ELM LEAF BEETLES

by Curtis Smith, Ph.D.  

Q. I am in Las Vegas on a piece of property surrounded by about 10 elm trees, 1 pine, 3 maple and 2 chinquapin oaks. Our elms are under siege! First, we got these little beetles about 3/8" long with yellow and green stripes and yellow insides (yes, we squish them when we can!), then we got these guys that look like ladybug larvae - 4 legs up front, soft body, lengthwise stripes of black and yellowish-green. Next we got little yellow pupal sacks with yellow insides again (they got washed out of the trees in one horrendous rain I think). Now we're back to the beetles again. The leaves on our trees are eaten down to the veins - all of the green is gone! It doesn't seem to matter whether the trees have been radically pruned in the last few years or are all old growth, and it doesn't look like other elm trees in this town are getting devastated like ours. A sideline - we can't even sit outside without beetles dropping into our coffee, food, etc. HELP! I've tried leaving messages with a lot of people. I'm afraid that without the leaves, we will lose all of our 70-year-old elms, and the trees are a major part of the charm of this property. As such, we have been planting other trees (fruit, honey locust, etc.) amongst the elms, but.... Do you have any suggestions?

Linda K.
Las Vegas, NM

A. You have described elm leaf beetles in their adult (beetle) phase, as well as juvenile and pupal stages. They make elms look bad but rarely kill the trees outright unless the trees are unhealthy for other reasons (such as last year's drought). There are several approaches to try - several chemical sprays are effective, also a biological insecticidal spray of Bacillus thuringiensis var. San Diego can be helpful. Since the trees are pretty well defoliated, you may not have much success this year. The insects will probably return next year (to neighboring trees as well).

They may try to overwinter in your attic (or the void between ceiling and roof in flat roofed houses). In late winter as their hiding place warms, they may begin emerging and accidentally enter you home - the vacuum is the best means of managing them at this time. Remember to empty the vacuum bag outside - don't just put the vacuum in the closet after vacuuming.

Next year when you notice their return, the sprays may be employed to control the first generation in May. As the larvae crawl down the trunk to pupate at the base of the tree, they may often be trapped in burlap wrapped around the trunk. This may then be removed and burned. If you choose to use a spray product, you will probably need to hire someone with the equipment to reach the top of the trees. Remember, however, that elms are really tough trees and will often survive the beetles for years.

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Q. I have a friend here in DeBaca County who has purchased some EUROPS Daisy and Hibiscus plants for her flower beds. She would like to know if these can be left out all year long or do they need to be brought in the wintertime? Thanks so much for you help.

Lisa
Ft. Sumner

A. EUROPS daisies are tough in many ways but don't tolerate freezing, so they won't survive outdoors in your county. Tropical hibiscus will freeze if left out over the winter, but a few relatives of hibiscus are hardy. Of the real hibiscus, the Hibiscus moscheutos cultivarsare hardy in much of New Mexico. This hibiscus has very large blossoms, and they die back to the ground after freezing in the fall but return from their roots in the spring. They should survive in DeBaca County, especially if the roots are covered with straw mulch after the tops freeze down or if they are grown in a sheltered area that doesn't freeze too deeply. They are listed to be hardy to Zone 5(USDA hardiness zone system). Some irrigation will be required (once a month in most winters).

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Q. Enclosed is a sample of a plant that has caused some controversy. Some people think that it is illegal. I know it’s not but can’t remember its name. What is this plant with a leaf that looks a little like marijuana?

Anonymous

A. The sample you sent, leaves with the suspicious look but strong smell, blue flowers, and seeds in a panicle is called the lilac chaste-tree, or vitex. Its scientific name is Vitex Agnus-castus. It is not illegal, it is not narcotic, but will probably give someone a terrible headache if they tried to smoke it. It is well-adapted to arid conditions (with limited supplemental watering). The flowers are attractive and produced over a long period in the early summer. The flowers can range from blue to pinkish to almost white. The plant can produce a small tree if pruned into tree form or can be allowed to grow as a shrub.

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Q. I have a willow tree that seems to be "raining" down what feels like moisture in hot weather. Is this common? What is the tree doing? If you look at the tree with the sun behind it, you can see the particles falling.

Pat J.
via internet

A. This is a common occurrence in the summer. The most likely cause is an infestation of aphids in the leaves of the tree. The aphids feed on the liquids in the leaf of the tree. This “sap” is high in sugar and low in protein, so a large quantity of sap must be consumed. Surplus water and sugar (in the form of a syrupy substance called honeydew) is excreted by the aphids. This is the material “raining” down. The windshield of a car parked under the tree will soon be covered with little sticky drops of honeydew. Some people complain of damage to the paint on cars as a result of this.

Aphids may do relatively little damage to an ornamental shade tree, so they are more of a nuisance than a danger. If the tree is small enough, you may be able to manage the infestation by spraying a strong jet of water into the tree. This washes the aphids from the leaves of the tree, stopping them from feeding until some of them find their way back into the tree’s leaves (many will die, but many will return). When they are not feeding on the leaves, the raining of honeydew will also cease.

If you think more drastic measures are required, there are insecticides that may be used to effectively control aphids. Check the labels of insecticides at local nurseries for a product available in your area that can be used for management of aphids.

Because you must apply this material to the leaves at the top of the tree as well as lower leaves, it is difficult for a homeowner to spray a large tree. In the case of such a tree, it would be wise to hire a licensed pesticide professional.

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Q. Can I grow a tree from planting cherry and peach pits? How can it be done?

A. The cherry, like all temperate fruit trees, requires a “chilling” period or winter to prepare the seed for growth. The hard shell of the pit does not need to be removed, but the seed should be placed in moist vermiculite or peat moss and stored in the refrigerator for six to eight weeks before planting. Do not let the seed dry before beginning this treatment.

Once the seed has been treated by chilling, it may be planted - outside if the weather is already cool, or in a pot in a window or greenhouse. If planted outside, it will experience further chilling and begin growing in the spring. If planted in a pot, it will begin growing in a few weeks.

Plant several seeds because it is possible that only a few will grow. In about seven to ten years you may begin eating cherries from your tree. If you graft a part of your seedling onto a mature tree, you can cut several years from the wait. The fruit from your seedling may be tasty, or it may be bitter. Like apples and peaches, this is a plant that will not produce a seedling exactly like the parent.

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Q. I have a beautiful Chitalpa, which keeps losing its leaves in great masses. According to the local agricultural extension office, it is not a matter of a disease but rather of cultural practices. I been told the soil might be too alkaline or that I water too much because I planted some day lilies under the tree. What happens is that the leaves start out healthy, then develop yellowish spots, the veins start turning brown, spots like brown spots on roses develop and the leaves become fairly dry and drop off. I would appreciate your advice very much.

Christian T.
via internet

A. This is a problem that has been challenging us as more and more people plant Chitalpa trees. These symptoms develop each summer here in New Mexico creating a mid-summer leaf drop. The trees often refoliate following the onset of monsoon rains and cooling temperatures. However, the leaves usually develop symptoms and drop again once the monsoon rains end. However, as you will see in the information below, supplemental irrigation does not seem to prevent the problem.

Samples of Chitalpa leaves with symptoms that you described have been sent each year to Dr. Natalie Goldberg, NMSU Extension Plant Pathologist, who has looked for a causal organism. The following paragraph is her response to these samples:

“No plant pathogenic microorganisms were isolated from the sample submitted which I am also certain is not Catalpa, but the hybrid Chitalpa, a cross between Catalpa and Desert Willow. I have had a number of samples of this plant over the past few years and I am getting more and more as the tree is being used more in landscapes. I have two at my house and, to be honest, I would not plant them again nor do I recommend them without some reservations. The problems I see are yellow to brown spots on the leaves, leaf blight, wilt and premature defoliation. Trees may exhibit some or all of these symptoms. The symptoms occur on trees that are well watered as well as those that do not receive much water. The symptoms seem to occur in summer when the days really start heating up. Several branches on my trees wilted and defoliated in July of last year. I pruned out the dead limbs and the tree leafed out fine in the spring, but I am just waiting for it to happen again (since it's happened each of the last three years). We have never isolated any pathogen from the samples submitted. I really feel this is a response to environmental stress, but neither increasing or decreasing water seems to help. However, John White, Dona Ana County Horticulture Agent, and I both feel that this hybrid requires watering along the lines of its relative, the Catalpa parent, rather than the Desert Willow parent. Your question about acidifier is a good one. I have not tried this, but it just might help - used at a labeled rate and applied as directed, I'm pretty certain it wouldn't hurt.”

Dr. Goldberg stated that she has observed some trees that look good and in our discussion the possibility of pH being a factor was considered. We hypothesized that acidification might help. So, as you mentioned, the alkalinity of the soil may be a factor.

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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 a an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. Dr. Smith and Dr. George Dickerson host Southwest Yard & Garden, a weekly program for gardeners in the Southwest. It airs on KRWG in Las Cruces Monday-Friday at 6:30 p.m., Thursdays at 1 p.m. and Saturdays at 11:30 a.m.; on KENW in Portales on Saturdays at 10 a.m.; and on KNME in Albuquerque on Saturdays at noon and Fridays at 2:30 p.m.

Questions or Comments? Email editor@nmjournal.com