Craig A. Ramey

Mortality of gallinaceous birds associated with 2% zinc phosphide baits for control of voles in alfalfa

Nontarget hazards to 52 ring-necked pheasants and 51 California quail were studied using 2·0% zinc phosphide (Zn3P2) steam-rolled-oat (SRO) baits to control gray-tailed voles in 12 (0·2-ha) enclosures planted in alfalfa. Pen raised birds were wing-clipped and 25–26 of each species were randomly assigned to three Zn3P2 baited or three control baited enclosures (eight or nine birds and 23–24 voles in each). Twenty-four birds of each species were also monitored twice daily using radiotelemetry. Following acclimation and pre-baiting (7 days), 2·0% Zn3P2 or control (0·0% Zn3P2) bait was broadcast by mechanical spreaders, and birds were observed or monitored for 14 days post-baiting. Zinc phosphide deaths, supported by necropsy results, occurred in 69% (1826) of the pheasants, and none (026) of the quail. Other bird deaths were associated with six predator attacks, four accidents, and three escapes. Eight birds were missing at the completion of the study. These losses were not significantly different between species, baiting groups, and radiocollar status. The occurrence of all but one Zn3P2 death (1718) within 24 h of exposure was highly significant (p 1 day post-baiting. Sublethal toxic effects of Zn3P2 were observed in two pheasants. Postulated attributes of the efficacious bait (> 94% mortality for voles) that may have decreased nontarget exposure and environmental risks (particularly to quail) are discussed. Plans for research to assess the potential hazard of Zn3P2 to wild, free-ranging pheasants following a typical vole control program in alfalfa are underway.

Safe efficacy of three strychnine alkaloid bait concentrations for hand-baiting control of plains pocket gophers

In November 1990, field efficacy studies using milo baits formulated with 0.35%, 0.75%, or 1.30% strychnine alkaloid were compared to a placebo (0.0% strychnine) for controlling plains pocket gophers (Geomys bursarius) near Pleasanton, Texas. These data were required by the US Environmental Protection Agency (EPA) as partial fulfillment for the maintenance of the rodenticide registrations of the US Department of Agriculture. Each of four treatment units (TUs) within a block (2) was randomly assigned one of the four baits. Within each TU, 15 gophers were captured (balanced roughly for gender) and instrumented with radio transmitters. Following a pretreatment acclimation averaging 4.1 days, bait (4 g) was placed in active pocket gopher burrows by hand-baiting. Pocket gopher mortality was measured by monitoring the fate of radio-equipped pocket gophers (n = 123) both pretreatment and posttreatment. Lack of gopher movement on two consecutive days indicated death, and the carcass was retrieved. Strychnine mortality was based on chemical analyses of carcasses, and it occurred in 0.0%, 66.7%, 96.3%, and 89.7% of gophers from the 0.0%, 0.35%, 0.75% and 1.30% TUs, respectively. Natural mortality was 7% on the placebo TUs. All three strychnine treatments provided significantly increased mortality over the placebo (P < 0.0001) using Fishers exact test for paired comparisons. A difference in gopher mortality occurred between the 0.32% and 0.77% strychnine treatments (P = 0.003), but not between the other comparisons (0.32% vs 1.30%, P = 0.18 and 0.77% vs. 1.30%, P = 0.24). Gopher carcasses recovered posttreatment indicated 68 of 86 (79.1%) had strychnine alkaloid residues. The non-target strychnine hazard (using least-squares means) by treatment were 4.85 ppm (0.35%), 8.04 ppm (0.75%), and 9.47 ppm (1.30%). Carcass residue differences were not detected among strychnine treatments (F = 2.48, df = 2, 3, P = 0.23). Fortunately, non-target exposure was greatly decreased because all carcasses with strychnine residues were recovered underground at a mean depth of 0.51 m (SE = 0.027, range 0.15-1.17 m). Placebo-baited TUs had 27 survivors and 2 deaths from unknown causes. None had detectable strychnine levels. No non-target mortalities were documented during carcass searches and radio-tracking activities.

Evaluation of a 2-active ingredient gas cartridge for controlling northern pocket gophers

Abstract The efficacy of a four-ingredient (two active and two inert) gas cartridge to control northern pocket gophers in an oat-alfalfa hay field was evaluated. The reformulated rodent gas cartridge was jointly developed by the Denver Wildlife Research Center and Pocatello Supply Depot to replace the currently registered eitht-ingredient gas cartridge. The reformulated cartridge contains sodium nitrate and charcoal as active ingredients, with Fullers earth and borax as inert ingredients. When ignited, the active ingredients produce primarily carbon monoxide. Four test areas (one control and three fumigated) were randomly established with 15 sample plots (each 0·008 ha) on each test area. Active burrow systems were treated: (1) in the sample plots; (2) outside the sample plots but within each test area; and (3) in the buffer zone around each test area. Pocket gopher activity on each plot was determined pre- and post-testing by an open-hole index. Although there was an increase in pocket gopher activity on the control test area and declines of 7·1, 13·3 and 30·8% on the three test areas receiving the gas cartridges, the difference in activity was not statistically different ( p = 0·174). The 17·1% mean reduction in pocket gopher activity in the fumigated test areas was substantially below the minimum standard efficacy of 70% established by the U.S. Environmental Protection Agency for fumigants. This result was similar to two previous studies conducted with the original eitht-ingredient gas cartridge for the control of northern pocket gophers.

Potential risks to ring-necked pheasants in California agricultural areas using zinc phosphide

Both wild-caught (32) and pen-reared (29) ring-necked pheasants (Phasianus colchicus) were studied using radio-telemetry in agricultural areas including: milo (sorghum — Sorghum vulgare), rice (Oryza sativa), corn (Zea mays), alfalfa (Medicago sativa), melon (Cucumis melo), and weeds. Following capture, demographic data collection, and radio-collaring, they were released into agricultural habitats near Meridian and Nicolaus, CA. After 7 days of acclimation, habitat use and mortality of radio-collared birds were monitored daily using radio-telemetry with Global Positioning Satellites units to record their locations. Randomly selected Meridian alfalfa fields (≈160 acres) were treated with 2% zinc phosphide (Zn3P2) on steamed rolled oat (SRO) baits for vole control, whereas, Nicolaus alfalfa fields (≈160 acres) were treated with placebo baits. After ≈5 weeks of radio-tracking during September and October 1996, no pheasants were killed as a result of the Zn3P2 baiting. Baits lost substantial potency (>30%) during their exposure to field conditions after 24 h. Most pheasants died from avian or mammalian predation (n=34, 85%) with pen-reared pheasants more vulnerable to predation than wild pheasants. All mortalities were found in habitats other than alfalfa; upon dissection, they did not have SRO baits (either control or treated) in their gastrointestinal tracts.

Seasonal marking efficacy of Dupont oil blue A dye on steam-rolled oat groat baits for valley pocket gophers

Abstract We examined if Valley pocket gophers (Thomomys bottae) exhibited a seasonal preference for consuming steamed-rolled oat (SRO) groat bait treated with 1.6% Dupont oil blue A (fat-marking dye). Field tests were conducted in California alfalfa fields during winter, summer, and fall, and in walnut orchards during winter and summer. Five treatment units (TUs) were established each with ∼60 burrows for each season and habitat studied during 1997–1999. SRO groat marker bait (4 g ) was placed inside each active burrow. All bait sites were re-opened about 96 h later and examined for the presence (all or some) or absence of bait. The average bait site disturbance after 4 days of baiting was 78.2%. Traps were used to capture gophers up to 5 days after baiting. Valley pocket gophers (n=744) were examined for the presence of blue dye in their cheek pouches, skin/fur, and fat. We expected that if gophers moved the bait, their cheek pouches and fur would be marked; if they consumed bait, their fat would be marked. In alfalfa, 54.2%, 46.8%, and 65.7%, of gophers were marked (trapping on days 5–9) by blue dye in one or more of their cheek pouches, skin, fur, or subcutaneous fat in the winter, summer, or fall, respectively. In orchards, 57.1% of gophers were marked in winter and 53.4% in summer. Of those that were marked, all (100%) had their fat dyed blue, followed by skin/fur (34.4% males : 43.7% females ) and cheek pouches (5.7% males : 10.1% females ) . ANOVA results indicated no difference in seasonal marking efficacy in either alfalfa or orchards (F=3.59, P=0.0598 and F=0.12, P=0.7384, respectively). The usefulness of 1.6% Dupont oil blue A dye as a marking agent for Valley pocket gophers was not demonstrated overall or for any season in either habitat. Therefore, a better marker for this gopher is needed. Some factors that may have influenced these results were discussed including: (1) baiting methodology (∼66% of the bait sites were devoid of bait at the end of the study), (2) species specific dye properties, (3) bait acceptance (i.e. aversion to the dye), or (4) availability of alternative foods.

Weatherability of a steam-rolled oat groat chlorophacinone ground squirrel bait under field and laboratory conditions

Abstract Investigations of the weatherability of spot-baiting for ground squirrel control in northern CA field studies were conducted with a registered bait consisting of 0.01% chlorophacinone (an anticoagulant rodenticide) on steam-rolled oat groats. For reference purposes, a laboratory test was later conducted in an environmental chamber simulating some of the observed weather conditions. Three weathering plots were established in alfalfa for field tests. Each was baited with rodenticide fortified bait that was handled the same as for a simultaneous control project. Test areas were protected with wire mesh to prevent bait consumption by birds and mammals. Bait samples were collected daily over 7 days, then frozen, and shipped for analysis. Test No. 1 conducted under wet conditions showed a 71% loss of chlorophacinone after 1 week. Test No. 2 demonstrated a 57% loss of chlorophacinone under drier conditions. Test No. 3, a 24 h test under very wet conditions within the alfalfa field irrigated by overhead sprinklers, had a 92% loss of chlorophacinone. Laboratory studies using controlled environmental conditions: light (16 h light:8 h dark), with a mean relative humidity of 98%, and a range of temperature 11.1–27.8°C (52–82°F) showed ≈50% loss of the chlorophacinone. The magnitude was less (37% at 7 days) in the environmental chamber when corrected for water weight gain.