Is there any preventative action one can do in the winter when white flies are dormant to minimize their return in the summer? I have them on my grapes. Currently, the vines are pruned and the ground underneath is bare.
There really isn’t much you can do during the winter. In general, most insects are in some dormant stage where they remain shielded from the generally adverse conditions of the winter season. Nature has allowed insects to develop this way over time so they may continue on from year to year. This same protection will protect them from most all of the traditional treatments so for now, you need to wait till it warms and they become active.
In fact the best time to get them is in the spring, just as they hatch and get active, because the simple act of reducing the first of the season’s hatch can easily have the biggest impact on how they develop the rest of the year. In short, reducing this initial hatching will reduce the amount that will have a chance to be born. It’s really a game of numbers; reduce the total number active in the spring through early summer and in general, there will be a lot less during the middle to end of the season.
To do this, good whitefly prevention includes periodic treatments with something like the organic MULTI INSECT KILLER every 2 weeks. If done on a regular basis, you’ll be able to stop not only the whiteflies, but just about any pest that might find your grapes attractive. So for now there isn’t much you can do but spring will soon arrive and with it the whiteflies.
Here are direct links to the information and products listed above:
Whitefly Control: http://www.bugspray.com/article/whiteflies.html
Multi Insect Killer: http://www.non-toxic-pest-control.com/concentrates/multi-purpose-insect-killer-24-oz