Q. I planted two Mandarin oranges from different nurseries this past spring.  One did very well in full sun from the git-go. The other had leaves that were turning yellow.  I applied iron and nitrogen fertilizers, but it didn’t do much after a week. So, I constructed some shade over at and it started looking green again. Sometimes plants need to “acclimate” to their new desert climate.   A. It sounds like you’ve got your answer; intense desert sunlight caused leaf yellowing. But it begs the question, “why only one of the trees if they were both mandarin orange?” You said the trees came from different nurseries. That might be part of the answer.             But first, eliminate other potential problems before I get to the nursery explanation. Make sure your trees share the same microclimate, the soil in both locations was similar with similar drainage, the soil mix used to plant both trees was the same, that the roots were kept moist and planted no more than half inch below the soil surface, that they were staked and watered thoroughly after planting. Sometimes yellowing on citrus can be for other reasons.             You may be observing differences in how and where your trees were grown versus our harsh, desert climate. A local nursery used to bring in citrus trees for sale in containers and put them in an area that had partial shade. They could put them in full sun and sell them from there, but they didn’t. Too risky. Sometimes yellowing can be from high light intensity.             Plants grown in a greenhouse, under partial shade or in a cool, coastal climate produce leaves that are different from leaves grown during our harsh desert sunlight and low humidity. When tender plants are plunged directly into our strong sunlight and low humidity, the leaves may scorch, yellow or drop from the plant. The plant is not dead but quickly produces a new set of leaves very different from its old ones. The newer leaves are smaller, thicker, tougher and better capable of handling desert sunlight and humidity. The plant has become “acclimated”. Yellowing from an iron problem happens on new growth and lowers the health of the plant making it more susceptible to heat problems.             Observe where nurseries are selling plants. Plants sold from shady areas may struggle when planted in full sun. Plants grown in a greenhouse need two or three weeks of “acclamation” before they are plunged into an intense desert landscape. This is true of vegetable transplants as well.             If you suspect you have a plant which may be acclimating to its new environment, sometimes it’s easier to strip off the leaves or prune the plant so its new growth is better acclimated to its new desert environment. In your case, wait until fall and remove the shade. Let the mandarin orange “acclimate” to its new home during the cooler fall weather.

Q.  We have lots of aphids in our good-sized oak trees that are dropping sap on our cars and the sidewalk. Short of cutting the trees down, do you have any suggestions on how to get rid of the aphids? Not from the reader but aphid sticky exudate on oak. A. Blame their high population number s this year on our wet and humid spring weather. The fastest and probably cheapest way to get rid of them is to drench the soil beneath the tree with a systemic insecticide diluted in a bucket of water. This dilution will help you spread it more evenly everywhere under the tree. aphids on pomegranate             The pesticide I’m telling you to use has the active ingredient imidacloprid in it. This insecticide is systemic so when you pour this around the base of the tree, diluted in water, the roots will take it up and transport it to the leaves. Since the aphids are sucking juices out of the leaves, they ingest this toxin and die. Leaf curl on plum from early feeding and leaf expansion             There are several trade names of this pesticide that contain imidacloprid. The most popular with homeowners is the Bayer product with the trade name “Tree and Shrub Insect Control”. Any product that you use must contain imidacloprid in the ingredients. The easiest and probably safest way to apply it is a “soil drench” but it can be sprayed on the leaves as well. One of the many products that contain imidacloprid. It is now the most used insecticide in the world.              The label will tell you how much of this pesticide is applied to one tree. Follow the directions on the label for a soil drench application. When you are finished with the application, rinse the bucket three times with fresh water and apply these “rinsates” under the tree as well. Wear unlined plastic gloves and eye protection when mixing and applying this product and rinse, or dispose of them, afterwards. Chitalpa black aphid             Consider spraying these trees during the wintertime, from top to bottom, with a dormant oil. Apply an extra dose to the base of the tree where aphids might be hiding. Dormant oil sprays applied during the winter are very effective in reducing the populations of aphids, scale insects and spider mites for the next growing season. Entrance to an ant colony on the orchard floor.             Ants love aphids. They “milk” ants of this sugary sap for their own use. If you look at the tree trunks carefully, you will see a steady stream of ants going up and down the trunk. They are also part of the aphid problem and should be controlled. Follow the stream of ants back to the opening of the underground nest. Sprinkle 10 or 15 “crystals” of ant bait directly at the opening of the nest. I use a product called “Amdro”. The nest will be empty the next day.

Join me in this episode of Desert Horticulture. I discuss the grasshopper invasion, those giant wasps that have been flying around and the fruit salad tree. Is it any good?

I received this recipe for pear tomato jam I thought might interest some of you.  For many years I helped my mother canning, storing, and making jams and jellies for a family of six. I finally quit making jellies about 4 years ago. I liked making jellies from strawberries and crushed pineapple; Apricot and pineapple; and Yellow Pear tomato with pineapple.   My own recipe: 4 cups tomatoes crushed ( I have a 30+ year old Oster chopper 1 8 oz can crushed pineapple Combine to make 5 cups of fruit (you may need a small amount of water 1-2 teaspoons lemon juice which keeps the jelly from turning dark 7 cups sugar 1 package pectin Follow the Pectin instructions. Keep up the good information Loretta

Join me on this Desert Horticulture Podcast where I discuss different methods of controlling aphids in landscape trees, using drip tubing instead of drip emitters to water landscape trees and how to use plants that don’t belong in the desert, in the desert. Join me as we discussed these and other topics in this Desert Horticulture Podcast. Download my podcasts from Google Podcasts, Apple Podcasts, Spotify, Stitcher, iHeart Radio, and Tune In + Alexa.