They plague every gardener's nightmares. Like something from a sci-fi movie, they are green with long legs and antennae and long piercing mouths with which they suck out fluids. They eat 100 times their body weight, and—worst of all—they multiply asexually by the dozens in a day!
My first experience with aphids as a beginning gardener was watching the leaves on my plum tree wilt. The flowers fell off and died instead of producing fruit. This prompted me to research what I could do to protect my fruit trees. Here is what I learned.
In fall it is time to start your preventative measures for aphids on fruit trees for next year. After harvest, a zinc sulfate application on plums and prunes will provide zinc to the trees as well as hasten leaf fall disrupting the aphid life cycle.
If aphids are a chronic problem in your fruit trees, you can apply supreme- or superior-type oils to kill overwintering pests during dormancy this winter. This helps to start the following season with a clean slate.
In the spring, start monitoring your trees for aphids as soon as leaves begin to bud. Check for aphids on the underside of the leaves on several areas of your trees at least twice weekly. Ants tend aphids and collect their honeydew and large numbers of ants climbing up your tree trunk is an indicator that you may have aphids. Over watering and over fertilizing can increase aphid populations so only apply the minimum necessary for healthy plant growth.
One excellent way to reduce aphid populations is to knock them off with a strong spray of water.
Several natural predators feed on aphids including lady beetles, green lacewings, brown lacewings, syrphid flies, and soldier beetles. Predators can be released onto the trees but often appear naturally in significant numbers when there is a significant aphid population. Where aphid populations are localized on a few curled leaves or new shoots, consider pruning these areas out. Drop the infested plant parts in a bucket of soapy water. If insecticide sprays are needed, insecticidal soaps or horticultural oils are generally the best choice. Avoid using broad-spectrum insecticides which will kill natural predators and consequentially could increase your aphid population.
In our area, it can help to keep weeds under control near your trees.
With these tips, you can save your home orchard from an aphid invasion like the Men in Black saved earth from an alien invasion and go back to sleeping soundly throughout the night. Good luck!
References:
Agriculture and Natural Resources, University of California (2019). Leaf Curl Plum Aphid. Retrieved from http://ipm.ucanr.edu/PMG/r606301811.html
Flint, Mary Louise (2018). Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, Third Edition. Oakland, CA: The Regents of the University of California Agriculture and Natural Resources.