Williamson County Result Demonstration Report

2001 BOLL WEEVIL TRAP CAPTURES FOR
WILLIAMSON AND MILAM COUNTIES

Dale A. Mott
EA-IPM

Ron Leps
Extension Agent-Agriculture

Hutto, Williamson County, Precinct #4

SUMMARY: Twenty boll weevil pheromone traps were monitored from May 8 through October 22. Overwintering boll weevil trap catches were highest on May 15 and steadily declined until the week of July 2 when no weevils were captured. Boll weevil trap catches remained low through August 7. Trap catches then increased as the cotton across the area matured. Late season catches of boll weevil peaked on Aug 14, at which time much of the area cotton had been treated with harvest aids.

OBJECTIVE: Establish a trap-line of 20 traps in the Southern Blacklands, Williamson and Milam Counties. Monitor traps once a week during the cotton season to monitor seasonal abundance of boll weevils. The trap line is provide baseline data to evaluate progress of the boll weevil eradication program.

Trapping adult boll weevils with pheromone traps is a reliable measure of boll weevil activity and has been used in the Southern Rolling Plains Eradication Program and elsewhere to monitor efforts to reduce weevil numbers over large areas. A comparison of trapping data before eradication and each year of the eradication program can provide a relative measure of the impact of the eradication program on weevil numbers during the spring when weevils are emerging and again during the fall as weevils move to overwintering sites. As part of its current IPM programs, the Texas Agricultural Extension Service traps boll weevils only during the spring at a limited number of sites in the Blacklands. However, an expanded program that includes season long trapping at more locations is needed to provide sufficient data to monitor the eradication program throughout the Blacklands Zone.

MATERIALS & METHODS:
A trap line was established in Williamson and Milam Counties. Twenty boll weevil phermone traps were set up on May 8, 2001 and were serviced and monitored on a weekly basis. Boll weevil phermone baits were replaced every second week and kill strips were replaced every fourth week. Traps were placed in fields close to overwintering boll weevil habitats where cotton is normally grown. Thirteen traps were placed in Williamson County. Traps were placed at 1 mile intervals along paved highways. Traps 1-5 were placed on FM 1660 between Hutto and Rices Crossing. Traps 6-10 were placed on FM 1331 between Circleville and the intersection of CR 418. Traps 11-13 were placed on FM 1331 from Hare to the Milam County line.

Seven traps were placed in Milam County. Traps 14-17 were located on FM 1331 between the Williamson County line and the intersection of FM 486. Traps 18-20 were located on FM 1915 just southwest of the Little River Bridge.

RESULTS AND DISCUSSION:
The mean number of weevils/trap/week is displayed below (Table 1 and Figure 1). Boll weevil numbers were very low throughout the monitoring period compared to previous years (Table 2). The average number of weevils caught per trap per week at the three locations was 1.1, 1.1, and 0.4 at FM 1660, FM 1331 and FM 1951, respectively.

The highest number of weevils was captured May 15. As greater numbers of weevils could have emerged prior to this date. At that point, numbers averaged 1.5 weevils per trap, this was 8 times fewer than during the same date in 2000 when the mean catch was 13.3 per trap.

Numbers of weevils caught in traps steadily declined in May and June and was very low in July. On August 8, mean number of weevils per trap per week increased to 4.1. At this time, early, August, the first fields in the area were being treated with harvest aids. Other fields only had mature, green bolls. From that point own, numbers of weevils were erratic, with some traps catching higher levels of weevils and most traps not catching any.

Mean number of weevils caught per trap per week over the entire 2001 season was 0.4 compared to 8.7, 10.0 and 18.0 for 2000, 1999, and 1998, respectively (Figure 2). It is difficult to deduct what exactly caused such low levels of weevils in 2001 compared to the previous 3 years. However, it was quite evident that the number of weevils emerging from diapause in the spring of 2001 was low compared to previous years. The fall of 2000 was a very dry until mid-October when frequent rainfall events began to occur. Prior to that time most of the cotton had been harvested and stalks destroyed in a timely manner, which should have reduced the potential of overwintering boll weevils. During the fall of 2001, boll weevils were kept in check by the initiation of the Southern Blackland Boll Weevil Eradication Program which began spraying in late July of 2001. This prevented numbers from increasing a great deal through the fall.

Table 1. Mean number of Boll Weevils per trap per week. Williamson and Milam Co. Boll Weevil Trapline, 2001

                                                                                         Mean # of weevils/trap/week
                                                                                                            Location

Table 2. Mean number of Boll Weevils per trap per week for the same date of previous years. Williamson and Milam Co. Boll Weevil Trapline, 1998-2001

                                                                                         Mean # of weevils/trap/week
                                                                                                            Year

Figure 2: Comparison of the average number of boll weevils caught/trap/week for 1998-2001, Williamson and Milam Co., 2001