11-Aug-09 09:36 | Eric Stafne

Rainfall during or near harvest is a big problem with grapes.  Yesterday and last night in Stillwater we received 2.25 inches.  Rain can lead to berry splitting and and an entry point for insects (green June beetles and wasps) as well as disease.  It is important to keep a close eye on the forecast and schedule your harvest accordingly.  If you see rain and wish to spray a fungicide, keep in mind the PHI.  Some products can be up to 14 days.  Do you want to wait 2 weeks before you harvest?  Depends on where your sugar levels are and maturity of the fruit.  Rain can cause a dive in the sugar level, so either harvest before the rain comes or you may need to wait until the sugars get back to a desired level.

One of the reasons why California is such a great place to grow grapes is that they have a Mediterranean climate.  It does rain much (if at all) during the harvest period.  We are not so lucky living in a continental climate, so we must endure the occassional thunderstorm in August.