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When your avocado tree runs into trouble.

More than 300 readers recently shared their avocado-growing experiences with Sunset (see pages 118 to 123). A few reported problems. Here's a look at avocado troubles and what to do about them. Premature fruit or flower drop

Some friut and flower drop is normal, but excessive shedding is not. Cold or fluctuating temperatures and drying winds combined with inadequate soil moisture can be the culprits.

What to do: Keep trees as healthy as possible with proper watering and care as detailed on pages 121 to 123. Your crop may be affected for a year, but normal weather should prevent long-term ill effects. Little or no fruit set

If an avocado tree blooms but sets little or no fruit, inadequate pollination is one likely cause.

Among other things, adequate pollination depends on the climate in your area, weather conditions at bloom time, and whether bees or other pollinating insects are on duty when flowers open.

But the timing and sequence of flowering are key factors. The flowers of some varieties open pollen-receptive on the morning of the first day and pollen-producing on the afternon of the second day (type A flowers; 'Hass', 'Mexicola', and 'Reed' have them). Other kinds open pollen-receptive on the afternoon of the first day and pollen-producing on the morning of the second day (type B flowers, like those on 'Bacon', 'Fuerte', and 'Zutano').

Cooler temperatures along the coast and in northern California can mix up bloom times so they overlap, increasing chances for pollination to occur naturally.

Warmer temperatures inland and in Southern California keep flowering patterns more constant, and single trees may need pollination help to set good crops.

What to do: Bees, flies, and wasps help pollination ("production really picked up when I got a beehive," one Sunset reader wrote). So do nearby trees that bloom at the same time and have opposite bloom patterns. You might try grafting the limb of a pollenizing variety onto your tree (one that blooms at the same time as your variety but has opposite flowering patterns; a 'Bacon' onto a 'Hass', for example). Your county extension agent can suggest an appropriate choice. Small, finger-shaped fruits

Often called "cukes" or "cocktail avocados" (see photograph at left), these form after the embryo of a pollinated flower dies. Drying winds or sudden heat or cold spells can cause them, especially on 'Fuerte' and Mexican-type avocado trees.

Pick mature fingerling avocados and let them ripen. They're always seedless. Some readers peel and cut them in half, then serve them with a dip on top as an hors d'oeuvre. Brown spot on fruit bottoms (end spot)

Dark, rough spots and cracking appear on bottoms of mature fruits. Lack of soil moisture and very dry conditions can cause this. Some varieties, such as 'Bacon' and 'Zutano', are especially susceptible.

What to do: Water regularly but not too heavily. Pick mature fruits promptly; once symptoms appear, affected fruits won't keep much longer. Le aeI

Tips and margins of leaves turn brown and die; burned leaves drop prematurely. In severe cases, crop is reduced. Inadequate soil moisture, drying winds, or too much salt in the soil could cause this.

What to do: Make sure the tree is getting enough water. Use a soil sampling tube, soil auger, or shovel to check soil moisture at various depths. See page 121 for advice on how to water. Irrigate heavily--to 3 feet or more--about every fourth time to leach salts from the root zone. Yellow leaves

Young leaves that turn yellow while veins remain green show chlorosis, indicating an iron deficiency. Overall light green leaves may indicate a nitrogen deficiency or chronic water shortage.

What to do: For chlorosis, apply chelated iron to the root zone, following package directions. For nitrogen deficiency, fertilize as described on page 121. Sunburn

Yellow or black areas appear on the fruit or branches or both, then become dry and corky.

What to do: Paint exposed trunks with white water-base paint, or place cardboard shields around the trunks of young trees. Exposed limbs of mature trees need sun protection too, especially after leaf drop due to wind or frost. Paint upper surfaces white or wrap limbs with paper. Avocado root rot

No Sunset readers reported trees infected with avocado root rot, but it's a serious problem where it occurs.

Watch for these signs: On infected trees, leaves turn pale green and droop, foliage becomes sparse, and branches near the top of the tree die back. Small fibrous roots below the soil surface are either black and decaying or missing. The infected tree usually deteriorates over one or two seasons.

The cause is cinnamon fungus (Phytophtora cinnamomi), which is widely distributed in soils throughout Southern California, especially in neighborhoods that were once avocado groves. Poor drainage and excess soil moisture aggravate it.

What to do: There is no complete cure for root rot, and you can't easily rid the soil of the fungus. But you can reduce the chance of infection by careful watering. When you water, move the hose to different places around the root zone to avoid oversaturating any one area, and water only when dry soil indicates the need for it.

If you're buying an avocado tree, you might ask for one that's grafted to a rotresitant rootstock, such as 'Duke 7'.
COPYRIGHT 1985 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1985 Gale, Cengage Learning. All rights reserved.

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Date:Mar 1, 1985
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