Vineyard mealybugs (Hemiptera:Pseudococcidae) are an increasing matter of concern for
grape growers, as the economic losses resulting from their infestations continue to increase.
Several species of mealybugs are present in California, but the vine mealybug (Planococcus ficus,
Signoret) is the one creating most problems. It is an invasive species introduced ~20 years ago,
and not yet under control. The control is complex in conventional viticulture but is even harder in
organic production where systemic insecticides (e.g. spirotetramate) are not available and only
contact products are allowed. These products cannot easily reach the insect population often
located under the bark. This project aimed to compare on a large vineyard trial the efficacy of most
common and best-suited products commercially available in organic production: pyrethrins, neem
oil, diatomaceous earth, Chromobacterium subtsugae. The project also controlled for side effects
on grapevine physiology and grape composition related to spraying dusts and oils on leaf and berry
surfaces. The experiment was set up as a randomized complete block design with 4 treatments plus
control and 4 replicates. Each replicate was 1 acre large for a total size of the trial of 20 acres. The
vineyard was planted with Pinot Noir and moderately infested with mealybugs.
None of the products were effective in controlling mealybugs on the trunk and performed
similarly. Pyrethrins were the least effective in controlling mealybugs on leaves, while
diatomaceous earth and neem oil were most effective, but not significantly different from the
control. An inverse relationship appeared between efficacy on the leaves and presence in the
cluster. The most effective products had larger amounts of mealybugs inside the clusters, and the
least effective products on leaves had fewer mealybugs in the clusters. Plants treated with neem
oil had significantly lower stem water potentials. Treatments did not have any significant effect on
gas exchange measurements, except for one date, when azaguard had cooler leaves and higher
photosynthesis and stomatal conductance. Diatomaceous earth never significantly reduced
photosynthesis or stomatal conductance, even though it well covered the leaves with dust.
Although not statistically significant, we observed a strong tendency in sugar content. Brix level
was lower in the control than in all other treatments and reached up to 1.9 °Bx of difference in the
second measurement date. This delay in ripening was significant at the pH level when the control
had a significantly lower pH than most of the other treatments.
This project provides new and unbiased information that will help organic growers to
choose the right products to apply for controlling mealybugs in vineyards.