Evaluation Of Insecticides For Control Of Western Orchardgrass Billbug

G.C. Fisher, J.T. DeFrancesco and S. Rao

Introduction

The western orchardgrass billbug (Sphenophorus venatus confluens Chittenden), is a serious pest of our orchardgrass grown for seed in the Willamette Valley (Kamm 1969; Fisher et al. 2002). This pest is a beetle, more specifically a weevil, not a "bug". In the spring the beetles that overwintered in or near the field margins become active. At this time they mate and feed on developing grass blades that are still folded longitudinally and just beginning to emerge from the plant crowns. As these leaves grow and elongate in March and April, distinctive, paired feeding holes about 1/4 to 1/3 inch in diameter become noticeable.

Females insert eggs into the bases of differentiating stem tissue in the plant crown or between the leaf sheath and stem from early May through early July. Eggs hatch in one or two weeks and the larvae feed in stems and crowns through September. This larval feeding damage is quite serious and often results in significant die-out in heavily infested fields if control measures are not taken. Needless to say, seed yields drop drastically after a field becomes infested.

Even though there is but one generation per year and the life cycle of the billbug is fairly simple, few effective control strategies have been developed other than proper timing of an effective insecticide timed to kill the adults in the spring. The application is timed so that most of the overwintered beetles are in the field and actively feeding but before females begin to deposit eggs (early May).

Although post-harvest open field burning would seem to be an effective control, it really isn't. This is because at the time of burning, the billbugs are usually still deep in the crowns and roots of the orchardgrass and fairly well protected from the short-lived fires. Example: one of last year's burns in part of a heavily infested field resulted in a reduction of only about 1/3 of the field population when compared to the population of billbugs in the unburned parts of the field. In fact, burning orchardgrass fields seriously infested with billbugs has in the past often resulted in large "dead areas" because the weakened crowns are unable to rebound from the damage caused by both billbug and fire.

A succession of insecticides beginning with the chlorinated hydrocarbons (Aldrin, Dieldrin), followed by diazinon 14G and most recently Lorsban 4E, have been the most cost effective means of controlling billbugs in orchardgrass grown for seed. Lorsban 4E is applied at 1 quart per acre, usually in late April just before heavy machinery will damage the differentiating crowns of the orchardgrass. The goal is to apply insecticides in late April when billbugs are active in the spring but before significant egg laying has begun (early May).

It is essential that Lorsban (and any other insecticide that will be developed to control this pest) be applied during a light rain. This insures the insecticide will reach the crown where the billbugs live, feed, seek cover and reproduce. If it is not raining during application, the insecticide residue dries on the leaves above the billbugs. Furthermore, Lorsban essentially does not rehydrate with subsequent rain showers. It stays where it dried, above and away from the billbugs.

Poor control of billbug with Lorsban over the last few years has been observed in many commercial fields as well as in our field trials. Insecticide tolerance, poor coverage, and possibly applying product too early - before billbugs have all come out of hibernation appear to be the most likely underlying causes.

Objective

A major objective of our research in orchardgrass has been to find and label new insecticides to control this serious pest. Few, if any, biological control agents other than isolated epizootics of a naturally occurring fungus disease of billbugs have been observed to exert much control of the western orchardgrass billbug. It is highly likely that certain strains of endophytic fungi exist that could provide effective control of this billbug. Obviously an endophyte containing orchardgrass variety would not be acceptable as livestock pasture or feed!

Discussed below are results of trials conducted on grower fields with "challenging" infestations of the western orchardgrass billbug. The objective was to compare promising insecticides with a likely fit in our grass seed industry for control of billbug.

Methods - Trial 1:

A field trial was conducted in 1999 in a 5-year old commercial field of orchardgrass (cv. Pennlate) in Linn County near Corvallis. Treatments included: thiacloprid (Calypso 2E) @ 0.125 lb. a.i./a, bifenthrin (Capture 2EC) @ 0.1 lb. a.i./a, chlorpyrifos (Lorsban 4E) @ 1.0 lb. a.i./a, Spinosad (Success 2SC) @ 0.094 lb. a.i./a, and lamda-cyhalothrin (Warrior) at 0.03 lb. a.i./a. An untreated control was included for comparison. Insecticides were applied on 4/20/99 with a CO₂ backpack sprayer equipped with a 3-nozzle boom (TeeJet 80003vs flat fan) at 30 psi, at a rate of 38 gallons of water per acre. Treatments were applied to 25 x 25 ft plots in a completely randomized design with five replicates.

On 4/28/99, treatments were evaluated by digging and breaking apart five crowns (each approximately 1.0 sq. ft.) per plot for detection of billbugs. A series of three screens were used to collect and remove billbugs from each sample.

Commercial harvest of the orchardgrass seed occurred on 7/15/99. On 7/23/99, five crowns (each approximately 1.0 sq. ft.) were dug from all plots, placed in a greenhouse and watered to stimulate regrowth. On 9/1/99, the number of new, viable shoots per sample was recorded. On 9/8/99, crowns from the Capture, Warrior and untreated plots were broken apart and sieved through a series of three screens to determine billbug population (adults, pupae and larvae).

Methods - Trial 2:

In 2000 the trial was repeated in a 6th year orchardgrass field (cv. Pennlate) using larger plots to counteract the effects of adult migration into the more effective plots from the less effective plots and the adjacent untreated areas of the field. Treatments were applied by the grower to 100 x 450 ft strips. Treatments included: bifenthrin (Capture 2EC) @ 0.078 lb. a.i./a applied either once or twice, chlorpyrifos (Lorsban 4E) @ 1.0 lb. a.i./a, Spinosad (Success 2SC) @ 0.094 lb. a.i./a. Insecticides were applied in the equivalent of 28 gallons of water per acre as broadcast sprays using a 50 ft boom. Treatments were applied on 4/14/00; a second Capture application was made on 4/21/00. An untreated control was included for comparison.

Treatments were evaluated on 5/4/00 by digging and breaking apart ten crowns (each approximately 1.0 sq. ft.) per plot, using a series of three screens to collect and remove billbugs from each sample.

Also in 2000, and again in 2001, two 3-acre plots were treated with Capture 2EC Insecticide/Miticide in late April with 5 and 6.4 ounces product per acre ( 0.09 to 0.10 lb a.i./a) to control western orchardgrass billbug. Sprays were applied during light rains with commercial sprayers using 25 to 35 gallons of water per acre.

Results - Trial 1

Table 1. Effect of insecticides on western orchardgrass billbug population and shoot regrowth in orchardgrass in 1999.

^a Crowns removed from field 7/23/99 (after harvest) and evaluated on 9/1/99

Table 2. Effect of insecticides on western orchardgrass billbug population in crowns of orchardgrass after regrowth in 1999.

¹ number of billbugs determined on 9/8/99
² means in columns followed by the same letter are not significantly different at the p=0.05 level.

At first glance, Capture 2EC does not appear to be the highly effective product it is for controlling billbugs. However, we believe plot size was too small, allowing immigration of billbugs from plots sprayed with less effective products and untreated areas occurred for at least 30-40 days post spray. This effect blurred both adult control (Table 1) and subsequent reduction of larval numbers (Table 2) that should have been noticed.

Regardless, single applications of either Capture^® 2EC or Warrior^® 1E did result in substantial reduction of billbugs after 8 days (Table I). 2).

Results - Trial 2

In trial 2, there was a significant difference between treatments the results of which indicate just how effective Capture 2EC can be in controlling adults of the western orchardgrass billbug (Table 3).

Interestingly, spinosad (Success 2SC) from DowAgrosciences appears to have good activity on billbug, too. Spinosad is an insecticide derived from the fermentation process of an Actinomycete, Saccharopolyspora spinosa, and is a "reduced risk" insecticide. Note that Lorsban 4E apparently did not provide control of western orchardgrass billbug in either trial.

Table 3. Effect of insecticides on western orchardgrass billbug infesting a commercial stand of orchardgrass produced as a seed crop, 2000. 

Field observations in 2000 and 2001 on 2 and 3 acre size plots treated with Capture^® 2EC for control of western orchardgrass billbug.

Within hours of applying Capture insecticide to orchardgrass fields, disoriented billbugs are observed between rows. However, it has been our experience that it takes one to two weeks to begin seeing the full effect of a Capture application. In two heavily infested fields where 40% or more of the plant crowns displayed adult feeding damage just before an application of Capture in the third week of April, it was difficult to find more than 1 or 2 % of the crowns with adult feeding damage the subsequent spring.

Discussion

A crisis exemption for Capture 2EC was determined appropriate and granted by the Oregon Department of Agriculture beginning at 6 AM on April 3, 2002. As with Lorsban, when used to control this pest on orchardgrass, it is necessary and highly recommended that this application be made during a light rain to insure penetration of product through canopy to the crowns of the grass where the billbugs are active.

In brief, one application of 6.4 fl. oz/a of product may be applied to orchardgrass for billbug control. Capture 2EC Insecticide/Miticide is a Restricted Use Insecticide due to toxicity to aquatic invertebrates and certain fishes. It must be applied by ground only and must have a 25 foot buffer zone between sprayed areas and water. It is also highly toxic to bees if sprayed directly over them or onto bloom that bees are actively foraging upon.

A special note of thanks is extended to Western Farm Service's Bob Schroeder as well as the Rohner family and James VanLeeuwen for the service, support and patience that made these trials possible. In addition, Mr. David Priebe of the ODA worked tirelessly in developing this crisis exemption and through his efforts growers were able to use Capture during the spring, 2002.

References:

Kamm, J. A. 1969. Biology of the billbug Sphenophorus venatus confluens, a new pest of orchardgrass. J. Econ. Entomol. 62: 808-812.

Fisher, G, , S. Rao, M. Mellbye and G. Gingrich. 2002. Grass Seed Pests. In PNW Insect Management Handbook 2002, OSU, Corvallis, OR (in press).

This report has been published with a grant from the Oregon Seed Council

 [Contents] [Author Index] [Credits] [Home]

2001 SEED PRODUCTION RESEARCH
AT OREGON STATE UNIVERSITY
USDA-ARS COOPERATING
Edited by William C. Young III
William.C.Young@oregonstate.edu

The internet version of this report
was formatted by Sara Griffith
Sara.Griffith@oregonstate.edu

http://www.css.orst.edu/seed-ext/Pub/2001/