June 14 through June 28, 1999
Dr. Lynell Tanigoshi (WSU Vancouver, entomologist), Geoff Menzies (WSU Vancouver, Lynden Satellite Station, manager), Steve Midboe (Whatcom Farmers Co-op), and Brent Clark (Clark’s Berry Farm).
The black vine weevil, Otiorhynchus sulcatus is a serious pest on raspberries in western Washington. The adult stage can be one of the most common insect contaminants of machine-harvested fruit. There is very little tolerance for this pest in raspberries. A pre-harvest spray of the insecticide, Brigade (bifenthrin) applied to the raspberry canopy is the industry standard for controlling this key pest. There is significant interest in investigating practical, alternative strategies which if used in an IPM program, might help reduce the potential for black vine weevils to develop resistance to Brigade. Cryolite Bait, manufactured by the Gowan Company was registered temporarily in Washington under section 24(c) during the 1999 season. It may have the potential to provide another option for raspberry growers and help reduce the reliance on Brigade for weevil control.
On June 14, Cryolite Bait was banded in the row at two rates (3.1 pounds and 4.6 pounds of formulated product per 1000 feet of row). The bait was delivered with a tractor-drawn, ground-driven, Valmar air-assist spreader treating approximately a two-foot wide band centered on the hill. With this equipment, two adjacent rows were treated with a single pass. The equipment setting used for the low rate of application was the lowest possible adjustment on the spreader. Raspberries are planted in rows 10 feet apart. These rates of application are equivalent to 13.5 pounds and 20 pounds of product per acre at a material cost of approximately $54 and $80 per acre. This material contains 20% by weight, the active ingredient, sodium aluminofluoride. Each of the 3 treatments (low rate, high rate, and untreated check) was replicated four times and randomly placed within each replicate. Each of the 12 plots was 4 rows wide and 90 feet long.
Plots were sampled in the evening 3, 7, and 14 days after treatment using a 10-ft. long by 3-ft. wide drop- cloth placed on both sides of the row. After the drop-cloth is placed on the ground, the top training wire at each end of the 10-ft. section is grasped firmly and shaken vigorously to dislodge adult black vine weevils. Specimens are identified, counted and then returned to the plot. Two adjacent samples were taken from the center ten feet of the center two rows within each plot on each sampling date.
Black vine weevil development in the soil was studied carefully at this site from early April through mid-June. At the time of the application, black vine weevils had completed their development in the soil and most if not all had transformed to the adult stage, emerged from the soil, and were active in the raspberry canopy.
Both rates of Cryolite Bait reduced the black vine weevil population compared to the untreated check 3, 7, and 14 days after treatment. The difference between both rates of cryolite and the untreated check was not statistically significant 3 days after treatment but was at 7 and 14 days after treatment. There was no significant difference between the two rates of application. The values shown in Table 1 are the average of 8 drop-cloth samples for each treatment on each sampling date.
Table 1. Cryolite Bait Efficacy 3, 7, and 14 Days After Application
|
Treatment |
Rate |
Average Number of Adult Black Vine Weevils per 10 ft. section |
||
|
3 DAT |
7 DAT |
14 DAT |
||
|
Cryolite Bait |
3.1 lbs/1000 ft. |
2.9 a |
4.3 a |
3.9 a |
|
Cryolite Bait |
4.6 lbs./1000 ft. |
3.4 a |
3.4 a |
2.3 a |
|
Untreated |
7.0 a |
10.8 b |
11.5 b |
|
Means with different letters were significant at P= 0.05 level by Tukey’s test
This single application of Cryolite Bait reduced black vine weevil populations by up to 65-80% two weeks after treatment. This was in spite of rainfall 3 days after treatment which may have leached some of the active ingredient from the bait and reduced its effectiveness. Based on these encouraging results, cryolite has potential as a supplement to controlling black vine weevils in raspberries. The level of control observed in this trial is inferior to the standard Brigade program and would have resulted in weevil-infested fruit with machine harvesting. For this reason, the plots were sprayed in late June prior to harvest with Brigade. This level of control may be satisfactory in hand-picked fields which can usually tolerate higher insect populations at harvest. Consideration must also be given to adult weevils, which if uncontrolled would then survive throughout the summer to lay eggs. These eggs hatch into larvae, which can cause additional feeding damage to roots during the winter and following spring.
Further study with this material, if registered again, should explore the potential benefit of two applications prior to harvest as well as higher application rates as allowed by the label. This material shows promise and may be most practical for early season (mid-April) treatment of over-wintering adult black vine weevils and spring-emerging clay colored weevils. Small-scale lab studies have shown that Cryolite Bait controls both of these species.