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January 07, 2003
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DESERT BLOOM: Pine Blight

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If you've looked at trees around Las Vegas lately, you've probably noticed that quite a few pines are showing large brown or grey areas. And some just look flat-out dead. For many of these sickly trees, the problem's actually a disorder called 'Aleppo Pine Blight'.

Aleppo pines are generally desert-hardy. They can deal with heat, and once they've gotten established, they can tolerate freezing temperatures, as well. They grow pretty quickly, too, which makes them an attractive option for new homes. They tend to be prettier when they're young, and get scraggly as they with age. Like so many of us.

In the book 'Plants for dry climates' the authors say that Aleppos are probably the best pine for desert conditions.

But, there are times when even a hardy tree shows indications of suffering. This winter seems to be one of those times. This year, the problem looks more severe than it's been in recent memory. Usually, the blight shows up on younger trees, but now it's appearing on young and older trees alike.

If you've noticed a pine with a problem, take a closer look to see if it's Aleppo Pine Blight. If it is, the difficulty probably started to show up in the late fall, although in some areas it can appear in spring. You'll see dead needles on a branch. If the disorder isn't too severe, the growing tips will still be green. This is hopeful, because a green tip may actually come back and the limb will survive. It won't fill in blank areas, but the branch will live. If it's an advanced case, the entire branch, or branches, will die. Dead needles will stay on the plant for months.

If the tree gets severely weakened by this disorder, then other problems will follow. Opportunistic organisms, like insects, and fungi, and bacteria - of course they're going to move into a susceptible tree and make a bad situation worse.

The cause of Aleppo Pine Blight isn't any insect or microorganism, so there isn't any pesticide that'll take care of the problem. In fact, it doesn't seem to have any single cause. Mostly, this disorder is a result of how the tree was first planted, where it was planted, and how it's been treated since being planted.

It's a sad story, but a true one, that if a plant hasn't received the proper watering and nutrition, it's going to suffer. This is just common sense. Aleppo Pine Blight seems to be a remarkably clear case, and the problem just gets made worse when we have high heat, bright light and drought. Don't those conditions sound familiar?

So what exactly causes it?

Probably one big reason is - water. When the air temperature is high, and the wind is blowing, the tree has to work hard to pull water from the soil.

If there's not enough water, then the plant dries out. Too much water, where there's poor drainage, and the roots rot. If the roots aren't healthy, then the plant doesn't get the water and nutrients it needs to survive.

When the soil gets too warm, then it dries out quickly, and the plant can't obtain water.

Now, this might be interesting, but the big question: is what do you do - prevent it? Cure it? Prevention's always the best bet.

First, plant the tree right. Whenever you put a plant in the ground, it's important to make sure that water will drain out of the hole. Don't put gravel in the bottom of the hole, since that'll block drainage. And when you irrigate an Aleppo, make sure that you water it deeply. The water should go at least three feet deep. It's more important that the plant get more water less often, as long as the soil isn't compacted, or hardpan, or full of caliche.

Once it's in the ground, pay attention to fertilization. If the tree's planted in a lawn, you might be tempted to think that the lawn fertilizer will serve both purposes, but grass is very efficient at taking up all the nutrients it can get. The tree needs its own.

But - you don't want to overfertilize these trees, since that actually weakens them. And only fertilize when there's enough water. If water isn't available, fertilizing actually stresses them even more. When you apply plant food, use a quick release one that has fairly low nitrogen, less than 20%.

At Cooperative Extension we recommend that in March you use an eighth of a cup of low analysis fertilizer for each inch of tree diameter. Do the same in May. That's it. Don't fertilize in the fall.

One way to prevent soil temperatures from getting too high is to put a few inches of bark mulch or something like it around the root area. But keep the mulch away from the trunk of the tree itself, since that can cause another set of problems.

For KNPR's Desert Bloom, this is Dr Angela O'Callaghan of the University of Nevada Cooperative Extension. Take care of yourself, and your plants.

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