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Aphids are a huge problem because they reproduce rapidly

Q: I have a small crape myrtle tree with leaves that were constantly wet this year. The ground and plants underneath were always wet. Now that the leaves are gone. I can see the branches are also wet. Another tree I have is perfectly dry and normal. What’s causing this and how can I correct it?

A: This wetness was caused by one of the leaf-sucking insects, most likely aphids. If you inspect this wetness, I think you will find it is shiny and sticky as well as wet. It probably attracts flies, bees and other insects.

Aphids suck plant juices from the leaves and then exude a shiny, sugary liquid that drops on the leaves, limbs and plants below it. There are about 4,000 different kinds of aphids, and about 10 percent of them cause problems to our plants.

In the eastern United States, there is a special aphid, called the crape myrtle aphid, that causes these problems only on crape myrtle. Several aphids specialize only on certain plants. But there are also aphids that are general feeders and infest different plants as well.

Aphids are a huge problem because they reproduce rapidly in the spring without the help of male aphids. Later in the season, females can be found flying from plant to plant giving birth to living young wherever there are succulent young leaves nearby. If you don’t get them under control, they can spread.

To add to this problem, ants pick them up and distribute them because they like the sugary liquid they produce from sucking plant sap. Controlling ants in the spring is one way to reduce their spread in the spring.

There are lots of predatory insects and even fungi that attack them during the growing season, but their reproduction and spread are so rapid that these biological controls can’t keep up with their rapidly increasing numbers.

I guarantee there are winged females and overwintering eggs hidden at the base of woody plants and tucked into nooks and crannies on the trunk and stems.

What to do? Spray both trees with dormant oil this winter to suffocate both the eggs and the overwintering females. These dormant oils are made from paraffin or mineral oil. Neem oil, although it might be effective, is not a dormant oil.

Select a warm, sunny day without wind for spraying. Mix the dormant oil with water at the rate recommended on the label. The oil is emulsified and can be diluted with water for spraying.

Spray the trees from top to bottom, covering the trunk and all the limbs. Aphids like to overwinter at the base of plants where it’s out of the weather, so spray there as well. Remove weeds where they can hide during the winter.

Q: The paloverde tree in our daughter’s yard looks like it has damage. The top has some dead branches in it. We have had to remove some limbs because of this problem. Can it be saved?

A: There are several different kinds of paloverde used primarily in desert landscaping. All have tender new growth that can be severely damaged when exposed to intense sunlight. It is important these trees are pruned throughout their lives so that the tree’s canopy shades the trunk and limbs.

Pruning them in a fashion that exposes limbs and the trunk to intense sunlight causes damage such as limb death that becomes visible a few years later. It’s a progression that usually starts with bad pruning practices.

This progression starts when too much is removed from these trees. When too much is removed, the limbs and trunk are exposed to high-intensity desert sunlight.

Intense, direct sunlight on young limbs first causes a discoloration. As this direct sunlight repeats day after day, exposed areas of limbs and trunk facing the sun die. Water can’t move through dead areas of the trunk and limbs.

Unless this sunburn causes severe damage, the top of the tree probably looks fine. The tree can still move water around the damaged area from roots to tree branches. The damage could be as much as 50 percent of the limb and trunk area, and the tree looks fine.

This damage from sunburn attracts insects such as borers that feed on living parts of the tree close to the damaged area. This feeding by borers causes even more damage that reduces water movement to the limbs. Perhaps the first year or two, trunk and limb damage goes unnoticed because the canopy looks fine.

But at some point, the damage becomes severe enough that water movement from roots to the canopy is reduced. Limbs start dying back because the tree can’t get enough water past the damage. This usually happens during the heat of the summer when demand for water is highest.

The homeowner now notices the limb death in the canopy. The homeowner removes dead limbs. This exposes the tree to more intense sunlight and further damage. Tree damage is so severe and unsightly the homeowner considers removing it. This is the tree death spiral.

What to do? Damage to the tree might be already extensive. Decide whether you can live with this damage or not. If not, have the tree removed.

If you decide to keep the tree, then encourage it to heal as quickly as possible. Contribute to this healing by giving it enough water on a regular basis and apply fertilizer in early spring.

Q: Our lawn was beautiful during the summer but started turning brown when it got cold here in Mesquite. This is a fescue lawn, and we were told it would stay green all winter long.

A: There are several different kinds of fescue, but the fescue used for lawns is technically called turfgrass type tall fescue. Tall fescue lawns stay green through the winter in our Mojave Desert climate if they receive an application of nitrogen fertilizer in late fall and night temperatures don’t drop below about 15 degrees.

If the lawn is without nitrogen, and nighttime temperatures drop below freezing, fescue lawns will go dormant and turn brown. Apply a high-nitrogen fertilizer or compost to the lawn late in the fall before freezing temperatures.

You can use any fertilizer if the first number is the highest number on the bag. Examples can be 21-0-0, ammonium sulfate, applied two to three weeks before freezing weather hits. In our Las Vegas climate, applications would be around Thanksgiving or possibly even later if nighttime temperatures don’t drop below freezing.

Nitrogen, the first number on the fertilizer bag, is responsible for a plant’s dark green color and encouraging new leaf and stem growth. It can keep plants from going dormant during the winter.

There is a nefarious side to late applications of nitrogen. Nitrogen applications made in late summer or early fall can compromise our winter-tender plants such as many types of citrus. Applications of high-nitrogen fertilizer to these plants late in the growing season can cause them to be more susceptible to freezing temperatures. Never apply high-nitrogen fertilizers during fall to plants that might freeze during the winter.

Q: I have some shrubs in my yard that are getting rather scraggly looking. I was wondering when and how far back I can prune it back in to shape.

A: First, decide if now is the best time for pruning them or not. You can prune anytime during the winter months. Some plants look better through the winter if they are pruned now. Other plants look fine now but might not look as good if you were to prune them.

Remember, if you prune now, you will have to look at them for the rest of the winter. If these are flowering shrubs, prune them soon after they finished flowering. If the shrubs do not have ornamental flowers, prune them anytime during the winter.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.

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