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Garden Q&A

Smother Spider Mites With Oil Sprays

May 06, 1999|ROBERT SMAUS | TIMES GARDEN EDITOR

Question: For the last few years my tomatoes have been decimated by red spider mites. Do you have a solution?

--D.L., Ontario

Answer: I spoke to several experts, and they agreed that the best control for this warm-weather pest is a light oil spray, such as Pest Fighter Year-Round Spray Oil, Saf-T-Side or SunSpray. You'll find tomatoes listed on the label as approved for spraying, along with a recommended dilution.

The experts mentioned a few precautions: water beforehand so the tomatoes are not dry, spray early in the morning and do not spray when temperatures exceed 95 degrees or you may burn some leaves. These are minor annoyances when you consider that light oil sprays are not poisons but work by smothering the pests, so your tomatoes are perfectly safe to eat.

Next best would be the miticide Kelthane, which has been around for years. It is a poison but one with relatively low toxicity. The same precautions mentioned above apply.

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Q: I am interested in starting a vegetable garden. I have been offered several tons of composted horse manure. I was told that it is OK to plant vegetables in composted manure without any other amendments. Is this true?

--J.G., Agoura Hills

A: Even when it's been composted, and even when it's from a horse, straight manure is too salty to plant in. It can be toxic to plants.

Horse manure is better than steer manure but is still relatively low in its ability to hold moisture and nutrients and is high in salts. Horse manure is especially high in boron, although it may not have as much sodium as steer manure, according to soil scientist Garn Wallace at Wallace Laboratories in El Segundo.

Even when it's well-aged and composted and thoroughly leached by rains, horse manure can be used only sparingly. Wallace has found that 1 cubic yard tilled into every 1,000 square feet is about the maximum you can safely use.

If you want to pursue this further (since the manure is free), you should have a sample tested by a soil laboratory, and it can tell you how much you can use safely.

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Q: I just purchased a home with a large grapefruit tree that badly needs trimming. Can I cut it back severely?

--B.H.

A: Citrus specialist and Ventura County farm advisor Ben Faber tells me that commercial citrus are pruned regularly to keep the fruit within reach and to let light inside the tree so fruit forms in the interior as well as at the edges.

If trees get too big, they are either "scaffolded" to bring them down to size--say, 12 or 15 feet, down from 24 feet--or they might even be "stumped" to bring them way down. How low is too low to cut? Says Faber: "Well, you can't go below the graft," usually near ground level.

In other words, yes, you can severely prune citrus. The result may not be aesthetically pleasing, but pruning will eventually increase the size of the fruit and bring it back within your reach. Cut branches just above a side branch.

Be aware, however, that the tree "remembers how big it used to be," as Faber puts it, and will quickly send out masses of new growth. The more you remove, the more the tree will regrow and the longer it will take to make new fruit. You will need to prune all this new growth so that it is not too dense and so it is properly spaced throughout the tree.

Make sure the interior of the tree does not get too dark as growth returns. You will also have to prune yearly, because the tree will try to get back to its original size.

It's important to protect formerly shaded bark from sunburn. Paint the bark with a flat, white interior latex paint until the bark is once again partially shaded.

Generally, a pruning this severe is a bad idea on ornamental garden trees, as it can cause branches to be very weak and break, or will require constant pruning to keep the tree small. But the object of growing citrus is to get fruit (that you can reach).

Bob Smaus' garden coverage is published Thursdays in SoCal Living. Write to Robert Smaus, SoCal Living, Los Angeles Times, Times Mirror Square, Los Angeles, CA 90053; fax to (213) 237-4712; or e-mail robert.smaus@latimes.com.

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