From Elms to Oaks to Maples To

F a nice big shade tr<' Iedge of the fairway sua turns brown and starts t; From Elms leaves in the middle of the si mer. it is important to det. mine whether neighboring healthy trees need protection. Because there ; - to Oaks several diseases that cause leave wilt suddenly and turn brown, t H superintendent may need to un- sult a plant pathologist or an ex- to Maples to.. perienced arborist for an accural diagnosis. The three main vascular wilt Superintendents who replaced elm trees felled diseases of trees are Dutch elm dis- by Dutch elm disease with oaks and maples may ease, Verticillium wilt and oak wilt. Each is caused by a different now be confronted with a new battle against fungus that is extremely patho- Verticillium wilt and oak wilt genic on particular species of trees. Dutch elm disease has received a lot of notoriety, but little has been reported in popular literature con- cerning the other two wilt diseases. However, a great number of re- search reports on Verticillium wilt and oak wilt have been published by pathologists in scientific jour- By E.B. HIMLICK nals during the past 20 years. Verticillium wilt leaf symptoms (above) on a twig of an affected blue ash tree. Wilting foliage (right) has advanced throughout the crown of this tree. Many leaves on the outer twigs have fallen off. Verticillium wilt disease is reported throughout the the diseased branches or trunks. United States and in many other Plants that develop a limited Verticillium wilt, caused by the countries. (Refer to the table for amount of branch wilt during the fungus Verticillium albo-atrum, trees and shrubs susceptible to summer may show additional wilt has become increasingly prevalent Verticillium wilt.) and dieback the following year, among plantings of shade and or- and others may recover and not namental trees and shrubs. The Disease symptoms—External wilt in succeeding years. Plants disease affects a wide variety of un- and internal symptoms are vari- having extensive or general wilt related annual and perennial plants able and often difficult to recog- throughout the crown are often but seldom occurs in wooded areas nize. Usually the. first external dead by the end of summer. or in forest stands. Verticillium symptom is sudden wilting of fo- Sapwood discoloration often oc- wilt has been known to occur on liage on one or several twigs on a curs in twigs and branches show- planted trees for over 50 years. branch. Later the entire branch or ing advanced stages of foliage wilt. New tree and shrub species are the whole crown may show typical The discoloration is found by continually being reported as sus- wilt symptoms. Most plants first making a long slanting knife cut ceptible to this fungus. Presently, show symptoms in June or July; across the end of a branch sample. about 80 tree and shrub species and however, some trees may wilt as In most trees the sapwood discol- varieties growing in the United soon as new foliage is produced in oration occurs as streaks of vari- States are known to be susceptible the spring. ous shades of brown. Infected ma- to Verticillium wilt. It is probably Other external symptoms that ple, magnolia and sumac show safe to say that Verticillium wilt may indicate Verticillium wilt are light to dark green streaks. affects more kinds of ornamental general decline in current twig The Verticillium wilt disease plants than any other disease. The growth, dieback of individual can only be positively identified by disease is not always fatal but does twigs and general yellowing of the having a laboratory diagnosis cause a large amount of branch foliage. Occasionally trees, such as made from infected branches. This kill so that ornamental value is of- the maple and the tulip, develop service can usually be obtained by ten lost and many affected plants elongated dead areas of bark where sending two or three branch sec- eventually must be replaced. The the inner bark has been killed on tions cut from recently wilted branches to the plant pathology department of a local college or university. Immediately after the material is collected it should be placed in a plastic bag and mailed. Care of infected trees—The fungus is parasitic on living tissue of many plants and can live over a year in dead organic matter in the soil. The fungus spores or micro- scopic filaments, known as hyphae, gain entry into the vascular sys- tems of plants through wounds made on the roots, branches or trunk. Wounds on the trunk caused by lawn mowers afford excellent areas for infection to occur. Such wounds should be treated by cut- ting away the damaged bark and Typical discoloration is often observed in the deseased sapwood of twigs and branches cut painting the exposed wood and in- from infected Norway maple trees. jured bark area with a standard tree dressing paint. Trees or shrubs suspected of having Verticillium wilt should be watered immediately. Susceptible plants occasionally show symptoms of the disease while they are in a weakened condition following (Continued) MAPLES veys indicate that it is no ad- ing to new areas as rapidl) plant (Continued) redbud, Russian olive, smoke tree, pathologists had believed i dd. transplanting. Drought conditions sumac, tulip tree and viburnum. Recognition of the dis se— may cause wilt symptoms on af- Any of these plants mentioned Oak wilt symptoms ma\ appear fected trees to be more severe. Af- should not be used to replace plants any time from May until frost oc- fected trees should be watered ev- killed by the disease. Generally, curs in the fall. Known hosts of the ery 10 to 14 days with the equiva- narrow and broadleaf evergreen oak wilt fungus include 36 speci< s lent of two inches of rainfall. A trees and shrubs may be considered of oak and six tree species closely portable water sprinkler may be safe replacements. (See table for a related to oak: Allegheny and bush used. If the affected plant survives, complete list.) regular watering at two to three chinquapin, tanbark-oak and week intervals should continue dur- American, Chinese and Spanish ing dry periods in the summer of Oak Wilt chestnut. In early stages of the dis- the succeeding year. Although Verticillium wilt is ease wilting and browning of the foliage usually appear in the upper Also, affected plants should be common on many kinds of orna- crown. Among trees of the red oak fertilized to stimulate vigorous mental trees and shrubs, oak wilt growth. For quick response, the presents a threat only to species of group, which includes red, black, pin and shingle oak, wilting rapid- fertilizer should be injected into the oak. The fungus causing oak wilt ly progresses downward until the soil in liquid form or applied to the is technically called Ceratocystis entire tree is affected. Partial to soil surface and watered in well. fagacearum. Once the oak wilt dis- complete defoliation occurs within Urea can be applied on the surface ease becomes established in a leaf or injected at the rate of 13 pounds wooded area it can steadily pro- a few weeks after the first symptoms start to show. Some per 1,000 square feet. gress until a large number of val- leaves that are still green fall and Branches killed by the disease uable trees eventually are killed. have typical muddy green or brown can be pruned. Pruning diseased At present the disease is restricted margins. Frequently, brown dis- branches will not eliminate the fun- to the eastern part of the United coloration may be found in the out- gus that is present in the trunk or States. It has been reported in 19 er sapwood of wilting branches. roots of the affected plant. All states ranging from Pennsylvania pruning tools should be carefully in the east, Arkansas in the south, White and bur oaks usually have sterilized with rubbing alcohol be- Nebraska in the west and Minne- only a few branches that wilt the fore using on any other plants. sota in the north. The disease is first year. In succeeding years oth- believed to be native to the United er branches may die, giving the Future tree and shrub selec- States and is not known to occur in tree a stagheaded appearance. In- tions—Tree and shrub species any other country. Fifteen years fected white and bur oaks may per- most frequently affected with ago it was thought to be a serious sist for several years, whereas in- Verticillium wilt are: ash, barber- threat to the entire oak timber pop- fected red and black oaks usually ry, catalpa, elm, magnolia, maple,. ulation, but intensive national sur- die in one growing season. As in Once oak wilt becomes established (left) in a wooded area, it can steadily progress until a large number of valuable trees are killed. The oak wilt fungus ("above) on the wood surface has produced a fungus mat under the bark. The center raised portion is part of the fungus growth that apparently pushes the bark loose to help form a crack through which insects enter. jm Wilt Susceptible Locust, Black Almond Magnolia, Saucer, Southern, Star, Apricot Maple, Amur, Black, Boxelder, California Boxelder, Japanese, Ash, Black, Blue, European, Norway and varieties, Red, Ore- Green, White gon, Painted, Striped, Sugar, Azalea Sycamore Barberry, Japanese Oak, Pin, Red, Turkey Boxwood, Korean Osage orange Camphor tree Pagoda tree Picnic beetles and larvae feeding on an oak Carob Peach wilt fungus mat. The insects become con- Catalpa, Western Persimmon taminated with the fungus spores and frag- ments and carry them to wounds on healthy Cherry Pepper tree trees.

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