You Can Make a Difference
Shot hole borers and the diseases they carry, and Asian citrus psyllid and huanglongbing disease are serious invasive pests of concern. Do your part to help prevent their spread. If you go camping this summer, don't move firewood from your home to the campground. For backyard citrus growers, find out if you are in a quarantine zone for Asian citruspsyllid. You can make a difference. Read the posts above to find out how.
You can also contact your local UC Master Gardener Program or UC Cooperative Extension Office to learn about invasive species that may be found in your community, or you can volunteer at a local park, refuge, or wildlife area to help remove invasive species.
If you missed reading any of our invasive species action week posts, you can access them here:
California Invasive Species Action Week Red Imported Fire Ant
Wild Pigs Asian Citrus Psyllid and Huanglongbing Disease
Invasive Plants Shot Hole Borers and the Diseases They Carry
Resources
UC IPM Exotic and Invasive Pests
UC Riverside Center for Invasive Species Research
California Invasive Plant Council
California Department of Fish and Wildlife
- Author: Anne Schellman
- Contributor: Karey Windbiel-Rojas
How did these pigs become wild?
As is the case with many introduced invasive species, wild pigs were an accidental creation. Spanish missionaries brought domestic pigs to California in 1769 for consumption, but after being released for foraging and not recaptured, they escaped domestication and became feral (wild). These feral pigs later bred with Russian wild boars, which were also brought to the state for sport hunting in the 1920's.
What is the problem?
Wild pigs are destructive pests with wide and ravenous appetites for a variety of plants and other animals. They compete for food with both wildlife and farm animals and will kill and eat wildlife and small farm animals. When wild pigs root through the soil to find food, they disturb native vegetation and dig up land meant for livestock to graze. When they enter urban areas, they can cause extensive damage to home lawns and gardens.
It is estimated that wild pigs cause $1.5 billion dollars in economic damage to agriculture and the environment every year in California.
Not only are they destructive, wild pigs can spread disease. They are known to carry several important pathogens that can be infectious to humans such as E. coli and Salmonella. They carry potentially devastating diseases to domestic livestock and wildlife and are hosts to 35 parasites that can affect multiple animal species. The 2006 outbreak of E. coli in California spinach fields is thought to have originated in wild pigs, though this has not been verified.
The California Department of Fish and Wildlife considers wild pigs game animals. They can be managed through exclusion, trapping and/or shooting. To learn more about wild pigs and their management, read the Pest Notes: Wild Pigs.
- Author: Sonia Rios
- Author: Niamh Quinn
- Author: Eta Takele
Wild pigs currently exist in 56 of California's 58 counties and can be found in a variety of habitats ranging from woodland, chaparral, meadow, grasslands and in agriculture cropping systems. Wild pigs are commonly found in the foothill areas, and they prefer areas of dense brush, however the drought has led them to encroach into orchards. Wild pigs can cause significant damage to farm and rangelands, natural resources, environmentally sensitive habitats, and property. Wild pig depredation on livestock and poultry can cause high economic loss (Choquenot et. al. 1996). Also, wild pigs can carry a number of diseases and parasites that can be transmitted to livestock, wildlife, and humans. In California, wild pigs can be carriers of Brucellosis, Cholera, Leptospirosis, Tuberculosis (Bovine, Avian, and Swine), Q fever, Trichinosis, Toxoplasmosis, Pseudorabies, and Plague (Barrett and Tietje 1993).
DESCRIPTION OF THE PEST
Domestic swine were imported to the United States by European settlers in the 1700s. Whereas Domestic swine foraged freely, eventually becoming semi-wild, or “feral” (CDFW 2017), California's wild pigs were descendants of the Eurasian wild boar, introduced to Monterey County, California in the 1920s. The physical characteristics of California's wild pigs vary significantly throughout the state. Some exhibit the long hair and snouts, small erect ears and angular shaped bodies of their wild boar ancestors, while others have short hair, long floppy ears, and a barrel-shaped body. Colors range from solid black to red, striped, grizzled or spotted (CDFW 2017). Domestic pigs that are unmarked and roam freely are also considered to be wild pigs.
DAMAGE IN CITRUS
Cultivation operation disruption
Evidence of wild pigs' presence is obvious even if you don't see them physically. Wild pigs use their snouts to root up the ground in search of food, including plant roots, fungus, and other items. Wild pigs are omnivorous, consuming both plant and animal matter. In general, wild pigs feed on: grasses and forbs in the spring; mast and fruits in the summer and fall; and roots, tubers and invertebrates throughout the year.
Wild pigs will feed on insects and underground vegetation. This rooting behavior can disrupt parts of the orchard floors. it could lead to the trees becoming susceptible to root rot diseases that could spread throughout the grove. They are also known to eat fruit off of the lower branch scaffolds. Pigs will contribute to erosion which can affect water quality and also create large uneven basins, or wallows in moist soil during hot weather. Both rooting and wallows can disrupt the application of irrigation water by ruing or displacing irrigation equipment and resulting pools can become breeding habitat for mosquitoes.
Food safety
Wild pigs can also create a food safety issue. Growers are now required to show a Food Safety Good Agricultural Practices for California Citrus Growers (GAPs). This practice is focused on the grower's particular role in providing safe citrus fruits for consumers. The grower should assess the impact of domestic, livestock and wild animal activity for potential pathogen contamination of the grove and fruit. The assessment should include the extent of intrusion, nearness to the grove, proximity to harvest and other relevant factors. Based on the assessment, the grower should put into place measures to exclude domestic animals and minimize the intrusion of wildlife into the grove.
- The grower should monitor the grove and adjacent land for evidence of animal activity and the potential for contamination of fruit or equipment.
- The grower should return bins to packers if there is evidence of contamination.
- When the assessment or monitoring indicates possibility of contamination with pathogens, the grower should take action as needed to minimize potential for contamination of the fruit and to prevent the harvest of any potentially contaminated fruit
Pre-Harvest
- The grower should perform a documented evaluation of the grove environment for changes that may be likely to result in contamination of the citrus fruit with pathogens. Evaluation should include inspection for:
o Evidence of animal intrusion such as downed fences, presence of live or dead animals, animal tracks or animal feces. If animal intrusion is detected, measures shall be taken to remove or prevent from harvest any potentially contaminated product.
o Presence of potentially contaminating materials (e.g. uncomposted manure, etc.) likely to pose a contamination risk to the grove to be harvested.
o Evidence that the irrigation water source and delivery system may potentially be compromised.
For more information regarding Citrus GAP: http://ccqc.org/wp-content/uploads/2009/05/Final-Food-Safety-GAP-document-_Oct-26_.pdf
MANAGEMENTClassified as a game mammal in California, wild pigs provide year-round hunting opportunity and fall under the jurisdiction of the California Department of Fish and Wildlife (CDFW). A hunting license and a tag is required to hunt wild pigs. If wild pigs are causing damage to your property, pigs can be trapped or shot, but this requires a depredation permit. Contact your local CDFW representative for further details on depredation permits (https://www.wildlife.ca.gov/Conservation/Mammals/Wild-Pig/Depredation).
Monitoring and Management Strategies
Fencing
Fencing can be extremely effective but because of costs it can be extremely prohibitive. However, on smaller scales, exclusionary fencing can be an effective option. One of the most effective designs seems to be the installation of sturdy wire mesh fencing. The bottom wire should be either tightly stretched on the ground surface or buried. The addition of an electrified wire about 6 to 8 inches off the ground is also recommended. The fence should be at least 36 inches high. Electric fencing alone has also been shown to restrict the movement of wild pigs also. Poorly designed and constructed fences will significantly increase repair and maintenance time. It is important to carefully consider the costs and benefits of fencing for pig exclusion before embarking on such a venture.
Trapping
Trapping can be an effective method of removing wild pigs from your orchard. The most commonly used traps are box traps and corral traps. Corral traps are much larger than box traps and are designed to capture multiple pigs. It is important to consider that all wild animals can be unpredictable when approaching captured pigs.
In some counties, the agricultural commissioner has trappers who can assist; other counties have contracts with USDA-Wildlife Services to assist with problematic pigs.
Toxicants and Repellents
Currently there is one toxicant registered for use on wild pigs in the United States (EPA Reg. No. 72500). This product is not currently registered for use in California. This product may only be used to control wild pigs on pastures, rangeland, forests, non-crop areas, and crop lands. This bait may only be applied in hog feeders equipped with heavy lids (8 to 10 lbs. of total weight) on bait compartments so as to limit direct access to bait by nontarget animals. This product may be toxic to fish, birds and other wildlife. Dogs and other predatory and scavenging mammals and birds might be poisoned if they feed upon animals that have eaten the bait. Wild pigs must be conditioned to accept feed from the bait dispensers and to open the weighted lids to bait compartments.
Repellents are not generally considered effective against many mammalian pests and this is also true for the management of wild pigs.
Collecting information on wild pig damage
UCANR is asking California growers and landowners to help keep track of the state's wild pigs and the damage they are causing through a new Wild Pig App. The app is available for download on Apple and Android devices and will collect information on wild pig damage throughout California. Cell service at the site of pig damage is also not required to collect the information. The information collected will be used by University of California Cooperative Extension Specialists and Advisors to learn more about wild pigs in the State.
Download the app at your App Store to participate in the wild pig damage project without the app, landowners and growers can fill out a short survey at http://ucanr.edu/wildpig2016.
Additional Resources
Barrett, R. H. and G. H. Birmingham. 1994. Wild Pigs. The Handbook: Prevention and control of wildlife damage. Cooperative Extension Division, University of Nebraska-Lincoln.
California Department of Fish and Wildlife <https://www.wildlife.ca.gov/Conservation/Mammals/Wild-Pig> Accessed: 24 July 2017.
Barrett, R. H., and W. Tietje. 1993. The wild pig in California oak woodland: ecology and economics. Conference Presentation Summaries. Univ. of California, Berkeley.
Coping with Feral Hogs. Texas A&M AgriLife Extension Service.
Feral Hog Biology, Impacts, and Eradication Techniques (PDF). 2010. USDA APHIS Wildlife Services New Mexico.
Finzel, J. A. and Baldwin, R. A., (2015) Pest Notes: Wild Pigs. UC ANR Publication 74170
Hamrick, B., M. D. Smith, C. Jaworowski, B. Strickland. 2011. A Landowner's Guide for Wild Pig Management(PDF). Publication 2659.
Jay-Russell, M. T., A. Bates, L. Harden, W. G. Miller, and R. E. Mandrell. 2012. Isolation of campylobacter from feral swine (Sus scrofa) on the ranch associated with the 2006 Escherichia coli O157:H7 spinach outbreak investigation in California. Zoonoses and Public Health. 59:314-319.
Kreith, M. 2007. Wild pigs in California: the issues (PDF). AIC Issues Brief No. 33. Agricultural Issues Center, University of California.
Sweitzer, R. A. and D. H. VanVuren. 2002. Rooting and foraging effects of wild pigs on tree regeneration and acorn survival in California's oak woodland ecosystems (PDF). USDA Forest Service General Technical Report PSW-GTR-184.
Waithman, J. 2001. Guide to hunting wild pigs in California. California Department of Fish and Wildlife, Wildlife Programs Branch.
West, B.C., A. L. Cooper, J. B. Armstrong. 2009. Managing wild pigs: A technical guide (PDF). Human-Wildlife Interactions Monograph 1:1.
Where Did They Come From?
Domestic pigs were released in California in 1769 to be raised for consumption. Some of these pigs were not recaptured and became feral. In the 1920's, Russian wild boars were brought to California for sport hunting. Since both types of pigs belong to the same species, they interbred. Their descendants are called wild pigs.
Why are They a Problem?
Male wild pigs can weigh up to 200 pounds, and females up to 175 pounds. These large animals root through the soil to find food, disturbing native vegetation and digging up livestock forage. They compete for food with both wildlife and farm animals, as well as kill and eat wildlife and small farm animals. In urban areas, wild pigs cause extensive damage to lawns and gardens.
Wild pigs carry 5 major waterborne pathogens that can be infectious to humans, are hosts to 37 parasites that can affect multiple animal species, and can carry potentially devastating diseases to domestic livestock and wildlife. The 2006 outbreak of E. coli in California spinach fields is thought to have originated in wild pigs.
Management and Control
Since wild pigs pose a significant potential disease threat to humans, domestic livestock and native wildlife, an effective management program is necessary.
The California Department of Fish and Wildlife considers wild pigs game animals. They can be managed through exclusion, trapping and/or shooting. To learn more about wild pigs and their management, read the Pest Note: Wild Pigs.
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- Author: Jeannette E. Warnert
UC Cooperative Extension is asking California farmers and landowners to help track the the state's wild pig population, reported Julia Mitric on Capitol Public Radio News. Signs of the pig's presence are hard to miss, UCCE advisor John Harper told the reporter.
"It looks like you came in with a rototiller and just uprooted everything," he says. "It's like ground squirrel mounds or gopher mounds on steroids because the pigs can go over such a large area."
California's wild pigs have a variety of origins. Harper says many are descended from domestic pigs who were released into the wild by humans or escaped on their own and bred with game hogs such as the Russian boar hog. Wild pigs root around in the soil for truffles and small plant roots with their sharp tusks tear, destroying plants and grasses that sheep and cattle like to graze on. They also open up the land for erosion and invasive species.
"So you might get something like 'medusahead,' an invasive grass that tends to crowd out other more desirable forage species," Harper said.
A team of UC Cooperative Extension scientists have created a GIS-based mobile app that works on Android and Apple devices to make it easy for landowners to participate in the study.
“Rangeland managers and farmers can enter data into the app from the field so that we can estimate the land area and economic impacts of feral pig damage over a longer time period,” said Roger Baldwin, UC Cooperative Extension wildlife specialist in the Department of Wildlife, Fish, and Conservation Biology at UC Davis.
Learn more and sign up to participate in the study on the UC Agriculture and Natural Resources news website.