Sometimes I assume that, given our dry and cool environment, I have seen the vast majority of pest and disease issues in the area. I seem to know when the questions about aspens will arrive:
Early summer: “What is the orange liquid coming out of the trunk?” Answer: could be Cytospora canker. Usually doesn’t end well.
Mid-summer: “How do I get rid of all these aspen shoots coming up in my lawn?” Answer: You won’t. Moving would solve the problem.
Late-summer: “All the leaves on my aspens get this black spot, and the leaves fall off. Is my tree dying?” Answer: It probably is, because it’s an aspen tree, but the fungal disease, Marssonina leaf spot, is the cause. Rake up your leaves in the fall and discard them.
Similarly, I tend to know when the questions about the lawn going brown (mid-July), the powdery substance on the leaves of the squash plant (August) or the worms in apples (October) will start coming in.
But this year has been different. Way different. All that rain (4-6 inches, depending on location) and snow, followed by two weeks of temperatures near 90 has created the ideal conditions for diseases and insects. And by ideal, I mean the “perfect storm.”
During the past seven years, I have never seen aphids this bad. Leaf-curling plum aphids (fruit trees), black cherry aphids (tart cherries), green peach aphids (peaches, apricots and most vegetables), cabbage aphids (cole crops, including, you guessed it, cabbage) and pea aphids, most commonly found on, you guessed it, alfalfa.
At this point in the season, if the insects haven’t curled the leaves yet, you can always try a forceful jet of water to wash them off. If the aphids lose a leg, or get displaced to the ground, the odds of them getting back on the plant are slim. Other than that, there really isn’t much you can do about controlling them. But as my friend Courtney does, cut out this article, stick it in a drawer and save it for next winter, because that’s when you can start the control of the upcoming invasion.
On trees and shrubs that get hammered by aphids, try applying a horticultural oil during the dormant season. The best time would be late February through early April before bud break. The oils, a highly-refined petroleum product, are applied to the trunk and branches, smothering the eggs and overwintering females.
If you see aphids during the season, and the hose isn’t doing the job, try insecticidal soaps and oils, focusing on the undersides of the leaf. The nice thing about these products is they leave no toxic residue, so they don’t kill natural enemies that migrate in after the spray.
Lastly, and maybe most importantly, use flowering plants in your landscape, as the nectar and pollen are valuable food sources for the adult stages of beneficial insects, such as lady beetles, green lacewings and syrphid flies. Their larval stages are voracious consumers of aphids – much more than when they are adults – and could end up being the most effective form of aphid control in the garden.
Darrin Parmenter is the director and horticulture agent of the La Plata County Extension Office. Reach him at firstname.lastname@example.org.