This year we have seen a variety of diseases that usually don't happen frequently in Colorado. We have confirmed anthracnose on Ash from Aurora, and just this morning, found anthracnose on Oak here at the CSU campus. http://www.ext.colostate.edu/pubs/garden/02930.html is a link to the fact sheet on Sycamore Anthracnose, but control measures would be similar for Ash and Oak.
We are also seeing samples of Oak Leaf Blister on a regular basis this year. http://www.umassgreeninfo.org/fact_sheets/diseases/oak_leaf_blister.pdf is a fact sheet from U of Mass on oak leaf blister that shows some really nice pictures of the blisters on oak leaves. Older blisters can often be confused with anthracnose.
We are also still seeing effects of the prolonged fall/winter (2010-11) drought on trees and shrubs. Winter watering is critical in our area for survival of trees and shrubs. http://www.ext.colostate.edu/pubs/garden/02926.html is a fact sheet that talks about healthy trees and tree roots and provides insight on what can affect the growth of a tree via the roots.
There may be some residual effect of the cool temperatures in May and June on vegetable production in the home garden. The coolness has pushed back fruit set on a lot of the warmer season vegetables, so be patient with your plants.
Lastly, there are a lot of aphids out there. A blog post from Gardening After Five has some recommendations on control, http://gardeningafterfive.wordpress.com/2011/07/08/year-of-the-aphid/.