Reports of heavy honeydew deposits from vine mealybug have increased in San Joaquin Valley vineyards this season, and researchers, as they refine some new controls, urge growers to use field sanitation at harvest.
The vine mealybug (VMB), Planococcus ficus, is a sucking insect found first in the Coachella Valley in 1994 and at several SJV sites by 1998. Although similar to the common, native grape mealybug found mainly on trunks and spurs, as well as clusters, the VMB is found throughout vines, including the roots.
VMB excretes great volumes of honeydew, which crystallize on vine parts, promote sooty mold growth, and damage fruit quality. Its crusty formations differentiate it from the more liquid honeydew of the glassy-winged sharpshooter.
With no preference by variety, the phloem-feeding VMB affects bud development the subsequent year, and losses have reached 30 percent on reduced-vigor vines.
Walt Bentley, University of California Extension entomologist at the Kearney Agricultural Center, Parlier, says he's getting more and more calls about VMB. “It's been here around Fresno for a while, but we are beginning to see what could become a mushrooming situation.
“Of course, we've seen much of it on Thompson Seedless because it's the variety with the greatest acreage. So far we have not detected it north of the San Joaquin River. We have seen it in table grapes in Tulare County and even in isolated, two-year-old plantings in San Luis Obispo County.”
After VMB appeared in the Coachella Valley, he recalled, table grape growers there controlled it with an intensive chemical program. By the mid-1990s it appeared in table grapes around Arvin, particularly in vineyards whose owners also had vineyards in the Coachella Valley. Kern County growers have gained control of it with Admire through drip or mini-sprinklers.
Bentley said he realizes many grape growers, particularly those making raisins, do not have the resources for such programs. “Even at the lowest rate, 16 ounces, Admire is going to run about $60 an acre, and we've found a single, 24-ounce application to be best.”
In 1996 and 1997 it turned up in the Del Rey and Selma areas of Fresno County, and Bentley said, “we in UC Extension, working closely with the California Table Grape Commission, gave it a lot of play with newsletters and grower meetings.”
Even so, he added, many more reports came in 2001, most from growers and PCAs who said they knew nothing about it. “The problem is it can be hard to detect early in the season. It can start in a corner of a vineyard and maybe the grower doesn't pay much attention until it gets severe.”
Before bud break
Although some practices for chemical controls were worked out in the Coachella Valley earlier, they ended with the death of UC entomologist Harry Shorey.
However, progress has been made since with chemicals Bentley said. Lorsban applied before bud break is very effective. Admire through drip from early May into early June has been successful, although on flood-irrigated vineyards, an irrigation must be made immediately following application to the soil.
The researchers French plowed along vine rows to expose roots, sprayed Admire on the soil, and put water on within two hours.
In insecticide trials they found that Lannate applied in early June will hold on the leaves for about three weeks and reduce, but not eliminate, VMB. Applaud, a growth regulator, has also been effective but for a shorter period.
“The key is to make an application beneath the vine canopy to reach the crown, the base of the canes, and where clusters are formed,” he said.
Rocky Malakar-Kuenen, a post doctoral researcher at KAC, and others are trying now to integrate use of Admire with encouragement of Anagyrus wasps that parasitize VMB. They have seen up to 89 percent parasitism, but that's in late September after the damage is done.
The issue with the parasite is it only reaches VMB in exposed areas of vines. It doesn't get under the bark. VMB also hides protected there from insecticide sprays, so the aim is to apply material to the exposed roots, or to the vine when adults move out onto the foliage.
All stages can be transmitted from vine to vine, but the flightless crawler, “bug” stage of VMB on windblown leaves is readily carried from infested vines to new hosts. Vineyard equipment also carries crawlers, particularly in raisin and wine varieties.
Bentley is optimistic that a VMB pheromone developed by UC, Davis entomologist Jocelyn Millar will be another tool. “The compound is stable and will last at least six weeks and will pull in flying males from a considerable distance. Traps with the pheromone will allow detection early in the season before damage occurs. It could also be useful for nurseries.”
The pheromone is being tested this season and Bentley said he hopes growers can detect pockets of infestation early and then head-off any spread with the French-plow and Admire method or topical sprays of Lannate or Applaud.
On another front, the team is moving this season with use of the pheromone for mating disruption, seen as a potential biological answer for dealing with early concentrations of the pest.
For the moment, Bentley recommends that growers alert field workers to watch wetted areas of honeydew on the bark of vines. “You need to know that and deal with it immediately early in the season or mark the area at harvest. Because of the way VMB moves, you tend to see it on the edges of a vineyard first.”
All machines that move from vineyard to vineyard, including harvesters, mechanical pruners, even rotary mowers, are potential vectors for the pest. He suggests that equipment working in an infested vineyard be steam cleaned or washed down with a 2 percent chlorine solution before it is used in a clean vineyard.
VMB also goes to palm, fig, pomegranate, and several ornamental plants. Although frost will kill it in the above-ground portions of the vine, it survives on the roots.