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You love them but you hate them...those big English walnut trees.

You love them but you hate them . . . those big English walnut trees

A love-hate relationship is what many Westerners have with their English walnut trees. Widely planted throughout the mild-winter West, these trees produced commercial crops for decades. As groves gave way to new homes in urban areas, many of the trees remained as mature landscape features.

Unfortunately, home gardens are not always the best places for walnut trees. Many trees have succumbed to a variety of ailments that are aggravated under normal landscape conditions. If you have a valuable walnut tree in your garden, here's what to expect from it and how to keep it healthy.

First, the all-too-familiar bad news

As landscape trees, walnuts are constantly messy. In spring they shed enough pollen to make the neighbors sneeze, and they drop catkins and blighted small nuts. During summer, they're often filled with nut-eating squirrels who drop empty hulls, staining patios and decks below; the nuts not eaten get buried in pots and flower beds, where they sprout into tenacious, tough-to-pull young trees. And if any nuts at all are left to harvest, they're often full of worms--thanks to the walnut husk fly or the codling moth. If all that isn't enough, in autumn walnut trees litter the ground with big leaves.

Despite these problems, few people would ever consider cutting down their walnut trees. Their spreading canopies provide cooling shade--much appreciated during hot summers--and make them handsome focal points of the landscape.

Water deeply but keep the tunk dry Walnut trees need regular deep watering during the growing season. However, if the soil around the base of the trunk is kept moist, trees are likely to get crown rot; this stunts growth, turns foliage yellow, and often kills the tree.

If you suspect crown not, cut into the bark near the base of the tree and look for light brown to blackish dead areas. These can girdle the main trunk. Walnuts growing in lawns are most susceptible and, once infected, often die within a year.

To prevent crown rot, keep the soil dry within 4 feet of the trunk by waterning in a double basin (with an inner ring to keep water away from the trunk), or adjust sprinklers accordingly. Do not plant grass or other plants within this dry zone.

In crown rot's very early stages, its spread can sometimes be halted by exposing the crown (remove soil around the trunk base to expose large roots), but this is best done with the advice of an extension agent or a professional arborist.

Fertilize regularly

Keep walnut trees growing vigorously by making regular applications of nitrogen fertilizer. The University of California recommends a total of 3 pounds of actual nitrogen per 1,000 square feet of root area, divided into two feedings--the first as the leaves unfold in spring, and the second just before harvest in fall. If you have trees growing in a lawn, divide the feeding into three or four applications to aboid burning the grass. Water thoroughly afterward.

Watch for insects and disease

The size of a walnut tree makes controlling most pests very difficult without professional help. Here are some of the most serious problems. Others include walnut blight, aphids, scale, and leaf-chewing caterpillars.

Blackline. This serious virus disease is common in the San Francisco Bay Area and surrounding areas of northern California, and in some parts of Oregon. It causes an incompatibility between the English walnut and its common rootstock, the black walnut. The top of the tree gradually dies while the rootstock often suckers prolifically.

Blackline is impossible to control, but you can remove the dead top and develop three or four suckers as main limbs for a new black walnut canopy.

Walnut husk fly. This small fly spends most of its life cycle underground but emerges in summer to lay eggs in the hulls of maturing walnuts. Hulls of infested nuts turn black and are often mushy and full of maggots; meats often fail to develop or become moldy. If you're lucky, only the shell will be stained and the nut will be edible, although messy to hull; wear gloves.

It's very difficult to control walnut husk flies on a single-tree basis. If there are many trees in your area, your entire neighborhood will need to be sprayed.

Codling month. It causes wormy nuts, but usually in only a small percentage of the crop. Spray timing depends on location; consult your cooperative extension agent.

What about squirrels?

There's not much you can do to prevent raids by these arboreal acrobats. A 3-foot-wide ring of aluminum flashing wrapped around the trunk may keep squirrels from climbing into a tree that's completely isolated from utility wires and other plants; make sure to loosen the ring as the tree grows. Other than that, all you can do is learn to live with the squirrels or remove the tree.

If you want to plant a walnut tree

You'll need plenty of room for the tree to spread: it can reach 60 feet high with an equal spread. Plant in deep, well-drained soil, choosing a spot well away from patios and decks.

You can escape some of the problems of older trees by selecting the right variety. In northern California and the Pacific Northwest, you can often avoid codling moth by planting late-leafing varieties, such as "Franquette' and "Hartly'. Trees grafted to "Paradox' rootstock are better able to withstand wet soils. Walnuts on Manregion rootstocks are resistant to blackline.

In warm-winter areas of Southern California, early-leafing varieties like "Payne' are best adapted because of their lower chilling requirement. Extra-hardy varieties of Carpathian walnuts, such as Ambassador', are most reliable in cold-winter mountain areas.

Your cooperative extension office can provide additional information on variety selection.

Photo: Stately Walnut trees such as this one in Yuba City, California, provide priceless shade. In a lawn like this, deep ring of gravel around trunk helps keep in dry

Photo: She's lucky--squirrels and bugs left her some of harvest. Collect walnuts as they fall, remove hulls, wash, and dry in the sun

Photo: Spreading branches of 35-year-old walnut tree in Los Altos, California, cradle tree-house platform. Conopy combines with that of nearby silver maple to shade deck

Photo: Hungry squirrel nibbles ripening nuts on this Sacramento walnut tree. Half-eaten nuts litter the patio and drop--often with a painful thud--on the heads of anyone sitting below (bottom photograph)
COPYRIGHT 1986 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1986 Gale, Cengage Learning. All rights reserved.

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Date:Sep 1, 1986
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