A huge collection of insects, mites, or diseases are always present in our environment, but specific types of pests are active only during certain seasons. They gain the upper-hand when a plant is weak or stressed. While healthy plants can also become infected, they usually rebound quickly by using their built-in mechanisms to begin the repair. After some research, I found the following pests are most active in the autumn.
Whiteflies typically appear in the fall and prefer certain families of plants such as lantana, lisianthus, hibiscus, mallow, and vegetables. They are pale colored and are about one-sixteenth inch long. Symptoms include some defoliation, leaf wilt, and stickiness. Check the underside of leaves for the immature, sucking sap stage. It resembles a dew drop. Since you’ll probably notice high numbers of whiteflies, a soapy water spray kills them off, but you may have to spray again a few days later. Parasitic wasps (Encarsia formosa) attack whiteflies, and they don’t sting people or pets. Most insects in your garden are actually helpful.
Mites are active late spring through fall. They pierce and suck juice from foliage of juniper trees, aloe, yucca, Italian cypress, and pyracantha. Their tiny round bodies have eight legs as observed through a magnifying glass. They cause a spray of multiple shoots (witch’s broom) in trees and browning of foliage associated with fine webbing. They also cause odd growths on the blades of aloes. A forceful spray of water or mild soapy water knocks them off the foliage. Green lacewing feed voraciously upon spider mites, whiteflies, and other small insects.
Most broadleaf plants are susceptible to cotton (Texas) root rot. This soil fungus, which is indigenous to the desert, appears typically in the autumn. Quick collapse or plant death happens, and there is no control. Plants that are desert-adapted are least susceptible to this disease, and grasses, palms, and yuccas are immune.
Last, but not least are aphids. Spring and fall, when the temperatures are 70 to 80 degrees, are ideal for these soft-bodied insects to suck the juices from tender plants, such as roses, milkweed, oleander, yucca flower stalks, and many others. The sticky honeydew is messy, but causes little damage. Ladybugs and lacewings feast on aphids, so you may want to keep the aphids around. If not, just hose off the plant with a strong blast of water.
Attention: Spots are still available for the 2020 Master Gardener classes, which run from Jan. 21 through March 24. Sessions are held Tuesdays from 9 a.m. to 4 p.m., with an hour for lunch. The cost is a very worthwhile $200. Classes are taught by University of Arizona professors and expert Master Gardeners at the Pima County Extension Center, a quick ten-minute drive from Quail Creek. Please call 520-648-0808 to register. What a great learning opportunity that is close to home.