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EFFICACY OF VARIOUS SOIL INSECTICIDES AGAINST WESTERN CORN ROOTWORM IN FIELD CORN, 2002

EFFICACY OF VARIOUS SOIL INSECTICIDES AGAINST WESTERN CORN ROOTWORM IN FIELD CORN, 2002 (F36) CORN (FIELD): Zea Mays L., 'Pioneer 3394' EFFICACY OF VARIOUS SOIL INSECTICIDES AGAINST WESTERN CORN ROOTWORM IN FIELD CORN, 2002 R. R. Youngman Department of Entomology Virginia Polytechnic Institute and State University Blacksburg, VA 24061-0319 Tel: (540) 231-9118 Fax: (540) 231-9131 E-mail: youngman@vt.edu C. A. Laub claub@vt.edu T. A. Dellinger tdellin@vt.edu Western corn rootworm (WCR): Diabrotica virgifera virgifera (LeConte) In 2002, several soil insecticides were evaluated for their effectiveness against Western corn rootworm (WCR) larvae in a no-till continuous cornfield at the Virginia Tech Kentland Research Farm in Montgomery Co. All treatments were applied at planting and consisted of three granular insecticides, one pre-treated insecticide seed treatment, and an untreated check. The test was located in a 5-acre field with a combination McGary and Purdy dark gray silt loam soil type. The field has been planted in corn every year since 1999. Plots of 25 ft x 10 ft (four rows wide) were arranged in a RCBD, with all insecticide treatments and an untreated check replicated five times. Prior to planting, 10 baited wire traps and 10 bait stations were installed in the plot area on 30 Mar to estimate the relative levels of seedcorn maggot, wireworms, and annual white grub infestations. The baited wire trap method consists of 20 untreated corn seeds (pre-soaked in water for > 12 h to facilitate germination) spaced evenly in a 3-inch wide x 24-inch long strip of hardware cloth (0.25-inch mesh). The hardware cloth strip is bent lengthwise along a 45° to provide strength and to keep the seeds in place. The bait station method consists of an 8-oz mixture of 1:1 untreated corn and wheat seeds that were pre-soaked in water for > 12 h. The baited wire traps and bait stations were buried at a soil depth of 2 and 6 inch, respectively. Following installation in the soil, a black plastic trash bag was placed over each baited wire trap and bait station to facilitate solar heating of the soil. On 15 Apr, all baited wire traps and bait stations were removed from the soil and evaluated for the presence of any pest insects. In addition, at the baited wire traps, the corn seeds and seedling roots were inspected for signs of feeding injury. On 24 Apr, all plots were planted at the rate of 28,000 seeds/acre (Pioneer '3394') on 30-inch rows using an Almaco, 2-row Max-Emerge planter. All insecticide treatments were applied in front of the presswheels in a 5-inch wide T-band directly over the row. For the granular insecticide treatments, the standard granular applicator was removed from each row unit and replaced with a wooden holder designed to hold an inverted pint canning jar (Mason) for dispensing the granules. Attached to the underside of the wooden holder was a plastic funnel and tube through which the granules flowed. A single opening, drilled into the metal lid of each jar, was calibrated to deliver the granules accurately at a speed of 3 mph. The possibility of mixing one or more insecticides was avoided by using a separate jar and lid for each treatment. At the start of application, a jar containing the appropriate insecticide was inverted and placed in each of the wooden holders. This method helped minimize soil compaction because the tractor made only one up-and-back pass per plot. For the pre-treated, insecticide seed treatment, the granular insecticide applicators on each row unit were shut off and disengaged from the planter drive unit. The seed hoppers for each row unit were emptied of any corn seeds and then refilled with the pre-treated seed treatment. After all assigned plots were planted, any remaining pre-treated seeds were removed before refilling the hoppers with non-treated corn seeds. Stand counts were taken in all plots on 1 Jul by recording the total number of emerged plants per 60 row-ft (i.e., 15 ft per row across the four rows within each plot). Because of a distinct height effect in one of the treatments, plant heights were taken in all plots on 2 Jul by recording the heights of five consecutive plants from one of the two center rows within each plot. A plant height measurement was based on the length of the corn plant from the soil surface at the base of the plant to the tip of the longest extended leaf. On 3 Jul, the roots of five consecutive corn plants were dug from one of the center two rows of each plot and washed of excess soil before root injury ratings were made. Corn rootworm injury ratings were based on the Iowa 1- 6 scale (1 = no feeding damage to 6 = three or more root nodes completely destroyed). A two-way ANOVA and Fisher's protected LSD were used to analyze differences in stand counts, plant heights, and root injury ratings among treatments. The results of the baited wire trap method showed a low to moderate level of pest pressure. Of 189 recovered corn seeds (out of 200), 10 seeds (5.3%) exhibited feeding injury. Also recovered with the baited wire traps were a total of 3 wireworms, 2 seedcorn maggots, and 2 white grubs. In contrast, the bait station method failed to detect any wireworms; however, a total of 3 white grubs were found associated with the bait stations. Stand counts (i.e., plants per 60 row-ft) ranged from 39.6 for Lorsban 15G to 92.4 for the insecticidal seed treatment Clothianidin (Table 1). The treatment source of variation for stand count was highly significant (P < 0.0001) according to ANOVA. The stand count in the Clothianidin treatment was significantly higher than those of all other treatments. Stand counts in the Aztec 2.1G (49.8) and Force 3G (48.4) treatments were significantly higher than that in the Lorsban 15G treatment. Also, no significant differences in stand counts were detected among the check (44.2), Aztec 2.1G, and Force 3G treatments. Plant heights ranged from 42.8 inch in the check to 54.5 inch in the Clothianidin treatment (Table 1). The treatment source of variation for plant height was highly significant (P < 0.01). The mean plant height in the Clothianidin treatment was significantly greater than those of all other treatments except Force 3G (50.4 inch). Likewise, the mean plant height in the Force 3G treatment was significantly greater than the check. No significant differences in plant heights were detected among the check, Aztec 2.1G (47.3 inch), and Lorsban 15G (47.4 inch) treatments. Root injury ratings ranged from 2.7 for Clothianidin to 5.1 for the check (Table 1). The treatment source of variation for root injury rating was highly significant (P < 0.0001). The check root rating of 5.1 was significantly higher than those of all other treatments which averaged 2.9. Unlike stand counts and plant heights, no significant differences were detected in root ratings among any of the insecticide treatments. Also, no insecticide phytotoxicity was observed in any plot during the course of the experiment. Given the relatively low pest pressure detected on 15 Apr, we are unable to fully explain the dramatic differences in stand counts and plant heights observed among some of the treatments in this test. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Arthropod Management Tests Oxford University Press

EFFICACY OF VARIOUS SOIL INSECTICIDES AGAINST WESTERN CORN ROOTWORM IN FIELD CORN, 2002

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(F36) CORN (FIELD): Zea Mays L., 'Pioneer 3394' EFFICACY OF VARIOUS SOIL INSECTICIDES AGAINST WESTERN CORN ROOTWORM IN FIELD CORN, 2002 R. R. Youngman Department of Entomology Virginia Polytechnic Institute and State University Blacksburg, VA 24061-0319 Tel: (540) 231-9118 Fax: (540) 231-9131 E-mail: youngman@vt.edu C. A. Laub claub@vt.edu T. A. Dellinger tdellin@vt.edu Western corn rootworm (WCR): Diabrotica virgifera virgifera (LeConte) In 2002, several soil insecticides were evaluated for their effectiveness against Western corn rootworm (WCR) larvae in a no-till continuous cornfield at the Virginia Tech Kentland Research Farm in Montgomery Co. All treatments were applied at planting and consisted of three granular insecticides, one pre-treated insecticide seed treatment, and an untreated check. The test was located in a 5-acre field with a combination McGary and Purdy dark gray silt loam soil type. The field has been planted in corn every year since 1999. Plots of 25 ft x 10 ft (four rows wide) were arranged in a RCBD, with all insecticide treatments and an untreated check replicated five times. Prior to planting, 10 baited wire traps and 10 bait stations were installed in the plot area on 30 Mar to estimate the relative levels of seedcorn maggot, wireworms, and annual white grub infestations. The baited wire trap method consists of 20 untreated corn seeds (pre-soaked in water for > 12 h to facilitate germination) spaced evenly in a 3-inch wide x 24-inch long strip of hardware cloth (0.25-inch mesh). The hardware cloth strip is bent lengthwise along a 45° to provide strength and to keep the seeds in place. The bait station method consists of an 8-oz mixture of 1:1 untreated corn and wheat seeds that were pre-soaked in water for > 12 h. The baited wire traps and bait stations were buried at a soil depth of 2 and 6 inch, respectively. Following installation in the soil, a black plastic trash bag was placed over each baited wire trap and bait station to facilitate solar heating of the soil. On 15 Apr, all baited wire traps and bait stations were removed from the soil and evaluated for the presence of any pest insects. In addition, at the baited wire traps, the corn seeds and seedling roots were inspected for signs of feeding injury. On 24 Apr, all plots were planted at the rate of 28,000 seeds/acre (Pioneer '3394') on 30-inch rows using an Almaco, 2-row Max-Emerge planter. All insecticide treatments were applied in front of the presswheels in a 5-inch wide T-band directly over the row. For the granular insecticide treatments, the standard granular applicator was removed from each row unit and replaced with a wooden holder designed to hold an inverted pint canning jar (Mason) for dispensing the granules. Attached to the underside of the wooden holder was a plastic funnel and tube through which the granules flowed. A single opening, drilled into the metal lid of each jar, was calibrated to deliver the granules accurately at a speed of 3 mph. The possibility of mixing one or more insecticides was avoided by using a separate jar and lid for each treatment. At the start of application, a jar containing the appropriate insecticide was inverted and placed in each of the wooden holders. This method helped minimize soil compaction because the tractor made only one up-and-back pass per plot. For the pre-treated, insecticide seed treatment, the granular insecticide applicators on each row unit were shut off and disengaged from the planter drive unit. The seed hoppers for each row unit were emptied of any corn seeds and then refilled with the pre-treated seed treatment. After all assigned plots were planted, any remaining pre-treated seeds were removed before refilling the hoppers with non-treated corn seeds. Stand counts were taken in all plots on 1 Jul by recording the total number of emerged plants per 60 row-ft (i.e., 15 ft per row across the four rows within each plot). Because of a distinct height effect in one of the treatments, plant heights were taken in all plots on 2 Jul by recording the heights of five consecutive plants from one of the two center rows within each plot. A plant height measurement was based on the length of the corn plant from the soil surface at the base of the plant to the tip of the longest extended leaf. On 3 Jul, the roots of five consecutive corn plants were dug from one of the center two rows of each plot and washed of excess soil before root injury ratings were made. Corn rootworm injury ratings were based on the Iowa 1- 6 scale (1 = no feeding damage to 6 = three or more root nodes completely destroyed). A two-way ANOVA and Fisher's protected LSD were used to analyze differences in stand counts, plant heights, and root injury ratings among treatments. The results of the baited wire trap method showed a low to moderate level of pest pressure. Of 189 recovered corn seeds (out of 200), 10 seeds (5.3%) exhibited feeding injury. Also recovered with the baited wire traps were a total of 3 wireworms, 2 seedcorn maggots, and 2 white grubs. In contrast, the bait station method failed to detect any wireworms; however, a total of 3 white grubs were found associated with the bait stations. Stand counts (i.e., plants per 60 row-ft) ranged from 39.6 for Lorsban 15G to 92.4 for the insecticidal seed treatment Clothianidin (Table 1). The treatment source of variation for stand count was highly significant (P < 0.0001) according to ANOVA. The stand count in the Clothianidin treatment was significantly higher than those of all other treatments. Stand counts in the Aztec 2.1G (49.8) and Force 3G (48.4) treatments were significantly higher than that in the Lorsban 15G treatment. Also, no significant differences in stand counts were detected among the check (44.2), Aztec 2.1G, and Force 3G treatments. Plant heights ranged from 42.8 inch in the check to 54.5 inch in the Clothianidin treatment (Table 1). The treatment source of variation for plant height was highly significant (P < 0.01). The mean plant height in the Clothianidin treatment was significantly greater than those of all other treatments except Force 3G (50.4 inch). Likewise, the mean plant height in the Force 3G treatment was significantly greater than the check. No significant differences in plant heights were detected among the check, Aztec 2.1G (47.3 inch), and Lorsban 15G (47.4 inch) treatments. Root injury ratings ranged from 2.7 for Clothianidin to 5.1 for the check (Table 1). The treatment source of variation for root injury rating was highly significant (P < 0.0001). The check root rating of 5.1 was significantly higher than those of all other treatments which averaged 2.9. Unlike stand counts and plant heights, no significant differences were detected in root ratings among any of the insecticide treatments. Also, no insecticide phytotoxicity was observed in any plot during the course of the experiment. Given the relatively low pest pressure detected on 15 Apr, we are unable to fully explain the dramatic differences in stand counts and plant heights observed among some of the treatments in this test.

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Arthropod Management TestsOxford University Press

Published: Jan 1, 2003

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