This time of year is a busy time for home horticulturists. Now that we have finished fertilizing landscape and fruit trees and increased irrigation as temperatures warm, we turn to pest problems.
Spring growth attracts overwintering insects. Soft, succulent new growth is easy to feed on. Insects like aphids move to new spring growth to feed and have their young. Expect aphids to begin feeding and multiplying on the undersides of leaves now and through cool weather.
If your landscape is a healthy one, you will see an explosion of ladybird beetles or ladybugs and green lacewings. The young of these insects are voracious feeders upon small, soft-bodied insects like aphids. These adult predators lay eggs in areas where their young can easily feed.
Signs that aphids are present and feeding are the curled edges of new leaf growth. However, what might attract your attention more are ants. When the leaf is turned over and the leaf edge uncurled you will see adult aphids and their young feeding. Their feeding creates a sugary sap that ants relish.
Soap and water sprays directed on them and spaced several days apart are usually enough to control aphids. Most people will spray the top sides of the leaves to control insects. But when aphids are inside the curls on the underside of the leaf, they can be a challenge to control with just soap and water.
If you an adherent to organic methods of pest control then multiple sprays directed toward the tops and bottoms of leaves will be necessary. Most organic methods do not persist. Multiple applications may be needed a few days apart for good control.
Question: We have a 20-year-old olive tree in our front yard diagnosed with Verticillium wilt disease. The north third of the tree appears to be healthy. If we remove this tree, what distance from the old hole is needed for the new tree? We would a replacement tree to provide shade. We are looking at oak, pine, ash, spruce or fir.
Answer: That’s unfortunate. Hopefully the diagnosis was correct and it is not something else that caused it. The information you received about the disease sounds correct. This disease is present in the soil and enters the tree via the roots.
Olive has very few pest problems and an excellent tree for the desert. Verticillium wilt disease is rare in olive here but does occur. Symptoms include the death and dieback of individual limbs for no apparent reason.
Trees resistant to Verticillium wilt disease and good choices for you in our desert include live oak such as Heritage or holly oak, ornamental pear, European pear, honeylocust, apple, crabapple and any of the conifers such as pines.
Eucalyptus is also resistant but a lot people do not like eucalyptus since it can be “messy”. I would not recommend spruce or firs since they do not grow well in our climate.
If you want warmth from the winter sun then conifers (pine) or any evergreen tree (such as our southern oaks) is not a good choice for you. I would stay with ornamental pear or honeylocust for seasonal shade, disease resistance and good looks.
Once inside the house they may set it up residence if there is a food supply, places to hide and nest. In cases like these, sprays called “crack and crevice” treatments would be recommended until you can get them under control.