Grape Mealybug and Scale Management

In a survey last year, we found that mealybugs overwinter as young nymphs.  These nymphs matured into adult females with a peak around fruit set and first instar nymphs (the first ones to come out of the eggs, and also the ones that are the best vectors of grape leafroll virus) increased to their maximum between fruit set and berry touch.  The first instar nymphs are also most susceptible to insecticides; however, they spend most of their time under the bark, protected from insecticides that rely on contact to work.  In the survey conducted last year, mealybugs and scales were found only on vines with trunks with thick peeling bark (trunks over 5 years old)

As part of a research project, my crew has been monitoring mealybug and soft scales in commercial vineyards.  In the past week or so, they have started to find adult female mealybugs  and new scales have also been found.  This matches the timing observed in 2014.

How can you tell whether there are mealybugs or scales in your vineyard?  Peel back the bark from trunks and look for cottony white spots that are indicative of mealybug or the dark brown conical shells of scales.  Often both of these insects are tended by ants that feed on the “honeydew” that the insects secrete.

White mealybug egg clusters on trunk

Mealybug development progresses from tiny dark salmon-pink  nymphs through to adult females which are pink and covered with white waxy scales.  The males have wings and might be found infrequently under the bark shortly after they emerge.

Egg cluster with first instar nymphs

Adult female mealybugs

Adult male mealybugs

Scales progress from small amber coloured crawlers to larger, very dark brown adults.

Young, amber coloured scales

Immature and mature scales

Scales being tended by ants

Malathion 85E and Safer’s Insecticidal Soap are registered for control of both mealybug crawlers and scale insects. Diazinon 50W is registered for control of mealybugs.  Malathion, Diazinon and Safer’s Insecticidal Soap can be applied against the crawler (first nymphal) stage of mealybug and scales; however, our observations indicate that mealybugs generations are not synchronous so there is a range of growth stages present at any given time.  This means that you might kill a few of the crawlers when they are outside the bark with a spray (between fruit set and bunch close), but there are many more still protected under the bark.

Movento 240 SC is mobile in the phloem so it will move from treated leaves into new leaves and also into the phloem in the trunk where mealybugs and scales feed, well under the bark.  It is registered for control of mealybug and suppression of Lecanium scale.

Because Movento must be absorbed by leaves and translocated to the trunk where mealybugs and scale are feeding, it is best to wait until there is adequate foliage to absorb the spray.  To optimize absorption and systemicity of Movento, it should be tank mixed with a non-ionic surfactant (e.g., Agral 90 or Ag-surf), methylated seed oil (e.g., Hasten), or horticultural oil at a suggested rate of 0.2 % v/v (2 L/1,000 L).  Movento 240 SC should not be applied during bloom.  You must wait at least 30 days before making a second application.   The labelled rate of Movento 240 SC is  365-585 mL/ha.   Make sure not to exceed the maximum seasonal application of 920 mL/ha/year.  We are still learning about the best rates and timings for Movento. At this point, my best guess is to apply 2 applications of 460 mL/ha, one at prebloom and a second 30 days later.

In this year’s trial, we will be looking at the effectiveness of different combinations of rates and timings of insecticides against mealybug and scale insects.