Chemicals can be used to help stop olive fruit, pollen

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Question: I have recently planted a 36-inch box Wilsonii olive tree only to subsequently be told that olive trees will fruit and make a nasty mess. I've also been told that it is possible to significantly reduce or eliminate the fruit by spraying, although no one can tell me what that spray is. Is there any light you can shed on this subject to include the product and recommendations for its application?

Answer: I love olive trees except for the terrible problems they cause for our residents and friends who have allergies. In these cases, they are a terrible menace when planted in large numbers in a community. Buying a so-called "fruitless" olive does not guarantee they will be pollenless.

There are two ways to control the fruit and only one way to control both fruit and pollen. The older method was to buy Olive Stop or a similar product containing NAA for short. Any of the chemicals recommended for eliminating fruit that contain NAA must be sprayed on at the time of bloom, usually twice, once early in the early bloom stage and another later when more of the flowers are open. This is because the chemical must come in contact with the inside of the flower, causing the fruit to abort.

As you can see from this, the flower is already open and releasing pollen. This is true also of another chemical called Florel, which contains ethephon. Follow label directions exactly as written.

Another chemical occasionally used is called Embark. It contains mefludide and is sometimes used to suppress growth of woody plants and eliminate fruit on olives. It also is sprayed close to flowering and during the early stages of flowering and may not suppress pollen release.

A third option, and the one I recommend for fruit and pollen reduction, is spraying with a chemical called Maintain. Trees can be sprayed from late January to early April before any flower bud formation. The chemical causes any flowers that form in April and May to wither and fall off without setting fruit and without releasing pollen. It will cause some malformed leaves to occur, called strapping, but they're not very noticeable unless you have a trained eye.

Read the label. This product is relatively dangerous to the applicator and, although not a restricted-use product, I would highly recommend that a commercial applicator be hired to apply it unless you are skilled in these kinds of operations.

You can contact any company that advertises olive fruit prevention and ask them if they use Maintain. All of these sprays work for only a single season, and must be applied every year. Trees under stress, radically pruned, or with valuable sensitive plantings under them should not be sprayed without special precautions.

Q: I have a problem with euonymous plants (deciduous or evergreen shrubs) dying. These are all plants that have been in the ground 8 to 10 years. Now, they are getting a white spot on their leaves and shortly afterward, the plants die.

A: I am not sure what you mean by a white spot, whether this white spot can be rubbed off or whether it is permanent. These plants do get powdery mildew, which looks like the leaves have been dusted with white flour.

If it is powdery mildew, it usually means they are not getting enough sun or the canopy of the plant is not open enough for air movement, or both. Powdery mildew, unlike other fungal diseases, requires very little humidity to become a problem. It is spread by splashing water from overhead irrigation or rain hitting the leaves, and splashing on others, carrying the disease to these leaves and so it spreads.

You can buy a dust or spray to control powdery mildew, but that just circumvents the problem and it will come back. The long-term way to control it is to get more sun on the plants (move or prune them to open the canopy up and get some air movement through the plant), improve their health with fertilizers and appropriate watering.

A white spot also can mean scorching of the leaves due to direct intense sunlight. This type of damage cannot be rubbed off with your fingers. It is permanent damage to the leaf. The plant may be in the wrong spot such as intense sunlight or lots of reflected heat and/or light from windows and a west or southwest exposure and planted in rock.

If this is the case, then you need to move it away from this intense location into one that is more cooling with less intense sunlight. However, 8-year-old plants are probably too old to move successfully unless you are very experienced. This is not a desert plant and cannot handle this kind of exposure. It does not like rock mulch very much, so put it in organic mulch on the soil surface.

If it has only one drip emitter, put two or three depending on its size. If you are watering every day, spread your watering out longer but water deeper each time you apply water. Make sure you fertilize this plant in the spring with a good tree shrub fertilizer.

Q: I live on an acre in the Northwest part of the Vegas valley and planted numerous Mondel pine and FanTex ash trees eight years ago. I hired landscapers who put drip irrigation on these trees. The trees are planted in bark with cement curbing with grass covering half of the tree area. Tree roots are coming to the surface in the grass area. We have redone the watering system with bubblers now to water more effectively. So what do I do about the roots?

A: What is the purpose of the landscape trees and grass? Grass usually means there is some recreation on it and you may want to keep the grass if it weren't for the roots. Watering grass around trees usually keeps the trees irrigated once they are established.

These are trees that are going to get big. It is really difficult to get enough water to large trees on drip irrigation. I am rather surprised that you have such shallow roots on both the ash and the pines. They are not typically known for having shallow roots.

This might mean you have soil that does not drain very well, or there is some hard impervious layer down there such as caliche and/or you are irrigating very shallow and frequently with drip. It could be any or all of these.

You have some alternatives. I am not a big fan of drip irrigation on trees that get more than 20 feet tall. I just believe it is too hard to get a large enough volume of water on, and over, a large enough area using drip irrigation and not having problems. Trees like to have a lot of water applied at one time so it gets deep and then allowed to dry out before the next irrigation. Desert trees have the same amount of water applied at each application but you can wait longer between irrigations.

You can remove a few of the problem roots on the surface up to about the dripline of the trees. It most likely will not hurt anything if they are at least getting some roots down deeper. You can convert the drip to a flood irrigation basin near the trees trunks.

With trees already established, you would have to trench and redo the irrigation system with bubblers and put shallow basins around each tree to capture the water from the bubbler.

Or you can try to modify the drip irrigation system with more emitters and higher volume emitters around the trees. Ideally, it would be nice to have an emitter about every 2 to 4 square feet depending on how sandy your soil is.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension.

If you have gardening questions, call the master gardener hot line at 257-5555 between 8 a.m. and 5 p.m. Monday through Friday, or contact Bob Morris by e-mail at Extremehort@aol.com.