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Aluminum phosphide (ALP) is used extensively for burrowing mammal control. However, recent changes have been made to the ALP label which could substantially limit its utility for burrowing mammal control in the future. As such, I developed surveys to help quantify the impact that these changes are likely to have on ALP usage and vertebrate Integrated Pest Management in California. These survey findings were compared to information gathered from the California Department of Pesticide Regulation’s Pesticide Use Report for 2010 to relate the survey findings to the broader spectrum of users throughout California. I found that 49,005 lbs of active ingredient (AI) of ALP was used for burrowing mammal control in 2010, with most applications occurring in residential areas, applied primarily by licensed Pest Control Operators who specialize in vertebrate IPM. Most applications were applied to control pocket gophers, while ground squirrel and mole burrow systems were also treated. Collectively, new buffer and posting restrictions resulted in expected losses of 70% and 26% of agricultural applications of ALP for pocket gophers and ground squirrels, respectively. The impact of restrictions in residential areas may be even more extreme, with estimated reductions in ALP applications ranging from 70-98%. Alternative control methods were typically considered less efficacious than ALP. Furthermore, 13-34% of respondents indicated that they would no longer control these pests in areas where they could not use ALP. Insufficient or ineffective management programs targeted at these pests could result in increased economic damage, greater human health and safety concerns, and increased environmental degradation. Even though ALP has a safe track record in California, ALP users were willing to obtain greater training on its safe use while adhering to a 67% increase in the previous 15-foot buffer restriction, if it meant relaxing some of the current restrictions. Because of the extreme importance of burrowing mammal control, combined with the high efficacy and safe track record of ALP, perhaps these or alternative mitigation steps should be considered to ensure the safe and effective use of ALP. Otherwise, it is quite possible that the estimated 85% reduction in future ALP applications for burrowing mammal control could result in far greater negative consequences than the benefits gained from the new regulations.

Rodenticides are often used to control burrowing rodents but have not been overly efficacious for Belding’s ground squirrels due to poor bait acceptance. This has left alfalfa growers searching for alternative options for controlling this rodent species. As such, we tested aluminum phosphide and gas cartridge burrow fumigation in an alfalfa field in Butte Valley, CA, to determine if either of these approaches were efficacious and cost effective for controlling Belding’s ground squirrels. A comparison of the number of burrows treated and the number of burrows reopened 48-hours post-treatment indicated that both burrow fumigants were highly effective (aluminum phosphide = 94-98%, gas cartridges = 100%). The average cost per application was $1.05 and $2.92 for aluminum phosphide and gas cartridges, respectively. Given the almost 3-fold difference in cost of application between the two approaches, aluminum phosphide appears to be the more practical approach for Belding’s ground squirrel control. Although we currently lack an approach for estimating the amount of damage that Belding’s ground squirrels are likely to cause to an alfalfa field, it seems plausible that burrow fumigation could be a cost effective approach to reduce damage caused by this species, particularly if long-term control can be obtained. Possible long-term management options for Belding’s ground squirrels are discussed.

Fumigation with either gas cartridges or aluminum phosphide is often considered to be an effective method for controlling California ground squirrel populations, although few studies have corroborated their effectiveness. Additionally, utilizing aluminum phosphide in combination with gas cartridges could increase effectiveness of both fumigants by indicating additional burrow openings through escaping smoke from gas cartridges and allowing for treatment of these additional openings with aluminum phosphide, which is a cheaper and potentially more effective material. Therefore, we compared the efficacy of gas cartridges, aluminum phosphide, and a combined treatment on ground squirrel populations from mid-April through early May 2009 to determine which was most effective. We established 4 plots (3 treatments plus control) at each of 2 treatment sites in Madera County, California. All plots were between 1 and 2 ha in size with survey areas of 0.3 - 0.5 ha centrally located within the plot. Ground squirrels were visually counted within survey areas for 3 consecutive days prior to treatment. Following counting, treatments were applied. Forty-eight hours post-treatment, squirrels were again counted within survey areas to determine percent control. These counts were repeated the following 2 days. All treatments were then reapplied for the same plots, with similar surveys again following 48 hours post-treatment. We found that all fumigation methods resulted in marginal to exceptional control of ground squirrels (percent control: gas cartridges = 62 - 86%, aluminum phosphide = 97 - 100%, gas cartridges + aluminum phosphide = 59 - 71%). We suggest aluminum phosphide use could be expanded to increase ground squirrel control in California, given its high efficacy combined with its relatively cheap material cost.

This field efficacy trial using aluminum phosphide tablets for controlling the valley pocket gopher was conducted on land farmed by California State Polytechnic University, Pomona, California. The treatment blocks were located in moderate to heavily infested cover crops in deciduous orchards. Each of 2 treatment blocks contained 10 study plots, as did 2 control blocks. All burrows in the treatment blocks as well as a 100-foot-wide buffer were treated by placement of 2 to 4 Fumitoxin® tablets in each of 1 to 3 probed holes. Both treatment units had a 90% decline in pocket gopher activity, judged by the open hole census method, after the first treatment, and 100% reduction after burrows missed in the first treatment were treated. All burrows in the control plots remained active throughout the entire trial. All treatment points in the study plots were flagged and 33%, including 6 burrows remaining active in the 2-day post-treatment period, were examined for proper tablet placement. The importance of proper aluminum phosphide tablet placement is discussed.

An industrial hygiene study was conducted to monitor levels of phosphine gas exposure of applicators and bystander environment during use of aluminum phosphide tablets where used to treat rodent burrows, or when entering treated fields and adjacent buildings. State-of-the-art Draeger Pac III monitoring units and Draeger Phosphine Badges were placed on 33 applicators using Fumitoxin® tablets to treat ground squirrels (Spermophilus spp.) and pocket gophers (Thomomys spp.). Applicators represented both frequent and infrequent users. Agricultural and urban area applicators and bystander conditions in 9 California counties were monitored. Bystander sites were monitored with the Pac III data logging equipment. Thirty concrete slab or raised foundation buildings and 9 outdoor park and almond or walnut production sites were monitored for phosphine gas. No applicator phosphine exposures were above either the permissible 8-hour Time Weighted Average (TWA) of 0.3 ppm (Permissible Exposure Limit - PEL), or the 15-minute Short Term Exposure Limit (STEL) of 1.0 ppm. Higher exposures were observed for non-certified infrequent users than for certified or non-certified frequent applicators. The average TWA for applicators was 0.035 ppm, about 10% of the PEL. Label directions are satisfactory to avoid excessive worker exposure and environmental impact. Several work practices were associated with higher exposure potential, and recommendations were made for their mitigation to further reduce exposure. All exposures to PH3 were related to poor handling procedures that could be avoided by following the label and proper training. Average PH3 levels at potential bystander sites inside and outside residences were well below the 0.3 ppm TWA. No building registered over 10% of the PEL. In the outside trials, there were only 2 Pac III readings of over 100 that indicated detectable 8-hour TWAs at ground squirrel sites. The sites were very heavily infested, and PH3 only slightly exceeded 10% of the PEL. No PH3 was detected above pocket gopher burrows in any field site. When used according to the current label, the potential PH3 exposures of applicators and bystanders are low relative to the Low Observed Adverse Effect Level and are within existing occupational standards. Training was associated with lower worker exposures of certified applicators and non-certified frequent users compared to non-certified infrequent users.

Current limitations on pesticides for managing prairie dog populations underscore the need for additional research on candidate compounds. I conducted this study to determine the efficacy and cost-effectiveness of two registered burrow fumigants (aluminum phosphide and gas cartridges) and three unregistered burrow fumigants (methyl bromide, chloropicrin, and a methyl bromide/chloropicrin mixture) for managing black-tailed prairie dogs. All five fumigants reduced burrow activity 94% to 97%, as measured by a plugged burrow technique. Total costs for materials and labor for the registered products, excluding application equipment, were nearly twice ($30.00 to $38.50) the cost of the unregistered fumigants ($15.25 to $16.25).

An industrial hygiene study was performed monitoring levels of phosphine gas workers are exposed to when applying aluminum phosphide tablets to rodent burrows. Clothing and gloves were monitored for phosphine gas from residual dust. Air in the breathing zone was monitored with short and long term monitoring equipment. No levels of phosphine exceeding the legal permissible exposure limits (PEL) was detected and although residues were detected on clothing, the levels were usually quite low and dissipated in open air to undetectable levels within 12 to 17 hours in all but a few cases. Hand application was also compared to a mechanical (closed system) type application device which resulted in significantly lower phosphine exposure.

Bandicota bengalensis, a predominant species inhabiting irrigated fields is a potential pest on agricultural crops and is known to live in extensive burrow systems. The burrow opening covered with mud which is an indicator of its activity seems to be discontinuous. An analysis of burrow systems and their occupations indicated reuse of abandoned burrow systems by new entrants. A study simulated in semi-natural conditions supported the view that there is occupation of old burrows by new immigrants. Non-effective barriers, and availability of Panicum repens on bunds, a food alternative, may support the population influx. Availability of old burrow systems due to chemical control and natural predation often result in a ready made habitat for the immigrants and new recruits to reinfest the irrigated fields. Total dismantling of the burrow system and agricultural practices in irrigated field retards the reinfestation.

Field trials were conducted to test the effectiveness of a gas exploding device called ''Rodentorch" in reducing pest populations of ground squirrels and prairie dogs. Ignition of a propane/oxygen mixture injected for 30 seconds into burrows reduced prairie dog activity 13.0%. Doubling the injection time in prairie dog burrows to 60 seconds resulted in a 63.3% reduction. Reduction in ground squirrel activity was 40.6% after a 45 second injection time. Comparative trials on ground squirrels using EPA registered gas cartridge and aluminum phosphide fumigants resulted in 90.8% and 83.7% reduction in activity, respectively.

Vertebrate pest control measures may have an impact on nontarget wildlife. Bird and rodent control programs using avicides and rodenticides in California have been, and are currently being, examined by the California Department of Fish and Game on a routine basis. Each pesticide used has its deleterious side effects. This paper reviews these side effects and suggests possible future impacts which could be expected.

Biologists of the Denver Wildlife Research Center are currently investigating ways of managing mountain beaver (Aplodontia rufa) populations and are developing methods for alleviating mountain beaver damage to conifer trees being grown for timber in the Pacific Northwest. Studies initiated in I 986 indicated that aversive conditioning with Big Game Repellent Powder (BGR-P) dusted on cull Douglas-fir (Pseudotsuga menziesii) seedlings placed in burrows significantly reduced mountain beaver damage to planted seedlings treated with BGR-P and to untreated seedlings. Trials also showed that strychnine-sword fem (Polystichum munitum) baits prepared with a 4.9% (active) strychnine paste concentrate (SLN Reg. No. ID-870003) are very effective and selective for mountain beaver control. Other subjects discussed include results of several probes with toxic baits and phosphine gas, trials with a drug and a wetting agent to induce hypothermia, destruction of underground nests to prevent reinvasion, and mountain beaver behavior associated with controlling damage.

The California ground squirrel (Spermophilus beecheyi) is widely distributed throughout California. It causes serious damage to agricultural crops. Tests were conducted to evaluate the fumigant aluminum phosphide (Phostoxin®) and to compare it to the commonly used gas cartridge. Treatments consisted of applying either a single-dose (two 3-gm tablets) or double-dose (four 3-gm tablets) of aluminum phosphide, or 1 U.S. Fish and Wildlife Service gas cartridge in each burrow in the study plots. The burrow opening was then plugged with 1 sheet of newspaper and sealed with soil. Burrows in the control plot were plugged with newspaper and sealed in the same manner. All plots were retreated 4 days after the initial treatment. Overall, the aluminum phosphide treatments were more effective than the gas cartridge treatments in terms of the reduction in the number of ground squirrels seen and in reopened burrows observed after treatment. The single-dose aluminum phosphide treatment was as effective as the double-dose treatment. The gas cartridge treatment required a greater amount of time for application and did not achieve very effective control. Many aspects of this fumigation technique remain unknown and continued research is necessary.

Techniques for controlling California ground squirrels (Spermophilus beecheyi) include trapping, shooting. acute toxicants, anticoagulants, and fumigants. These techniques are described and compared and the available information on their efficacy and economics is discussed. This kind of analysis is essential if growers are to make logical decisions regarding the various control options.

The two most commonly used fumigant formulations, one generating hydrogen cyanide (HCN) and the other phosphine (PH3), were compared in paired field trials using the spoon-gassing technique. The two formulations were equally effective in reducing rabbit numbers seen in spotlight counts. The PH3-generating formulation was more convenient and slightly cheaper to use. Safety and humaneness aspects of the two formulations are discussed and alternative formulations (generating HCN and PH3) are considered. The potential usefulness (for rabbit control) of some other fumigant gases is briefly reviewed.

Common methods for mole control are baiting with earthworms impregnated with thallium sulphate or strychnine, gassing with pellets developing phosphine, and trapping. Seasonal cycles in burrowing activity make it difficult to evaluate results of expensive control campaigns and may give a false impression of efficiency.

Rat reduction measures were done in 171 villages of Panvel Block in Kolaba District of Maharashtra State, India. It started with rat preventive measures to doors and windows and the spraying of BHC and Malathion around bamboo matting huts. With the onset of rains trapping was done by “Deoras traps” inside houses and poison baiting by zinc phosphide on the outside. Rat burrows were closed by broken glass after the pumping in of BHC 10% dust, or sulphur fumes, or HCN or aluminum phosphide tablets. Lastly as the rains subsided zinc phosphide capsules dipped in melted wax were put on field borders and Malathion 1% sprayed in the field near crops. Total rats reduced were 20,260, of which 17,325 were by trapping and 2,935 by baiting. In the col lection, R. rattus species predominated and female rats were more in numbers than the males in all species of rats reduced. The cost of operations minus the salary and allowances of permanent staff came to Rs. 9,000/-. Public Health and Agriculture aspects were joined together and the rat reduction was done only for four months in the year when the monsoon was on, the paddy fields were full of water, and the rats migrated to residential areas for shelter. Public motivation was done by showing the damage and utilizing the rat skin and meat.