| Specific Diseases of Trees, Shrubs and Ground Covers | ||
|---|---|---|
| Host Plant and Disease | Description | Management Options |
| Oak (Quercus) | ||
| Anthracnose
(fungus) (Figure 60) | Irregular tan or brown areas are found on the leaves, especially along the major veins of the leaf blade. The condition usually is noticed in late spring on lower parts of the plant. Deformation and twisting of leaves often result from infections that occ Most common on white oak, but also on other species. | Rarely life threatening; control not necessary. |
| Bacterial leaf scorch (bacterium) | Browning of leaf margins progressing toward the middle of the leaf. At first a single branch may be affected, often near the top of the tree. Leaves at the base of the branch develop symptoms first, but soon all leaves on the branch or limb are affected. Over time the diseased tree becomes less vigorous, leaves drop, and dieback occurs. May be confused with physiological leaf scorch. Oaks are most susceptible, but it has been reported on red maple, elm, and sycamore. | No feasible management available. Remove badly diseased trees. Keep trees as healthy as possible until disease becomes severe enough to remove them. This disease cannot be easily or positively diagnosed without special tests in the laboratory. |
| Chlorosis or yellowing
(physiological) (Figure 61) | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. Symptoms similar to those described for maple, but iron deficiency instead of manganese deficiency is the usual cause. Most common on pin oak and white oak. | See under maple. Use iron trunk implants. Obtain information from OSU County Extension office or consult a professional arborist. |
| Leaf spots (fungi) | Several different fungi cause spots of various sizes, usually round, often with a colored border. | Control measures not usually necessasy. These leaf spots are not serious or life threating. |
| Leaf blister
(fungus) (Figure 62) | Circular, raised, blister-like, green, yellow to white areas up to 1Ž2 inch in diameter appear on upper leaf surface. Disease occurs on "red oaks" and is more prevalent in wet years. "White oak" group is also susceptible, but less commonly affected. | Not usually serious enough to warrant control. |
| Lower trunk and buttress root rots (fungi) | See honeylocust for description of Gano-derma rot. Another common cause is a spongy yellow-orange shelf fungus growing at the base of the diseased tree. These lower trunk and root rots usually become apparent only on older trees and trees with injuries to the bark. | Preventing wounds is the key management option. See under honeylocust. Any injury at base of tree, such as lawnmower wounds, is a likely point of invasion by these fungi. |
| Oak wilt (fungus) | Wilting of leaves develops, usually first in the upper crown. Leaves become pale green, followed by yellowing or bronzing. The discoloration spreads from the margin toward the leaf midrib. Symptoms progress downward until all foliage is affected. Trees may die within a few weeks. A dark discoloration develops in the sapwood of wilting branches. The disease can be confirmed by laboratory tests. | Oaks of the red oak group are most susceptible. White oaks are less susceptible, with only a few branches dying each growing season. Removal of diseased trees is recommended. The fungus can spread from a diseased tree to an adjacent healthy oak through natural root grafts. Therefore, deep trenching between such trees is sometimes recommended. Once a tree is infected, control is not possible. |
| Powdery mildew
(fungus) (Figure 63) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, Some cultivars of English oak are particularly susceptible. | On most species, control is not necessary. |
| Scorch and dieback (physiological) | These diseases commonly result from winter damage as well as from poor root function coupled with high temperatures and moisture shortage. In some cases, bacterial infection of the plant is involved. Scorched leaves are brown around the edges and sometimes between the veins. Leaf yellowing and wilting may occur in late summer. Dieback and decline is often mistaken for Verticillium wilt. No wood streaking is present, however. Girdling roots may also cause these symptoms. See Chapter 7 for identification of Verticillium. | |
| Twig cankers (fungus) | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. | |
| Wetwood or slime flux (fungus) | Wilting and yellowing of foliage is followed by premature defoliation. One limb of the tree may be affected first. Gradual dieback may be apparent. Yellow-brown, brown, black, or greenish-black streaks may be found in outer rings of wood of infected branches. In herbaceous plants, the vascular system of stems and roots are discolored. | |
| Pachysandra (Pachysandra) | ||
| Leaf and stem blight
(fungus) (Figure 64) | Leaves appear first with brown blotches and finally as a blight. A brown to blackish stem rot with orange-brown, visible spore pustules develop. | Remove diseased plants. Improve air circulation by thinning plants. If necessary, spray with a properly labeled fungicide, beginning as soon as new growth appears in the spring. |
| Leaf yellowing | Overall yellow coloration of foliage develops, often in sunny locations or in sites with high soil pH (greater than 7.0). | Avoid planting in full sun location. Since pachysandra is an acid-loving plant, modify soil pH to about 6.5 if possible. |
| Peach, Ornamental (Prunus) | See "Purple leaf plum." | |
| Periwinkle (Vinca) | ||
| Stem blight and dieback
(fungus) (Figure 65) | Individual stems wilt and blacken. Dark brown to black leaf spots may occur. | Avoid overhead irrigation. Spray with a properly labeled fungicide, beginning when new shoots appear in the spring. |
| Root rot (fungus) | These diseases commonly result from winter damage as well as from poor root function coupled with high temperatures and moisture shortage. In some cases, bacterial infection of the plant is involved. Scorched leaves are brown around the edges and sometimes between the veins. Leaf yellowing and wilting may occur in late summer. Dieback and decline is often mistaken for Verticillium wilt. No wood streaking is present, however. Girdling roots may also cause these symptoms. See Chapter 7 for identification of Verticillium. | |
| Photinia, Oriental (Photinia) | ||
| Fire blight (bacterium) | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. | |
| Pieris (Pieris) (Japanese Andromeda) | ||
| Chlorosis | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. | Check soil pH, and if alkaline, modify to about 6.5 or lower. Improve drainage and maintain mulch. |
| Dieback
(fungus) (Figure 66) | Individual branches dieback. Both dieback diseases described under rhododendron are potential problems of Pieris. | |
| Root and Crown rot (fungi) | See "Rhododendron." | |
| Pine (Pinus) | ||
| Canker (fungus) | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. | |
| Chlorosis or yellowing | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. Needles light green to yellow with limited annual stem growth. | In addition to causes on page 31, air pollution maybe the cause on white pine. |
| Dieback (physiological) | See "Juniper." | |
| Needlecasts and
needle blights
(fungi) (Figure 67) | Pines, primarily Scots, Austrian and red, are subject to needle infection by several fungi. The fungi cause various spots ranging from black to whitish. As the disease progresses, the needles brown and fall from the trees. | Plant pines in open sites where they can get sun and moderately drying winds. Do not crowd plants. Spray during infection periods with properly labeled fungicides. Infection periods vary depending on the particular fungus involved. Thus, a specific diagnosis is necessary to correctly schedule fungicide applications. Fungicides usually not necessary in the landscape. Fungicides are important on Christmas tree farms. |
| Needle rust
(fungus) (Figure 68) | Small, cream-to orange-colored pustules on needles. The pustules later break open to reveal an abundance of orange, dusty spores. Red pine is very susceptible. The fungus is not found on five-needled (white) pines. | Destroy the alternate hosts (goldenrod and wild asters) near valuable plantings of red pines. Plant pines in full sun where moderate air movement will dry plants off after dew or rains. Spray plants in the fall with a properly labeled fungicide. Seldom damaging except on very young trees. For Austrian pine, the alternate hosts are ironweeds. |
| Pine wilt (nematode) | Early symptoms are on individual branches; the needles droop, turn brown, and adhere. Normal resin flow from cut branches ceases. Usually the entire tree is killed within a few months. Laboratory examination is necessary to confirm the diagnosis. | Increase the vigor of pines with fertilization if needed. Apply deep root waterings during dry spells. Promptly remove and destroy all pines in the area that have died from this disease or that have been confirmed to be infected with the nematode. Red pine is very susceptible, also on Scots and Austrian. Five-needled pines reported to be resistant. |
| Salt burn
(chemical) (Figure 69) | See "Juniper." White pines are quite sensitive to salt spray. | |
| Scorch and dieback | These diseases commonly result from winter damage as well as from poor root function coupled with high temperatures and moisture shortage. In some cases, bacterial infection of the plant is involved. Scorched leaves are brown around the edges and sometimes between the veins. Leaf yellowing and wilting may occur in late summer. Dieback and decline is often mistaken for Verticillium wilt. No wood streaking is present, however. Girdling roots may also cause these symptoms. See Chapter 7 for identification of Verticillium. | |
| Seasonal needle drop
(physiological) (Figure 70) | In late September and October, the inner and older needles often turn yellow and drop in great numbers. This is a normal process, but often causes homeowner concerns. Occurs on all pines but especially noticeable on white pine. A healthy white pine should retain three years of needles in summer and two years in winter. | Plant in a well-drained site, water during extended dry periods, and follow other practices to avoid stress. This will prevent the two-year needles from yellowing and falling a year before they should. |
| Tip blight
(fungus) (Figure 71, 72, 73) | Dieback of tips of Austrian, red, mugo and Scots pine. Disease often visible early in the season. Stem tips are killed before needles reach full size. Small, black fruiting bodies develop at the base of needles and on the old cones. Resin may ooze from the diseased stem tips. Usually occurs on lower branches first. | Where feasible, removal and disposal of diseased twigs may be helpful. If fungicides are used, spray just before new growth starts, followed by one or two more sprays at 14-day intervals. Use a properly labeled fungicide. Fertilize and water trees when needed. |
| White pine root decline (fungus) | Bud break in the spring is delayed. Needle growth is retarded and may be yellowish. Trees die and needles are reddish brown and do not drop. A canker forms at base of tree. The inner bark is brown to olive-brown. | No control. Plant white pines in well-drained sites. |
| Poplar, Cottonwood, Aspens (Populus) | ||
| Canker and dieback (fungi) | Cankers develop on stems, twigs, and trunk. Dieback continues until trees are killed. Lombardy poplar is often killed by canker-causing fungi. | Lombardy poplar is very susceptible and should not be planted. Prune and destroy branch cankers. |
| Leaf rust (fungi) | Orange, powdery pustules on underside of leaves. Usually not prevalent until late summer. | Common on some species, others not affected. Rarely affects health of the tree. |
| Leaf spots (fungi) | Several leaf spot diseases have been identified. Some cause defoliation on susceptible species. | Not usually serious enough to threaten the life of the tree. Collecting and destroying fallen diseased leaves may be helpful. |
| Privet (Ligustrum) | ||
| Powdery mildew (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, or chrysanthemums. Others affect newer shoots, such as on roses, flowering dogwood, London plane tree, or crabapples. When new shoots are affected, leaf curling and shoot stunting and twisting may be severe. | Control usually not necessary. |
| Twig blight and canker (fungus) | Stems dieback and pinkish or salmon-colored fungus fruiting bodies develop on the stems. | European or common privet is susceptible. Other species reported to have resistance. Prune and destroy diseased stems. |
| Purple leaf plum and other Prunus (Prunus) | ||
| Black knot
(fungus) (Figure 74) | Black, rough galls develop on the twigs. Neglected trees are especially subject to this disease. Black knot is found on some plums and some cherries, not on flowering almond. | Prune knotted twigs from large branches during the winter. If necessary, spray with a properly labeled fungicide. Increase the vigor of plants with fertilization if needed. Apply deep root watering during dry spells. |
| Blossom and twig blight and dieback (fungus) | Blossoms turn brown and collapse. Leaves and twigs become infected and fruits rot. Branches then die back from the infection outward. In damp weather, small growths or masses of powdery, brown fungus spores can be seen over the canker or actual site of the infection, and on the rotting fruit. Flowering almond is very susceptible to dieback. | Prune and destroy infected branches. Rake and destroy fallen plant debris. Spray with a properly labeled fungicide just before blossoms open and again 10 days later. |
| Leaf curl
(fungus) (Figure 75) | Ornamental peaches are commonly affected by this disease. In the spring, the leaves emerge thickened, misshapen, and reddened. Defoliation follows. Fruit- bearing species of peach are very susceptible, as are some native wild cherries. Some species cause malformation on stems and fruits. | Spray in late fall, after all leaves have dropped, or in the early spring before buds swell. One properly timed spray should be sufficient. Use a properly labeled fungicide. |
| Leaf spot (fungus) | Spots often have reddish borders. On cherries and cherry laurel, spots turn brown and centers fall out as they age. Do not confuse this disease with bacterial shot-hole (see below). Worse in wet seasons. Leaf drop may be extensive. | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, On some very susceptible Prunus species or cultivars, fungicides may be necessary. |
| Powdery mildew (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, | Seldom serious on plums, but can be on some of the cherries. |
| Shot-hole leaf spot (bacteria) | Small spots are found evenly over the leaf surface. The infected tissue dries up and falls out, leaving holes about 1/8 inch in diameter. The holes are generally smaller than those described under fungal leaf spot (above). Ornamental cherries are particularly susceptible. | Plant the trees in sunny locations. Prune away shade-producing vegetation. Do not crowd plants. |
| Redbud (Cercis) | ||
| Canker (fungus) | Sunken, black stem and twig lesions; leaves wilt and turn brown as the stems are girdled. Branch dieback can be extensive. Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. | Winter injury and drought stress may result in increased susceptibility. Avoid wounding; fertilize and water when necessary. |
| Verticillium wilt (fungus) | Wilting and yellowing of foliage is followed by premature defoliation. One limb of the tree may be affected first. Gradual dieback may be apparent. Yellow-brown, brown, black, or greenish-black streaks may be found in outer rings of wood of infected branches. In herbaceous plants, the vascular system of stems and roots are discolored. | |
| Rhododendron (Rhododendron) see Azalea | ||
| Chlorosis, yellowing
(Physiological) (Figure 76) | Caused by theoil pH being too high (above 6.5) | Lower soil pH. |
| Dieback (fungus) | Caused by the fungus, Botryosphaeria. First symptom usually is drooping leaves on an individual branch. Leaves are rolled inward. A reddish-brown sunken canker girdles the stem. | Prune out dying stems, following accepted practices. Fungicides are not effective. This disease will be worse if plants are under stress from winter injury and drought. Keep the plants mulched. |
| Dieback
(fungus) (Figure 77) | Caused by a species of Phytophthora that invades the stems or leaves. Brown leaf lesions are an early symptom. Can be confused with the dieback disease described above. | No effective control, other than pruning. Maintain mulch. |
| Powdery mildew (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, | More of a problem on some cultivars of azalea. Control not usually necessary on rhododendrons. |
| Root and crown rot
(fungus) (Figure 78) | Caused by one of several species of water mold fungi. Reddish-brown discoloration of roots and of the stem at or below the soil line. Entire plant wilts. | Planting site should be well-drained. Keep the plants mulched properly. |
| Rose (Rosa) | ||
| Black spot
(fungus) (Figure 79) | Black, round to irregular spots with fringed margins mainly on the upper leaf surface. Tissue around the spots may turn yellow. Defoliation often occurs. Small purplish spots occur on the canes. | Destroy infected leaves and canes of the previous year. Use an effective spray program with a properly labeled fungicide beginning when leaves emerge in the spring. Avoid overhead irrigation, especially late in the day or at night. Prune away shade-producing vegetation to improve rapid drying of foliage. Some varieties have been reported to be resistant or tolerant to black spot. See Table 5. |
| Brown canker
(fungus) (Figure 80) | Small, reddish-purple spots occur on stems, petioles, leaves, and petals. Stem cankers later turn white and enlarge the following spring into oval, light cinnamon areas studded with small, black, protruding spore-bearing pustules. Stems sometimes are girdled with cankers. | Prune out all infected canes and remove or destroy them. Heavy pruning may be necessary if many cankers are present. |
| Botrytis blight
(fungus) (Figure 81) | Buds and partially opened flowers turn brown and decay and are often covered with a powdery gray mold. Irregular tan or brown areas are found on the leaves, especially along the major veins of the leaf blade. The condition usually is noticed in late spring on lower parts of the plant. Deformation and twisting of leaves often result from infections that occ | Seldom serious enough to require control. |
| Crown gall (bacterium) | Infected plants do not flower well. Galls form at the crown or at the point of grafting. | Remove and burn severely infected plants. Keep plants vigorous with fertilizer and water as needed. |
| Powdery mildew
(fungus) (Figure 82, 83) | Younger leaves often affected first, often becoming curled. | Can occur when rainfall is low or absent. Humidity high at night and low in the day is favorable for development of this disease. Fungicides may be necessary. Some cultivars are reported to be resistant. |
| Rust (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, Not common in Ohio on garden roses. | |
| Stem canker or graft canker (fungus) | Small, pale yellow or reddish spots that increase in size, later turning brown, occur on bark usually near the ground. The cankered wood dries; bark cracks; and small, black fruiting bodies dot the cankered area. Infection enters through grafting wounds, cut stubs of canes, or other wounds. | Use measures outlined under "Brown canker." When pruning, cut back to nodes; do not leave stubs. |
| Russian Olive (Eleagnus) | ||
| Canker and twig blight
(fungus Phomopsis) (Figure 84) | Elongated, reddish-brown stem cankers kill the stems, resulting in dieback. Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. | Avoid wounding the branches. Follow accepted pruning practices. Do not prune when trees are wet or immediately after rains. |
| Verticillium wilt (fungus) | Wilting and yellowing of foliage is followed by premature defoliation. One limb of the tree may be affected first. Gradual dieback may be apparent. Yellow-brown, brown, black, or greenish-black streaks may be found in outer rings of wood of infected branches. In herbaceous plants, the vascular system of stems and roots are discolored. | |
| Serviceberry (Amelanchier) | ||
| Fire blight (bacterium) | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. | Occasional; usually not serious. |
| Leaf spot (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, | Not common. |
| Powdery mildew (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, | Control not usually necessary. |
| Rust (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, | Control not usually necessary; not common. |
| Spirea (Spiraea) | ||
| Fire blight, (bacterium) | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. Reported, but not common. | |
| Leaf spot (fungus) | Small round spots on some species, but not common. | Control not necessary unless watered overhead or in wet summers. |
| Spruce (Picea) | ||
| Canker
(fungus Cytospora) (Figure 85, 86) | First symptoms are browning of needles and dying of selected lower branches. Cankers occur on branches inside crown near the trunk. Swellings, accompanied by white, oozing pitch, occur at the canker. The fungus spreads to higher branches. It is most common on trees more than 15 years old. | Prune affected branches at trunk of tree when no rain is expected. Fertilize and water as needed. Vertically mulch if needed to improve the root health. Wounds caused by insects or mechanical injuries appear to be necessary for infection. Also drought stress is a predisposing factor. Serbian spruce reported to be resistant. |
| Needlecast (fungus Rhizospaera) | One-year-old needles discolor and have very small, black, fungal fruiting bodies in rows on the needles. Needles fall. Spruce needlecast can also result from soil compaction, heat stress, or herbicide toxicity. | Most frequent on blue spruce, not common on Norway spruce. |
| Sumac (Rhus spp.) | ||
| Leaf spot (fungus) | Brown spots with purple-brown borders. Spore-bearing structures visible in the center of the spot. | Usually not serious enough to require control with fungicides. |
| Powdery mildew (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, | No control necessary. |
| Verticillium wilt (fungus) | Wilting and yellowing of foliage is followed by premature defoliation. One limb of the tree may be affected first. Gradual dieback may be apparent. Yellow-brown, brown, black, or greenish-black streaks may be found in outer rings of wood of infected branches. In herbaceous plants, the vascular system of stems and roots are discolored. | Not common. |
| Sweet Gum (Liquidambar) | ||
| Canker
(fungus) (Figure 87) | Cankers develop, girdling the stems, causing dieback. Fruiting bodies of the fungus develop in the cankered bark. "Bleeding" around the cankered bark has been reported in some cases. | Fertilize and water trees as necessary to keep them in a vigorous growing condition. |
| Chlorosis or leaf yellowing | Yellowing of leaves between the veins, the veins remaining green. | Often caused by unavailability of iron in high pH soils. See under "Oak" for remedy. |
| Sycamore (Platanus) and London Plane Tree (Platanus) | ||
| Anthracnose
(fungus) (Figure 88) | New leaves may be killed. Damage looks similar to frost injury. Older or mature leaves show small to large, irregular dead areas along the veins. In the spring, bud blight and twig cankers occur with some dieback. The lower portions of the tree are damaged more severely. Crooked branching and a witches broom-like proliferation of twigs are also common symptoms. Defoliation occurs after leaf blight in the spring. New leaves develop by summer. | See "Anthracnose" on page 28. Spring sprays are often ineffective because bud infection can occur during the previous autumn. Some cultivars of London plane tree are reported to be less susceptible. Cool temperatures at bud-break are important in affecting severity of this disease. |
| Powdery mildew
(fungus) (Figure 89, 90) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, On new growth during summer, causing leaf distortion. | Control typically not necessary or feasible. |
| Scorch and dieback (physiological) | These diseases commonly result from winter damage as well as from poor root function coupled with high temperatures and moisture shortage. In some cases, bacterial infection of the plant is involved. Scorched leaves are brown around the edges and sometimes between the veins. Leaf yellowing and wilting may occur in late summer. Dieback and decline is often mistaken for Verticillium wilt. No wood streaking is present, however. Girdling roots may also cause these symptoms. See Chapter 7 for identification of Verticillium. Considerable leaf scorch and defoliation occurs in late summer, especially during dry seasons. | |
| Tulip Poplar (Liriodendron) | ||
| Leaf spotting and yellowing (physiological) | Leaves develop large brown to black spots, turn yellow and fall during late July and August when trees are subject to water stress because of planting site problems or hot, dry weather. | See "Scorch and dieback" under general problems on page 32. |
| Viburnum (Viburnum) | ||
| Bacterial leaf spot
(bacterium) (Figure 91) | Small, circular to angular, brown, water-soaked spots. Spots become irregular. | Not common or rare on most landscape species. Has been noted on European cranberrybush, Burkwood, viburnum, Koreanspice viburnum, and Juddii viburnum. Worse during wet season or when using overhead watering. |
| Downy mildew
(fungus) (Figure 92) | Certain species will develop gray, sometimes water-soaked spots on the underside of leaves, with brownish, scorched areas in the upper leaf surface. As the disease worsens, defoliation can be severe. Common in wet seasons or if watered overhead. | Prune away shade-producing vegetation. Do not crowd the plants. Avoid overhead irrigation. Spray with a properly labeled fungicide. V. opulus is particularly susceptible. Not common on most other species. |
| Powdery mildew (fungus) | White, powdery areas appear on leaves, stems, flowers, or buds. If the infection is widespread, the entire leaf blade may be covered with a thin, white fungal, powdery growth. Some mildew fungi affect older leaves first, such as on oaks, lilacs, zinnias, | A common problem on V. lentago and V. prunifolium. Rare or not found on other landscape species. |
| Walnut (Juglans) | ||
| Anthracnose
(fungus) (Figure 93) | Irregular dark brown spots on leaflets. Yellowing occurs around the spots, and leaf drop occurs in late summer. Leaf fall is often extensive. | Since this is a disease that occurs late in the summer, little actual damage to the tree occurs. May be feasible to spray small trees. |
| Western Sand Cherry (Prunus) | See "Purple leaf plum." | |
| Yew (Taxus) | ||
| Chlorosis or yellowing (several potential causes) | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. | Do not plant in poorly drained soils. Examine for black vine weevil feeding on leaves, roots, and lower stem. If black vine weevil is present, use chemical controls. |
| Root rot
(fungus) (Figure 94, 95) | These diseases commonly result from winter damage as well as from poor root function coupled with high temperatures and moisture shortage. In some cases, bacterial infection of the plant is involved. Scorched leaves are brown around the edges and sometimes between the veins. Leaf yellowing and wilting may occur in late summer. Dieback and decline is often mistaken for Verticillium wilt. No wood streaking is present, however. Girdling roots may also cause these symptoms. See Chapter 7 for identification of Verticillium. | Plant in well-drained sites or improve drainage if possible. |
| Salt burn (chemical) | See "Juniper." | |
| Zelkova (Zelkova) | ||
| Dutch elm disease (fungus) | See "Elm." | Zelkova is only mildly susceptible to Dutch elm disease. Prompt pruning of infected branches is often an effective control. |
| Canker (fungus) | Young twigs and branches die from the terminals and appear burned. Branches may be bent over at the tip, resembling a shepherd's crook. Dead leaves generally remain on the branch. Affects members of the rose family. |