Anytime you're dealing with extreme weather (too wet, too dry, too hot or too cold) you need to be aware of the potential for disease and pests. Plant disease and insect pests will more readily infect stressed plant materials, like those in extreme heat.
Leafminers are in full force this year. However, the columbine that they inhabit can be cut to the ground and will produce fresh leaves. Other pests may require more aggressive treatment. For the first time, I have found evidence of leaf tiers in my yard. Leaf tiers are the caterpillars of moths. In their larval forms, they range from 3/8" to 2" in length and vary in color from light to dark green or from cream to yellow. They build silken nests around a plant's foliage, which they inhabit individually or in groups. Yes, the package is really cool, but I definitely don't want the gift.
One of the best indicators on what is destroying your plant is the actual damage caused. Are there holes from the leaves being chewed? Is there residue from the insect's presence left on the plant? Is the damage localized on one type of plant? Is the damage occurring on new or old growth? You can use all of this information to determine what is attacking your garden and make the appropriate decisions on how to deal with the problem.
Once you find the damage you can start researching. You can use online tools to determine the pest as well as simply asking other gardeners. A really good local resource is the county extension agent. You bring them your problem plant material and let them know all the helpful information you have found. The more clues you find, the better your chances of finding the right perpetrator. If they don't know the answer, they can send it to be examined.
It's best to look ahead and try to avoid as many problems as possible. Even a few minutes in the garden can make a difference and give you more enjoyment later in the season.
Landscaper at Busch Gardens