Q: I have been told by tree men that I need to prune my fruitless mulberry every year, and different arborists have recommended different types of trimming. I don't know whether they are telling me the truth or just looking for work. What do you recommend?

A: Fruitless (male) white mulberry (Morus alba) is a high-maintenance tree because of its weak wood, rapid growth and invasive surface roots. Still people plant it as a small- to medium-size ornamental shade tree because it tolerates poor soil and heat. It also very quickly attains a mature height and spread of 20 to 30 feet.

Fruitless mulberries are usually pruned in one of two ways. One is to regularly crown-reduce the top, sides and individual branches of the tree. "Crown reduction" involves shortening the extent of branches by pruning back the leader to shorter secondary branches that are sufficiently vigorous to take over as the new leader. It is necessary because of the very rapid growth of this tree and its relatively weak wood. If you do not control the growth of the branches, they will probably break. Any arborist who works on your trees should do the work in conformance with American National Standards Institute (ANSI A300)/Tree Care Industry Association (TCIA) standards.

Second, many people manage their fruitless mulberries with "pollarding cuts." This pruning method is commonly used around the Bay Area on beech, black locust, catalpa, horse chestnut, linden and particularly London plane tree or sycamore. I think everyone has seen those grotesque-looking sycamore trees along our roads in the winter with large knobs at the foreshortened ends of branches.

Pollarding can be done only on species that sprout prolifically, and should be instituted when the tree is young and the branches are small in diameter where the cuts will be made. That way you avoid large wounds and the invasion of decay fungi. The trees then sprout from latent buds under the bark just below the pollarding cuts. The sprouts grow very rapidly (as much as 6 feet in one growing season).

You then prune off the sprouts annually. The tree will develop large knobs at the pollarding cuts over the years and there will be a large number of sprouts from each knob, making a full canopy. The annual sprout removal can be done with a pole pruner by very low-skill or low-cost workers or gardeners, but they must be careful not to scar the old knob wood or decay may invade the scaffold branch.

By the way, you should know that fruitless mulberries have very shallow roots that can damage walks, decks, patios, garden walls and pipes. You might want to install a root barrier if your trees are near valuable infrastructure.

Q:My yard contains a very large, very productive lemon tree. It was planted against a tall building that cuts its direct sunlight in the afternoon. The fruits that are not harvested develop a white powder with a greenish tint. Sometimes the fruits that are harvested in a timely manner develop this powder sitting in a bowl. It has survived two extreme prunings and multiple smaller prunings in the past decade. Can you tell me whether this is a fungus or a mildew? Is there a treatment?

A: Well, it sounds like you've got the perfect breeding ground for powdery mildew. The person who selected the planting location deserves a strong slap on the back - with a moldy lemon. Its location directly against a building with little sunlight, and the methods of pruning, create an atmosphere for the mildew to thrive. Mildew can affect any part of the plant, such as fruit, flowers or leaves.

The mild San Francisco climate, coupled with the shady location of your tree and the dense, succulent sprout growth that results from heavy pruning unfortunately caters to the growth of mildew. Since you cannot move your large tree to a sunnier location, you will have to manage the mildew with pruning. You should have your tree trimmed with thinning cuts to create better air circulation and sunlight penetration to dry the leaves and fruit. The plants surrounding your lemon tree should also be pruned to allow for maximum aeration and sunlight.

Replace any spray irrigation around your tree with drip emitters or soaker hoses to reduce that humidity in the immediate area. Removing all of the old fruit and other infected parts of the plant and regularly cleaning up fallen fruit and leaves will help prevent the mildew from spreading. Mildew spreads by windblown spores and can continue living on portions of the tree that have been removed, so make sure to dispose of the infected plant material off your property.

Now, as far as your harvested lemons are concerned: Just like sunlight, water inhibits the growth of mildew by washing the spores off the infected plant tissue. You may want to wash and dry your lemons before letting them sit in a bowl indoors. If all else fails, you know what they say ... when life throws you lemons, make lemonade!