How would pesticide vapor drift behave near a valley?
While @Gordon Stanger gave an overall perspective about pesticides in general in his answer you can deduce some key points about the micrometeorological conditions of the area.

Assuming pesticides as relatively large aerosol particles/droplets spayed quite close to ground they are mainly dry deposited to surfaces. If your house is as close to the pesticide spaying areas as your schematic implies, you might have a problem (assuming pesticides are dangerous to you, more in @Gordon Stangers answer) only if during the spraying air gets trapped into the valley.

Assuming the spraying is only done in daytime and summertime the chances of an inversion in the valley are smaller and they would only stabilize the air preventing mixing with your valley air and pesticide air.

Strong winds (if the location is near a coast (probable sea breeze) or it's otherwise known to be windy) might carry some pesticides to your direction, but overall adding vertical mixing dramatically lowering the average concentrations.

Your most worst case scenario is if calm (not windy) very sunny days are very often. Sun will in different times of days heat at least either of the slopes of the valley causing air to rise on that side. Replacing air is sucked from the other side creating a steady flow from pesticide rich agricultural areas to your valley. Pesticide being assumed a large aerosol will deposit most likely in the valley (if not in the bottom then in the drafts uphill).

Also rainy weather is good for you as the pesticides will most likely wet deposit near their source.