Apple tree turning brown in August

I have two dwarf Jonathan apple trees with leaves that are turning brown. They were sprayed once in the spring and they have a drip irrigation system. One tree has a few apples. The other has no apples.

Is there anything I can have done to save these trees?

S.J.
Rio Rancho

Answer:

If you had sprayed recently I would suspect chemical burn. However, since it was so long ago, that probably is not the cause of leaf browning on your apple trees.

The irrigation system could be a cause of problems. If the drip emitters have clogged, the tree may not be receiving sufficient water. Check to see that the emitters are providing the expected amount of water each time you irrigate. Are you providing enough water each time? Remember that drip irrigation provides water in gallons per hour, not gallons per minute. You will need to run the system longer than a sprinkler system. Do you have enough emitters to moisten a rather large area at the dripline and outward? (I can't tell you how large an area because the quantity of water needed will depend on the size of the tree.) Irrigation that provides sufficient water in the spring may not be enough in the heat of the summer. Do you irrigate often enough? In the sandy soils of much of Rio Rancho, you should irrigate once every 10 days. If the soil is silt or clay or if there is a thick layer of mulch over the roots, then irrigate once every 14 days. Also, be sure the water is supplied where the actively-absorbing roots are located. This is below the drip line and outward, not at the base of the trunk.

Finally, if none of these suggestions address your specific problem, look for spider mites. They often attack apple trees (and other plants) at this time of the year. You will notice them as a covering of lint and dust on the leaves and twigs of your apple tree. If you see these signs of spider mites, you can do something to help your tree. There are miticides (mites are not insects, so you should use a miticide) that can be sprayed onto the tree.� Be sure to follow all directions on the label when applying any chemical. Watch the weather forecast and if possible apply the chemical on a cool, cloudy and wind-free day.

If you prefer not to use a miticide, you can also just wash the plant with a strong jet of water several times a week. This is effective in washing the spider mites and their protective webbing (the lint-like material) from the tree. This is especially easy to do with dwarf trees and other small trees.

The mites will return and new mite eggs will hatch, so repeated treatments are necessary whether you are washing the tree or applying a miticide.

If the problem was spider mites, your trees are probably not dead. The mites will have damaged the leaves and the tree will defoliate early, but they should grow again next year. They may be weaker than they would have been otherwise, but they should recover.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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