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Citrus trees' alternate fruit bearing remains a phenomenon.

Byline: JOSHUA SISKIN

Q. I have a Valencia orange tree, I believe it's a dwarf

(9 feet tall) and is about 20 years old. My problem is fruiting. Year before last the tree was full of normal sized oranges, last year I only had 15 to 20 very big oranges and this year I've probably a couple of hundred but they are only the size of limes. They normally ripen around Christmas, so I don't know how they taste yet. Any ideas?

A. True dwarf citrus are grafted onto 'Flying Dragon' rootstocks. They usually do not exceed 7 feet in height, so you probably have a semi-dwarf tree. If you plan on acquiring a dwarf citrus in the future, verify that the rootstock is 'Flying Dragon' before purchase. Fruit of dwarf and semi-dwarf Valencias should be the same size as that found on standard trees.

Orange trees, like most citrus, tend to exhibit alternate bearing. This means that they produce heavily one year and lightly the next. No one really knows what causes this phenomenon, although there is speculation that depletion of carbohydrates during a heavy crop year leads to fewer fruit the next. Of course, if you thin your orange tree, the remaining fruit should get larger. It could also be that the hot spells this summer stressed your tree and have delayed fruit development. It might ripen later than usual.

In truth, alternate or biennial bearing is a phenomenon that is common to nearly all fruit and nut trees, to one degree or another. Some trees, such as pistachio, walnut and pecan, are extreme alternate bearers, producing an abundance of nuts one year, and virtually none the next. Why is this so? The answer could be related to the enormous amount of resources utilized in making the shells that cover the nuts.

The only way to mitigate alternate bearing in citrus is to remove fruit as soon as it ripens.

One of the advantanges of growing citrus is that you can store it on the tree for several months after it is ready to eat.

Research has shown, however, that removal of citrus fruit as soon as is ripens allows for a larger crop the following year. By contrast, storing fruit on the tree may significantly decrease crop size the next year.

Q. My lime tree has had leaf miner disease the past four years. I have sprayed it with Spinosad, but the new leaves still curl from the pest.

I don't know of another remedy.

I am willing to spray it again but don't know if I should with fruit on the tree.

Would it be toxic to us if we eat the fruit that has been sprayed? If so, what other remedies could you suggest? It seems that there are always limes in various stages of growth, so I can't wait until we've picked all the fruit.

A. Spinosad is an eco-friendly product that, while affective if used properly, usually requires repeat applications. As many as six applications per season are advised since the product is photosensitive and breaks down in sunlight within a week of application. Always target flushes of new growth since that is where leafminer moths lay their eggs. Follow application directions carefully and remove all leaf-miner infested leaves. Spinosad products are non-toxic to most vegetables and fruits, but you should always check the label before application. An advantage of Spinosad is that it is harmless to beneficial insects such as ladybugs, lacewings and parasitic wasps.

Spinosad consists of metabolites produced by friendly aerobic bacteria known as actinomycetes. If you keep a compost pile, you will undoubtedly have seen actinomycetes. They appear as thick white strands encountered when turning over the pile.

About 20 years ago, a vacationing scientist discovered a new species of actinomycetes growing in the soil of an abandoned rum distillery on the Caribbean island of St.Thomas. Since then, this exotic species of bacteria has yet to be found anywhere else on Earth. Meanwhile, though, the St. Thomas bacteria has been cultured on a commercial scale. Two of its metabolic by-products are mixed together and marketed as Spinosad.

Spinosad is effective primarily on caterpillars. When sprayed on the new growth of a plant infested with caterpillar pests, such as citrus leafminers or cabbage loopers, it should cause the pests' death within several days. However, since the pests are in various stages of development, repeat applications are usually needed so that the larvae or caterpillars are continually targeted as they hatch from the eggs.

Citrus leafminers are tiny caterpillars, later becoming moths, that burrow through citrus leaves - creating squiggly patterns. Cabbage loopers are those thin green caterpillars that lay their eggs on fall and winter crops in the cabbage family, including broccoli, cauliflower and Brussels sprouts.

- Dave Hadley

West Los Angeles - Madelyne Barnett

Santa Clarita

Tip of the Week

Nick Kurek, who lives in Granada Hills, writes: "I have done very well with orchid trees (Bauhinia) for many, many years.

They look great and aren't messy like a jacaranda or mulberry. I've also seen them on some of the streets in North Hollywood. After growing about 15 or 20 years, the high winds we get here split the trees apart. Splitting may be because they really would like to be big bushes rather than trees. I have planted a new one next to the old one so that we'll be ready when the old one splits. We get lots of seedlings every year when the pods open and drop their large seeds. The seeds are hardy and germinate wherever they fall."

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(1 -- 2 -- color) If you thin your orange tree, it should produce larger fruit. Eco-friendly Spinosad kills caterpillars, but is nontoxic to most plants and beneficial insects such as ladybugs.
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Title Annotation:HOME+GARDEN
Publication:Daily News (Los Angeles, CA)
Date:Dec 5, 2009
Words:966
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