Historically, people frequently brought species of plants and animals with them from their native lands to California, either accidentally or intentionally. Some introductions did unexpected damage while others had positive outcomes (food and horticultural crops).
Many invasive plant problems began as ornamental plants for sale by nurseries and garden centers or as host for insect pests (silver leaf whitefly on poinsettia, vine mealybug on nursery plants). Today, exotic and invasive pests, including plants still make their way into California through commercial nurseries, import trade and national and international travel.
Many exotic and invasive pests are of major concern in California. The glassy‐winged sharpshooter (an insect) and purple loosestrife (a weed) are two invasive species that are established in some areas but still threaten to invade other areas.
Invasive species of concern to California’s grape industry include European grapevine moth (EGVM) and light brown apple moth (LBAM), have not yet established themselves in all grape growing areas, but have already been costly to the state and the grape industry.
Invasive pests costly to growers
One of the worst invasive insects in California, vine mealybug (Planococcus ficus), continues to cost growers substantially in time, management and lost yields. It was first identified in California’s Coachella Valley in the early 1990s and continued to spread north into the southern San Joaquin Valley in 1998. Now established in over eighteen counties, VMB control has become a standing insect management cost for growers annually. Vine mealybug (VMB) is also an economic pest of vineyards throughout the world.
All VMB life stages can be found year‐round in an infested vineyard. During winter months, VMB eggs, crawlers, nymphs, and adults are found under bark, under developing bud scales, and on roots. Most are found on the lower trunk near the soil line and on roots. As temperatures warm in spring, VMB increase in numbers and become more visible. This is due to increased reproduction and movement from the trunk to the cordons and aerial parts of the vine.
By late spring and summer, they are found on all parts of the vine: under bark, on trunks and cordons, on first‐ and second‐year canes, leaves, clusters, and roots. In the Coachella Valley, the numbers of VMB are largest in mid to late spring and decline dramatically (two‐ to tenfold) in midsummer. In the San Joaquin Valley, the increase in numbers begins in late spring with peak densities occurring from the end of June through the middle of August.
Several species of ants can be found in association with the vine mealybug. The ants have been observed transporting VMB around on the vine, feeding on the honeydew produced, and fending off natural enemies.
Because five different mealybugs impact grapes, it important for growers to know what type is in their vineyard. Each have peculiarities in development and periods of greatest susceptibility to chemical management. Growers should have mealybugs properly identified by their local UC Cooperative Extension office, Agricultural Commissioner or California Department of Agricultural entomologist. Proper identification will ensure that the best management strategies can be implemented for the mealybug of concern (More information can be found in Mealybugs in California Vineyards; ANR 21612)
Invasive pest challenges continue
California’s grape industry continues to be challenged by new pest introductions. Light brown apple (LBAM) and European grapevine (EGVM) moths are the most recent insect introductions impacting California grape growers.
Although growers have spent money on pesticide applications to manage isolated populations, grape growers and their industries have mostly been affected by the pest rating that identifies them as quarantine pests.
Growers in quarantine areas have worked closely with the USDA, CDFA and the local County Ag Commissioners to comply with the mandated programs so fruit can continue to be harvested and moved to their respective markets.
One pest of most concern for California agriculture and the states residents is the brown marmorated stink bug (BMSB) now found in 33 states. Although not established in California, it has been documented on several occasions in different parts of the state including Los Angeles and Solano counties. BMBS has the ability to fly, which helps it move to new locations outside of infested sites.
However, its primary movement into new areas has been through human activity by hitchhiking in vehicles, equipment and anything else that gets shipped over long distances. Native to Asia, it is thought that BMSB arrived in packing crates shipped to the Eastern United States. It has a large host range that includes grapes and many of the fruits and vegetables grown in California.
Damage can be substantial when BMSB populations are not identified early and managed appropriately.
Apple growers in the Mid‐Atlantic states have reported losses of $37 million representing 18 percent of their fresh apple market.
In addition to physical fruit damage, growers and wineries would also have to contend with the off flavors produced by BMSB that gets crushed for wine or juice.
Homeowners in the Mid‐Atlantic states also reported large BMBS populations taking refuge in their homes during the winter months and becoming a nuisance when the insects are frightened or smashed, releasing an odor — hence the name “stink bug”. It is important for growers and residents to take odd or unique looking pests to their local university advisor, ag commissioner or state ag department entomologist for proper identification. Identifying invasive pests early is key to protecting California’s billion dollar agricultural industry.
Ratings for pest status
Pests vary as to the potential and actual harm they present to California's agriculture; its environment and the general public.
Based upon the severity of harm, its economic impacts, and the degree of difficulty to manage such pests, a pest rating system is used nationally to rank agricultural pests. The rating that each pest is assigned will aid the county and state in determining the best course of action to take and prevent or control their establishment.
What can be done to stop the spread of exotic and invasive pests?
1. Don't bring foreign plant or animal material into California when you travel or spread species from local quarantine areas to non‐infested areas.
2. Learn to identify invasive species new to California. Contact your local UC Cooperative Extension office or Agricultural Commissioner for help identifying suspected invasive species or look at the UC IPM or CDFA Web site.
2. Report invasive species in your area. Contact your local UC Cooperative Extension office or Agricultural Commissioner to report invasives and to get information on controlling invasive species on your property. We will be successful in stopping bests by early detection and management before establishment.
For more information visit the UC IPM Exotics and Invasive Pests page and Pest Notes on Invasive Plants and Woody Weed Invaders.
Information on BMSB
BMSB‐Northeastern IPM factsheet: http://ucipm.ucdavis.edu/PDF/MISC/stinkbug_alert.pdf
BMBS‐CDFA factsheet: http://www.cdfa.ca.gov/plant/PPD/PDF/Halyomorpha_halys.pdf