| Specific Diseases of Trees, Shrubs and Ground Covers | ||
|---|---|---|
| Host Plant and Disease | Description | Management Options |
| Hawthorn (Crataegus) | ||
| 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. | Many species or cultivars are resistant or only slightly susceptible. |
| Leaf spot
(fungus) (Figure 40) | English hawthorns are susceptible to a summer leaf spot that can lead to extensive defoliation. The disease begins as a tiny purple spotting. Leaves yellow and drop as the disease develops on younger foliage. 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, | Plant resistant or immune species or cultivars. Chemical control often necessary for susceptible English hawthorns if they are planted. Most hawthorns are not susceptible. |
| Rust on leaves, fruit and stems
(fungi) (Figure 41, 42) | The most important rust species on hawthorns in the landscape affects twigs, stems, leaf petioles, and fruits. These plant parts become distorted and by summer an abundance of orange-yellow spores form, especially on the fruit. Leaf rust may also occur in some cases. Twig dieback can occur. Washington hawthorn is especially susceptible. | The spores from the hawthorns spread the rust to susceptible junipers, the alternate hosts. Plant resistant hawthorns or do not plant near susceptible junipers. Fungicides can be used beginning as the leaves unfold and continuing through the flowering period. |
| Hemlock (Tsuga) | ||
| Canker (fungi) | 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. | Most often affects plants in an unfavorable planting site such as exposure to full sun. Keep plants mulched, and water during dry periods; avoid injuries. |
| Needle browning (physiological) | Salt spray often results in damage. Some browning of older needles is a normal process in the fall. | Do not plant near streets or roads where salt is commonly used. |
| Rust
(fungus) (Figure 43) | Hemlock rust commonly occurs on young shoot tips, where it causes twisting and deformation. 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, | Usually not serious or life threatening. |
| Hickory (Carya) | ||
| Anthracnose (fungus) | 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 | Control is seldom necessary. |
| Leaf spot (fungus) | Several leaf spots may occur on hickory. None are usually serious or they occur late in the season. | Not usually serious enough to warrant control measures. |
| 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. | |
| Holly (Ilex) | ||
| Black root rot (fungus) | Plants are chlorotic and may be stunted, eventually with dieback. Roots are stunted and blackened. | Inspect hollies in containers before purchase. Remove diseased plants once disease is confirmed. |
| Purple leaf spots (fungus) | Large, sometimes irregular spots occur on leaves. The spots may be yellow, brown, or black. Do not confuse with spine spot. 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, | Several kinds of leaf spots are reported; control is usually not necessary. Not common. |
| 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. | |
| Spine spot (insects or mechanical) | Small, gray spots, sometimes with purple, halos are found on the leaves. Once said to be caused by spines of adjacent leaves, but is caused by feeding of the holly leaf miner insect. | Control of insects with appropriate sprays may be necessary. |
| Honey locust (Gleditsia) | ||
| Ganoderma rot (fungus) | A decay or rot of lower trunk and buttress roots occurs on older or mature trees. There may be no outward symptoms at first. Later large, shelf mushroom fruiting bodies grow at the base of the tree. They are cream-colored on the lower surface and brownish-red and shiny on top. | Preventing lawn-mower wounds or any other injury to the bark and roots is the key to preventing this disease. If wounds occur proper treatment immediately is necessary, but not always successful. |
| Honeysuckle (Lonicera) | ||
| Leaf blight (fungus) | Large areas of leaves turn dark brown and curl, and there is a whitish growth visible on the lower leaf surface. The disease is favored by cool, wet weather. | Avoid overhead irrigation. Prune away shade-producing vegetation. If necessary, spray with a properly labeled fungicide, although seldom 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, | Not common or serious. |
| Horsechestnut and Buckeye (Aesculus) | ||
| Leaf blotch
(fungus) (Figure 44) | Small to large irregular, reddish-brown spots with yellowish edges occur on leaves in late June or July. Spots enlarge with browning and curling of leaflets. The disease is more prevalent on lower leaves. | Plant in open sunny areas to increase air movement and leaf drying. Chemical control not usually necessary. Bottlebrush buckeye appears to be resistant. |
| 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 recommended. |
| Scorch | 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. Often confused with leaf blotch and vice-versa. | Often present by late summer, especially on Ohio buckeye. Watering may delay onset of scorch. |
| Hydrangea (Hydrangea) | ||
| Foliar diseases (fungus) | Leaf spot, powdery mildew and leaf rust may occur occasionally on some species, but usually not serious. | Control usually not necessary. |
| Ivy, Boston and Virginia creeper (Parthenocissus) | ||
| Leaf spot
(fungus) (Figure 45) | Small, circular, light tan spots develop on plants in cool, damp areas. Blighting and leaf deformation may occur later. 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, | Generally not serious enough to warrant control. |
| 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, On Virginia creeper, but not serious. | Does not warrant control. |
| Ivy, English (Hedera) | ||
| Bacterial leaf spot and
stem canker
(bacterium) (Figure 46) | Leaf spots are brown or black and often appear water-soaked with reddish margins. Leaf stalks become black and shriveled. Canker forms in the woody portion of the vine. | Remove infected plant material. Avoid splashing water and watering later in the day. If necessary, spray with a properly labeled bacteriacide. |
| Japanese Kerria (Kerria) | ||
| Leaf and twig blight (fungus) | Round to angular brown spots, with darker borders. Leaves yellow and die. Stem cankers develop and cause dieback of stem tips. | Prune out diseased tissue. Fungicides may be necessary in severe cases. |
| Juniper (Juniperus) | ||
| Dieback (physiological) | Needles and small branches turn brown and die. Larger branches and sometimes an entire side may be involved or the entire plant dies. | Avoid planting in dry, hot locations or in heavily shaded sites. Cover ground around plants with mulch to conserve water and control soil moisture variation. Fall watering is important. However, excess water may drown the roots. |
| Fall browning (physiological) | Some interior and older needles brown and fall in autumn, as a normal process. | Be sure the plants are well watered and mulched, otherwise no control is needed. |
| Phomopsis tip blight
(fungus) (Figure 47, 48) | Damages new growth and succulent branch tips of junipers from mid-April through September. Older, mature foliage is resistant to infection; therefore, most blighting occurs on the terminal 4 to 6 inches of the branches. Affected foliage first turns dull red or brown and finally ash-gray. Small gray lesions often girdle branch tips and cause blighting of foliage beyond the diseased tissue. Small, black, spore-containing fungal fruiting bodies develop near the base of dead tips. Use a hand lens to view these diagnostic fungal structures more easily. Most infections usually occur in April through early June and again in late August through September. Very few infections occur in mid-summer or during the winter months. Repeated blighting in early summer can result in abnormal bunching (witches' broom) and discoloration of the foliage, stunting of young plants, or in severe cases, plant death. | Management options for Phomopsis and Kabatina tip blights are essentially the same for both diseases; except for fungicide controls. When purchasing new plants, select those that have been reported to have disease resistance. Table 3 has information on relative disease resistance to Phomopsis and Kabatina of several juniper selections. Space new plantings to provide good ventilation and air circulation and avoid heavily shaded areas. Avoid wounding plants, especially in spring and fall. Water plants in early morning so the foliage will dry as soon as possible. Maintain adequate fertility, but do not over-fertilize. Prune out diseased branch tips during dry summer weather and destroy them. Do so only when plants are dry and no rain or overhead irrigation is expected for several days. Avoid excessive pruning or shearing. Chemical control of these tip blight diseases normally is not necessary in established landscape or windbreak plantings. Occasionally, fungicide applications may be needed on susceptible junipers to control Phomopsis blight. Application of certain copper-based (Phyton-27, Kocide) or thiophanate (Cleary's 3336, Topsin-M) fungicides at 7 to 21 day intervals during rapid plant growth in the spring will give adequate control of Phomopsis but not Kabatina tip blight. Kabatina blight infections occur in the fall, and there currently are no fungicides labeled for control of this disease. These fungal tip blights are often mistaken for damage due to mites or insects. |
| Kabatina tip blight (fungus) | Symptoms first appear in February and March and well before those of Phomopsis tip blight. The terminal 2 to 6 inches of diseased branches throughout the juniper first turn dull green, then red or yellow. Small ash gray to silver lesions dotted with tiny, black, fruiting bodies of the fungus are visible at the base of the discolored tissue. The brown, desiccated foliage eventually drops from the tree in late May or June. Foliar blighting occurs only in early spring; it does not continue through the summer. Blighting is also restricted to the branch tips and does not cause extensive branch dieback or tree death. The primary infection period for the Kabatina fungus is thought to be in autumn, even though visible symptoms are not apparent until late winter or early spring. Infection often is associated with small wounds on branch tips caused by insect feeding or mechanical damage. | |
| Rust
Cedar--apple rust
Cedar--hawthorn rust
(fungi) (Figure 49, 50) | Dark brown, corky, spherical to kidney-shaped galls are produced on the leaves and stems of Eastern red cedar and some other species of Juniperus. During spring rains, the galls develop elongated, orange, gelatinous projections called spore horns. These spore horns produce spores that cause infections on alternate hosts. Alternate hosts are crabapples and hawthorns. | Hand pick galls in early April if only a few are present. Do not plant susceptible junipers near susceptible apples, crabapples, or hawthorns. See Table 4. |
| Cedar-quince rust
(fungus) (Figure 51) | Slight swellings on stems and twigs of susceptible junipers. The affected twigs are hardly noticed until yellow-orange, jelly-like spore masses form in late April and May. The twigs may die back. | The most important alternate hosts are hawthorns, especially "Washington." Most other species are not generally severely infected. Do not plant susceptible junipers and hawthorns in the same area. |
| Salt burn (chemical) | Browning of branches occurs on side toward roadway where drift blows salty water onto plants or where salt-laden snow is shoveled onto plants. | Prune out dead material in spring. Use protective barriers in problem areas, or use salt-tolerant plants. Some junipers are tolerant or resistant. |
| Leucothoe (Leucothoe) | ||
| Leaf spots (fungi) | Several species of fungi cause leaf spots that may vary in color and size. | Fungicides may be necessary in some cases. On isolated plants pick off and destroy affected leaves. |
| Lilac (Syringa) | ||
| Bacterial blight (bacterium) | Young shoots are marked by black stripes. One side of the shoot may be black. Water-soaked spots appear on leaves. Flower buds may be completely blackened. The problem is serious in wet weather and may be confused with frost injury. | Prune out infected branches. Avoid excessive fertilization. Thin plants to improve air circulation. Prune away shade-producing vegetation. Chemical sprays are not effective. |
| Leaf roll and scorch | 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. | |
| Leaf spot and blight (fungus) | Large brown spots with rings occur in damp weather. As they age, they commonly crack in the center. 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 a common or serious problem. |
| Powdery mildew
(fungus) (Figure 52) | 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, | Common lilac most susceptible. |
| London Plane Tree (Platanus) | See "Sycamore." | |
| Magnolia (Magnolia) | ||
| Frost injury | Flower buds or flowers are browned and killed when temperatures below freezing occur. | Early-flowering species such as star magnolia and saucer magnolia are most commonly affected. |
| Leaf spot (fungus or bacterium) | Large, irregular spots form on older leaves in damp weather. 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, | Fungal leaf spot is seldom a serious problem in Ohio. Bacterial leaf spot has the potential to be serious, especially in nursery situations with overhead watering. Any practice directed toward maintaining dry foliage is beneficial. |
| Maple (Acer) | ||
| Anthracnose blight
(fungus) (Figure 53) | On Norway maple, narrow, irregular, brown streaks of dead tissue along the veins sometimes develop. On sugar, red, and other maples, large, irregular brownish areas between and along veins occur with symptoms similar to physiological leaf scorch. Small fruiting bodies on and near the veins sometimes can be seen with a hand lens. Some defoliation may occur. 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 | Control with fungicides usually not necessary. It may be helpful to rake and destroy fallen leaves to reduce over wintering inoculum of the fungus. NOTE: Black maple is often affected with another type of anthracnose. Circular tan to brown spots are scattered over the leaf surface. A different fungus is involved. |
| Chlorosis or yellowing | Leaves on one or several branches develop yellowing between the veins. The veins remain green. In other cases, entire leaves yellow due to various physiological stresses. 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. | Interveinal chlorosis of red, silver, sugar, and Norway maples in Ohio is often due to nutritional deficiencies as a result of soil pH above 6.5. At high soil pH, manganese becomes unavailable. Lowering soil pH (often difficult), spraying foliage with micronutrients, or using trunk implants of manganese materials is sometimes recommended, especially for red maple. See your OSU County Extension Office for information. |
| Phyllosticta leaf spot
(fungus) (Figure 54 and 55) | Several fungi cause leaf spots on maple. The most common is Phyllosticta leaf spot. A light tan spot develops up to 8mm in diameter. Tiny black fungal spore bodies dot the surface. | Leaf spots on maples are seldom severe enough to warrant chemical control. |
| Tar spot
(fungus) (Figure 56) | Another spot, called tar spot appears as shiny black spots up to .5 to 2 cm across. They look like spots of dried tar. | Control seldom necessary. Generally not damaging and occurs late in the season. |
| 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, | |
| Scorch and dieback
(physiological) (Figure 57) | 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. | |
| Verticillium wilt
(fungus) (Figure 58, 59) | 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. | Red maple less susceptible than Norway, sugar, and silver. |
| Mock orange (Philadelphus) | ||
| Bacterial leaf spot (bacterium) | 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, | Avoid overhead watering; not common in the landscape. |
| 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, | Controls not usually necessary. |
| Mountain Ash (Sorbus) | ||
| Cankers (fungi) | 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. Almost always develops on stressed trees (recent transplants, drought, winter injury, etc.) | |
| 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. | |
| Scorch and canker complex (fungi and environmental causes) | This is a major cause of mountain ash decline. Sunscald injury to the bark (southwest and west side) or any other injury to the bark provides entry points for one or more fungi. As cankers develop, yellowing or browning of leaves in the crown or on individual branches occur. | Any protection from the sun of the thin bark on the south and west side will be helpful, and care to avoid all other types of injury to the bark is suggested. |