Here in NW ontario we have plenty of water, and in my area good soil. There is only one main problem here that I see:

Cold: Record low here is -40C ( in the 60s), but due to the recent warming trend, we havnt gone below -30C. Relatively speaking, thats a nice zone jump, but in the larger picture, its still cold LOL.

If the temps stayed above -25C for a low (I dont get that cold for weeks at a time even now) I could get away with so much more here....

I don't worry about ppt as long as the well holds out. The top fruit threats here are: spring freezes, hail, birds, coon, wind, lack of chilling, winter kill of figs etc, and surely something else if anything survives that.

Right now this heat has me concerned. We are running way above normal. But if we get one cold month we'll be OK.

Different seasons have different worrries: Winter time is the cold; Spring time is temperature fluctuate; Summer is the pests; Fall is squirrel and two legged...

I grow blueberries in our yard, in Madison, Wisconsin. It took me about 10 years to finally get a handle on soil pH, our native soil has pH around 7.6, way to high for blueberries. With that issue resolved, the biggest remaining threat is winter browsing of the shrubs by our local rabbit population. I'm still working on that one...

y biggest worry is the late spring frost which kills my Apricot flowers. When The weatherman say frost tonight I try to hang Xmas lights around the trees I don't know if it helps.
My other big worry is the fungus infection last season the fungus in our area was very bad because of record heat and rain but I am prepared for it next season with sprayers and and antifungal bottles. When it comes to fungus I close my eyes about the organic idea. Last season I lost the first seedlings of tomatoes, cucumber, squash and pepper to BLIGHT. I Have to put new seedlings but were sprayed the same day planted. I learning.

Problems here in Wisconsin:

1) Late spring frosts and oddball spring weather ala 2012.
2) Aphids and spider mites.
3) Drought (but nothing a little irrigation can't handle).
4) Poor pruning decisions on my part.
5) Fireblight.

In approximately that order. Others have issues with deer, but my "orchard" is in the city and fenced.

I forgot the squirrels they eat the best of my fruits and they come at night while I am sleeping. I try to scare them with pp gun but hay they don't care. The Problem also they are not aware of birth control pills.

MN issues:

(+) is longer growing season. easily a full month vs. 30 years ago

(-) is significantly more potential for late frost damage.

(-) is new bug issues.

(.) neutral is precip. seems more variable but I have good drainage and ability to irrigate

I am with oldryder,
My biggest challenges are coming with changing weather/seasonal patterns.

growing season is longer here as well, but that "early" spring just seems to wake stuff up too soon. Our frosts are not much later but the plants are all more advanced when they come....the long mild falls could become useful for late ripening varieties and second garden plantings...but I sure do miss the snow, and I thought I left ticks behind when I came north.

I have not noticed a large change in pest/disease pressure yet, but I do believe it is coming. FB at least is seen now and then and used to be almost unheard of.

I'm also in Madison, WI, and the rabbits are a pest all right. My neighbors just have to put up with circles of chicken wire around almost everything (they haven't gone for my thorny gooseberries, and didn't touch the tomatoes this summer.). I need to fence my blueberries again, the rabbits have been "pruning" them.

I've mounded my blueberries above the native soil, in a mix of peat moss and compost, and mulched with wood chips. I still add sulfur and acidic fertilizer occasionally, but they seem fairly happy.

Western Montana:

Arid, but have a good well;

Late frosts, pollination issues in cool spells;

Squirrels, deer, occasionally kids;

Unpredictable season length;

Changing weather patterns (it's 45 F right now!!);

Only serious bug issue is codling moth- very little rust, some fireblight, quite a bit of powdery mildew in certain seasons, but that's manageable

NW Wyo:

No worries, just challenges.

Deer--they eat & burnish their horns, grasshoppers--they eat and eat and eat.

Apricots, plums, cherries, sometimes apples like to bloom before last 20 degree frost.

Winter hardiness tends to be an issue.

Have plenty of well water, but keeping things watered often enough on gravel and sand can be an issue--which delays growth, fruiting & requires patience.