Tips for Effective Vine Mealybug Management in Grapes

Vine mealybug feeds on this grape cluster. (Photo: George Zhuang)

 

FIGURE 1: A heavily infested ‘Thompson Seedless’ cluster. (Photo George Zhuang)

The movement of vine mealybug typically starts from the lower vine sections underneath the bark of the trunk, where they commonly reside during the dormant period. During early spring in the San Joaquin Valley (SJV), there can be new eggs hatching underneath the bark, not often seen by the vineyard managers until the population increases and starts to move up from trunk to the cordon and shoots.

 

Rather than a complete movement of the whole population up the trunk, it is better to consider that the population increases in spring and early summer and much of the next generation moves to the leaves and clusters as the vine matures (but there are always some mealybugs still on the vine trunk). Typically, growers notice the honeydew and sooty molds when the vine mealybug has already fed on the leaves and clusters, but in heavy populations the trunk can have a “wet” appearance even before the population moves to the leaves.

After harvest, the vine mealybug population again accumulates on the trunk and even the roots (just below the soil surface) for overwintering.

Control Is Important
Growers need to control the population before it gets into the fruit, and in 2016 we saw some heavily infested grape clusters in some vineyards having irreversible damage to fruit yield and quality (Fig. 1). For some winegrape growers, an additional concern is that vine mealybug is the vector of grapevine leafroll-associated viruses (GLRaVs), which can reduce yield, delay fruit maturity, and reduce wine quality.

Therefore, early scouting is critical to implement a proper management program with the best timing and selection of insecticide materials. However, if you had heavy mealybug population and damage previously, you should be considering your strategy early in 2017 to prevent crop damage.

First, monitor and prevent the introduction of vine mealybug from infested vines or vineyards. This pest does not walk quickly or far, but it does move between vines and even vineyards. There is a natural spread from infested vines by wind and birds, the transportation of equipment and tools from infested vineyards (e.g., harvesters and shears from field crews) and the movement of contaminated fruit, pomace and canes/leaves which can all aid the dissemination of this pest.

FIGURE 2: A pheromone trap for vine mealybug. (Photo: UCCE)

Trapping Techniques
Pheromone traps, such as a red delta trap (Fig. 2) baited with a synthetic vine mealybug sex pheromone, can be used to monitor vine mealybug. This technique is most useful when you don’t have any mealybug in the vineyard and you’re trying to monitor for new arrivals. Depending on the size of the location, two traps in a small vineyard or two traps per 80 120 acres can be placed on the edges of the block near the road or adjacent vineyard.

In the SJV, the first significant flight of male vine mealybug is in June, and traps should be placed around this time of the year to monitor the counts of male adults on a biweekly basis. Peak flights occur from August to October in the SJV. The number of male mealybug catches will be important to identify the presence of vine mealybug, however, the count will be of less value to tell the density of vine mealybug. Note, however, that if you had considerable damage in 2016, using pheromone traps may not be as important as visually following the population development and increase in the block.

Figure 3: Honeydew will have a dark and wet appearance on the grapevine trunk. (Photo: George Zhuang)

Field Crew Identification
Visual sampling of mealybug can be easy. Training the field crew to identify the signs of vine mealybug feeding is the most efficient way to make an early detection. The large amount of honeydew on the trunk and cordon (Fig. 3) will have a dark and wet appearance. The active movement of ants along the trunk is another good indicator of vine mealybug infestation.

Having the field crew trained and scouting during the pruning, leaf removal, and harvest stages can help to spot and mark the infestation areas and treat them after harvest or the next season. Vine mealybug identification posters are useful to train your field crew. Once the presence and density of vine mealybug have been identified, certain strategies will be implemented to reduce the population. Here we will focus on conventional vineyards (for organic vineyards, the options will be more limited).

The Importance of Ant Control
Adult female vine mealybug is relatively immobile and the large amount of honeydew it secretes attracts ants (e.g., native grey ant, the most common in the SJV). Ants are not only tending and protecting vine mealybug from predation and parasitism, but also moving vine mealybug along the grapevine. Controlling ants will expose the vine mealybug under the attack of parasitoids and predators to reduce its population density and slow its spread.

Effective Mating Disruption
Similar to the theory of pheromone traps, this method requires a much higher concentration of vine mealybug sex pheromone than pheromone traps in the vineyard to confuse the male adults to disrupt their successful mating.

Synthetic sex pheromone is dispersed through the whole vineyard using dispensers or sprayable formulations. Mating disruption is most effective when the mealybug population is low.

Insecticide Control
There are a couple of insecticides which growers can apply to control vine mealybug, and more information about the timing and rates of these insecticides can be found at http://ipm.ucanr.edu/PMG/r302301911.html.

Among all the insecticides, Movento (Bayer Crop Science) is most widely used on grapevines to control vine mealybug. The timing of spray is especially important to achieve the maximum effectiveness of control. Movento is a foliar-applied translaminar insecticide and it has to get into the vine through the active leaf first and then the metabolite changes to an “enol” and it is this metabolite that helps kill the mealybug. The insecticide acts as a lipid biosynthesis inhibitor – basically it inhibits metabolic processes that primarily deal with lipids and fats and the mealybug can’t move, molt, and feed. The mealybug will die off more slowly than with some contact insecticides – so managers need to be patient. Also, the enol will stay in the vine for a long time so it can kill mealybug long after the Movento is sprayed on the vine.

The insecticide acts as a lipid biosynthesis inhibitor – basically it inhibits metabolic processes that primarily deal with lipids and fats and the mealybug can’t move, molt, and feed. The mealybug will die off more slowly than with some contact insecticides – so managers need to be patient. Also, the enol will stay in the vine for a long time so it can kill mealybug long after the Movento is sprayed on the vine.

 

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