Battle Royale: The Thrip vs. The Mite Vs. The Lacewing
In this space you are expecting a word or two about Syrah and grape growing, I realize. Nope, no tractor roll this year to report. The mean weather that swept in during Pinot noir flowering in late May/early June revisited us for an encore during Syrah flowering a few weeks later. As a result the Syrah clusters were light and loose, eliminating the need to drop any fruit but only setting enough to make very little wine. And that is farming. Every year ushers in a new crop but always with a little twist. I would like to think that other aspects of vineyard management benefit from accumulated knowledge, however. Here in my little controlled, non-native environment, learning how to achieve ecological balance, that hallmark of sustainability, is an ongoing process. It is an imposition of order that has its origins from when mankind turned from hunting and gathering and began to plant seeds. But even as I gain knowledge of how to farm more sustainably and efficiently using organic products, it seems a new development rears its head every year to keep me on my toes. Recently that head has been attached to an insect’s body.
Let’s start with mites. Every vineyard seems to attract the spider mite, from whence I do not know. Pacific or Willamette mites will find a new planting of Vitis vinifera with time, pretty much regardless of local climate, or local flora and fauna. You need a hand lens to see the little guys and really need to search the underside of the leaves to find them. The damage of these sap-sucking insects is readily apparent once a population builds and to rid ourselves of such a small target is very tricky indeed. Smothering them with organic oils has been our strategy this year, but the key is reaching the entire leaf surface with oil.
While the mites have found us out here even in the wilds of the Northern Sonoma Coast where there are very few vineyards, another insect popped up a few years ago where it should not have. The thrip. Larger than a mite and more mobile, the thrip is not effectively controlled with oils. Our entanglement with the thrip was not predicted by the California Agricultural Cooperative Extension office, a reflection of the terra incognita that we have entered in the Northern Sonoma Coast. The UCDavis Integrated Pest Management (UC IPM) handbook says thrips are generally not economically detrimental to a winegrape crop. Well, I have an update for both of them.
Under the Roussanne and Marsanne headings in the French ENTAV/INRA/OIV Catalogue des Vignes, a cryptic aside adds “thrips” to the universal triumvirate of winegrape susceptibilities – powdery mildew, downy mildew and botrytis. If the thrips are left unchecked, the Roussanne leaves at the shoot tip turn bronze, curl up and fall off. So, at first, I thought that our dabbling with Roussanne and Marsanne had something to do with our vineyard-wide infestation. So few folks have planted Roussanne and Marsanne in California, that I can’t blame California based UC IPM for underestimating their damage. But the breadth of our infestation always puzzled me since we have but 0.4 acres of Roussanne and 0.2 acres of Marsanne and 47 acres of “non-vulnerable” varieties that have indeed shown varying degrees of vulnerability to the little pest. I figured they must be really invasive if they can be attracted by so few vines yet infest an entire vineyard. Then last year some neighbors over two miles distant experienced outbreaks of thrips that went undiagnosed until one vineyard had that depressingly denuded, brown-tipped look…AND THERE WAS ONLY PINOT NOIR PLANTED THERE! (Ah ha, I hear a viticultural thesis topic calling out.)
While we have found an organic insecticide effective in eliminating thrips for a season, the thrips do eat the mites. Hmm, don’t want to kill the thrips only to have a flare up of mites. This spring I’m experimenting with a general predator that eats both thrips and mites: the green lacewing, Chrysoperla carnea. Adapted to arid conditions and a range of temperatures, I’ve found the adults on occasion in the vineyard as they are easily visible to the naked eye, with clear wings and slender green bodies that run _ of an inch in length. The adults eat pollen and nectar, but the larvae are predatory omnivores: Lacewing larvae voraciously attack their prey by seizing them with large, sucking jaws and injecting a paralyzing venom. The hollow jaws then draw out the body fluids of the pest. From egg-hatch to cocoon, they will eat 70-100 thrips, mites, aphids and caterpillars, among other herbivores and eggs, over a period of 14 to 17 days. Fortnight dispersals of these Alien-like creatures will keep an active population in the vineyard. Happy adults who have found the table well-laid may lay their own eggs around our vineyard if they find the conditions hospitable. A well-laid table consists of flowering border plants placed around the vineyard. I’m hoping that managed blackberry shrubs will do the trick. If you’ve ever hacked back a blackberry vine during the growing season, you may have noted that the new growth produces inflorescences which open and pollinate. My preliminary inquiries have given me reason for optimism on this front (yes, lacewing adults like blackberry pollen). Imagine, this invasive weed (we live in blackberry heaven) may become an ever-blooming host for my lacewing adults.
But nature is an unpredictable mistress. What if some insect eats the lacewing larvae? What if the adults simply disperse far from my vineyard after emerging from their cocoons? Invasion of The Minute Pirate Bug! Tune in next year for an update.