Since 2010 we've been using a insect net to protect from wasps. The conditions change year to year and sometime we don't need insect netting and other years we use just bird netting. Usually the warm years, where the grapes are ripening early and the sugars are high while the wasps are still quite active are the conditions that bring the wasps to the grapes. It becomes a big problem if you have the above conditions then you get a heavy rain, the vines soak up the rain and the grapes swell and crack. After that the wasps can really smell the sugars and are all over the grapes in a day. Some grapes are more prone to cracking than others after a big rain so this is a factor also.
Covering the grapes is critical and we've used the kootenay covers since 2010. They are tough and do not let in any insects that would harm the grapes. Kootenay covers were developed for tree fruit crops but we decided to try them for grapes and in terms of resilience to the elements and keeping the bugs out they are great. The draw back is that it is white and reflects the September sun which is desperately needed for ripening. The other draw back for grape us is the holes are quite small and while good at repelling insects it also means little light gets through and the grapes are partially shaded by the cover.
In 2012 with 940 degree days and 85 days from flowering to harvest we achieved 20 brix on the Leon Millot that were only covered with bird netting - not the insect netting. This year with 1030 degree days and at least 95 day growing period from flowering to harvest we achieved 21-22 brix. We were expecting 22-23. While there is so many factors that determine the ripeness and sugar content at harvest, we have found in the years that we have used the kootenay covers the brix seems lower than what we would have expected and we believe it is that too much light is reflected and the shading is a factors also.
We've obtained a new netting for this coming year that is black and the openings while small are many and will let in lots of light. Shade factor is about 4-5% in the new net where as with the kootenay covers it is about 15%. 10% more sun should make some difference.