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Sunday, June 22, 2014

Olive Tree Dropping Leaves, Leaves Yellowing

Q. I have an olive tree that is approximately 20 years old.  It loses leaves year round and in excess. Some leaves are yellow but most are green. It is planted in lawn. It is watered twice a day for a total of 10 minutes. What can I do to stop this excessive leaf loss?

A. Olive trees are evergreen so they will constantly lose leaves during the year. The heaviest leaf fall should be in the spring during new growth or during the winter if there is a hard freeze.
Not the readers olive tree.
            These trees are tremendously versatile and can withstand droughty conditions as well as fairly wet conditions. They can handle a wide range of soil types.
            They handle abusive pruning techniques. That is the main reason they are used here.
They are resilient and respond quickly after being damaged, either by humans or the environment, as long as they get enough water. Being planted in lawn, I would assume they are getting plenty of water.
            If the canopy of the tree is beginning to thin, it is because there is not enough new growth to replace the leaf drop. If the lawn is fescue in good condition and well-managed, it should be receiving plenty of water. If the lawn is bermudagrass, then that is a different story.
            Fescue lawns require frequent irrigations because of their shallow roots compared to trees. Olive trees are deeper rooted and require water less often but with higher volumes so the entire root system is irrigated. Growing in bermudagrass they might require supplemental water besides lawn irrigation.
root knot nematode on tree roots. this is mulberry but it will be similar.
            Olive trees growing in lawns usually develop roots closer to the soil surface than without grass because of the shallow lawn irrigations. I would not think leaf drop would be a big problem unless your soils stay wet between irrigations.
            Normally soils that stay wet are described as heavier soils and have a high percentage of clay. This should not be a problem in sandier soils.
            Olive trees have few pest problems but one that can cause excessive leaf drop and stunting of growth are nematodes. The usual nematode is the root knot nematode, the same one that damages many vegetables, fruit trees, ornamental trees and shrubs.
            The only way to find out if this little guy has invaded the roots of your tree is to dig down through the grass, find some olive roots, and inspect them for little knots or round balls growing along the length of one or two-year-old roots.
            Even if you find them there, there is nothing really you can do to get rid of them. The recommendation would be to fertilize and water the tree separately from the lawn to encourage more growth. More growth helps to cancel out the stunting effects from the nematodes.
            Have someone knowledgeable about pruning do some selective limb removal throughout the tree canopy. By removing some of the unnecessary limbs, more growth will be forced into the remaining limbs and will provide better light penetration into the canopy.

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