The stakes are high in the battle to keep the European grapevine moth (EGVM) from becoming widely established in California’s 40 grape growing counties.
State and federal governments are out front monitoring where EGVM have migrated to from Northern California and enforcing quarantines to mitigate its spread. However, for now growers are alone and all-in in the counteroffensive that has great economic and environmental importance to the state’s largest horticultural crop.
There will be no mandatory eradication program in the foreseeable future because the state has to jump through far too many regulatory hoops for that to happen very quickly.
“It is fish or cut bait time for growers and PCAs if we are really going to eradicate this thing at this point,” said University of California IPM Advisor Walt Bentley, stationed at the UC Kearney Ag Center, Parlier, Calif.
EGVM has pretty well established itself in several areas of the premium wine grape country called California’s North Coast. There are more than 1,300 square miles under quarantine in parts of Napa, Sonoma, Mendocino and Solano counties. Growers are in a life-and-death struggle to turn back a seemingly well-entrenched worm that destroyed crops in at least two vineyards last season.
However, the pest has not shown up in any significant numbers elsewhere in the state, even though it has been caught in traps in at least three areas.
There are two small areas in Fresno County (90 square miles) and Merced County (108 square miles) where multi-finds have triggered quarantines. However, there have not been any new multiple finds outside quarantine areas in about two weeks and, therefore, no new quarantines.
Bentley said confining it to those two Central Valley locales will fall upon quarantine area growers.
Although a relatively easy worm pest to control, “growers and PCAs cannot take Lobesia botrana for granted. In the quarantine areas it will require aggressive, preventive treatments on grapes.” It should be so aggressive that Bentley reluctantly admits it should fall outside integrated pest management parameters.
This is particularly true for vineyards where EGVM have been trapped and fields bordering those vineyards. North Coast growers within six-tenths of a mile of any vineyards where EGVM have been identified are asked to be aggressive in control strategies.
Although grapes are its primary host, stone fruit hosts EGVM. There Bentley is recommending a “less aggressive” but still preventive control program for stone fruit within quarantine areas.”
Bentley and others went to Chile last year to see first hand how to handle EGVM. It became established there in 2008. “When we were there, it had not been found in stone fruit. However, after we left it was found in a plum orchard adjacent to a heavily infested vineyard.”
He warned that like many other tortricids like Oriental fruit moth (OFM) and Oriental leafroller (OLR), EGVM may cause damage in crops other than grapes.
Bentley is recommending an aggressive, preventive program for at least two reasons.
• Establishment of this pest in California grape and fruit growing areas will disrupt marketing worldwide of California products.
Countries where EGVM has not been found likely will invoke stringent import rules or not accept California fresh fruit and grape products altogether from quarantined areas and maybe the entire state.
• Secondly, establishment of EGVM would drastically change existing IPM programs. “It would turn our whole IPM approach in grapes and other crops upside down,” he said.
“The implications of this pest becoming established go far beyond direct management of the pest,” he added. “You may not have the European grapevine moth in your vineyard, but you sure do not want it.”
Fortunately no larvae or eggs have been found.
“There has been no damage to this point, but it is such a tenuous balance between it becoming established and the possibility of keeping it out; I hate to see growers and PCAs cut corners and risk establishment. The risk of establishment is too great not do to apply preventive sprays.”
Any EGVM in the Central Valley are now in their second generation. They will likely require two treatments in grapes.
For stone fruit, Bentley is recommending one control spray targeting EGVM, likely along with sprays for OLR or OFM.
He endorses the grapes treatment program recommended by Sonoma County UC Farm Advisor Rhonda Smith and his IPM coordinator counterpart in Northern California, Lucia Varela.
Intrepid 2F (methoxyfenozide) or Altacor (chlorantraniliprole) are suggested for the initial treatment for the second generation. If a second treatment is warranted, Success, Avaunt, Delegate or Agri-Mek are recommended.
However, the thorny maximum residue level (MRL) issue comes into play for that second-generation treatment.
“After Intrepid it can become a can of worms because Altacor, Avuant and Delegate do not have MRLs for Taiwan. I have already received calls from growers who may be shipping grapes and fruit to Taiwan and are concerned about what to use,” Bentley said.
He is recommending Bt for that second spray. “It has a fairly long residual and is pretty affective against this worm,” Bentley added. Another second spray alternative would be a pyrethroid.
In the battle against EGVM, Bentley had high praise for the California Department of Food and Agriculture’s aggressive trapping program that was initiated last fall when the first EGVMs were identified in Napa County.
The state put out more than 40,000 traps this season to detect where the insect pest may have hitchhiked from the North Coast.
“Trapping has been so beneficial. The state got on this before it could get out of hand — thank goodness.
“Getting out as many traps as the department did after the first finds last fall is a huge accomplishment.”