Citrus Under Attack
By Jim McLain, Ventura County Star, Calif.
Jan. 7–In a matter of months, a tiny but prolific moth that prevents young citrus trees from producing fruit by devouring nutrients in leaves has invaded nearly every lemon and orange orchard in Ventura County.
The citrus leafminer, a barely visible creature that flies from dusk to dawn and spends its days hiding — and eating — on the underside of leaves is increasing costs at agricultural nurseries and orchards where trees are less than five years old.
Fruit production in older trees appears unaffected so far, but some in the county’s $200-million-plus citrus industry say they are worried.
“It’s huge,” said Larry Rose, sales manager at Brokaw Nursery in Ventura, which sells about 60,000 trees annually to citrus growers.
“It’s hit so hard and so thoroughly… We didn’t see anything before Aug. 3…. When it hit Ventura, it was just like within days it was everywhere… It just shuts down the machine that feeds the tree.”
The citrus leafminer — its scientific name is Phyllocnistis citrella — is known to growers worldwide. It invaded California in 2000 from Mexico and has migrated north to the state’s center, arriving in parts of Ventura County early last year.
An expert said the insect and its larvae block an immature tree’s ability to produce fruit by burrowing into leaves and “mining” the chlorophyll, a nutrient most plant life needs for growth. In heavy infestations, the leaves dry, curl up and sometimes fall away.
“The leaf flush is fed on so extensively that it doesn’t grow,” said Tom Roberts, an independent pest control adviser with some 30 grower clients in Ventura and Santa Barbara counties. “The tree will produce leaves to replace lost leaves before it produces fruit, so you get a tree that never produces fruit.”
Southern California is the last citrus-producing area in the world invaded by the pest, Roberts said.
Naturally occurring predator and parasite bugs control it in other areas, but it will take two to three years for their Southland populations to reproduce in large enough numbers to be effective.
Most pesticides work too slowly and frequently kill beneficial bugs along with the bad ones, disrupting growers’ integrated pest management programs designed to curb pesticide use.
When he is in orchards where predator bugs are attacking the citrus leafminer, Roberts takes samples to groves not under siege.
“We can move them around physically when we find them in large numbers by taking leaf cuttings, putting them in a grocery bag and putting them out elsewhere so we can get the parasites established in other places,” he said. “I think the most important thing is to not panic and use chemicals when they may not be needed.”
But Brokaw Nursery and others with vulnerable immature trees must fight the pest with chemicals applied through drip irrigation systems to get their trees’ first fruit. The pesticides work, Rose said, but results aren’t evident for weeks and the effect doesn’t last long, necessitating costly repeated treatments.
“We’re sitting here getting nailed while we’re waiting for it to take effect,” he said. “We expect just a lot of problems with this for a couple of years until it’s a more moderate infestation.”
Because Brokaw Nursery has been battling the pest for only five months, Rose declined to predict what it will cost his company. He said a smaller citrus nursery in San Diego County spent more than $60,000 last year on measures to contain the citrus leafminer. Brokaw Nursery recently launched a costly screening program involving frequent tree inspections and removal of the insects before they can reproduce.
Roberts said he has seen fruit damage in some lemon orchards possibly caused by the pest. So far, though, there is no credible research proving the citrus leafminer caused it.
Leslie Leavens-Crowe, office manager at Leavens Ranches with some 600 acres of citrus and avocados in Ventura and Monterey counties, called tree leaves “manufacturing centers” for fruit production. If its leaves aren’t functioning at full capacity, she doesn’t see how a tree can produce fruit good enough to compete in a global citrus market.
Rose of Brokaw Nursery agrees.
“There has been an indication that this pest does not reduce economic yield on mature trees, but it has to reduce the vigor and operation of the tree,” he said. “I can’t believe that isn’t going to result in either less fruit or smaller fruit size.”
According to the Agricultural Commissioner’s Office’s latest report, lemons were Ventura County’s No. 3 crop in 2005 with grower revenues totaling $179.2 million. Valencia oranges, the ninth-ranked crop, grossed $23.2 million.
The citrus leafminer is a light-colored moth barely 1/8 of an inch long with a wing span of about 4 millimeters, according to the UC Davis Web site. The bug has silvery and white iridescent forewings with brown and white markings and a distinct black spot on each wing tip.
Because most citrus growers have mature trees, the pest is not a major problem for the industry, said Earl McPhail, Ventura County’s agricultural commissioner. It is mostly damaging trees in residents’ yards along with young groves.
Grower Henry Vega, who with his father owns 65 acres of lemons and 20 acres of avocados and manages 350 additional acres mostly planted in avocados, agreed with McPhail, but said the pest must be watched carefully.
“So far it really hasn’t been an issue here, but it may be later on. We’ve really not done a whole lot about it,” said Vega, president of the Ventura County Farm Bureau. “It’s not a big issue right now, but it’s something we’re definitely keeping an eye on.”
ON THE NET: http://www.ipm.ucdavis.edu
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Copyright (c) 2007, Ventura County Star, Calif.
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