ORNAMENTALSAND
TURF
ORNAMENTALS
The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
Alternaria blight was diagnosed in the Plant Disease and Insect Clinic at North Carolina State University on September 11, 1996. This is the first report of this disease in North Carolina. The following information is taken from a 1985 description of the disease by Dr. Arthur Engelhard, University of Florida, in Plant Pathology Circular No. 277.
The poinsettia (Euphorbia pulcherrima Willd. ex Klotsch) is a popular, short-day plant grown for its colorful bracts and marketed from late November through Christmas. Poinsettias are raised commercially in greenhouses and outdoors under saran in the southern parts of Florida. Landscape plantings of poinsettia are popular in central and southern Florida. Dozens of both standard and multi-flowering varieties are available which can be finished in many forms: trees, pixies, hanging baskets, planters and traditional 6 to 8 inch pots. Rhizoctonia, Phytophthora, Pythium, Corynebacterium, Botrytis, and Sphaceloma are common and destructive pathogens on poinsettia in Florida, requiring constant vigilance in the cultural program to minimize losses. A new disease caused by Alternaria euphorbiicola Simmons and Engelhard, which causes symptoms on leaves, bracts, petioles, cyathia, and stems was observed inflicting commercial losses on poinsettia in Florida, first in 1984 and again in 1985. The disease known as Alternaria blight causes a variety of symptoms, some of which might be confused with bacterial canker (Corynebacterium flaccumfaciens Hedges pv. poinsettiae Dye and Kemp) or scab (Sphaceloma poinsettiae Jenk. and Ruehl).
Disease Development and Symptoms. Conidia of Alternaria euphorbiicola are air-borne and can survive dry periods to cause disease when moisture becomes available. Environmental conditions in outdoor production areas are more disease conducive than greenhouse conditions, presumably because of frequent prolonged leaf wetting periods from evening through mid-morning of the following day.
Leaf infections initially appear as 1 to 3 mm diameter spots with tan centers, dark, thin margins, and a chlorotic halo. As spots enlarge, they often track along lateral veins of the leaf. Spots enlarge to form irregular necrotic lesions, 25 mm across or larger. Leaves with several spots become chlorotic and absciss. Infected, developing leaves exhibit crinkling and general distortion. Certain leaf symptoms, such as distortion with unilateral stippled chlorosis and necrosis of large leaf areas on both apical and lower leaves, suggest possible involvement of toxins or disease metabolites in the disease syndrome.
Stem infections are characterized by sunken, light to dark brown lesions 1 to 2 mm in diameter, enlarging to 25 mm or longer. Infections near the apex can result in tip dieback. Leaves near a stem infection and leaves with petiole infections generally become chlorotic and absciss.
Host Range. At present, only certain varieties of Euphorbia pulcherrima are known to be susceptible to Alternaria euphorbiicola, though a thorough investigation of host range has not yet been performed. The Gutbier V-14 cultivars Glory, White and Jingle Bells, and Eckespoint C-1 are very susceptible. Gutbier V-10 Amy appears intermediate in susceptibility and Annette Heff cultivars Dark Red, Top White, Brilliant Diamond, and Hot Pink are quite tolerant, with only small leaf spots forming on the tolerant cultivars. Other cultivated and native Euphorbiaceae may be susceptible.
Control. Alternaria blight is extremely difficult to control on susceptible cultivars grown outdoors. Effective disease control requires the following practices:
Borers generally infest stressed or weakened trees. Field-grown
trees and shrubs that suffer from lack of irrigation in dry weather
may become attractive to borers. Over-fertilization may also make
trees susceptible to borers. On the other hand, perfectly healthy
nursery stock may be infested when large numbers of borers emerge
from adjacent woodlands with wind-broken or otherwise stressed
trees. Hurricane Fran left an enormous amount of wind-thrown,
broken and stressed trees. The tremendous amount of slashed and
broken twigs will probably become a giant breeding source for
borers that will threaten stressed trees. If the numbers of borers
become high enough, even perfectly healthy trees may be attacked.
Judging from the increased reports of ambrosia beetles and other
borers after Hurricane Hugo, an increase in populations of borers
in shade trees is likely to happen this fall and next summer. Most
of the borers that infest shade trees are clearwing moth borers,
roundheaded borers, flatheaded borers, ambrosia beetles and bark
beetles.
The ash borer infests lilac and ash. This native species occurs over much of the eastern United States and greatly limits the usefulness of lilac in the landscape. It has one generation per year. Peak emergence of the adult moths is May in North Carolina. Ash borers are caterpillars of clearwing moths that closely resemble paper wasps; however, the moths do not sting. Females lay their eggs on the trunks of lilac and ash. The young caterpillars bore in and make a blotch mine under the bark which results in a noticeable canker. The moths emerge the following year from a neat hole chewed by the caterpillar 6 or 7 inches higher than the canker. Forest and landscape ash trees are a source of the borers. Younger trees seem to be more heavily infested than older trees, perhaps because young trees are more susceptible to stresses such as drought and transplant shock. Once ash trees are established, the borers will probably be much less of a pest. Any action taken to reduce stress on ash trees will make them less susceptible to these borers. Lindane is commonly used for borer management because it is readily available, it is labeled for such use, and it lasts longer than other pesticides similarly labeled. However, Dursban is more toxic to moths and caterpillars in the clearwing moth family and Dursban is reasonably persistent. The best way to monitor for ash borers is to use pheromone traps that attract the males. When you start catching males, you know that females are present. Spraying pesticide every 14 days until the population declines should be adequate for control.
Peachtree borers are also caterpillars of clearwing moths. Female
moths lay eggs at the base of flowering almonds, peaches, cherry
laurels, plums and ornamental cherries. From the eggs hatch tiny,
white caterpillars that bore into the bark and excavate a tunnel in
the cambium at the base of the tree. If several borers infest a
tree, the cambium may be completely girdled beneath the bark, and
the tree will die. The borers pupate inside the infested tree
during late spring and summer and then emerge as moths a few weeks
later. These moths emerge throughout the growing season, but the
great majority of them are in flight between August 15 and
September 15. Consequently, most of the borers can be preventively
managed by spraying with Dursban or Thiodan around the first of
September. Only the very base of the trunk needs to be treated.
The only control measure available during the dormant season is to
attempt to gouge the borer out from under the bark without injuring
the tree excessively.
People with dead pines are often startled to hear the clicking or rasping noises of southern pine sawyers from under the bark. They assume this is the southern pine beetle, but bark beetles are too small to make noise heard all the way through the bark. Sawyers are abundant in North Carolina and are very sensitive to the health of pines. Very soon after a pine reaches the point of no return, adult sawyers fly to and chew holes in the bark, then lay eggs under the bark. Sawyer larvae hatch and bore in the sap wood for a while, then tunnel directly into the heart wood and tunnel back and forth before pupating about a year later. One reason pines are best cut in the winter for log homes is that during warm weather the sawyers infest the logs and soon degrade the wood with their tunnels. As the grubs feed, they force sawdust out of the trees. Pinewood nematodes are carried by sawyers and perhaps other beetles. New sawyers feed on the bark of conifer twigs and infest the new tree with nematodes from the tree the beetle emerged from. Because sawyers feed on the bark of healthy trees, it is possible for such trees to become infested with pinewood nematodes at that time. There is no practical way to control sawyers other than keeping trees in good health (avoiding soil compaction, irrigating in dry weather, using proper fertilizers, etc.).
The twig girdler is a longhorned beetle that attacks basswood, dogwood, elm, hackberry, hickory, honeylocust, oak, pecan, poplar, sourwood, zelkovia and various fruit trees. The grayish brown beetles are about an inch long and have long antennae. The beetles emerge in late summer and feed on tender bark and tips of twigs. Female beetles chew grooves around the twigs of the host trees and then poke their eggs under the bark usually at a leaf along the girdled terminal. The girdled portion of the branch soon dies, breaks over and then and usually falls to the ground. Several twig girdler grubs feed in a fallen branch until the middle of the following summer. The grubs fill their mines with wood particles and frass as they feed. Pupation occurs in a cell formed by walling off a portion of the mine with fibrous frass. A new generation of adults emerges in late summer and starts to feed on the tender bark again. Dozens of branches may be girdled and fall to the ground from a large tree. Nursery stock become ragged and unattractive. Collection and burning infested twigs and branches during the fall or winter is an effective method of control, if the trees to be protected are located some distance from infested stands. To control the adult beetles in pecans, growers apply Sevin by air during mid-September. The beetles are active from mid September into early October. Sevin or Dursban in early and late September should give adequate control.
The twig pruner lays its eggs in the new bark by slitting the
surface at leaf axils in late spring. When the twig pruner eggs
hatch, the grubs bore into the twig. As the grubs mature, they
bore down the twig. Later in the summer infested branches from 1/4
to 2 inches in diameter fall out of the trees; these branches will
have been girdled from the inside! They should be raked up and
burned because the overwintering grubs are inside. Trees under
stress seem to be more attractive to the adult twig pruners than
trees in healthy condition. When twig pruners are active in an
area, thought should be given to spraying susceptible plants with
lindane or Dursban the following spring to prevent damage for the
coming season. Drought stress may make young trees attractive to
twig pruner adults. On the other hand, trees growing too fast may
become susceptible as well. If nursery stock is putting on more
than an inch of trunk diameter per year, it may be worthwhile to
hold back on the fertilizer next year to avoid borer problems.
Flatheaded borers are the immature stages of metallic wood boring
beetles. Species in the genus Chrysobothris are particularly
troublesome to hardwoods, boring into the trunks of maples,
crabapples and other hardwoods. The flatheaded appletree borer is
the most common flatheaded borer in nursery stock. These and other
flatheaded borers are attracted to weakened trees, especially those
with thin bark such as young apples, dogwoods, maples and others.
Drought or defoliation or some other stress may cause trees to
become susceptible to flatheaded borers. Trees newly set out in
the landscape may be particularly susceptible to flatheaded borers.
Such trees should be protected by insecticides (Dursban, lindane)
during their first year or two in the landscape, and their trunks
should be wrapped in some sort of tree wrap to prevent sun scald of
the bark or other wounds that might attract the adults for
ovipositing on the stressed trees.
Ambrosia beetles usually infest declining or dead hardwood branches, stumps and trees. These beetles infest maple, elm and numerous other hardwoods. Ambrosia beetles tunnel into the sapwood and heartwood of various dying, weakened or recently felled hardwood trees. Even otherwise vigorous trees may be attacked if there are wounds on the trunk or dead patches of bark. When ambrosia beetles attack a tree, they bore straight into the sapwood and heartwood sometimes as much as 10 to 12 inches (on big landscape trees). Eggs are laid in this tunnel, and the young larvae hatch and chew out small egg cradles that radiate from the adult tunnel like teeth on a comb. The larvae apparently do not eat wood, they feed on fungi (the so-called ambrosia) that grow on the surface of the wood in the tunnels and egg cradles. Female ambrosia beetles possess specialized structures called mycetangia in which the ambrosia fungus is carried in from one host plant to the next. The adult beetles have special pouches in which they carry some of the fungi as they colonize new trees. Fortunately the ambrosia fungi are not systemic nor highly pathogenic. Because ambrosia beetles are boring insects, infested trees can be treated with lindane or Dursban to prevent additional infestation.
Two types of ambrosia beetles are of special concern, Asian ambrosia beetles and black twig borers. The Asian ambrosia beetle, Xylosandrus crassiusculus, was first discovered in the U. S. in South Carolina in 1974, it has since been detected from Florida to Texas and Indiana and North Carolina. It is a pest of ornamental, fruit, nursery and transplanted trees. Adult beetles bore into twigs, branches and small trunks and introduce a symbiotic fungus on which the grubs feed. Visible symptoms include wilted foliage, boring dust and numerous small holes. Slender pencils of frass may extrude from the bark. Large numbers of attacks or the cankers produced by the introduced fungi (ambrosia) may kill the tree. With this species, the beetles bore galleries straight into the wood from 1 to 3 cm or more. The tunnels then branch one to six times in the same plane following an annual ring. In small trunks and branches, the galleries go straight in or spiral upward from the point of attack around the stem or limb, branching upward or downward from the spiral gallery. Because most of the boring is done in the sapwood or heartwood, it is possible to save plants infested with Asian ambrosia beetles. Prune out any dead wood and spray the remaining stems as soon as convenient with lindane or Dursban and then treat again in six weeks. It may be necessary to treat again in another six weeks to completely protect plants.
The black twig borer, Xylosandrus compactus, is one of the few
ambrosia beetles that attacks many kinds of trees and shrubs that
appear to be perfectly healthy! This beetle occurs primarily in
counties along the coast. It is very small, dark and more or less
oval in top view. The largest specimens are just over 1/16 inch
long. Female beetles attack twigs or branches and bore in to the
pith (or if the twig is large, bore into the wood about one half to
one and one half inches. After the females bore into a twig, they
form a small chamber in which the mostly female eggs are laid. The
tiny grubs feed on the fungi which grow on the walls of the brood
chamber. The grubs pupate and then (if males happen to have
developed) the new beetles mate before leaving the twig to infest
new twigs. If the twig is small, only one female may attack it.
If the twig is larger, up to 20 females may attack it. In the
summer, it takes about a month for a egg to develop into an adult
beetle. In the winter, development is much slower. The adults
overwinter inside the damaged twigs. At least one of the fungi in
the ambrosia is Fusarium solani. Infested twigs usually dieback
to a point below the brood chamber. Although the ambrosia fungi
usually do not kill the whole plant, the dieback of twigs can have
considerable impact on the appearance of infested trees and shrubs.
Over 224 plant species in 62 families are susceptible to the black
twig borer. Once the beetles are noticed attacking an ornamental,
the plant should be sprayed with Dursban to prevent further
attacks. If the infestation is discovered in the spring, it may
take several applications spaced at 6 week intervals to completely
protect the plants. There are two factors that may give long term
control. If we have a harsh, cold winter, the weather may kill the
black twig borers back to southern Georgia. The other factor most
people have a little more control over is fertilizer. I believe
that the black twig borer is going to particularly infest trees and
shrubs that are over fertilized (or that grow in a lawn that is
over fertilized). However, the black twig borer also infests
woodland trees that are never fertilized. Until we have a winter
with two weeks of cold weather, the black twig borer is likely to
become a familiar pest to nurserymen along the coast.
The black turpentine beetle is robust, brown to black with a barrel-shaped body, and 5/16 to almost 3/8 inch long (the largest of the bark beetles attacking pine in North Carolina). The larva is a legless, brown-headed grub. When full grown, the 1/2-inch long grub has brown bumps along each side of its body. The pupa is fragile, white and somewhat oval. Black turpentine beetles occur throughout the Piedmont and Coastal Plain of North Carolina, especially after drought or other disturbances. All species of southern pines and red spruce are attacked by the black turpentine beetle. Loblolly and slash pines are the most seriously injured hosts. Turpentine beetles are capable of killing the best trees in a stand. However, attacks of this pest do not always prove fatal. Death of the tree usually occurs only when the infested tree has been weakened from other causes, or when so many beetles attack that the tunnels overlap and girdle the cambium layer under the bark. Black turpentine beetles are attracted to the odor of resin at bruised bark or freshly cut stumps. They usually attack weakened or injured trees before spreading to nearby healthy ones. On occasion, they directly invade green, healthy trees. The beetles usually attack within 6 feet of the ground. They bore entrance holes into the soft inner bark and chew out tunnels between the outer bark and wood. Trees often exude pitch stained with bark fragments. Rows of eggs are laid in grooves on both sides of these tunnels over a period of several months. Grubs hatch in about 10 days. The young grubs feed together on the soft inner bark for 5 to 7 weeks, making broad, fan-shaped communal galleries. Pupation takes from 10 to 14 days, after which new adults emerge from holes chewed through the bark. The length of a life cycle is 3 to 4 months, depending upon the temperature (longer in cold weather). There are 2 to 3 overlapping generations per year, and all stages of development can be found under the bark of infested trees throughout the year. Keeping trees healthy by avoiding injury to trees such as excessive grading around the roots and alleviating stress by proper fertilizing and watering during droughts is the best means of preventing beetle attack, especially during the warm months of the year. If only a few beetles attack a tree (less than one pitch tube per diameter inch), control measures may not be necessary since the beetles are frequently killed by the flow of pitch in the tree. However, if the beetles are numerous, they should be destroyed before they lay eggs. If only a small number of pitch tubes are present, the pitch tube can be struck soundly with a heavy rubber mallet or sledge. This crushes the pitch tube, closes the entrance tunnel, and squashes the beetles and grubs in the gallery beneath. Since trees may be re-attacked, frequent inspection is necessary for at least 1 year. Wounds or breaks in the bark that may attract beetles can be painted with a standard tree paint. To protect trees from further infestation, the trunks can be sprayed with Dursban or lindane following label directions carefully. It is probably a good idea to spray trunks of healthy pines nearby to prevent their infestation also. Do not apply pesticides to wet bark.
The southern pine beetle is short-legged, stout, and about 1/8 inch long. The fore part of the head is notched, and the hind end of the body is rounded. Mature beetles are dark reddish-brown with slightly lighter wings. The egg is pearly white and just visible to the naked eye. Larvae grow to about 1/8 inch long. They are legless grubs with glossy, reddish-brown heads and wrinkled, curved bodies. The pupa is delicate, white, and shaped similar to the adult. Southern pine beetles breed in all species of yellow, white, red, and spruce pines, and in red and Norway spruce. Shortleaf, loblolly, Virginia, and pitch pines appear to be the preferred yellow pines. The southern pine beetle is especially damaging to stands of poor vigor. Outbreaks are often triggered by soil-moisture stresses and by man-caused disturbances. Southern pine beetles usually attack trees that are at least 15 years old. The first sign of an infestation is usually browning of tree crowns and pitch tubes on the bark. Typically, pines are killed in groups ranging from a few trees to several hundred acres of trees. The beetles often kill trees quickly by girdling them and by transmitting a blue stain fungus that plugs conductive tissues and degrades lumber. Southern pine beetles become active in the spring about the time redbuds and dogwoods bloom. Either singly or in small groups, the insects first attack weakened and damaged pine trees; they may then spread over larger acreages. In pairs, the beetles invade the tree's main stem. During outbreaks, thousands of pairs may attack a single tree. They usually attack the middle and upper trunk first. Each pair constructs an S-shaped tunnel one foot long between the bark and wood. The tunnels crisscross to form an intricate pattern that girdles the tree. Eggs are deposited in niches along these tunnels. The larvae, usually feeding in the inner and outer bark, can be seen when the bark surface is whittled away. After a few weeks, the larvae change to pupae, and new adults emerge in a few more weeks. The entire life cycle, under favorable conditions, takes from 30 to 40 days (three to five generations per year). The last brood of the season overwinters in various stages of development under or in the bark of infested trees. Trees should be kept vigorous by mulching and watering (but not over-fertilizing) and free from injuries and excessive grading around the roots. Infested trees should be cut down and debarked immediately. The trunks of healthy trees nearby should be sprayed with Dursban or lindane to prevent infestation, following label directions carefully. Apply only to wet bark.
Pine engravers attack the fissured bark of white pines, other pines and spruce. It breeds in logging slash and windfalls or trees dying of other causes. When heavy populations build up in this type of material, nearby healthy trees may be attack and killed. The adult is 1/8 to 3/16 inch long and brown to black in color. There are four tiny horns on each side of the tip the very hind end. Adults spend the winter on the ground and emerge in early spring to attack stressed, weakened and dying trees. When white pines are dug and stock piled in late winter, they may be stressed enough to attract pine engravers as the weather warms up in early spring. Most of the attack will be at the base of nursery stock where the bark is rough. There are three generations of pine engravers in North Carolina. The most important one for nursery stock is the overwintering generation. Several pine engravers in one tree may completely girdle the plant from within. White pines dug during late winter should be closely grouped and protected by some sort of screening material to avoid pine engraver damage and damage by the bark beetle, Pityogenes. Pine engravers only attack trees with rough bark. When the trees have enough vigor, a pitch tube may form at the entry hole.
Pityogenes hopkinsi bark beetles normally attack the smooth bark of
weakened pine trees or the smooth bark of the lower limbs of
healthy pines that may be shaded excessively. Each place the
beetles bore in oozes resin which alarms nursery inspectors in
other states. In addition, we have had several reports of this
insect attacking white pines in the field as they are dug or within
one or two days of digging. They seem to be very sensitive to the
health of white pines and readily attack them whenever the trees
are under stress. Lindane is probably the pesticide to recommend
to protect nearby trees from attack. However, a demonstration in
three commercial nurseries in Burke County, North Carolina has
shown that protecting dug white pines with some sort of screening
gives complete protection from the attack of Pityogenes hopkinsi.
When these beetles were flying in early spring, no pesticide
applied (Dursban, Margosan-O or lindane) gave more than minor
protection even with spreader-stickers.
Pheromone traps are available for some of the borers that infest trees in nurseries and landscapes (i.e., ash borer, banded ash borer, dogwood borer, elm bark beetles, lesser peach tree borer, Nantucket pine tip moth, peach tree borer, peach twig borer, and rhododendron borer).
Gempler's Crop & Turf Management Supply, P. O. Box 270, Mt. Horeb, WI 53572 (Telephone: 1-800-382-8473, Fax: 1-800-551-1128): Traps and expensive pest management supplies. A list of suppliers is provided below.
Great Lakes IPM, 10220 Church Road, NE, Vestaburg, MI 48891 (Telephone: 517-268-5693): Traps and lures for monitoring insect populations.
Pest Management Supply, Inc., 311 River Drive, Hadley, MA 01035 (Telephone: 413-549-7246, Fax: 413-549-3930): Traps and other pest management supplies.
Trece Incorporated, 1143 Madison Lane, P. O. Box 6278, Salinas, CA
93912 (Telephone: 408-758-0205, Fax: 408-758-2625): Trap specialists.
Web page last updated on September 16, 1996 by Stephen J. Toth, Jr..
