Entomology 462 Ornamentals Pests: Borers

Transcription

1 Entomology 462 Ornamentals Pests: Borers David J. Shetlar, Ph.D. The BugDoc The Ohio State University, OARDC & OSU Extension Columbus, OH October, 2004, D.J. Shetlar, all rights reserved Woody Ornamental Pest Groups Borer Symptoms SUDDEN Plant Death Sawdust from Hole Sap/Pitch from Hole Gouty Growth on Trunk or Branch 1

2 Sudden death to spruce terminal caused by white pine weevil larvae. Bronze birch borer larvae usually cause host trees to die from the top down. Sawdust like frass produced by rhododendron borer. Dry sawdust being produced by a borer suggests that it is feeding in a dead area. Pitch mass caused by zimmerman pine moth larva. Sap or pitch flow suggests that the borer is feeding in living tissues. 2

3 Woody Ornamental Pest Groups Chewing Pests - Borers Beetles that are Borers - Roundheaded Borers (longhorn beetles) Flatheaded Borers (metallic wood borers) Bark Beetles (bark, shothole, ambrosia beetles) Weevils (shoot & root weevils) Moths that are Borers - Clearwing Moths Carpenterworms (leopard moths) Twig, Tip & Shoot Moths Roundheaded Borers (Cerambycidae) (adults are known as longhorn beetles) Elm borer adult, note antennae that are, at least, as long as body. Elm borer larva is oval in profile and produces an oval hole. Elm borer pupa. 3

4 Most roundheaded borers attack trees or shrubs that are dying or have recently died. In many cases, the plant may not overtly exhibit signs of death, at least to inexperienced plant care managers. The few roundheaded borers that attack stressed trees usually feed in the heartwood rather than the cambium area. This may weaken the structure of the tree, but does not kill it outright since girdling does not occur in the sapwood area. Unfortunately, the larvae of cerambycid larvae are commonly found under the bark of dead trees and are accused as being the cause of the plant death. Roundheaded borers usually make round or rounded-oval emergence holes. One roundheaded borer, the twig girdler has adults that cut a groove in small branches which cause these to eventually break and drop. Their larvae feed within the girdled branch. The oak pruner has larvae that girdle small oak branches that cause these to also break out of the trees. The larvae also feed in the dead branch. Both pests rarely warrant control. Locust borer adult on goldenrod, its favorite fall feeding ground. Locust borer emergence hole. Most longhorn beetles produce round or rounded-oval holes. 4

5 Pine sawyer adult and emergence hole. Pine sawyers normally don t kill pine trees, but adults transmit pine wilt nematodes that do! Pine sawyer larvae, lower left. Spotted pine sawyer adult. Oak Twig Pruner Adult Larva in twig. Sawdust-like frass being pushed out of pruned branch by larva. 5

6 Flatheaded Borers (Buprestidae) (adults are known as metallic wood boring beetles) Flatheaded appletree borer larva. Flatheaded appletree borer adult emerging. Adult flatheaded appletree borer. Flatheaded borers are called this because the first thoracic segments BEHIND the head are often expanded laterally and flattened. These larvae usually feed in the cambium or sapwood of host plants and they produce very flat and straight-sided burrows. By feeding in the sapwood, these borers commonly girdle their hosts, causing sudden death. The adults are called metallic wood borers because they are often coppery or bronze in color. Some are bright iridescent green or blue and are highly prized by beetle collectors. When the adults emerge, they usually produce flattened oval or D-shaped holes. The genus Agrilis has many species which are commonly encountered in landscape trees. The larvae of this genus are very thin and narrow with the thorax only slightly expanded laterally. Most adults in this genus leave characteristic D-shaped exit holes. 6

7 Bronze birch borer larva in sapwood. Bronze birch borer adult emerging. Honeylocust borer adult. Honeylocust borer emergence hole. Note characteristic D-shape. Bronze birch borer females tend to lay their eggs in bark fissures or under flaps of bark. Therefore, if a preventive insecticide is used, thorough coverage is essential for success. 7

8 Bark Beetles (Scolytidae) (also called engraver or ambrosia beetles) Cedar bark beetle adult. Cedar bark beetle larvae. Pine Ips beetle and emergence hole. These beetles are sometimes called shothole beetles. Bark beetles usually attack stressed or dying trees. As with longhorn borers, these beetles are often blamed for the death of their host tree. The European elm bark beetle transmits Dutch Elm Disease which is a fungus that the adult beetles pick up when they exit infected trees. These beetles feed on the branches of healthy elms and accidentally introduce the fungal spores. The fungus rapidly attacks the new trees, causing branch or whole tree dieback in a year or less. These dead or dying trees serve as new hosts for the beetles, thereby perpetuating the cycle of the beetles and fungus. Some conifer bark beetles, especially the southern and western pine bark beetles, perform mass attacks where an adult may find a weak or apparently healthy tree. Once located, this scout releases an aggregation pheromone that attracts hundreds of additional beetles. All the beetles bore into the tree at once, overwhelming it. In landscapes, recently transplanted larger trees and trees suffering from root damage due to construction or disease are especially prone to bark beetle attack. 8

9 Weevil Borers (Curculionidae) White pine weevil adult female laying eggs. White pine weevil larvae burrowing down leader. Leader killed by white pine weevils. Clearwing Borers (Sesiidae) This group is commonly listed as the Aegeriidae Lesser peachtree borer adult. Ash/lilac borer larva in lilac branch. Maple callus borer adult. Peachtree borer larva in sand plum. 9

10 The clearwing moth borers are some of the most common key pests found in urban landscapes. While they usually can not attack healthy plants, once they get established, they may reinfest the same plant year-after-year until it is girdled and killed. Some of the most important species are the dogwood borer, the rhododendron borer, the peachtree borer (in flowering peach, plum and cherry), the ash/lilac borer, the banded ash clearwing, and the oak borer. Most of the clearwing borer adults can be monitored by using pheromone traps. Traps are placed out two weeks before the species normally flies. When the first moth is captured (males fly first), there is usually 10 to 14 days before females are developed sufficiently to lay eggs. This allows for susceptible plants to be treated with preventive insecticides. Traps should be monitored three to four weeks after the first preventive application in order to determine if adults are still active. If so, a second treatment may be needed. Carpenterworms (several species) Diagram of lesser carpenterworm adult (top), larva (bottom), and pupa (right). 10

11 Carpenterworms are thick bodied moths that attack a variety of trees, especially willow, elm, ash, oak, cottonwood and maples. The larvae feed primarily in the sapwood and make scattered holes through the bark through which they expel sawdust-like frass. The larvae feed slowly and may take three to four years to mature. The larvae are first pinkish but become cream colored with rows of small black spots when mature. Attacks rarely kill their hosts, but their burrowing causes considerable disfiguring of the bark and can structurally weaken the trunk. A related pest, the leopard moth, has adults with white wings covered with black spots. This European import attacks most deciduous ornamental trees. Like the carpenterworms, attacks rarely result in sudden plant death, but affected trees may have easily broken branches. Trees tend to decline over many years of repeated attack. There are few controls registered for carpenterworm or leopard moth borers. Most recommend keeping susceptible trees in good health, especially avoiding bark damage or poor pruning. Maple Shoot Borers (several species of caterpillars) First symptom is usually sudden tip wilting and dieback. Upon looking closer, there us usually some frass being pushed out of a terminal hole. Maple shoot borer caterpillar. 11

12 There are several moths that burrow into the stems and shoots of deciduous trees and shrubs. The boxelder twig borer attacks boxelder and red maple. Larvae overwinter in dormant buds and burrow into shoots in the spring. This causes shoot death, swollen shoots and bushy growth. Several other species burrow into the shoots of silver maple and horsechestnuts. Most of these pests seem to prefer small trees. Attacks decrease when the trees mature. Early attacks can cause major problems in nurseries, because the plants do not develop straight trunks. Infestations in established landscape trees can usually be treated with judicious pruning. Pine Tip or Shoot Moths (several species, depending on location) EPSM pupa in damaged bud. Pitch pine bud killed by European pine shoot moth (EPSM). Note small pitch mass at base of dead bud. EPSM adult. 12

13 There are numerous species of moths in the genus Rhyacionia that are called pine tip or shoot moths. The European pine shoot moth and Nantucket pine tip moth are the two most common species attacking most ornamental and forest pines (except for white pine) in the northeastern states. The Monterey pine, Ponderosa pine and Southwestern pine tip moths attack pines in the Rocky Mountains and Pacific Coast States. Heavily attacked young trees, especially in tree plantations and nurseries, can be severely stunted and tend to have crooked trunks, making the trees unsuitable for ornamental use or lumber production. Most species attack buds as early stage larvae and some burrow down expanding shoots in early summer. This kills the buds and shoots, causing loss of leader dominance. Side shoots may eventually gain dominance, but the trunk will have a conspicuous crook. Insecticides are usually applied to kill larvae as they hatch from eggs and try to burrow into buds. Systemic insecticides are occasionally used to kill larvae once they have entered buds or shoots. Borer Control Cultural Use plants that are not prone to borer attack! Plant health care plants in good growing conditions can usually repel borer attacks. Avoid Plant Damage damaged plants are prone to attack. Biological Determine if present (parasites & predators) Usually not effective because they attack after infestation. Chemical Preventive- Adulticides: contact or stomach pesticides applied when adult is active. Select long residual materials. Curative- Larvacides: use systemic pesticides, being aware of translaminar and translocated activities. Translaminar activity is not usually effective against borers. 13

14 Woody Ornamental Pest Groups Chewing Pests Cambium Miners Moths - Flies - Beetles - (all uncommon and not usually damaging) Maple Cambium Miner This is a small dipterous pest. Some call these pests bark miners because they actually feed in the cortex and phloem immediately under the epidermis. 14