Earwigs in grapes – good bug gone bad

Earwigs are generalist predators and are active mostly at night. They like to hide in dark places, like the centres of grape clusters. They can be off-putting for consumers of table grapes and vineyard workers.

“Earwig Taint”

When disturbed or crushed during vinification, earwigs may release 2-methyl-1,4-benzoquinone and 2-ethyl-1,4-benzoquinone into the must, which give a smoky aroma and other off flavours in wine.

Monitoring and Thresholds

In a study conducted on Chasselas and Pinot noir in Switzerland, researchers found the following:

• Wine made from Chasselas or Pinot noir contaminated with 5 earwigs/kg fruit was not distinguishable from uncontaminated fruit
• Wine made from Chasselas contaminated with 0.6 g of earwig faeces (that’s a lot of faeces!) affected wine flavour and odour
• Wine made from Pinot noir contaminated with 10 earwigs/kg of fruit was described as reductive, acidic and vegetal

Management options

Insecticides

While no products are currently labeled for earwig management in grapes, there have been studies on the impact of insecticides labeled for other insect pests.

Malathion 85E

Malathion has been shown to decrease populations of both MALB and earwigs.

• 880 mL/ha
• Maximum 1 application per season
• Hand harvest: 4 day pre-harvest interval
• Machine harvest: 3 day pre-harvest

UP-Cyde

Cypermethrin has decreased earwig populations.

• 245 mL/ha
• Hand harvest: maximum of 2 application with minimum 7 day interval between applications and 7 day pre-harvest interval
• Machine harvest: maximum of 3 applications and 2 day pre-harvest interval
• Minimum of 7 day interval between applications

Success or Entrust

Spinosad (Success or Entrust) was shown to be very effective in reducing earwig population especially when applied at night. The effect was greatest 3 days after application.

• 182 mL/ha
• Maximum 3 applications per year
• 7 day PHI
• effective vs spotted wing drosophila but not lethal vs MALB

Admire

When imidacloprid was used to manage other pest species in orchards, it was “moderately disruptive” to earwigs.

• 200 mL/ha
• Maximum 2 applications per year
• 24 hour PHI
• 24 hour REI

Consider pre-harvest interval

It is especially important to take into consideration the pre-harvest interval when considering a spray program for these insects. As always, make sure to read the label before using any pesticide.  It should also be kept in mind that while not as intense as with live beetles, dead MALB can still taint wine between 3-6 days post mortem.

Because earwigs tend to hide inside clusters during cool nights, spray at night so that they are exposed to residues when they emerge the next day.

Repellents

KMS was effective short term in repelling both MALB and spotted wing drosophila. Based on these observations, the SO2 fumes produced by KMS may have some repellant activity on earwigs with no residue. This may be enough to move earwigs out of the clusters if applied right before harvest.

Sorting

Shaker tables are effective at separating MALB from the fruit, thus preventing extraction of MPs from the beetles during grape processing. The shaking motion forces beetles through the mesh into a collection and disposal area below.

Some new harvesters offer an optional destemmer that separates the berries from the stems, roller sorting tables and an air cushion that blows out any Material other than grapes (MOG), including MALB and earwigs.

Optical sorters employ a combination of destemmers, shaker tables and high-speed cameras and image-processing software to quickly scan and sort destemmed grapes to remove almost all MOG, including MALB and earwigs.

Don’t jump the gun on insecticide sprays

There’s no point in spraying for MALB or earwigs until harvest. So far numbers of MALB and earwigs have not reached the thresholds listed above for wine grapes. There are only so many insecticide applications allowed and the residual is no more than 7 days and you may just be wasting money. There’s also no guarantee that MALB or earwigs will end up with high enough numbers in vineyards to justify spraying. It’s a waiting game until just before harvest but best to be aware that the problem might flare up and keep monitoring.