
cotton fields will be vulnerable to bollworm moths for the next 7
to 10 days, and some fields for the next 3 to 4 weeks. High
quality scouting and a quick treatment response to thresholds are
especially important with the high insect pressure and potentially
high-yielding cotton crop.
The high levels of rapidly maturing fruit over a significant
proportion of north Carolina's cotton crop will push much of this
acreage to an early cut out, rendering cotton considerably less
attractive and susceptible to bollworms
, budworms,
European corn borers and fall armyworms
in the next few weeks. This should be a
significant benefit for cotton producers who have managed for an
early crop (though we have had substantial help from good moisture
and many degree day units).
Small to substantial amounts of Bollgard (B.t.) cotton have been treated with insecticide for bollworms in states to the south of North Carolina, including South Carolina and Georgia. Most of the reported bollworm establishment has been under bloom tags (blooms usually dried, but sometimes mushy) stuck to small developing bolls. I observed this phenomenon two years ago in my Bollgard plots in Onslow County. Although they offered no explanation for this damage, Monsanto Company scientists assured me that the B.t. protein endotoxin was present and active in the pink and dried flowers. Whatever the reason, bollworms seem to be exploiting this situation.
If recommended Bollgard scouting procedures are followed (see the Cotton Insect Scouting Guide), the proper treatment response to threshold levels of bollworms should be realized. Specifically, sample all areas of the plant for both squares and bolls, including bloom tag bolls. However, do not oversample tagged forms, but sample these bolls in the proportion in which they occur in the field. That is, if medium to large size bolls without a bloom tag make up 90 percent of the overall boll population in a cotton field, 90 percent of the sample should be large and medium bolls, while the remaining 10 percent of the sample should include the smaller bolls with possible bloom tags (including white and pink blooms). If the threshold of 6 percent economically-damaged squares or 3 percent bollworms 1/8 inches or larger is reached, the Bollgard cotton field should be treated with one application of a synthetic pyrethroid, then reevaluated about 7 days later.
Procedures for scouting for stink bugs are listed in the Cotton Insect Scouting Guide. Because less
insecticide treatment for bollworms, budworms and European corn
borers in Bollgard cotton is anticipated, stink bugs can generally
be expected to occur at higher levels in B.t. cotton. During the
course of normal scouting activities, all cotton bolls with
suspected stink bug damage should be cut open with a knife. If the
internal damage exceeds 2 percent, one of the more intensive stink
bug scouting procedures should be followed.
The weather during the past week has reduced the likelihood of
problems with spider mites in peanuts for this year. While spider
mites may still make a comeback later in the season, the threat of
a severe problem is considerably less now than several weeks ago.
On the other hand, the wet weather has created excellent conditions
for infestations of southern corn rootworms in peanuts. Growers
planning to treat their peanut crops with insecticide but have not,
should do so immediately. The effectiveness of insecticides
applied after August 5 begins to decline rapidly. Initiate
scouting for corn earworms, as it is presently the time of year for
these insects to begin to occur. Probably there is no insect pest
of peanuts that is easier to scout. Many unnecessary insecticide
sprays can be avoided if scouting and thresholds for corn earworms
are used.
Web page last updated on August 5, 1996 by Stephen J. Toth, Jr..
