Whilst harvesting at Jeff Coutelou’s last September I couldn’t help but notice white cardboard hanging from the trees and bushes around the vineyards. They were certainly not there in 2021 so what was going on?
It turns out that this is one solution to the increasing problem of Cryptoblabes gnidiella or honeydew moth. I wrote about the emergence of this new type of moth in 2020 here. This moth has spread rapidly from Italy to Provence and now into the Hérault and Aude areas of the Languedoc and is moving inland too. Scientists believe that one of the reasons for the increase in numbers and range is climate change. The moth takes 93 days from egg to adult when the temperature is around 18c but at 26c that reduces to 32 days and at 29c just 23 days. There is less time for the farmers and viticulteurs to react. Moreover the moth seems to be less present in the vineyards until July/August, just in time for grape harvest. (Scientists are still trying to establish where the moths go in the Spring and early summer though they do live on up to 80 different types of plant).
The larvae live inside the bunches of grapes, the female lays around 100 – 230 eggs and the grapes are emptied of juice and pulp as the larvae feed. The damage spreads to other bunches as juice drips on to them inviting rot.
What can be done? Well, chemical sprays as I mentioned in the previous article but organic producers cannot resort to those. Theoretically they could destroy bunches of grapes left after harvest either on the vine or on the ground as that is where the moths and eggs spend winter. However, that would be prohibitively expensive for all but the wealthiest producers. Sexual confusion traps (mentioned in that 2020 article) might also not work well as scientists don’t know whether the eggs are already fertilised in summer, remember how they aren’t sure where the moths spend Spring.
photos from http://www.vignevin-occitanie.com
Jeff is also trying to encourage green lacewings to live in the vineyards, these also predate on moths and their eggs and would form an extra defence. They also spend winter in the vineyards and are available to combat the moths all year round as needed. Until he finds out whether that will be successful Jeff must hope that the cards are successful. Unfortunately 2022 saw a significant increase in the number and spread of vines affected by honeydew moths.
French company Bioline have produced one answer and that is the white card in the trees. The cards contain microscopic wasps 0.8mm in length, called trichotop buxus as they are usually used to combat box wood moths. The wasps eat the eggs of the moth so by placing and opening the cards Jeff and others bring a parasite to the vineyard to solve the moth problem. Two potential problems remain, the cards need to be renewed every 3 – 4 weeks and adding a new insect to the biodiversity may have its own consequences (though no evidence of that has emerged yet).
March 20, 2023 at 3:39 pm
By coincidence I was watching the Attenborough episode last night. It had a piece on Wood Ants and how they breed and farm aphids that excrete “honeydew”. The ants go around licking the excretions from the aphids’ posteriors and then feed it to other members of the nest.
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March 20, 2023 at 4:04 pm
Yes, I watched that too. There’s strange worlds going on under our noses