European Grapevine Moth Talk of Sonoma Grape Day

By Maile Field

Almost 200 people met for Sonoma County Grape Day in Santa Rosa February 9, where they learned the latest news about the European Grapevine Moth (EGM) and the best way to control gophers, among other topics.
University of California researchers presented updates on development of Pierce's disease resistant grapes; changing the way grapes flower; and the relationship between cover crops and frost damage.  In addition to EGM, growers got an update on Light Brown Aplle Moth (LBAM) and how to differentiate these leafrollers from their common cousins, throughout their life stages.
The morning-long session was sponsored by the Sonoma County Winegrape Commission with presentations by the US Cooperative Extention.
North coast IPM advisor Lucia Varela dod not have good news for grape growers.  In addition to opening that "LBAM is here to stay," Varela said the newest invader, the EGM or Lobesia, "could potentially be a worse pest that any other leaf roller.
One feature that distinguishes the EGM is that is primarily feeds on flowers then berries.  It lays single eggs then applies a pheremone, marking the egg to deter other insects from laying eggs there.  Varela said an EGM could potentially produce one worm per berry, destroying an entire cluster.
The EGM is now in diapause, Varela said, which means the moth, which is about hald the size of the Oragne Tortrix, is in silky cocoons primarily in cordons and in the trunk of grape vines. "The moths will emerge around budbreak," she said.
The second generation can be expected in June and July, a third generation in August and September.
"We will see the first males emerge, followed by females about a week later.  Depending on who you read," Varela said, "egg-laying will occur three to five weeks later."
The unique singly-laid egg is shiny, pearly white, elliptical and flat, laid on smooth surfaces of developing flowers in spring and then  on berries in subsequent generations.  The eggs progress to a distinctive 'black cap' stage before emergence of larvae in seven to 11 days.
"You can monitor larvae as they come out," Varela said, "Look for clumping of flowers."
The worm looks very much like any other leafroller, according to Varela, but can be distinguished by a dark border on the segment behind the head and by its dark legs.
Later it becomes dark in color, and it can be blue, green, maroon or purple in the final stage before becoming a pupa.
The second and third generations hatch faster, in four to six days.
"What will catch your eye," Varela said, "is the webbing of two berries together."
She also advised growers to watch for wrinkling of berries signifying a worm inside.
The good news, Varela said, is many insecticides are available and she said the pest can be controlled using organic methods.
Trapping for EGM is being conducted on a county-by-county basis. Varela said that Napa, "the ag commissioner wants to be the one to do the trapping."
Sonoma County Agricultural Commissioner Cathy Neville addressed the group, reporting that her staff will be placeing 7,000 traps throughout Sonoma County starting March 1.
"I am just hoping we don't find it," she said.
But for EGM, unlike last year's advice regarding LBAM, growers in Sonoma were encouraged to set at least to traps per vineyard and a minimum of one per 30 acres.
"Place the traps so that the bottom of the trap touches the top of the conopy...you hvae to move it as the canopy moves," Varela advised. Traps should be baited with Lobesia botrana lures only, and should be checked weekly.
Following Varela, Central Valley IPM Advisor Roger Baldwin presented his research findings regarding gopher control.  Clearly trapping rodents was not only the cheapest method but also the most effective, according to Baldwin's trials at Gallo Familiy Vineyards' Laguna Ranch last year.  Baldwin conducted gopher trials using three methodologies, treating his blocks twice, once in spring and once in fall.  Using a Rodenator(r) resulted in a range of 0-55 percent control; success using baiting strategies (using strychnine) ranges from 30-56 percent; trapping plus fumigation produced 74-90 percent control.
Baldwin noted that the most efficacious strategy used fumigation only where trapping failed.  "The vast majority" of gophers were killed through trapping, he reported.
Baldwin's research founf the Gophenator(r), which is a new trap (Trapline Products, Menlo Park) slightly more effective than the century-old Macabee.
Growers also heard updates regarding Pierce's disease resistant grapevines at the Sonoma Grape Day event. Andy Walker told growers that many forms of Vitis in the southern United States and Mexico have a gene for resistence, an ability to block the movement of Xylella fastidosa, the pathogen causing Pierce's disease.
walker has been repeatedly cross breeding resistant progeny of those wild forms with vinefera in an attempt to produce palatable grapes that resist the deveistaing pathogen.
"We're making good progress," he reported.  Walker said his goal is a grape that is 97% vinefera.  So far he has had small amounts of wine made using grapes frmo a selection that is 94% Petite Syrah.
"We tried them," Walker said, They're not very good."