LEAFLET N0. 407
2/97

Commercial Boxwood Production

R. E. Bir, Extension Horticultural Specialist
T. E. Bilderback, Extension Horticultural Specialist
J. E. Baker, Extension Entomology Specialist
R. K. Jones, Extension Plant Pathology Specialist
Department of Horticultural Science
North Carolina Cooperative Extension Service
North Carolina State University

Introduction: Boxwood (Buxus L. sp.), thought to have been introduced to the United States in 1652, has long been associated with colonial architecture across North Carolina. It's suitability for formal and informal landscape use as edging, hedge, screen, accent and specimen plants makes boxwood a favorite of homeowners, landscape contractors and nurserymen.

There are two major production areas for boxwoods in the United States. One is on the West Coast in Washington, Oregon and north central California. The second is in the East, from Maryland into South Carolina and westward throughout Tennessee. The eastern production center is in the Blue Ridge and Great Smoky Mountains of North Carolina.

Boxwood Species and Cultivars

There are approximately 160 registered cultivars of boxwoods with about 115 cultivars and species available commercially. Only three species, Buxus sempervirens, L., Buxus microphylla, Sieb. & Zucc., and Buxus sinica (Rehd. & Wils.) M. Cheng var. insularis (Nakai) M.Cheng. (formerly B. microphylla var. koreana) and various cultivars of these species are grown as ornamentals. Flowers on boxwoods are inconspicuous. Cultivars vary from the species and can only be reproduced by asexual or vegetative propagation. Cultivars are usually chosen for introduction because they vary from the species in size, form, texture, leaf color and shape, fruiting, flower color, insect or disease resistance, or climatic adaptability. Some of the more widely grown boxwoods include the following:

Buxus microphylla 'Compacta' is hardy to USDA Zone 5. First distributed by Kingsville Nursery in Maryland and sometimes sold as 'Kingsville Dwarf,' it is the smallest of all boxwoods, averaging 1/2 inch of growth per year. Leaves are 1/2 inch long by 1/4 inch wide. It is popular as a bonsai plant.

Buxus microphylla var. japonica (Muell.) Rehd. & Wils., Japanese boxwood, is hardy to USDA Zone 5. It has been grown in the United States since about 1890 and is the most adaptable of boxwoods. Leaves are glossy, 1/2 inch wide by 1 inch long, medium green in shade and orange to bronze in winter sun. This variety flowers and seeds freely. It is an open, quick-growing shrub which can be 8 feet tall and 20 or more feet wide. Plant width is often difficult to determine because of layering.

Buxus sempervirens, L., common or American boxwood, isardy to USDA Zone 5. This boxwood is a wide spreading shrub or small tree with very dense evergreen foliage. The leaves are oblong-lanceolate to oval in shape, 1/2 to 1 1/2 inches long and are broadest at or below the middle. They are usually shiny, dark green on top and pale green on the bottom. Flowers, borne in early spring, are pale green. Although very old plants may attain a height of 20 feet, they more commonly grow 5 to 10 feet tall. This species and most of its cultivars are tolerant of cold weather. Production is best in the Piedmont and Mountain areas of North Carolina.

B. sempervirens 'Suffruticosa,' English or true dwarf boxwood is hardy to USDA Zone 5. English is the most popular and most widely grown cultivar of all boxwoods, predating 1753 in the United States It is a small, rounded-leaf form averaging about 1 inch of growth annually. The plant is rounded with tufts that resemble a cloud.

B. sempervirens 'Vardar Valley' is currently the most popular of B. sempervirens. collections made in Macedonia in 1934. It is considered be among the hardiest of B. sempervirens available. It is popular because it retains dark green color in winter and spring growth has a bluish cast. 'Vardar Valley' has a broad spreading habit reaching a height of 7 feet.

Buxus sinica (Rehd. & Wils.) M.Cheng var. insularis (Nakai) M. Cheng, formerly (B. microphylla var. koreana), Korean boxwood, is hardy to USDA Zone 4. It was introduced to United States in 1919. The growth habit is generally upright and open with widely spaced leaves, 1/4 to 3/4 of an inch long. It is cold hardy but foliage may bronze in winter.

B. sinica var. insularis 'Wintergreen' is hardy to USDA Zone 4. It originated in 1960. This cultivar's foliage is a dark green color that lasts through winter. However, it displays an open habit and is a heavy seed producer. A 16 year old plant may be 5 feet tall by 3 1/2 feet wide.

Buxus 'Green Mountain' is hardy to USDA Zone 4b. Introduced by Sheridan Nurseries in 1966, it also has dark green foliage color that persists through winter. It displays a dense pyramidal habit. A 10 year old plant may be 3 ft. tall by 1 1/2 feet wide. Ultimate size anticpated as 5 feet tall with a base 3 feet wide.

Buxus 'Green Velvet' is hardy to USDA Zone 4b. A 1973 Sheridan Nurseries hybrid introduction with a rounded habit and vigorous growth which holds color well through winter. Ultimate size anticipated as four feet tall.

Propagation

Boxwoods are propagated from semi-hardwood and hardwood cuttings. The best time for rooting is from late summer through fall (September through November). Cuttings should only be taken from healthy, vigorous plants that are insect and disease free. If a large number of cuttings needs to be propagated during warm weather, harvest them early in the morning. As the cuttings are collected, they can be tied in bundles of a known quantity and should be kept moist. The cuttings should be kept in a cool, shaded location during collection. After harvest, they can be transported to the propagation area, made into finished cuttings and inserted into the propagating medium.

Cuttings should be 5 to 6 inches long. Those of highest quality are from terminal growth. Pruners with scissor action blades are superior to those having a blade and anvil. Blade and anvil type pruners tend to crush and thereby destroy conductive tissues. Scissor action pruners slice cleanly. During cutting preparation, pruner blades should be sterilized periodically by immersing them into a container filled with either 70% isopropyl (rubbing) alcohol or a 10% chlorine bleach solution.. A 10% chlorine bleach solution can be prepared by mixing (by vol) nine parts of water with one part of household bleach. Leaves should then be stripped from the basal 2 inches of each cutting. Cuttings are then ready to be treated with a root promoting compound (auxin). Several powder and liquid formulations are available from commercial nursery supply-houses. Powder formulations are blends of talc plus one or more auxins and some may contain a fungicide. For liquid formulations the desired auxin is dissolved in an organic solvent, e.g., alcohol. Best rooting has resulted from formulations containing 3000 (0.3%) to 5000 (0.5%) parts per million (ppm) indole-3-butyric acid (IBA).

Whether using a powder or liquid formulation, never dip cuttings directly into the container of stock material. If any of the cuttings are infected with pathogens, they can contaminate the entire supply which then becomes a source of inoculum for all cuttings. A better practice, which reduces the possibility for contamination of the stock, is to transfer enough material from the stock container for immediate needs before treating cuttings. Any material remaining after cuttings have been treated should be discarded rather than returned to stock. To prolong shelf-life, containers of stock material should be kept tightly sealed and stored in a refrigerator when not in use.

The basal 1 to 2 inches of the prepared boxwood cuttings should be dipped into the talc auxin formulation. Cuttings may be dipped one at a time or in loose bundles when using liquid. Cuttings should be treated individually when using powders. The base of stems treated with powders should be moist so that posders will adhere to them. When using powders, the basal ends of the cuttings should be gently tapped on the rim of the container after dipping to remove any excess material. The cuttings should then be inserted into the rooting medium. Only the basal 1/2 inch of each cutting should be dipped into the solution when using a liquid formulation. Cuttings should remain in liquid formulations for only one to two seconds. Longer exposure can result in injury to the cutting. After dipping, allow approximately 15 minutes for stems to dry before insert cuttings into the propagating medium.

Cuttings may be maintained in a shaded area in rooting beds, flats or in individual pots filled with an appropriate medium. Media that have proven satisfactory for propagation of boxwood include sharp builder's sand, equal parts of peat and perlite or peat and sand. Bottom heating of the propagating medium to a temperature of 70 to 75 F (20 to 24 C) promotes faster rooting but is not absolutely necessary for success.. Cuttings should be inserted into the moist medium to a depth of 2 inches on at least a 1 inch spacing and then watered. Watering insures good contact between the lower portion of the stem and the rooting medium.

Cuttings root equally as well under intermittent mist or in moist, shaded areas. If using a mist system, set it to operate from 1 hour after sunrise to 1 hour before sunset. The frequency and duration of misting during each day will depend upon temperature, photoperiod, light intensity, relative humidity and air movement within the propagating structure. Frequency refers to how often the mist system is activated during any given period of time. If the system operates every 5 minutes, then the frequency is 5 minutes. Duration refers to the length of time that the mist is actually on (spraying water); for example, during a 5 minute frequency. If a system is set to operate for 5 seconds every 5 minutes, then the duration is 5 seconds and the frequency is 5 minutes.

As a starting point, the mist system can be set to operate for 5 seconds every 5 minutes. If foliage on the cuttings, or the medium remains too wet or too dry, adjustments in the misting frequency or duration should be made to correct the problem. Excess water on the foliage should be avoided since it provides an ideal environment for development of disease organisms. When the cuttings have rooted, usually in 8 to 10 weeks, discontinue misting or decrease watering, depending upon which type of propagating facility you are using. After rooting, cuttings should be allowed to harden off for at least 2 to 3 weeks before being potted or being placed directly into either outdoor frames or unheated greenhouses. During the hardening off period, it is extremely important that plants not be over or under watered. During this period, the newly formed root systems are extremely fragile. Stress as a result of water-logged or dry soils can permanently damage a root system and may cause stunting, decreased plant vigor or a reduction in quality. In severe cases part or all of the crop may die. Remember that even during winter months plants require water. Check rooted cuttings routinely and if the medium is drying, apply water.

During the first winter, cuttings placed outdoors should be well mulched, to decrease chances of winter injury. Natural materials such as pine straw, clean straw, and leaves make suitable mulches. Commercially available materials such as thermal blankets or white copolymer film can also be used over the plants to provide winter protection. The following spring the rooted cuttings should be removed from the overwintering area and be either field planted or potted into containers. Poorly rooted or weak cuttings should be discarded.

Field Planting

Avoid field planting boxwoods in lowland areas that tend to be wet, in frost pockets or where there is a high count of nematodes in the soil. Soil should be a well-drained sandy or silt loam high in organic matter. Disking in a cover crop such as oats or rye during the winter prior to planting a field to boxwoods will greatly improve soil tilth and increase its organic matter content. Prior to planting, have your field soil tested. Your Cooperative Extension agent is available to assist you in taking the soil samples properly.

Follow the recommendations provided on the soil test report. The nutritional status and pH of your field should be adjusted. Boxwoods grow best in a fertile soil adjusted to a pH of approximately 6.5. The preplant amendments should be either disked, plowed or rotovated to a depth of 10 to 12 inches. Soil should be worked until loose, friable and be free of clods and large pieces of debris.

In early spring, grade plants into three or four groups. Each group should contain plants of approximately the same size. From the time plants are removed from the overwintering area until planted in the field, extreme care should be taken to ensure they do not dry out. During the planting operation, bundles of rooted cuttings should be kept cool and moist by wrapping in wet burlap or similar material. Groups of plants of the same size should be planted in the same block or field. If there are vast differences in sizes between groups, they may need to be watered, pruned and fertilized differently to produce a high quality crop. Different groups may attain marketable size at different times which means that they will have to be dug at different periods. If plants of a similar size are maintained in the same block, both the cultural and digging operations can be made easier. Planting a block or field with ungraded stock can tie up an entire parcel of valuable production land until all plants are sold.

When setting plants in the field, a spacing of 2 feet between plants and 3 to 4 feet between rows is minimal. When designing field plantings, be sure to allow adequate space for pest management and harvesting. Plants should not be set in the field any deeper than they were growing during propagation. The roots should be spread uniformly in the planting hole or furrow. As they are set out, soil should be brought up over the roots and pressed firmly in place to remove any large air pockets that can cause the root system to dry out.

Recently planted fields should be kept moist, but not wet, until root systems have become established. Thereafter, regular irrigation, especially during drought periods, will avoid stopping plant growth as a result of water stress. During any given irrigation, between 1/2 to 1 inch of water should be applied. Depending upon soil type and texture, the amount of water should be sufficient to thoroughly moisten the soil throughout the root zone. Application of insufficient amounts of water are discouraged since they promote buildup of high soluble salts and encourage development of an excessive number of surface roots. If the soil has been properly amended prior to planting, no additional fertilizer may be required during the first growing season. Thereafter, regular soil analysis will dictate the frequency, grade and rate of fertilizer to apply to produce a high quality crop. Many complete fertilizers (those that contain nitrogen, phosphorus and potassium) designed specifically for production of nursery crops are available commercially. Their rate of application should be in conjunction with the soil test report. As a general recommendation, boxwoods require from 1 to 2 pounds of actual nitrogen per 1,000 square feet of production area per year. Fertilizers should be applied as early in the spring as possible, preferably before any shoot growth has started.

Container Planting

Boxwoods may also be grown in containers. However, containerized plantings require much closer attention than field plantings to produce a high quality crop. While a permanent irrigation system may be considered optional for field plantings, it is essential for container growing. Also, in addition to jamming plants together, additional precautions must be taken to provide supplementary winter protection (See AG-454, Preparing Nursery Plants for Winter).

Container grown nursery plants are produced in soilless media rather than soil. Soilless media offers several advantages over soils for container plant production: 1) they are light-weight 2) they are readily available commercially; 3) they are reproducible from one batch to the next; 4)they are less likely to be contaminated with pathogens; 5) most are very well drained and provide good aeration; and 6) they are inexpensive compared to good quality soil.

A soilless medium which has proven satisfactory for growing boxwoods is one consisting of 8 parts pine bark : 1 part sharp builder's sand (by vol.). Prior to planting, 10 pounds of dolomitic limestone, and minor nutrients (at manufacturer's recommended rates) should be incorporated thoroughly into each cubic yard of medium.

Rooted cuttings or liners can be grown in several different sizes of containers depending upon the individual grower's production scheme. Don't hesitate to discard poor quality liners or cuttings. It is extremely difficult to produce a high quality finished plant unless you start with a good quality liner.

Fertilizers that are readily soluble should not be incorporated into the potting medium. In many instances this has caused soluble salts injury to tender root systems.

Many controlled-release nursery fertilizers are available commercially for use in production of container-grown plants. They have been formulated for plants being grown in soilless media. Only a single application of these fertilizers may be required during a growing season and therefore decrease labor inputs. When top dressing, distribute the recommended rate uniformly over the surface of the growing medium in each container. Placing fertilizer in piles beside the plant stem on the medium surface, even at recommended rates, can cause soluble salts injury. Reapplication of fertilizer during the container production cycle will depend upon fertilizer solubility, plant performance, rainfall and irrigation management.

Shearing and Pruning

Shearing is the uniform removal of all or part of the latest flush of plant growth. Plants are sheared to encourage branching, increase compactness and density or to maintain a specific size or shape. If cuttings are inserted in ground beds in the fall of one year and not used for a year or more, shearing while they are in beds may be necessary.

During the first few years after planting, boxwoods should be sheared after each flush of growth to encourage additional branch development. Thereafter, they should only be sheared to maintain a desired shape or form. After the first year, shearing is generally done annually. Do not shear boxwood in late summer since this might force new growth that will not harden before frost.

Pruning is the removal of selected branches or plant parts. Plants are pruned to remove diseased, injured, dying or dead branches. Unwanted branches are also removed by pruning, especially when plants are being trained to a specific form such as topiary or espalier. Boxwoods are pruned, rather than sheared to maintain a natural shape and to keep plants at a desired size so that they do not outgrow their landscape value too quickly.

Boxwoods usually require some pruning in spring to remove any branches that may have been winter killed. Also, as plants get older, some of the older branches may be removed so that light can penetrate to the inner shoots. Continuous shading of the inner branches results in foliage drop from those shoots thereby decreasing plant value.

Winter Injury

An indicator of winter injury is when the foliage on entire branches turns rust-brown in color. This is particularly common in sunny, windy sites. Severe winter injury often causes death of entire branches in the center and top portions of the plant. A symptom of winter injury is sunken bark on the main trunk just above the soil line or in crotches and along the sides of main branches. In many cases the bark will separate from the wood and large patches can be easily stripped.

Winter injury often occurs when plant growth ceases during the summer by drought, heat or nutrient stress and then stimulated again by fall fertilization, excessive watering or prolonged rainy periods. In many cases, growth forced late in summer or early fall does not have time to harden and is easily injured by frost or cold weather. During mild winters, even plants that were cared for properly, may begin to grow during prolonged warm spells. With the reoccurrence of freezing temperatures the tender growth is easily injured or "burned back." In some cases such injury may not become evident until active growth begins in the spring.

Winter Protection

Winter protection for boxwood may involve siting fields to avoid sunny winter exposure. Installing a living or temporary windbreak will also help to reduce plant moisture loss. Sowing a cover crop such as annual rye will help to reduce frost heaving of the crop plants and soil loss through erosion. Container-grown plants require more elaborate measures of winter protection depending upon location in North Carolina. (See AG-454, Preparing Nursery Plants for Winter)

To reduce chance of winter injury, select cultivars that are suited for growing in your area, fertilize properly, and irrigate during drought periods. Winter injury can be reduced or avoided by proper cultural practices.

Preparing Plants for Sale

Container grown boxwoods can theoretically be marketed at any time of the year since they have been produced in their marketing package and no digging is involved.. To facilitate marketing and to avoid any chances for disagreement between buyer and seller concerning plant size, all nursery plants offered for sale should conform to the American Standard For Nursery Stock (copies available from American Association of Nurserymen, Inc., 1250 I Street, NW, Suite 500, Washington, DC 20005).

PESTS

Weeds

Weed competition must be managed to produce high quality plants profitably. This can be done through a program of good sanitation, judicious use of herbicides, mowing and cultivation. No single method will be satisfactory in all situations.

Weeds are unsightly and compete with crop plants for nutrients and water, and often harbor insects and disease organisms that can infect crop plants. A good practice is to take measures to reduce weed invasion of your nursery. If possible, eliminate the primary source of weed problems. Areas adjacent to the nursery should, if possible, be kept mowed to prevent weeds from seeding. Appropriate herbicides should be utilized to prevent weed seed germination in the crop growing area. Some hand weeding or use of spot herbicide treatment may be required. Selective herbicides and cultivation may be required to control weeds in adjacent noncrop areas. Several preemergence herbicides are available for use in boxwood production. You may select an appropriate herbicide by consulting AG-427, Weed Control Suggestions for Christmas Trees, Woody Ornamentals and Flowers.

Diseases

Two disease problems important in commercial production of boxwood in North Carolina are Phytophthora root rot and nematodes. These diseases are widespread and very destructive in the nursery. Boxwood diseases reduce the rate of growth, uniformity, quality of plants and can kill plants. Diseased plants which do not die in the nursery frequently die in the landscape.

Root Rot

Root rot is caused by the soil-borne fungus Phytophthora parasitica. The first symptom of root rot is loss of the dark, shiny green leaf color. Leaves gradually turn light straw colored when plants are grown in the sun or dull green when grown in shade. This usually appears on one branch or section of the plant, and gradually other branches are affected until the entire plant dies.

Phytophthora is a widespread fungus in North Carolina soils. It is most likely to occur in poorly drained soils, heavy clay soils and river bottom soil. During periods when soil is saturated with water, the fungus penetrates into feeder roots. The fungus moves up the roots causing a dark discoloration, eventually killing even the main stems. The outer cells of rotted roots slough off easily leaving only the central portion. In advanced cases of root rot, the bark on the main stems just above the soil may also slough-off.

Nematodes

Several nematodes damage boxwoods in North Carolina, including lesion (Pratylenchus vulnus) , root knot (Meloidogyne arenaria), boxwood spiral (Helicotylenchus buxophilus) and ring (Macroposthora xenoplax). These nematodes are very widespread making nematode decline the most common disease on boxwoods in North Carolina. Lesion nematode is the most common and damaging nematode on boxwood. It feeds inside the root causing extensive root decay very similar to that caused by Phytophthora. Root knot nematode causes small swellings or galls on the roots, but this nematode is not as common on boxwood. Above ground symptoms of nematode damage are often similar to those with Phytophthora root rot. Nematode damage can also appear as a twig dieback, excessive leaf drop, or overall bronze cast to the foliage often confused with winter injury.

Nematodes, Phytophthora root rot, fertilizer injury, winter damage or other injuries can occur in the same plant or plants making visual field diagnosis difficult or impossible. Before boxwood diseases or problems can be corrected, the cause must be diagnosed correctly. Submit entire plants or a sample of the foliage plus 1 quart of soil and feeder roots packaged in plastic bags to The Plant Disease and Insect Clinic for diagnosis. Check with your county Cooperative Extension agent for forms and additional information on submitting samples to the Clinic.

The key to growing boxwoods successfully in the nursery is to prevent the aforementioned disease problems. Sites for field production should be carefully selected for good drainage. Soil from selected fields should be assayed for nematodes before planting by the Nematode Advisory Laboratory, North Carolina Department of Agriculture. Check with your county Cooperative Extension agent for more information on the proper method of sampling, handling and packaging the soil and forms. If the assay shows that damaging nematodes occur in the selected field, choose another site for boxwoods.

Metalaxyl (Subdue) is labelled for control of Phytophthora root rot. Nemacure is labelled for control of nematodes in field production. Bolth of these productes are better as preventative than curative treatments. Nemacure is a restricted use pesticide.

Boxwood Insects and Mites

Boxwood Leafminer

Boxwood leafminer is most common pest of boxwoods in North Carolina. Imported from Europe, this small fly is a greater pest in the Mountains and Piedmont than in the Coastal Plain. All boxwoods can be infested, but slow-growing cultivars are less susceptible. Infested leaves usually become yellowish, and are smaller than uninfected leaves. Heavily infested plants become unthrifty.

Females insert their eggs into the upper surface of the leaf. The tiny larvae hatch and feed inside the leaf. Leaves first acquire a water-soaked appearance at the feeding site, followed by blisters on the lower leaf surface. The leafminers spend the winter in the blisters as larvae. The larvae are small, whitish to lemon-yellow maggots up to 3 millimeters in length.

Larvae pupate in early spring, and the pupae wriggle through the leaf in May to protrude from the lower leaf surface. The pupae are elongate (3 millimeters) and whitish to dark yellow in color with the legs and wings appressed to the body surface. In North Carolina, adult flies emerge from the pupae over a 2-week period in the spring, shortly after boxwoods have begun growing. Adult boxwood leafminers are 2.5 millimeters long orange, mosquito-like flies. They can often be observed swarming around boxwoods during the time weigelas are in bloom.

Boxwood Psyllid

Boxwood psyllids cause terminal growth to be stunted and leaves to become cupped. This forms a protective shelter in which nymphs feed. The nymphs mature and molt into adults in May or early June. Spray to control the adults in May or June. If a granular insecticide is used, it should be applied in early spring just before new growth begins. Adults feed until July or August when the females lay eggs. One to seven eggs are laid under the scales of the buds. The tiny psyllid develops but does not hatch from the egg until the following spring as the new growth begins. English and American boxwoods are affected, but American boxwood is most likely to be severely infested.

Indian Wax Scale

Indian wax scale is difficult to control. It feeds on azalea, camellia, Chinese elm, fig, Chinese and yaupon holly, jasmine, mulberry, persimmon, plum, quince and other ornamentals. A severe infestation of wax scale detracts from the appearance of the host plant because of the many dirty white scales and the copious honeydew that they excrete. A black fungus called sooty mold grows in the honeydew, disfiguring the plant further.

Indian wax scales begin to lay eggs in March. Each scale lays from 1,000 to 2,000 eggs. The oval eggs are pale purple and resemble purple pollen when shaken onto a white surface. By late May, tiny crawlers insert their sucking mouthparts into the host plant, then become immobile. After molting, each scale secretes wax in tufts. This is called the star stage. The young scales mature throughout the summer, producing more waxy covering (the cameo stage). These scales become increasingly tolerant to pesticides as they mature.

Boxwood Spider Mite

Boxwood spider mites are common pests of boxwood foliage. They cause tiny scratchlike marks on upper leaf surfaces as they consume the sap. All stages of mites feed on the upper and lower surfaces of the leaves. As they feed, they apparently inject a toxic saliva into the leaf, causing a small yellow spot to form. New plant growth seems particularly susceptible to attack.

Overwintering eggs are laid September and October. The lemon-yellow eggs are flattened on the bottom and slightly flattened on top. In mid-spring the eggs hatch into six-legged larvae that crawl about and feed freely for about 3 days. After a resting stage (about 1 day), the larvae molt into eight-legged nymphs. The nymphs are green and similar in appearance to the adults but smaller. The first nymphs feed for about 4 days and then go into a resting stage of about 4 days before becoming second nymphs. The adults emerge after a final resting stage of 4 days.

The eight-legged adults are slightly less than 0.4 millimeters long and green to yellowish brown in color. The body of the female is oval and tapered in the male. Mating takes place immediately after molting from the last nymphal stage. Each female lays 25 to 30 eggs. Because the entire life cycle takes from 18 to 21 days, there can be eight generations per year.

Twospotted Spider Mite

Twospotted spider mites are important pests on many ornamental crops in North Carolina. They have been reported on over 180 host plants, which include more than 100 cultivated species. Violets, chickweed, pokeweed, wild mustard and blackberry are common weeds from which infestations develop on nearby crops. Twospotted spider mites pierce the epidermis of the leaf with their sharp, slender mouthparts. When they extract sap, the mesophyll tissue.of the leaf collapses in the area of puncture forming a small chlorotic spot. After a heavy attack, an entire plant may become yellowed, bronzed or killed completely. The mites may spin so much webbing over the plant that it becomes entirely covered.

In North Carolina, twospotted spider mites overwinter as adults in the soil or on weed hosts such as violets and hollyhocks. In mild winter weather, twospotted spider mites continue to feed and lay eggs although development in the winter is much slower than in the summer. The eggs are spherical, ranging from transparent and colorless to opaque straw yellow. Six-legged, colorless or pale green to yellow larvae hatch from eggs. They develop into eight-legged nymphs that pass through two nymphal stages. After each larval and nymphal stage, there is a resting stage.

Adults mate soon after emerging from the last resting stage, and in warm weather the females soon lay eggs. Each female may lay over 100 eggs in her lifetime and up to 19 eggs per day. Development is rapid during hot, dry weather. One generation may take from as many as 20 to as few as 5 days to begin producing offspring. The eight-legged adults can be rusty green, greenish amber or yellowish in color. They usually have two, sometimes four, black spots on top and are about 0.4 millimeters long.

Bibliography

American Standard for Nursery Stock. 1997. American Association of Nurserymen, Inc. Washington, DC.

Batdorf, Lynn. 1995. Boxwood Handbook, A Practical Guide to Knowing and Growing Boxwood. The American Boxwood Society, P. O. Box 85, Boyce, VA 22620.


Published by

North Carolina Cooperative Extension Service


Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.