Galendromus occidentalis

There is really no better place to start our blog than in the vineyard.  The vineyard is the most important aspect of making great wine and Stephan puts an enormous amount of energy into coaxing the best fruit possible out of the lean shale soils of the west side of Paso Robles.  There are many aspects of maintaining the health of a vineyard but pest control definitely stands out as the most challenging.

Green spider mite on bottom of grape leaf as seen through a 10x loop

One troublesome pest that we are currently tackling in the vineyard is the spider mite.  Spider mites are tiny pests that fall into the arachnid class along with ticks and spiders.  They derive their name from the silk webbing that they produce on infested leaves.  Adult females are the largest of the group measuring approx .5 mm.  They prefer hot dusty conditions next to dirt roads or open dirt in gardens and travel on the breeze using their silk or catching a ride on a speck of dust.  Control of mite migration from vine to vine is one of the main reasons we (and other wineries) request that our guests drive slowly on the dusty dirt roads leading to and from our property.

Spider mite webbing on bottom of leaf

There are two types of mites that we battle in the vineyard at L’Aventure, the two-spotted spider mite and the pacific spider mite.  They start their initial infestation in a relatively small central spot but then radiate out looking for new food supplies.  Depending on conditions, infestations can grow to cover an acre in a matter of 5 to 7 days.  Mites damage grape leaves by sucking out and feeding on contents from individual cells.  The damage to the leaves is visible as a stippling effect that turns yellow, orange and red.  If the issue is not addressed leaves will continue to be eaten and eventually turn yellowish or reddish and drop off.  Being that green chlorophyll is where vines get their energy, the stippling on the leaves acts to stifle plant productivity effectively slowing the ripening process.  Ripening can stop altogether if leaves receive severe enough damage.

Spider mite grape leaf damage

For the past few years Stephan has been implementing a new approach to the vineyard by introducing biodynamic farming practices which prohibit the use of miticides and acaricides.  Instead of spraying, he is addressing the mite issue by introducing beneficial predators into the vineyard.  One of the big predators of spider mites are, strangely enough, other mites.

This past week, we released over 120,000 Galendromus occidentalis mites into the areas of the vineyard showing damage as well as their immediate surrounding blocks.  G. occidentalis are not much larger than the spider mites they hunt.  This particular species were selected due to their ability to hunt in the extremely hot and dry conditions of Paso Robles during the month of August.  Each female can lay up to 34 eggs  during their life cycle which, once hatched, have a lifespan of approx 44 days (9 days as immatures and then about 35 days as adults).  As adults they will eat 1 to 3 pest adults or up to 6 pest eggs per day.  They prefer the two spotted mite as prey but will eat other mites if they run low.

To maintain the pressure on the bad mites we monitor the life cycle of the beneficial mites and re-introduce a new population approx every two weeks if we continue to see signs of pest presence.  This approach does not rid the field of bad mites but rather keeps their population in check to minimize leaf damage and population spread.  Managed effectively, the introduction of predators should provide the vine enough protection so it can continue ripening its fruit to achieve the high quality that Stephan demands to be included in wines of L’Aventure.