Control of Crapemyrtle Scale

New treatment recommendations help combat crapemyrtle scale

Bill Sevier: Ask a Master Gardener

Saturday, July 30, 2016

Q: I have what I have been told is crape myrtle scale. How do I get rid of it? Lee, Tulsa.

A: We addressed the crape myrtle bark scale in this column last year, but some of the recommendations made by OSU regarding control have changed. The current recommendations come from Eric Rebek, state extension specialist for horticultural insects.

This insect is new to our area but is fairly prevalent. It came to the U.S. from Asia and first appeared in North-central Texas in 2004. It has subsequently spread northward into the Tulsa area from nursery stock and other sources of imported crape myrtles. This is the reason one should always inspect nursery crape myrtles for scale insect before purchase.

Like other scales, the life cycle begins with either the female scale or eggs overwintering on the crape myrtle under loose bark. When the eggs hatch, small mobile “crawlers” are produced, which migrate on the plant and may be spread to other crape myrtles by wind or birds. There may be two to three generations produced per year depending on the temperatures.

Once the female is fully developed, she mates and attaches to the stems and trunks of the crape myrtle, where she remains fixed and lays eggs for the next generation. She dies shortly thereafter, but the eggs survive under her covering until they hatch.

As the scales feed, they release a liquid called “honeydew.” This is similar to the behavior of aphids. The sugars in honeydew may support the growth of a fungus called “sooty mold.” This overgrowth produces large black patches on the bark of the crape myrtle. The mold is unsightly but is not significant in terms of the plant’s health.

This pest is easy to identify because it is the only scale insect to infest crape myrtles. The adult female is usually about 2 millimeters long and has a distinctive gray-white felt-like covering. When one of the females is crushed, a pink blood-like fluid is released.

The current recommendations for control are removal by hand and the use of winter dormant oils. Scrub down the trunk of the crape myrtle with a mild solution of dish-washing soap and water using a long-handled brush to remove the scale and sooty mold. This is effective.

Another treatment recommended is to spray the trunks of the trees with dormant oil in late winter. Winter dormant oil spray is a stronger concentration of a petroleum-based oil that is used in summer. Neem oil, while in other applications, will not be effective for this scale in winter.

Previously, systemic insecticides in the neonicotinoid family were recommended. These chemicals enter into the circulation of plants and kill the pest when they feed on the sap. They have been shown to be effective against crape myrtle bark scale but are no longer recommended. The reason for the change in policy is the concern that these insecticides enter the blossoms of crape myrtles and would be harmful to bees and other pollinating insects.

Garden tips

§  Divide and replant crowded hybrid iris (bearded iris) when dormant — July, August and into September. When planting, take care not to plant the rhizomes too deeply. Cover them with an inch of soil or less. Do not mulch iris.

§  Water all plants deeply and early in the morning. Most plants need approximately 1 to 2 inches of water per week. Rather than watering daily, water less often and more deeply.

§  Some trees such as sycamores and river birches lose large numbers of leaves in the heat of summer. Trees do this to reduce water loss from their leaves. It is a coping action by the tree; it is not dying.

Spider Mite Control on Tomatoes

Spider mites are difficult to control, problem in summer

Brian Jervis: Ask a Master Gardener

Saturday, July 23, 2016

Q: The leaves on my tomatoes are yellowing and dying. What should I do? R.R., Owasso

A: Far and away the most common cause of yellowing of tomato leaves this time of year is a spider mite infestation. Most Oklahoma gardeners will have some mites on tomatoes in the heat of the summer.

Adult mites are about 1/50th of an inch, and one needs a hand lens to see them. If you tap a leaf over a piece of white paper, sometimes they can be seen as tiny moving dots. With dense populations, some webbing of leaves may be seen as well.

There are many varieties of mites; tomatoes usually have the two-spotted mite. They are greenish and thrive when it is hot, dry and dusty. They can have a new generation every 5-6 days, and it doesn’t take long for a population to explode involving the whole plant.

Mites feed on a wide variety of vegetables, ornamentals, trees and houseplants. They feed on the underside of leaves where they suck out sap, producing yellow dots that develop into a bronzing of the leaves as if sandblasted. Eventually, leaves turn totally yellow, curl up and die.

Unfortunately, the diagnosis is the easy part. Control is difficult. Spider mites are arachnids, in the same family as spiders and ticks. Because they are arachnids and not insects, they do not respond well to standard insecticides.

A sharp stream of water will remove a significant number of mites, but beyond that, organic pesticides are the most effective. Man-made, nonorganic pesticides are not recommended because they kill the good insects helping to keep the mites under control.

Both of the organic pesticides — horticultural soaps and horticultural oils — are only effective if sprayed on mites directly. They are also the safest for your children, pets and the good insects. Because mites are commonly on the backside of leaves, they must be applied to both sides of leaves. Both preparations will need to be applied regularly, according to the labeled directions.

Horticultural oils come in two varieties — petroleum based, such as Sunspray, and others extracted from plant material. One of the best is neem oil, which is made from the seeds of the neem tree.

If you cannot control the mites with water, soap and oil, OSU suggests a trial of a short acting organic insecticide — pyrethrin — as long as you accept that it could harm some beneficial insects. It is available in several brands, some mixed with soaps and oils.

So the best strategy for homeowners is to monitor plants closely and to use what tools are available as early as possible. These tools may offer some control but are not likely to completely eliminate mites.

These measures may be unsuccessful. If spider mites cannot be controlled, it is best to pull up the plant and all its parts and send it to the landfill. You can then start with new plantings, looking toward a fall vegetable crop.

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For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.

Garden tips

• Make fall vegetable garden plantings in late July. Fact Sheet HLA-6009, “Fall Gardening,” gives planting recommendations for each vegetable as to when to plant and times to harvest. It also discusses strategies for dealing with the heat when planting a fall vegetable garden.

• Fescue lawns need 2 inches of water per week, Bermuda and Zoysia need 1 inch. Fescue usually will not survive the average summer without supplemental watering.

• Water plants deeply and early in the morning. Most plants need approximately 1-2½ inches of water per week.

Hot Weather Effects on Tomato Production

Tomato production sensitive to heat, humidity

Bill Sevier: Ask a Master Gardener

Saturday, July 16, 2016

Q: My tomatoes have stopped producing; they look OK and have a few blossoms but no tomatoes. What could cause this? Brad, Tulsa

A: Tomatoes often have diseases, pests or problems related to the environment that affects their production. The main causes of interruption of tomato production this time of year is hot temperatures.

Problems with disease and insect pests are usually evident on inspection of the leaves. Therefore, if the leaves are green and appear healthy, it is likely related to environmental factors. The lack of blossoms or the sudden loss of developing blossoms in summer is usually due to heat, water and humidity issues.

Tomatoes are self-pollinating and are dependent on wind to move the pollen from male to female blossom structures, which results in fertilization and development of fruit. If the pollen is not fertile, the flower withers and falls from the plant, called “blossom drop.” One of the main causes of blossom drop in summer is faulty pollination and is the reason tomato production decreases this time of year.

Pollen is finicky, and its fertility is sensitive to temperature and humidity. Evening temperatures out of the range of 55 to 70 degrees or persistent temperatures topping 90 degrees (especially with hot winds) during the day will prevent successful pollination in most tomato plants. This is the major cause of decreased summertime blossom and fruit production.

Tomato plants may also be stressed to extremes of heat, hot wind and water issues. This may cause the whole plant to go into survival mode. It will then grow leaves, which it needs to survive, at the expense of producing blossoms and fruit.

Two other situations reducing tomato productivity at any time of the growing season are excessive nitrogen fertilization and too much shade. Excess nitrogen causes the plant to grow tall with dark green leaves and few tomatoes. When there is not enough sunlight, the plants produce leaves to gather sunlight and not fruit. Tomatoes need full sunlight for best production

The good news is that in the early fall, as it cools, the pollen becomes more fertile, plants healthier and tomato production begins again. Tomatoes are often planted by some gardeners in mid-summer for a fall crop. Some of the tastiest tomatoes may be found in the fall production.

Another tomato heat-related fact is that when temperatures are over 85 degrees most tomatoes are unable to develop red coloring. Lycopene and carotene needed for red color development are not produced at these temperatures. However, mature-sized green-pink tomatoes will ripen and become red indoors, at room temperature and with no sunlight.

To reduce the likelihood of blossom drop, select tomato cultivars that demonstrate more heat tolerance. Examples are Traveler 76, Brandywine and Porter Improved (cherry tomato) suggested by OSU Extension. There are others.

Go to the tomato section of the Master Gardener website and review the four OSU fact sheets on growing and dealing with problems of tomatoes.

Garden tips

§  When watering your lawn, ornamentals or vegetables, always do so in the morning if possible. If watered in the evening, plants will go into the night still being moist. Most disease-causing organisms need moisture, and because they grow best at night, leaving leaves wet in the evening will promote many plant diseases.

§  Bulb onions are ready to harvest when the tops fall over. They should be removed and allowed to dry in a well-ventilated, shaded area. After the tops are completely dry, they may be stored in a cool, dry area.

§  For detailed information from OSU on mosquitoes and Zika virus in Oklahoma, do an internet search for Oklahoma State and “Pest e-alert.” This should find the document.

Wilting Plants and Fall Webworm Alert

Wilting in plants has many causes

Brian Jervis: Ask a Master Gardener

Saturday, July 9, 2016

Q: What would cause a shrub in my yard to wilt? I am watering it a lot, and it is still wilted. Carl, Tulsa.

A: Most gardeners associate wilted leaves with too little water and often that is the case. However, there are other causes of wilting for plants in the landscape and in houseplants.

To understand wilting, one must understand a plant’s circulation. Absorption of water in soil depends on having an adequate number of tiny hair-like roots. These absorb water, as well as nutrients and oxygen. After absorption, water is transported to the leaves by the cambium, a layer of tissue just under the bark. In the leaves, the pressure of water supports the leaf structure. Any interruption of the flow of water to the leaves results in loss of structural support, resulting in wilting.

It is not often recognized that too much water can produce the same effect as seen in a drought. Excessive water forces oxygen from the soil, which results in suffocation of roots which, oddly enough, prevents water absorption. Initially, this results in wilting, followed by yellowing of leaves and, if prolonged, death of the plant.

Protracted wet soil may be associated not only with changes described above, but also a higher incidence of root fungal diseases, diseases which love wet soil. These diseases, collectively called “root rot,” can kill the plant or lead to poor performance in the future.

Other conditions interrupting a plant’s circulation may produce wilting. These include temperature-related problems, either too hot or too cold. Hot weather causes water loss to exceed the ability of the plant to keep up with demand. Hot and cold weather may also damage roots in some plants. Mulch will help prevent this.

Excessive salt in the root zone, such as is seen from overdoing fertilization or from de-icers in winter, it will damage roots and cause wilt. Salt accumulation from fertilizers in houseplants is also a common cause of wilting. Periodic flushing of the potting soil with water will prevent this.

In addition, any condition that interrupts the flow of water in the above ground portion of plants will result in wilting. This includes circling roots, which strangle the plants, grass trimmer damage and string and wire bindings used to stake a tree or hold a root ball together.

One type of wilting not mentioned and that is reversible and insignificant is the wilting occurring in evergreen plants when it is cold. This is a way some plants have of protecting themselves from the cold, and it reverses with warming.

All of the above may cause wilting with or without progressive damage to plants. It is important then to try to determine what the problem is before launching into a vigorous watering program.

Master Gardeners can help you sort out the problem. Call their office helpline at 918-746-3701 or bring samples of plants into the office at the OSU Extension Center at gate #6 at the Tulsa Fairgrounds, 4116 E. 15th St.

Webworm alert

We are beginning to see large numbers of fall webworm nests in pecan, persimmon and occasionally redbud and other trees. These pests, as the name suggests, are usually more prevalent in the later part of summer and into the fall. This year’s early outbreak has prompted Eric Rebek, entomologist at OSU, to issue a “Pest e-alert” document, accessible online.

We had the same problem last year, and Rebek feels the large numbers of webs both years is related to a mild winter and wet spring.

These caterpillars build dense web nests around leaves on the ends of tree limbs. They devour the leaves within the webs and after leaves are eaten, expand locally to include new leaves. Even with large numbers of webs in pecans, the pests usually do not damage mature trees (in pecan orchards nut production may suffer). Although they are unattractive, mature trees will survive, but heavy infestations may injure or kill smaller recently planted trees.

Control is difficult. There is no effective way to predict or prevent the pests. Even though there are large numbers of parasites and predators, they are unable to control large outbreaks.

On smaller trees, the webs may be pruned out or removed by hand. Insecticides are usually not warranted. If a synthetic general purpose insecticide is used, it needs to be sprayed with enough force to enter the web. However, this is not practical or safe, especially in an urban setting. An alternative is to use one of two relatively safe organic insecticides — Bacillus thuringiensis (Bt) or spinosad. They are sold under several different brand names. These are sprayed on leaves next to the webs and will be consumed as the webs expand

Contact the OSU Tulsa Master Gardeners for more recommendations. Call 918-746-3701 from 9 a.m. to 4 p.m. Monday-Friday.

Controlling Nutsedge Weeds in Lawns

Nutsedge is tough weed to control

Bill Sevier: Ask a Master Gardener | Posted:

Saturday, July 2, 2016 12:00 am

Q: There is what looks to be nutgrass growing in my lawn. It is spreading; what can I do? A.K., Tulsa

A: Nutgrass is a common name for the troublesome nutsedge weeds. These weeds are sedges, not grasses nor are they broadleaved weeds. Therefore, the usual “weed killers” on the garden center shelves will not be effective herbicides.

Many sedges are troublesome in agriculture and for homeowners. Weed experts list yellow and purple nutsedge in the top 10 of the most difficult weeds to control. We have mostly yellow nutsedge; purple grows farther south. Another sedge called green kyllinga has also become a problem in lawns in recent years.

Yellow nutsedge is a vigorous grower. It grows twice as fast as turfgrass and can be seen towering above turfgrass a couple of days after mowing. The sedge is found in clusters. On inspection, the stems look like grasses but are different in that the stems are solid, triangular and have edges. This is behind the adage “sedges have edges.”

Nutsedge reproduces in two ways — from seeds and by underground “nutlets.” Nutlets are produced in abundance by roots called rhizomes. They are the source of the common name “nutgrass.” The nutlets may survive for years in soil, and each can give rise to a new plant when growing conditions are favorable. Spread of nutgrass to your lawn is often related to imported topsoil, mulch or contaminated nursery plants.

Control of nutsedge includes cultural and herbicidal approaches. Pulling the sedge will not remove the rhizomes or nutlets but can be effective if the plant is removed while young and before nutlets form. Because nutsedge thrives in moist soil, reducing the moisture in the area will help but will not eliminate established plants.

Several effective herbicides are available for yellow nutsedge. Some of the brand and chemical names are Basagran (bentazon), Image (imazaquin), SedgeHammer (halosulfuron) and Ortho Nutsedge Killer (sulfentrazone). These chemicals are safe to use on all of our turfgrasses, with the exception of Image. It cannot be used on fescue lawns.

Of these herbicides, SedgeHammer is a little more effective and also the most expensive. However, all of them are beneficial and are recommended.

These herbicides should be used in summer when nutsedge is actively growing, and most will need to be used twice during the summer, according to the labeled directions. Nutgrass has a waxy coat, so some of these chemicals will need a commonly available additive called “spreader sticker,” a soap-like solution that helps it stick to the plant.

These chemicals cannot be used among flowers or in the vegetable garden. For these areas, it’s either hand-pulling, digging or, if the weed is isolated in spots, the careful use of glyphosate, found in Roundup and other brands. Glyphosate does not migrate in soil, and most of the preparations are labeled for use around vegetables.

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For more information or to ask a question about gardening, contact the Master Gardeners at 918-746-3701 from 9 a.m.-4 p.m.

Garden tips

§  Harvest onions when most of the plant tops have fallen over. They will keep longer if the tops are allowed to dry completely before storage. Store in shaded area so that the onions will be well-ventilated.

§  Most varieties of mums are more productive if “pinched back” now. Either pinch off with fingers or cut to remove an inch or so of limb tips above a leaf. This results in the growth of new limbs and a fuller plant. Do not pinch after mid-July or it will interfere with fall blooming.

§  Watch for tiny, sap-sucking insects called aphids on roses, perennial flowers, shrubs and vegetables (especially tomatoes). They produce a sticky substance called “honeydew”. Many can be dislodged with a hard spray from your garden hose, or two applications of insecticidal soap will usually greatly reduce any aphid damage to your plants.

§  Crapemyrtles are one of the few shrubs that should be planted in the middle of summer. Growth of new roots of these plants occurs best with summer soil temperatures.