动态第726页 - 绿手指 - 养花技巧、花生病了怎么办、花园打理和设计

2017年09月18日

The eastern white pine, Pinus strobus, is a fast growing, easily transplanted tree. It can become quite large, requiring sufficient room to develop properly. White pine needles are bluish-green to medium-green with five per bundle, about 4 inches long, very thin, and not stiff. Used as a windbreak, the limbs are brittle and may suffer wind damage which can help lead to decline of the tree. In general, symptoms of decline include some pattern of needle yellowing or browning, shriveled bark on trunk and branches, oozing sap, and in some cases, death of the tree. Affected trees can range from 2 feet to 20 feet or more. The main factor is root decline.[图片]Symptoms and Diagnosis Inspect the roots for brown discoloration and the outer layer pulling off or not present. If the roots are white and healthy, then there are other problems. Other symptoms will be yellowing or browning of the needles and a limp appearance. Do not, however, confuse this with the normal yellowing and shedding of just older needles that occurs annually in the fall. The bark of the trunk and branches may shrivel and ooze sap. White pines suffer under conditions of urban stress, resulting in decreased vigor, less branching, shorter needles, and noticeable foliage chlorosis.[图片]Life Cycle There is no life cycle as the problem is environmental. There can be many contributing factors, one of which is air pollutants. Other factors can be soil pH, water-logged soil, drought, flooding, heat, and sudden extremes in temperature and moisture. Heat is a main consideration. Even though white pine grows from USDA Zone 3 to 8, it does not appear to thrive in the hot humid areas. Possible use as an understory tree in these areas may help it survive. A white pine in poor health can be attacked by two root pathogens which can speed the decline of the tree; however, they are not the cause of decline. These pathogens are Phytophthora and Verticicladiella. Fungicides are not recommended as the fungi are not the cause of the tree decline.[图片]Integrated Pest Management Strategies 1. Maintain plant vigor. When planting the tree, insure that the soil is moist, rich, well-drained, and on the acid side. The white pine can tolerate full sun though it will perform better in partial shade. Avoid hot, west-facing sites. 2. Select the planting area carefully. Do not use white pines as a windbreak. Since the branches are brittle, they can be damaged, causing stress in the tree. The brittleness can also lead to damage from snow and ice. Do not plant along roadways as salt spray is injurious to the tree. The tree is also subjected to ozone stress which causes needle tips to brown.[图片]3. Planting time. White pines are best planted in spring. If fall planting is done, care should be taken to amend the soil, fertilize, water thoroughly, mulch adequately, and consider application of an anti-desiccant during early winter. Avoid using winter salt on roadways and paths especially where traffic is high. 4. On-going care. Make sure the soil is adequately drained and that the tree is watered in periods of drought. Fertilize with an acid-type fertilizer like ammonium sulfate.[图片]5. Removal. Prompt removal of white pines suffering from decline is not required as they will not infect surrounding pines.

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2017年09月18日

Sphaeropsis tip blight is caused by the fungus, Sphaeropsis sapinea (also known as Diplodia pinea). It is one of the most destructive fungal diseases of pine trees in the Midwest. It is most common on Austrian pine but can also damage Scotch pine (Scots pine), ponderosa, and mugo pine. If not controlled, over a period of years, it will weaken and perhaps kill the tree.[图片]Symptoms and Diagnosis Tip blight most commonly affects trees 13 or more years old that bear mature pine cones, but it can also affect younger trees. The most obvious symptom is the browning and stunting of the needles of the new growth. The needles are retained on the tree. Excess resin flow builds up on the dead twigs and needle bases. Small black pimples (pycnidia) about the size of fly specks are very noticeable on the bases of the browned needles, on the dead twigs, and on the cone scales. The pimples are the fruiting bodies of the fungus. Infection usually begins on the lower branches and moves up the tree. Sphaeropsis tip blight may be confused with pine tip moth damage. In the case of the latter, the fungal fruiting bodies will not be present, but moth larvae and tunneling in the shoots will be evident.[图片]Life Cycle Symptoms of tip dieback are most common in spring from April to mid-June when the young emerging needles are soft and tender. They are most vulnerable for the two weeks when the buds first open. Spores are released from the fruiting bodies (pycnidia) and are moved by splashing rain, wind, animals, and pruning equipment. They are dispersed throughout the year. Under very moist, humid conditions, the spores germinate and infect the needles. Once the fungus infects the needles, tissue is destroyed and shoots and needles are stunted. Infected second-year cones are a major source of inoculum. Infected cones are often observed on plants that show no other signs of infection. Latent infection is common and may be symptomless.[图片]Integrated Pest Management Strategies 1. Keep trees healthy. Weakened trees are more susceptible to disease. Water during dry periods and fertilize according to soil test recommendations. Spores of Sphaeropsis sapinea are ever-present and can be found on the branches of most pine trees with the exception of white pine. Spores can infect without causing symptoms.[图片]2. Use fungicidal sprays.Infection of new shoots may be reduced significantly with properly timed fungicidal sprays. Fixed copper or Bordeaux should be applied twice during the period when buds are opening. Apply in late April to early May, when the buds just begin to open. Repeat application in one to two weeks. Other pesticides registered for use include chlorothalonil (Daconil), mancozeb, and thiophanate methyl (Cleary 3336). 3. Replace with more resistant trees. When dead or dying trees are removed, replant with trees that are less susceptible to Sphaeropsis tip blight such as white pine, spruces, or junipers.

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2017年09月18日

Injury due to salt is most common on landscape plants growing adjacent to highways, streets, sidewalks, and driveways that are regularly salted during the winter for ice control. Most of the salt used for deicing purposes is sodium chloride, ordinary rock salt or table salt. On highways, the major problem to plants is caused by salt spray kicked up by fast moving traffic on wet, salted roads. The salt spray is deposited on adjacent plants causing dehydration of evergreen leaves. In the city, the major problem is salt runoff washing into the soil. Salt in the soil may be absorbed by the roots and cause direct toxic effects.[图片]Symptoms and Diagnosis Salt spray causes bud death and twig dieback. Subsequent shoot growth at the branch base produces clusters of twigs known as "witches' brooms." Symptoms typically become evident in the spring. In evergreens and conifers, salt spray causes leaf browning or yellowing, needle tip flecking, and twig dieback. Salt in the soil is slower acting and may not affect plants for several years. Symptoms include an initial blue green cast to the foliage, marginal leaf burn or needle tip burn, reduction in leaf, flower and fruit size, premature fall coloration and defoliation, stunting, and a general lack of vigor. The symptoms often become evident in late summer or during periods of hot dry weather.[图片]Integrated Pest Management Strategies 1. Reduce salt use. The most important method of preventing salt injury to plants is reducing the amount of salt used for deicing. Pure salt should never be applied. Salt should always be mixed with an abrasive such as sand, cinders, or ash. This combines the melting power of the salt with the grittiness of the abrasive so less total salt is needed. Commercial deicing products containing calcium chloride may be used instead of rock salt. These products will not damage the soil but will still injure plants, so they too should be mixed with abrasives and applied with the same precautions.[图片]2. Apply salt carefully. Application should be limited to high risk locations such as high speed roads, intersections, hills, steps, and walkways. Avoid spilling or applying in heaps. 3. Leach salted soils. If salt has already entered the soil, water these areas heavily in the spring to help leach the salt out of the soil. This method, however, is only effective on well-drained soils. It is not effective on fine textured, compacted soils where water does not drain readily. 4. Protect plants. Plants may be protected from salt spray by placing materials such as plastic, burlap, plywood, or window screen on or in front of them. This provides a physical barrier that prevents salt spray from contacting the plant.[图片]5. Avoid planting in drainageways or in areas where runoff collects. Salt spray damage can be avoided by planting trees and shrubs away from the spray drift zone, at least 50 feet from a highway or further if downwind. Plants vary in their sensitivity to salt. It should be emphasized that even tolerant plants are not immune to injury.

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2017年09月18日

Rhizosphaera needlecast is caused by the fungus, Rhizosphaera kalkhoffii. The disease causes death and casting (dropping) of needles in spruces, especially Colorado spruce and occasionally white spruce. It is usually first evident on the lower branches of the tree and can cause severe defoliation and death of branches if allowed to persist. It rarely kills the tree.[图片]Symptoms and Diagnosis Infections take place in the spring, and symptoms show up about a year later. Infected 2-year old needles become spotted or mottled, some turning yellow and some developing a purplish brown color in late summer. Browning becomes general in late winter to early spring, and needles are prematurely shed during summer and fall, 12 to 15 months after initial infection. Black fruiting bodies are visible on discolored needles and even some green ones. The spores emerge from the stomates on the needles so appear in rows along the needles. Scattered lower branches are usually affected first and then browning progresses upward. Symptoms may be confused with spider mite damage. In the latter, mites and fine webbing may be visible; the lines of black fruiting bodies on the needles will also be absent.[图片]Life Cycle Rhizosphaera kalkhoffii overwinters in infected needles on the tree or ground. Spores are released from the infected needles in the spring, during wet weather. Spores are dispersed by splashing and dripping water. They infect newly emerging needles, as well as mature needles. Infection begins in spring, in April or May. Optimal temperature for fungal development on wet foliage is 77° F. Infection will occur in 48 hours if spores are present. Prolonged wetness can induce extensive infection.[图片]Integrated Pest Management Strategies 1. Select healthy plants. If spruce trees are dropping their needles, avoid using these trees in the landscape. 2. Remove infected needles and branches during dry, sunny weather. Prune out diseased branches and rake up fallen needles. Burn or remove the collected debris. Disinfect pruning tools between cuts by dipping in a 10% chlorine bleach solution. Oil tools when done to inhibit rust. 3. Avoid overhead watering.Water on the foliage can promote infection. Spores require moisture to germinate and infect.[图片]4. Improve air circulation to allow needles to dry more quickly. Maintain open spacing when planting or by mowing grass or brush. 5. Use fungicidal sprays. Severe infections should be sprayed with chlorothalonil (Daconil), thiophanate methyl (Cleary 3336), or copper-containing fungicides registered for use against this disease. Spray when the needles are half-elongated and again when fully elongated. A minimum of two years of treatment is recommended because of the organism's life cycle.

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2017年09月18日

Procera root rot also known as white pine root decline is caused by the fungus Leptographium procerum (syn. Verticicladiella procera). It infects the inner bark and sapwood of the roots and lower trunk of white pine. Although the disease is most serious on white pine, it can also kill Scots and Austrian pines.[图片]Symptoms and Diagnosis In the Spring, trees, aged 3 to 15 years, which have been infected for several years, show delayed bud break and reduced candle elongation. Mature foliage then fades, droops, and turns brown, in stark contrast to healthy trees nearby. Mortality appears to be at random with a few trees dying each year. Resin flow is visible at the tree base and is associated with a girdling chocolate brown to dark olive-brown canker under the bark. The trunk may be flattened on the affected side. Galleries of insects such as the pine root collar weevil may be found in the canker and provide a place for the fungus to sporulate. Weevils and other bark-infesting insects may serve as vectors for this disease. Although the fungus does not survive well in the soil, it may be spread by contaminated insects as they emerge from diseased trees and feed on healthy trees nearby.[图片]Integrated Pest Management Strategies 1. Planting. Avoid planting eastern white pine on wet sites. Trees planted on wet sites seem to be more susceptible to the fungus. Excessively dry sites also seem to predispose trees to attack.[图片]2. Sanitation. Remove and destroy infected trees including stumps, if possible. Do not replant eastern white pine among the stumps of recently killed trees. 3. Replant. If trees need to be replaced, do not plant a pine. Use arborvitae or spruce.

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2017年09月18日

The pinewood nematode, Bursaphelenchus xylophilus, kills conifers, especially pines, of many species. This pest is endemic throughout the eastern half of the United States. Scotch pine (Scots pine) is the most commonly affected host. The nematode is transmitted by sawyer beetles, a wood-boring bark beetle, through their feeding wounds into the resin canals. Here, the nematode will reproduce and hinder the movement of water through water-conducting tissues, eventually causing the plant to wilt. Locally destructive outbreaks have occurred in forest and landscape plantings of non-native pine species in Missouri and Illinois.[图片]Symptoms and Diagnosis Early symptoms of pine wilt are often inconspicuous or slight, giving way to a rapid decline. The first visible symptoms usually include fading green color and/or slight yellowing of limbs. This may be evident on one or a few branches or may develop on all simultaneously. In addition, within 48 hours after infection, there will be a visible loss of resin flow as observed on a cut twig. Trees often die so rapidly that brown needles continue to cling to the twigs. Diseased pines commonly die in early summer or early fall; some species require 2 seasons. Confirmation of the disease is done by microscopic detection of the pathogenic nematode in an examination of infested wood samples from the main trunk or affected branches. For diagnostic purposes, branch samples should be not be less that one inch in diameter and collected from freshly killed areas where needles are brown, but still attached.[图片]Life Cycle Once a susceptible host plant has been inoculated with the pinewood nematode via bark beetle feeding, the nematode will feed and multiply in the resin canals. Populations of 1,000 nematodes per gram of wood may occur when foliar symptoms appear. When plant stress factors, such as high temperatures, drought, or attack by other pathogens, increase, nematode populations will rise. After the host plant dies, the nematode will transform into a non-feeding form and this stage can be picked up by wood-feeding bark beetle larvae. This dispersive stage of the nematode will migrate to the pupal chambers of the bark beetle, then enter the bodies of newly formed bark beetle adults that will seek other tree hosts, and repeat the nematodes’ life cycle.[图片]Integrated Pest Management Strategies 1. Removal. Quick removal of an infected tree is important in order to break the nematodes’ life cycle. Infested wood should be burned or buried (not chipped and used as mulch) to prevent reproduction and overwintering of the bark beetles in infested wood. Periods of high temperatures in summer favor epidemics, as do periods of severe drought, but little else is known of factors that favor or prevent epidemics of pine wilt. 2. Select resistant varieties. Consistent with geography and climate, select evergreen trees that are more resistant to the pinewood nematode. These would include eastern hemlock; blue, Norway and Serbian spruce; and Jeffrey, pitch, Virginia, shortleaf, loblolly, and Eastern white pine. Avoid the more susceptible species such as Scotch pine (Scots pine), Austrian pine, Japanese black pine, Japanese red pine, jack pine, mugo pine, and long-leaf pine.[图片]3. Maintain healthy trees. While even a healthy tree may become infested with the pinewood nematode, stressed trees are more attractive to bark beetle feeding. Watering during extended drought periods, periodic light fertilization, and avoiding damage to the root system through construction or traffic will all reduce the chances of borer infestation and nematode transmission.

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2017年09月18日

Pine needle rusts are caused by over 20 species of Coleosporium the most common being C. asterum. It results in browning needles and the loss of lower branches. It is rare in the St. Louis area but may affect Austrian, jack, red, Scots, mugo, and ponderosa pines.[图片]Symptoms and Diagnosis The first sign of the disease is small yellow spots on the needles in fall and throughout the winter. In spring the spots develop spore-producing structures and the needles brown and die resulting in needle drop and the loss of lower limbs. Young pines are most affected.[图片]Life Cycle Pine needle rust requires an alternate host to complete its life cycle. Goldenrod and asters are most common. Infection on pine needles begins in late summer or early fall when spores released from the fungus growing on goldenrod or asters infects the needles causing small yellow spots. The fungus grows inside the needle where it overwinters. The following spring the fungus resumes growth and the yellow spots develop into white swelling, which grow well above the needle surface. At this time the disease may be confused with pine needle scale. The spore-producing structures split open and release orange colored spores, which then infect goldenrod and asters nearby. The fungus continues to produce spores that re-infect the alternate host until late in the season when spores that infect pine needles are formed, thus completing the rust’s life cycle. The life cycle is completed in one year.[图片]Integrated Pest Management Strategies 1. Live with the disease. Pine needle rusts do very little damage to mature established trees. Young trees or trees grown in a nursery may require more aggressive action. 2. Remove the alternate host. Pine needle rust needs both pine needles and an alternate host of goldenrod or asters to complete its life cycle. Removing these alternate hosts near pines that suffer from the rust disease can break the cycle. 3. Plant resistant species. Replace susceptible pines with Colorado or Norway spruce. White pine is resistant but is not an ideal choice for the St. Louis area.

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2017年09月18日

Phomopsis blight is a serious disease problem on eastern red cedar in Missouri. The fungal disease, caused by Phomopsis juniperovora, is widespread in this region and can infect arborvitae and cypress as well as juniper. Phomopsis is more of a problem on junipers in landscape plantings because young tissue is most seriously infected. Older plants are seldom killed by Phomopsis, thus it is not a concern in natural stands of juniper.[图片]Symptoms and Diagnosis The first sign of infection is the browning of needle tips. New shoots, in the yellow-green stage, will brown and die in their first summer. Progressive dieback follows, eventually killing an entire branch by girdling the stem. The fungus will progress to the main stem and can infect and girdle stems less than 1/2 inch in diameter. Infected needles turn light green, then reddish-brown, and finally an ashen gray. Life Cycle Phomopsis overwinters on needles and stems of young trees that were infected the previous year. The fungus is most abundant on dead tissue that has become ashen gray in color. Infective spores are dispersed by rain splash. Only seven hours of 100% humidity are needed for infection to occur when temperatures are 75 degrees F.[图片]Integrated Pest Management Strategies 1. Prune infected branches to prevent the spread of the disease. Remove dead tissue as well. The fungus can produce infective spores for up to 2 years in dead parts of infected plants. Prune in late summer when the weather is dry. 2. Plant resistant evergreens. Susceptibility to Phomopsis blight varies considerably among junipers. Ask for resistant stock at your garden or landscape center or consider planting another type of evergreen.[图片]3. Fungicides. Bordeaux mixture, other copper-based fungicides, and mancozeb are labeled for use on Phomopsis. These fungicides can be applied 3–4 times in the spring, at 10–14 day intervals to protect the new growth. They can be used anytime a flush of new growth occurs. Once the new growth matures in midsummer, discontinue further applications.

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2017年09月18日

Pestalotiopsis is a type of needle blight fungal disease that is primarily found on arborvitae (Thuja). It is usually considered a secondary disease that attacks foliage that has been injured or weakened by unfavorable weather or growing conditions. The disease may kill the smaller twigs where the infected needles died.[图片]Symptoms and Diagnosis The blight usually starts at the tip of the foliage and progresses towards the leaf base. Affected foliage color progresses from green to yellowish, then to a dark brown that looks almost black. Twig tips can also turn brown and have black, pimple-like, pinhead size, fungal fruiting structures dotting the surface. Usually, killed foliage is near the base of the plant where foliage is relatively dense. The plants may appear scorched.[图片]Life Cycle Infections can occur at anytime of year. However, spring is the most likely time because favorable weather conditions exist and plants are showing stress from winter conditions. Integrated Pest Management Strategies 1. Avoid over crowding plants to allow for sufficient sunlight and air circulation. 2. Keep plants healthy with good cultural practices. Follow proper watering, fertilization practices and minimize any mechanical and snow/ice damage, etc. that could cause an entry point for the fungus.[图片]3. Prune out dead foliage and twigs as soon as possible. 4. Application of fungicides should not be necessary. If necessary in certain circumstances (e.g. a nursery), copper fungicides are registered for this use as a preventative. Always read and follow product label directions before application to plants.

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2017年09月18日

Ozone is the most damaging air pollutant to plants. The action of sunlight (ultraviolet radiation) on molecular oxygen and oxides of nitrogen spontaneously generates ozone. The organic compounds in automobile exhaust enhance ozone accumulation. Ozone can move across great distances to cause damage to plants far from its origin and is therefore classified as a non-pointsource pollutant.[图片]Symptoms and Diagnosis The extent of damage depends on the concentration of ozone, the duration of exposure, and plant sensitivity. Acute damage to deciduous trees causes marginal leaf burn and dot-like, irregular-shaped lesions or spots that may be tan, white, or dark brown. Symptoms may spread over entire leaves. Another common symptom is bleaching of the upper leaf surface. Broad-leaved trees often exhibit these symptoms of stippling or red-purple or necrotic flecks on the upper leaf surface only.[图片]Acute damage to conifers causes browning at the same point on all needles in a bundle (needle cluster). Other symptoms include chlorotic (yellow) mottling or necrotic (brown to black) banding, tip burn, dwarfing, and tufted appearance due to early defoliation of older needles. Damage from ozone can be confused with other problems and, if suspected, a more detailed reference material (such as Diseases of Trees & Shrubs by Sinclair, Lyon, & Anderson) should be consulted. Life Cycle Ozone builds up to phytotoxic levels in the atmosphere during warm, sunny weather when pollutants accumulate in stagnant air. Accumulation often occurs during atmospheric inversions in valleys and basins bounded by mountains.[图片]Ozone may cause damage to plants far from the source of its precursors as masses of polluted air move overland. Ozone from natural sources (carried from the stratosphere or generated during electrical storms) alone is inconsequential for plant health, but may be added to that generated by humans. Integrated Pest Management Strategies 1. Maintain plant vigor. Plants that are in good health resist all type of injury better than weakened plants. Water during drought periods. Fertilize following a soil test report. Soil should be porous, well-draining, and not compacted.[图片]2. Select plants. Select plants tolerant of air pollutants. 3. Reduce emissions. Reduce emissions from the source when possible.

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