European Grapevine Moth (EGVM) – First Flight 2011

KICK THE MOTH OUT!

Large signs are posted throughout the Napa Valley to help raise awareness in the community.

The first flight is over and numbers are looking very good in comparison with last year.  In 2011, there have been 87 moths caught in Napa County – compared to almost 100,000 caught during the first flight in 2010.  However, there are also over 10,000 acres currently under mating disruption (MD), which will skew the findings.  When mating disruption is used, male moths are not only be hindered from finding a mate, but also have difficulty finding traps, which disperse the same sex pheromone to attract males to the females.  However, even with the wide usage of MD, 87 individual moths is a monumental improvement.

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Signs of EGVM – What to Look For

Bloom is an effective time to scout for EGVM feeding damage.  As larvae feed on flower clusters they form a web that creates clumps of flower caps, flower particles (stigma, anthers) and frass (excrement).  These clumps often turn brown and discolored as larva feed on the tissue.  At this point, damage is easier to identify than after bunch closure and into maturation.  Look for discolored clumping in flower clusters as well as white webbing.

Larvae create a webbing in the flower cluster while feeding.

Stuck caps and webbing form a sticky mass that can be more easily identified during bloom. Larvae will feed on all phases of berry development and eventually enter a berry.

 

Second Flight – What to Expect

The second flight will start in mid to late June when the larvae that are currently feeding on flower clusters emerge as moths, mate, and lay eggs on the green berries.  Cooler temperatures will delay the second flight and spread out the emergence of adult moths.  This makes it more difficult to time a single spray for total coverage.  A warmer June would help condense the lifecycle and give growers a concentrated window to target spray programs.

European Grapevine Moth (EGVM)

Overview

Mothe on the Vine

This adult moth is camouflaged in the canopy.

The fight against the moth rages on, and it appears we are winning.  In 2010, for Napa County, there were almost 100,000 moths caught during the first flight (bud break), over 1,500 in the second flight (berry set) and under 300 individual moths caught during the third and final flight (verasion to harvest).  The steady decline of catches in 2010 was promising but the true test would be the number of catches in the first flight of 2011.  So far, there have been less than 10 individual moths caught in Napa County (compared to almost 100,000 at this time last year).  In addition, there are more traps being monitored this year compared to last (~8000 in 2010 compared to ~16,000 this year).  State wide catches this year have been limited to only Napa and Santa Clara counties, compared to catches last year in Fresno, Mendocino, Merced, Napa, Sonoma, Solano, Lake, San Joaquin, and Santa Clara.  UC Cooperative Extension research indicates that we are currently in the peak of the first flight which correlates to peak egg laying.  Growers are urged to spray now in a timed effort to target newly laid eggs and young larva.

Life Cycle and Control Methods

Larval Damage

When this egg hatches the larvae will feed on the flower cluster.

Larva from the third (and last) generation of 2010 overwintered underneath the bark and are currently emerging as adult moths.  These moths quickly mate and lay eggs on the cluster primordial (right).  These eggs hatch, and new larva feed on premature cluster tissue.  At the peak of the first flight (now), growers target spray programs on newly laid eggs (ovicide) and early life stages of new larva (larvacide).  Conventional growers are urged to spray Intrepid or Altacor (both are an ovicide and larvacide).   Organic growers apply a cultivated bacterium (Bacillus thuringiensis) that, when consumed by the moth larva, block the midgut and cause death.  However, Bacillus Thringiensis (Bt) has a lower residual control effect compared to conventional sprays (7 days compared to 21) and organic growers must spray more frequently to achieve the same coverage.

Pheromone Disruption

EGVM pheromone disruptor twist tie hung high in the canopy where mating occurs.

In 2011 there has been a large focus on pheromone mating disruption.  Growers are urged to apply pheromone emitters throughout the vineyard (200 per acre) which dispense the same pheromone that females produce to attract a male.  With enough “false” pheromone in the air, males are unable to successfully locate a female and mate.  Pheromone disruption is most effective when populations are low and males are dependent on locating a female by tracking her pheromone.  In dense populations males are able to locate females by site and pheromone disruption is not effective.  Pheromone disruption is considered essential to lowering current low populations to undetectable, with eradication being the ultimate goal.

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