Irrigation for desert landscapes not enough for trees

Fruit-tree pruning workshops at the University of Nevada Cooperative Extension Master Gardener Orchard in North Las Vegas will not be held during the next three Saturdays; they will resume Jan. 15 when the pruning of almonds and pomegranates will be taught. I will be lecturing on basic pruning at the Springs Preserve at 8:30 a.m. Jan. 8.

Upcoming pruning classes at the orchard will include figs and persimmons Jan. 22 and fruit trees for small spaces Jan. 29. All classes at the orchard begin promptly at 10 a.m. For more information on these and other events contact the master gardener help line at 257-5555.

Q: We read your article in the paper on putting in a desert landscape when you have existing trees and plants. W e had a landscaper do work at our home and remove the small front lawn and install artificial grass. There is a flowering plum tree in the middle of this area and we plant seasonal flowers there. He installed a small circular hose that had small holes in it and we found this wasn't enough water for the tree. The tree started to wilt and it really looked bad for awhile, then we began to water it manually. It has now come back.

We would like to know what type of water sprinkler should have been put there and how much water should be given to this tree. The tree is about 12 feet high and about 12 feet wide. We would appreciate any help that you can give us. We are just amazed that a landscaper did this and, like you said, was unaware that the tree needs more water than what was provided .

A: This is a common occurrence when retrofitting existing landscapes to desert landscapes. The problem is that tree roots are so extensive when water is not applied in a controlled manner, such as in drip irrigation.

One technique is to go around the perimeter of the tree, about 4 to 5 feet away from the trunk, and sever the root system so that it regrows closer to the trunk where drip irrigation can be applied. When retrofitting these trees there are usually not enough emitters distributed under the canopy to satisfy their needs for water. So when you supplemented the tree with additional water it started to recover.

I would recommend that you try to apply somewhere around 30 gallons of water each time water is applied. If this is through drip irrigation, then you need to have enough emitters distributed under the canopy to apply 30 gallons during whatever the time duration for drip irrigation has been established.

If this is one hour, then 30 gallons should be applied through these emitters in one hour. If the timer is set for 30 minutes, then enough emitters need to be established so that 30 gallons is distributed in 30 minutes. An important consideration is to have these emitters distributed under the canopy in multiple locations.

Q: Last year, I lost all three of my papaya seedlings in my greenhouse to spider mites. Spraying them with recommended insecticides proved that the treatment was worse than the disease. It was a heavy infestation and also got on some of my citrus, which I was able to clear up. Is there some treatment that I can use to prevent this problem the coming year? I use the greenhouse to control the temperature above freezing.

A: Mites are one of the biggest problems in greenhouses and very difficult to control. One of the best methods of controlling spider mites is still soap and water sprayed every couple of days. Many miticides unfortunately kill the good or beneficial mites that are responsible for helping to keep the bad mites at bay.

Dust accumulation on the plants' leaves also interferes with the ability of beneficial mites to find the bad mites and control them, so periodic washing of the leaves helps.

Sanitation in the greenhouse is extremely important as well so plant debris can contribute to the problem.

Bringing contaminated plants into the greenhouse is another source and they should be held in isolation before bringing them into the greenhouse. These plants should be closely inspected for the presence of mites either before buying them or while they're in isolation.

Q: When should Seckel pears be picked in this climate? Mine are of good size and color now but they feel hard as porcelain.

A: I have never grown Seckel pear so I will refer to the harvest calendar available from Dave Wilson Nursery in California. It has the best harvest schedule I have seen. There are some things in there that are either mistakes or different than our area, but generally speaking it is within two weeks of our harvest dates. Of course harvest dates can fluctuate two to three weeks every year.

Bottom line, harvest the pears when they begin their color change, then keep them ripening at room temperature for anywhere from several days to a week and even more. You also can check the seeds; they should be dark brown with the pointed end still white or cream colored. You can find this chart online at: www.davewilson.com/homegrown/promotion/chart.html.

Q: My problem is similar to that in your article. There are five sprouts growing on the tree. They begin about 3 inches from the ground and are about 1 inch apart. One is 2 inches long and four are about 3 inches long. You said we should cut them off to encourage the tree to grow. Our tree is 2 years old and is beginning to grow out of the support wraps. I have replaced some of the supports, but I need advice on how to cut the growths as well as any information on cutting these growths (how far from the trunk) and when the tie supports can come off.

A: Sprouts or new growth arising from the trunk of small, immature trees should be left on the trunk until they are pencil-sized in diameter. At this point they should be removed very close to the trunk, leaving no stub.

Leaving small sprouts or new growth on the trunk of small trees helps to increase the diameter of the trunk and develop trunk strength through its tapering. If this as an older tree that does not normally sucker from the trunk, then it could be an indication of trunk damage due to insects, disease or physical damage from something like sunburn.

A few suckers left on the trunk helps it develop girth. If too many are left on the trunk, then it discourages the growth of young trees by diverting energy into these sprouts. If the trunk has good girth or diameter and appears to be strong, then go ahead and keep the sprouts pruned from the trunk. If the trunk appears to be weak, then leave this growth on the trunk to help strengthen it but remove it after one year of growth.

Make sure that you remove the growth as close to the trunk as possible. You can do this any time. The supports should come off of the tree after one season of growth. Hopefully by then, the tree is strong enough to stand on its own. If not, thin the canopy of the tree to reduce the effects of wind pushing on the canopy and the weight of the canopy itself.

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.