Section V: Soil Arthropods

Control ofthe Western Orchardgrass Billbug with Various Insecticides Glenn C. Fisher & Joseph T. DeFrancesco Dept ofEntomology, OSU Corvallis, OR 97331 (541) 737-5502 Fisherg@,bcc.orst.edu. [email protected]

A field trial to control the western orchard grass billbug (Sphenophorus venatus confluens Chittenden) wasconducted in a weak, oldercommercial field of Orchardgrass (cv. Pennlate) in Linn County nearCorvallis, Oregon. Experimental design was CRD withfive replicates. Plot size was 25'x25\

Treatments included: thiacloprid (Calypso 2E®), bifenthrin (Capture 2EC®), chlorpyrifos (Lorsban 4E®), spinosad (Success 2SC ), and lamda-cyhalothrin (Warrior ) and an UTC. Treatmentswere applied on 4/20/99 with a C02 backpack sprayers equipped with a 3-nozzle booms (TeeJet 80003vs flatfan) at 30psi,using an equivalent rate of 38 gallons of water per acre. Evaluation

1) On4/28/99 (8DAT), treatments wereevaluated by digging and breaking apart five crowns (each approximately 1.0 sq. ft.) per plot, using a series of three screens to separate and remove billbug adults from each sample. Live and dead billbugs were recorded.

2) Additionally, pitfall traps (three/rep) were monitored for adult movement activity within plots prior to and after application of sprays. Traps were inspected every 1 to 4 days from 4/15/99 (5 days before spraying) through 5/28/99 (39 DAT). Numbers of live, adult billbugs were recorded and removed from the traps after each inspection.

3) Grower harvested the field on 7/15/99. On7/23/99, five crowns (each approximately 1.0 sq. ft.) were dug from all plots, transferred to our field lab at OSU and watered as necessary to promote new shoot growth from the crowns. On 9/1/99 crowns were inspected carefully and numbers ofnew, viable shoots per core were recorded for each treatment. On 9/8/99, crownsfrom the Capture, Warriorand untreated plots were broken apart and the soil sieved through a series of screens. Numbers oflive adult, larval and pupal stages ofthe billbug were recorded.

RESULTS:

Lorsban 4E did not give control ofbillbug adults. This substantiates what fieldmen and growers have observed in commercially treated fields overthepastfew years. None of the treatments significantly reduced billbugs/crown at 8DAT compared to the UTC. SEP regrowth was comparable in all treatments, including UTC.

Given duration of adult migratory period in APR andMAY, plots should have been much larger to prevent interplot migration, colonization and infestation.

83 Table 1. Mean No. Billbug Adults (live) per crown 8DAT & Mean No. shoots per crown (new growth) on 1 SEP 1999.

Treatment Live Billbugs Shoot Regrowtha (8 DAT) (No./crown) Calypso 2E @ 0.125 lb. ai/Ac 1.8 42.2 Capture 2EC @ 0.1 lb. ai/Ac 0.7 45.7 Lorsban 4E @ 1.0 lb. ai/Ac 2.5 35.8 Spinosad 2SC @ 0.094 lb. ai/Ac 1.4 38.1 Warrior 1E@ 0.03 lb. ai/Ac 1.1 42.8 Untreated 2.2 32.9

Significance n.s. n.s. aCrowns removed from field 7/23/99 (after harvest), taken to field lab and maintained until evaluated on 9/1/99. Crowns approximately of one square foot surface area.

Table 2. Mean No. Billbugs and Mean No. shoots (re-growth)/Crown in Three of Seven Treatments..8.

Shoot Regrowth Mean No./Crown Treatment/a.i. per acre Mean No./Crown* Larvae Pupae Adults Total Capture 2EC @ 0.1 lb. 45.7 4.0 1.3 0.6 a 5.9 Warrior IE @ 0.03 lb. 42.8 3.1 1.0 1.0 a 5.1 Untreated 32.9 2.2 1.5 2.3 b 6.0 ** Significance n.s. n.s. n.s. n.s.

Crowns removed from field 7/23/99 (after harvest) andevaluated forregrowth on9/1/99; number of billbugs determined on 9/8/99. Crowns about 1 sq foot surface area.

84 Table 3. No. Billbugs Collected in Pitfall Traps by DAT for the Various Treatments. (APR 21- MAY 30) oo Mean Number of Billbugs per Treatment (No.s reported are Means/ 3 pitfall traps per plot) (Days after Treatment) Treatment 1 2 3 6 8 14 18 22 24 28 30 35 37 39 Total Calypso 0.8 a 0.2 a 6.8 ab 35.4 2.4 13.4 3.0 a 8.6 1.8 7.2 4.2 33.2 6.2 a 6.2 ab 136.2 ab Capture 10.2 b 5.8 c 15.8 be 48.2 4.8 20.0 12.0 b 6.4 5.2 6.4 4.8 43.0 11.6b 17.2 be 217.0 c Lorsban 0.8a 0.4 a 5.4 a 46.4 3.6 15.0 4.0 a 6.0 1.6 4.2 4.4 45.4 4.2 a 23.6 c 171.8 abc Spinosad 0.4a 0.2 a 5.2 a 35.4 4.2 7.4 3.8 a 4.8 1.6 7.6 3.2 26.4 3.6 a 5.6 a 114.2ab Warrior 12.6b 3.2 b 16.6 c 42.4 7.2 21.2 11.6b 9.8 3.8 8.8 6.2 24.6 5.4 a 10.0 ab 188.0 be Untreated 0.6a 0.4 a 7.0 ab 23.6 3.6 8.8 3.8 a 5.6 1.8 8.4 1.6 25.8 3.6 a 8.2 ab 107.6 a Significance *** ** * n.s. n.s. n.s. ** n.s. n.s. n.s. n.s. n.s. ** * *