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.