Issue: November 26, 2005

Apple with fuzzy stuff on the trunk | Cut hollyhock stalks

Apple with fuzzy stuff on the trunk

Question:

My neighbor has an apple tree that is about 4 years old. It is doing well, producing apples, etc., but recently it started to develop white fuzz on the bark. When you touch the fuzz, it turns red. It almost looks like cotton down. Do you have any idea what it might be? Is it a fungus?

Monica L.

Valencia Co.

Answer:

You have described the wooly apple aphid. This is a small insect that feeds by sucking the sap from the tree's bark and roots. These aphids cover themselves with a waxy material that looks like wool or cotton fluff. Sometimes they transmit diseases by carrying the disease from one tree to another. In large numbers, they can cause considerable damage by weakening the tree, especially young trees. It is such a problem that some of the dwarfing rootstocks for apple trees were developed to be wooly apple aphid resistant.

You can treat the aphid with insecticides or milder treatments, such as insecticidal soap and horticultural oil, when the aphids are active on the bark and twigs. Unfortunately, this aphid has a trick not available to most other aphids it can go underground and live on the roots. Most leaf-feeding aphids don't do this, but this apple aphid can hide underground where the insecticides are not effective. When they attack the roots of non-resistant varieties, they cause gall development. These galls (swollen areas of the roots) interfere with movement of water and minerals from the roots to the above-ground portion of the tree. This injures the above-ground part of the tree. The best way to avoiding this problem is to plant trees grafted on wooly apple aphid resistant rootstocks or choose resistant varieties of apple.

When you see the aphids actively feeding on the trunk, treat the aphids with the control measures mentioned above (labeled for use on apples to control wooly apple aphid). Give the trees adequate water and nutrients to maintain the health of the tree to allow it to resist the aphids on the roots for as long as possible. Older trees may show only minimal damage from aphids feeding on their roots, but younger trees may be severely injured.

A very small parasitic wasp provides a natural means of controlling the wooly apple. This wasp is very sensitive to insecticides and will not be effective if the tree is treated with chemical insecticides. Look for evidence of this wasp (tan-colored, dead aphid mummies) to determine if insecticides should be avoided.

If the tree requires replacement, choose one grafted onto a wooly apple aphid resistant rootstock.

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Cut hollyhock stalks

Question:

I have a question about hollyhocks. When should I cut down my hollyhock stalks? Should I do anything special to them?

Answer:

You can cut the hollyhock stalks just above the ground after they have finished blooming, or you can wait until the seeds form. If you want them to reseed themselves, wait until the seed pods have matured and split open to free the seeds.

There is no reason to treat the cut. It will dry naturally and not be a problem. Hollyhocks are usually considered biennials (plants that die after flowering in their second growing season). However, in our climate, they may sprout from the base of the old stalk to grow and flower the next year. If you do not want them to regrow, you should dig the stalk.

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For more gardening information, visit the NMSU Extension publications World Wide Web site at http://www.cahe.nmsu.edu/pubs/_h.

Send your gardening questions to:
Yard and Garden, ATTN: Dr. Curtis Smith
NMSU Cooperative Extension Service
9301 Indian School Road, NE, Suite 112
Albuquerque, NM 87112

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.