one of the reasons I am planting 900 walnut trees for my first round.

Assuming you eventually plan to harvest the walnut crop, that is definitely a farming activity. Still no depreciation for the land, though. :(

but I think I will be able to deduct the cost of the woolly Adelaide control and the spider mite control. that will be a direct cost.

That's where I run out of farming knowledge. I'm sure they're an expense that you'll need to track. I'm not as sure that you can deduct it immediately for the immature trees. You'd need someone with better farming knowledge than I.

how about the cost of fencing for the apple trees.

Another crop to harvest? If so, that's another expense that I'm sure will benefit you on your taxes, I'm just not sure how. I've always depreciated fences as land improvements, but there may be some special considerations for farming that I don't know off the top of my head.

As long as you're harvesting these tree crops, the trees themselves are also going to help on your taxes, probably through depreciation.

--Peter