Keep spider mites under control by washing cypress

: I have five, large Italian cypress that are all four years old. When I returned from my trip last week, I noticed one of them looking very dry and sick, I unfortunately watered it heavily for two days and it quickly died. I’ve been researching and reading about mites and cankers that the cypress is prone to. I’m concerned about the other four trees and what I should do.

A: The biggest problem for Italian cypress is overwatering, but that usually leads to unruly growth that does not remain upright. Cypress canker, which attacks the roots and trunk and can cause rapid death, is usually associated with cypresses other than Italian.

Spider mites can be a problem but usually can be kept under control by periodically hosing the tree with water to wash off dust. Dust acts as a barrier for many of the spider mites’ insect predators and inhibits their abilities to hunt and prey upon them. They prefer clean surfaces for hunting.

In most cases, if the plant is healthy, the predators will keep the bad guys in check. If we use insecticides, we can upset that balance so it should be reserved for “emergency” situations.

Fertilize cypresses lightly once a year and hose them off a couple of times a year during the heat of the summer. Italian cypress are Mediterranean plants and prefer hot, dry summers and can tolerate wetter, cooler times of the year.

Q: Is there any reason to whitewash the trunk of a tree with mature bark?

A: Whitewash is used to help reduce sun damage to the trunk and exposed branches of trees that are susceptible to borer damage. Wood that is sun damaged due to high light intensities is often very prone to attack by these wood-boring insects.

It depends what you are calling mature, but if there is clearly older bark, bark that is sloughing off, then there is probably no benefit. I would focus on the upper, south and west surfaces of any scaffold limbs.

Scaffold limbs usually arise from the trunk and are the major supports for the smaller branches. Their upper surfaces are the usual places that get attacked by borers. Less frequently, the trunk is attacked with the types of borers we have here. The most susceptible are peach and apricots.

Q: Why are my nectarines riddled with linear scarring, smallish and ripen while still a bit green? Some also have what looks like sap nodules on the surface.

A: This is damage from Western flower thrips. They start feeding at the time of flowering and continue feeding on developing fruit for most of the season.

Try spinosad applications right after flower petal fall in the spring and repeat them as the label permits you. Include the use of a spreader additive to the spray to help cover the fruit better. Avoid spraying flowers when they are open and spray at sun up or sun down to avoid hurting visiting bees.

Q: You had a timely article for me on the mimosa tree. Mine started to struggle with leaf scorch. I started deep watering and I added iron and zinc, and used a 15-15-15 fertilizer. After about three weeks, I had new growth on all branches and no scorch on the new growth. I should have started when the temperature increased.

Also, why should I never plant them in stones? My mimosa is in an area of about 250 square feet with stones surrounding it.

A: I think you just proved my point. Mimosa is difficult to manage in a rock landscape because rock landscapes add nothing back to the soil. Over time, the soil becomes depleted of nutrients and organic acids because nothing is added back to the soil. The organic acids from decaying organic material help these nutrients become available to plants.

With organic mulches, they are constantly decomposing and replenishing the soil with nutrients and helping stimulate important soil microorganisms and even worms. So by adding iron, zinc and the 15-15-15 fertilizer you began to replenish those nutrients that were depleted from your soil due to the presence of the inert rock mulch.

Some plants just do not do well under rock mulch and mimosa is one of them. Your other option is to add these fertilizers every year and in some way try to compensate for having that rock mulch. Either way is fine. It’s your choice. But you will have to add your fertilizer combinations annually for your mimosa to do well.

Q: My wife and I read your interesting article regarding white spots on cactus. Yes, we have them and didn’t know what to do about it. Now we do. I zapped the beavertail with a solid water stream and within seconds the spots were gone and the beavertail looked as good as ever. Many thanks for the simple solution to an otherwise difficult problem.

A: Remember that this does not get rid of them permanently. They will come back relatively soon and you will have to repeat spraying with your hose. If this becomes bothersome, then you will have to rely on a pesticide such as Sevin after you hose them off. Make sure you read the pesticide label before applying it.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.