Officials combat invasive insects in SLO County

County agricultural inspector Tom Morgan inspects an insect trap on a plum tree at the Master Gardeners' Garden in San Luis Obispo.
County agricultural inspector Tom Morgan inspects an insect trap on a plum tree at the Master Gardeners' Garden in San Luis Obispo. jjohnston@thetribunenews.com

The numbers are startling.  

During 2014, more than 2,800 exotic insect traps were placed in more than 6,000 residential yards, gardens and parks in San Luis Obispo County. A team of 28 county pest detection trappers checked those traps about 55,000 times throughout the year.

They are on the lookout for invasive insect pests that, if allowed to go unchecked, can spread plant disease, damage the county’s $960 million agricultural industry and destroy residential gardens and public parks.

“Early detection efforts, such as the ongoing trapping program, protect local agriculture and common home-grown fruits and vegetables by intercepting pests at very low populations, increasing the likelihood of successfully eradicating invasive pests,” said Martin Settevendemie, county agricultural commissioner.

Tom Morgan, an agricultural inspector and biologist, is one of the lead trappers in the county Department of Agriculture’s pest detection program. He unfolds one of the commonly used pest detection traps, a bright yellow sticky sheet of cardboard.

The trap is covered with dozens of gnats, flies and moths. Often called a blunder trap, these sticky sheets will collect any insect that flies into it, Morgan explained.

However, the most common type of insect trap used is a triangular open-ended cardboard box with a sticky surface that contains an insect attractant specific to a particular pest.

These traps stay in place from one to three months and are checked by trappers every other week. The sticky part of a triangular trap is on a removable card.

This allows the trapper to collect the card if it contains an insect of interest. The trappers are trained to recognize damaging pests and use magnifying glasses to examine the insect.

Back at the office, another technician will double check the find. It is then sent off to the California Department of Food and Agriculture where entomologists will make the final determination of the exact species of the insect.

“It’s an intricate system we use to identify these pesky critters,” Morgan said.

Trappers use a well-defined scientific method to decide where to place their different types of traps. Fruit flies, for example, are most attracted to stone fruit trees, such as peach and cherry trees, so that is where most of the fruit fly traps are placed.

They also move the traps around periodically to cover more territory and increase their likelihood of detecting pests.

“It’s a lot like fishing,” Morgan explained. “It’s good to relocate every once in a while to see if you can locate a good host.”

The pest detection program relies on the cooperation of homeowners who allow pest traps to be placed in their yards. In 2014, more than 6,000 county residents volunteered to allow insect trappers to place traps on fruit trees or landscape plants in their yards.

The traps are placed out of reach of children and pets.

Participation in the program is voluntary.

“A resident can say no at any time, and we will honor that,” Morgan said.

Traps are set for a range of exotic insects including Mediterranean, oriental, Mexican and melon fruit flies, gypsy moths, Japanese beetles, glassy-winged sharpshooters and the light brown apple moth. Recently, however, efforts have concentrated on the Asian citrus psyllid because those potentially destructive pests have shown up in traps in San Luis Obispo, Arroyo Grande and Cayucos.

That insect is of concern because it can spread a disease that is fatal to all types of citrus trees. The disease does not pose a threat to human health, but it threatens the county’s citrus crop — mostly lemons — which is valued annually at more than $12 million.

Once a damaging insect is found, state agricultural officials establish a quarantine area around the find. They also increase trapping in an effort to kill off the pests before they can establish a breeding population.

A quarantine area prohibits growers from exporting their produce from that area unless it is first inspected and approved by county officials to certify that the pest will not be spread by transporting the crop.

Nurseries are crucial in enforcing quarantine areas, said Victoria Hornbaker, citrus program manager for the California Department of Food and Agriculture.

“The nurseries serve as the front line when it comes to communicating with homeowners about the threat of the Asian citrus psyllid,” she said. “They play a critical role in helping homeowners keep backyard citrus trees psyllid-free, and it is imperative nurseries and garden centers throughout the state follow best management practices.”

The county has two quarantine areas for the Asian citrus psyllid. One covers 213 square miles from the top of the Cuesta Grade south to the southern boundary of the Oceano Dunes State Vehicular Recreation Area. The other covers 61 square miles around Cayucos.