动态第708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19日

Root-knot nematodes are microscopic, plant-parasitic roundworms in the genus, Meloidogyne. Normally they exist in sandy soil in hot climates or short winters, but they have spread to our region as well. In Missouri alone 40 species of parasitic nematodes exist. About 2000 plants are susceptible to infection by these nematodes, and they can cause global crop loss. Root-knot nematode larvae infect plant roots that drain the plant’s ability to take up water and sufficient nutrients. Because of their microscopic size the nematodes go unnoticed until serious symptoms appear. The pathogenic nematodes can allow entrances for root rots, and wilts. They can also transmit viral diseases.[图片]Symptoms and Diagnosis A plant infected with root-knot nematodes often exhibits the same signs of nutrient deficiency. It may be stunted, yellowed, or wilted, and can lead to premature death of the plant. Below the ground, the roots of the plant are swollen or knotted with root galls, and unless a plant is removed from the soil to examine the roots, the cause of the poor plant growth remains undetected. The appearance of the galls on the roots can be confused with nitrogen-fixing nodules common in the legume family. However it is easy to distinguish between them, as the nitrogen nodules can be easily rubbed off while the nematode galls cannot be removed.[图片]Life Cycle The root-knot nematode is parthenogenic, that is a single female can reproduce without males and a new generation can occur every 28 days if conditions are ideal. Inside the gall, the enlarged female appears as a shiny white body, the size of a pinhead. She deposits 300 to 500 eggs in a protective jelly-like material. These glistening white to yellow egg masses are present on the root surfaces. Juveniles emerge from the eggs in the soil and penetrate between and through cells at the center of the root, usually near the growing tip. These larvae actively feed and remain at this same site. The juvenile stage can over-winter even under very unfavorable conditions. New adult nematodes develop from the larvae and start the cycle again.[图片]Integrated Pest Management Strategies 1. Never buy or plant any stunted-yellowed plants. When a new plant’s roots are examined and its roots contain root knots that will not easily rub off, do not plant it. If someone gives you a division of their plant whose roots contain these root-knots, never add it to your garden because it will contaminate all of your healthy plants with the nematodes. 2. Keep plants healthy and avoid stressing plants and water plants during periods of high temperatures and drought. Also keep other insect pests and fungal diseases under control. Control weeds as they can act as hosts to these nematodes. Keep tools clean.[图片]3. ;Rotate crops, planting nematode resistant plants when possible. It may take 3-5 years to kill off these nematodes before replanting the same plant. 4. Destroy any plants you discover that are infested with root-knot nematodes and don’t compost them. Replace all the soil before adding a new plant to this area.[图片]5. Soil solarization has demonstrated some success in eliminating root-knot nematodes. Thoroughly moisten the soil and cover with clear plastic in full sun during the hottest months of the year. The soil must maintain these high temperatures for a period of at least 4-6 weeks to be effective. Re-moisten the soil under the plastic if it dries out. 6. No chemical controls are advised for home gardeners. Some restricted use chemicals are available for commercial, licensed applicators.

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2017年09月19日

A strain of the fungus, Phytophthora infestans, causes late blight in tomatoes. As the common name implies, Phytophthora is prevalent on tomato hosts in late summer, after the plants have bloomed. Late blight is more common in north central and northeastern states, but is observed in the Midwest when the humidity is high and temperatures are around 68 degrees F late in the growing season. Watch for the disease when cool, moist nights are followed by warm, humid days.[图片]Symptoms and Diagnosis One of the first symptoms of late blight is watersoaked patches on older leaves. Late blight attacks the older leaves first, then spreads to the fruit. Green-black watery patches develop on the upper surfaces of older leaves. These patches will enlarge quickly, and in moist weather, a downy growth may develop on the underside of the leaf. On the fruit, you will see rough, firm, dark-colored spots.[图片]Life Cycle The fungus overwinters on tomato and potato plant debris, including potato tubers. The fungus can produce spores over a broad range of temperatures although spores are most infective at temperatures of 68 degrees F with high humidity. The spores are transmitted by water or are wind blown and may be introduced from diseased plants in nearby gardens. The fungus invades the plant through leaf stomata. Infection rarely occurs when temperatures are higher than 80 degrees F and humidity is less than 90%.[图片]Integrated Pest Management Strategies 1. Plant resistant varieties. Several tomato varieties are designated as resistant to late blight. 2. Avoid overhead watering. Avoid working around plants when they are wet. Both of these practices can spread the fungal spores from plant to plant. 3. Clean up all garden debris in the fall. Remove and destroy any affected plants as soon as they are observed.[图片]4. Practice crop rotation. Do not plant tomatoes, potatoes, and celery in succession. All of these crops are susceptible. 5. Use a copper-based fungicide. Apply when symptoms are first identified. Reapply at 7–10 day intervals.

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2017年09月19日

If your tomato plants yellow and wilt on one side of the plant or one side of a leaf, they may have Fusarium wilt. Fusarium wilt on tomatoes is caused by Fusarium oxysporumsp. lycopersici. It is a soilborn fungus that is found throughout the United States, especially in warm regions of the country. The organism is specific for tomato and is very longlived in all regions of the United States. The disease develops more quickly in soils that are high in nitrogen and low in potassium. In addition, plants grown in sandy soils tend to contract this disease more often.[图片]Symptoms and Diagnosis Fusarium often causes yellowing on one side of the plant or leaf. Yellowing begins with the older, bottom leaves, followed by wilting, browning, and defoliation. Growth is typically stunted, and little or no fruit develops. Brown, vascular tissue can be found when the infected stem is cut at its base. Infected plants often die before maturing.[图片]Life Cycle Fusarium fungi survive in the soil or associated with plant debris for up to ten years. Disease development is favored by warm soil temperatures, and symptoms are most prevalent when temperatures range from 80–90 degrees F. The fungi enter the plants through their roots and are then spread throughout the plant by the plant's water-conducting vessels. Integrated Pest Management Strategies 1. Plant resistant varieties. These varieties are labeled VF and include cultivars such as ‘Spring Giant’, ‘Burpee VF’, ‘Supersonic’, ‘Celebrity’, ‘Manalucie’, ‘Better Boy’, and ‘Small Fry’.[图片]2. Remove infected plants from the garden. Removal of infected plants will help limit the disease's spread. Soil sterilization or fumigation will eliminate wilt fungi from the soil but are impractical for home gardeners. Soil replacement should be considered. 3. Avoid over-application of high nitrogen fertilizers. High soil nitrogen levels accompanied by low potassium levels can increase susceptibility to the fungus. Use a soil test to determine potassium levels and other nutrient deficiencies. 4. Avoid activity in wet plantings. Movement of wet soil from place to place via shoes or tools will spread the disease.[图片]5. Sanitize stakes and tomato cages at the end of the season. Avoid using soil-encrusted tools and supports season after season. A thorough cleaning with water will reduce most risk of transmitting the disease. 6. For four years, do not plant solanaceous plants in the area where infection occurred. Tomato, potato, pepper, and eggplant are all susceptible to the disease and may allow its survival year after year in the same planting area.

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2017年09月19日

Early blight is a fungal disease, Alternaria sp., that occurs on tomatoes throughout North America. Early blight can affect seedlings but is generally observed on older plants and is especially severe on plants of poor vigor. Plants infected with the fungus can display collar rust on the stems, infected older leaves, and fruits that crack at the stem. Infection on leaves is the most common symptom.[图片]Symptoms and Diagnosis The appearance of circular or irregular dark spots on the lower, more mature leaves is one of the first symptoms of infection. Eventually, the spots enlarge into a series of concentric rings surrounded by a yellow area. The entire leaf may be killed and will drop off the plant. Early blight can result in extensive defoliation, exposing fruit to sunscald and reducing yields. This disease typically progresses from the base of the plant, upward.[图片]Life Cycle Early blight spores survive on old plant debris or in the soil. Spores are spread by wind and rain, but occasionally, flea beetles transmit this disease. Fungal spores enter a host through wounds in the plant cuticle. Spores thrive in moist, warm temperatures (80–90 degrees F) and can persist in partially decomposed garden waste for at least a year. Integrated Pest Management Strategies 1. Plant resistant varieties. Varieties such as ‘Early Cascade’, ‘Floramerica’, ‘Jetstar’, ‘Manlucie’, ‘Supersonic’, and ‘Surecrop’ have some tolerance to early blight. These varieties will require a less intensive management program than susceptible varieties.[图片]2. Maintain plant vigor. Stressed plants are more susceptible to early blight. Water the plants regularly, but don't fertilize until the plants are well-established and in full blossom. Do not mulch until the soil is warm. 3. Do a thorough cleanup of the garden in the fall. Remove plant debris or till it into the soil. Pull weeds that compete for light, water, and nutrients, especially nightshade, horse nettle, and other weeds in the tomato family. 4. Rotate crops. Practice a 2- or 3-year crop rotation. Avoid planting eggplant or potatoes where tomatoes were last planted.[图片]5. Avoid activity when plants are wet. Confine staking and picking to times when foliage is dry. Disease is more readily spread when plant foliage is wet. 6. Protect clean foliage with a fungicide. Effective fungicides include copper (Kocide), chlorothalonil (Bravo, Daconil), mancozeb, or maneb. Apply at fruit set and reapply every 7–14 days.

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2017年09月19日

Clubroot is a fungal disease that affects a number of plants in the cabbage family including cabbages, radish, mustard and ornamentals such as candytuft. It is caused by the fungus Plasmodiophora brassicae and gets its name from the club-like roots it induces in infected plants. Its diagnosis is often missed as the infected plant part, the roots, are underground and out of sight.[图片]Symptoms and Diagnosis The first symptom is usually wilting during average daily conditions but recovery at night. The older leaves may yellow and die and the plants look stunted. Examination of the root system reveals enlarged roots that make them look club-like and reduced feeder roots. The reduction in feeder roots as well as disruption of the water conducting tissue in the roots causes the drought-like symptoms. Development of the disease if favored by a low soil pH (below 7.0), cool soil, and excess soil moisture. The organism can survive in the soil for over 10 years. Since most soils in the St. Louis area are above a pH of 7 the disease is rare in our area.[图片]Life Cycle Clubroot is a soil-borne fungus that infects plants through root hairs by zoospores. After infection the roots enlarge and many spores are produced in the swollen roots. The mobile zoospores can re-infect other roots on the plant or nearby plants. Late in the season resting spores are produced. When roots die and decay the resting spores are released into the soil where they can survive for many years and be transported through the soil by water movement and garden equipment.[图片]Integrated Pest Management Strategies 1. Remove diseased plants. The disease organism can reside in the soil for many years so although quick removal of diseased plants is recommended the disease may return if plants in the cabbage family are planted in the infested soil the following year. Also remove any cabbage family weeds such as wild mustard, which can harbor the disease.[图片]2. Add lime. Since problems are more severe in acid soils (pH 5.0-7.0) adding lime to acid soils can help control the disease. 3. Rotate crops Rotate where you grow cabbage, radishes, mustards, etc in your garden. Wait 5-6 years before replanting in an area.

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2017年09月19日

Blossom-end rot is a physiological disorder of tomatoes and peppers. It is a disturbance in the normal physiology of the plant. Because it is not caused by an insect or disease organism, fungicidal and insecticidal sprays are not effective in controlling the problem.[图片]Symptoms and Diagnosis An early symptom of blossom-end rot is a light tan patch on the blossom end of the green fruit. Over time the area turns dark brown or black and may become sunken or leathery. Fruit which is one-third to one-half developed is most commonly affected. Sometimes an internal black rot will develop in the center of the fruit with little or no external symptoms. Parts of the fruit not affected by blossom-end rot may be eaten.[图片]Causes of Blossom-End Rot The most common cause of blossom-end rot is fluctuating soil moisture. Moisture plays an important role in calcium uptake in the plant. When a dry period follows adequate moisture, calcium uptake can be reduced. Root damage due to deep cultivation or burning from improper fertilization can also restrict calcium uptake. Excessive applications of fertilizer containing ammonia can also result in symptoms. Less frequently, an actual deficiency of calcium in the soil may cause this rot. This is rarely the case in St. Louis.[图片]Integrated Pest Management Strategies 1. Maintain even soil moisture. Water regularly during dry periods and mulch plants with a 3–4 inch layer of organic material to help hold in soil moisture. 2. Avoid deep cultivation too near plants. 3. Modify your fertilizing practices. Use a fertilizer high in superphosphate and low in nitrogen. When adding nitrogen, use calcium nitrate rather than ammonia or urea forms.[图片]4. Get a soil test. If the above methods do not correct the problem, get a soil test and maintain soil pH at 6.5 to 7. 5. As a last resort, use a foliar spray of calcium chloride. Do not spray too often or in excessive amounts. 6. Tomatoes in container. For tomatoes grown in containers, apply a fertilizer specifically formulated for tomatoes. The fertilizer must contain micronutrients including calcium.

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2017年09月19日

Blossom-end rot, which begins with a small watery bruise on the blossom end of the fruit, is the result of a lack of calcium in developing fruits. This calcium deficiency can be a result of slow growth, damaged roots induced by extreme fluctuations in the surrounding soil moisture content, an excess of salts, or other fluctuating conditions during plant growth. Calcium deficiencies cause actively growing cells to die because they cannot retain water and nutrients.[图片]Symptoms and Diagnosis Blossom-end rot begins as a water-soaked, sunken spot on the blossom end (the end that isn't attached to the stem) of the fruit. The spot may enlarge and become depressed as the fruit grows. The spot may turn from brown to black and become moldy. Blossom-end rot can be distinguished from other rots by its confinement to the blossom end. It may also be confused with rotting fruit that results from the failure of female flowers to set fruit due to lack of male flowers or pollinating insects.[图片]Integrated Pest Management Strategies 1. Plant cucurbits in a location that has well-drained soil. 2. Mulch the plants and water properly to maintain a uniform moisture level in the soil. Avoid damaging the root system when hoeing or weeding. 3. Test the garden soil pH. Calcium may not be available to plants if the soil pH is too low or high.[图片]4. Limit the use of high ammonia fertilizers and fresh manure that may stimulate lush growth and add more salts to the soil. 5. Add calcium nitrate to soil or spray with 1% calcium chloride in order to boost the amount of calcium available to developing fruit. 6. Cucurbits in containers. For cucurbits grown in containers, apply a fertilizer that contains micronutrients including calcium. Many fertilizers formulated for tomatoes meet these specifications.

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2017年09月19日

Cucumber bacterial wilt is caused by the bacterium, Erwinia tracheiphila, and is characterized initially by wilting and drying of individual leaves, especially those exhibiting cucumber beetle injury. Cucumbers and muskmelons are more susceptible than pumpkins or squash; the disease is rarely a problem on watermelons.[图片]Symptoms and Diagnosis Infected plants initially show wilting and drying of individual leaves. As the leaves wilt and shrivel, stems may dry out suddenly. Later, wilting spreads to entire branches and vines. Wilting will occur during the middle of the day during periods with high water stress. The vine may recover at night. Eventually, however, the entire vine will wither, collapse, and die. In partially resistant plants, symptoms appear as dwarfing, excessive blooms, and branching. A good diagnostic test for this wilt is to cut a wilted stem near the base. Touch a knife blade to the cut and draw away from the cut. White to clear strings of the bacterial ooze will be strung out from the cut made on the infected plant to the knife blade. This diagnostic test is not 100% reliable. Further investigation may be necessary.[图片]Life Cycle The bacteria overwinter in the digestive system of the cucumber beetle. In the spring, bacterial wilt is spread from plant to plant through both the striped and spotted cucumber beetles that feed on cucumbers and other relatives of this family. The bacteria are released through the insect excrement and move into host plants through the stomates and wounds, most likely the ones made when the insects feed. Insects ingest more bacteria as they feed on infected plants, and the cycle is repeated.[图片]Integrated Pest Management Strategies 1. Protect plants with netting. Prevent cucumber beetles from feeding and infecting plants by covering them with netting or porous fabric. 2. Remove and destroy plant material when symptoms of wilting are first noticed. There are no cures for the disease. Beetles spread the bacterium from infected plants to healthy plants. 3. Grow susceptible crops on rotation every third year. Since beetles overwinter in the soil and carry the bacterium, the cycle can be disrupted by only planting the host in an area every third year.[图片]4. Avoid planting cucurbits next to corn. Spotted cucumber larvae also feed on corn; avoiding close plantings of these two crops may help control the beetles on cucurbits. 5. Grow varieties that tolerate bacterial wilt like butternut or acorn squash and Saladin or County Fair 83 cucumbers. No muskmelon varieties are known to be tolerant to bacterial wilt. 6. Dust plants with insecticide in the spring before the cucumber beetles have a chance to lay eggs (April-June). Apply pyrethrin or carbaryl (Sevin). Try an insecticide-bait combination such as Adios that has cucurbitacin, the beetle attractant, and a small amount of carbaryl (Sevin).

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2017年09月19日

Sycamore anthracnose is a fungal disease that can cause leaf drop, twig dieback, cankers and the sudden death of more than 90% of a tree’s new shoot growth. Although the disease is rarely fatal and trees will grow a second set of leaves, repeat infections will result in abnormal branching and will leave a tree stressed and more susceptible to other diseases and pests. American sycamore or buttonwood (Platanus occidentalis), London plane tree (P. x acerifolia) and Oriental plane tree (P. orientalis) may all be affected by sycamore anthracnose.[图片]Symptoms and Diagnosis Sycamore anthracnose is most common during the cool wet weather of spring and is often mistaken for frost damage. As new leaves unfold, they crinkle and turn brown, wilt rapidly and fall. Dark and sunken dead areas form along the veins of older leaves eventually expanding to include the entire leaf. The tree may also develop cankers on twigs and older branches resulting in twig dieback and the girdling and death of the larger branches. Small black dots, the fruiting bodies of the fungus, may be visible. The clusters of dead twigs will result in abnormal branching such as witches’ brooms or as the twigs die, break and fall, the tree will appear ragged. Reportedly, London plane tree is less susceptible to cankers than the American sycamore.[图片]Life Cycle The sycamore anthracnose fungus, Apiognomonia veneta, overwinters in diseased leaves and in cankers on twigs and branches. Spores are produced in spring and spread by rain. If the mean daily temperatures are 50 – 55 degrees F., the spores will germinate and the resulting infections will cause the death of new buds, shoots and leaves. The disease will be slight or will not occur by late spring or midsummer when the mean daily temperatures are 60 degrees F. or greater and the tree will be able to produce a second set of leaves. The fungus may also infect twigs and buds in fall after leaf drop.[图片]Integrated Pest Management Strategies 1. Be patient. The tree may appear to be dead but will probably recover and develop new leaves and shoots. 2. Practice good garden sanitation by raking up and disposing of fallen leaves and twigs. 3. Practice good cultural techniques to keep plants healthy and free of drought, nutritional or injury-induced stress. Water trees twice a month during dry winters. 4. Prune out dead branches when possible. Disinfect pruning shears in a 10% bleach solution between cuts to avoid spreading the disease. 5. Prune branches to improve air circulation reducing the length of time leaves are wet and thus susceptible to infection.[图片]6. Treat with a preventive systemic fungicide. This treatment may require the services of a certified arborist. 7. Spray with a preventive fungicide such as lime-sulfur (Bordeaux mixture) or chlorothalonil (daconil) when leaves begin to emerge from buds. Reapply two or three more times at 7-10 day intervals. Fungicides are not effective after the leaves have been infected. Large trees may require the services of a certified arborist. 8. Plant resistant species or cultivars. Oriental plane tree (zones 7-9) and London plane tree cultivars, ‘Bloodgood’, ‘Columbia’ and ‘Liberty’ are less susceptible to the disease than the American sycamore.

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2017年09月19日

Rose rosette disease, also known as witches’-broom of rose, is caused by a virus (Emaravirus sp.) that is spread by a very small, eriophyid mite. The disease is limited to plants in the genus Rosa but R. setigera, R. aricularis, R. arkansana, R. blanda, R. palustris, R. carolina and R. spinosissima are believed to be resistant. Its main host is the multiflora rose, which is considered a noxious weed throughout much of the United States. Interest in rose rosette has been generated by the threat to garden roses and its possible use as a biocontrol for multiflora rose.[图片]Symptoms and Diagnosis The earliest symptoms of rose rosette disease include a red pigmentation of the underside of leaf veins followed by sharply increased growth of vegetative shoots, which are typically more succulent than normal and colored in various shades of red. Leaves often become deformed, crinkled, and brittle with yellow mosaics and red pigmentation. As the disease progresses, leaves become very small, petioles are shortened, and most lateral buds grow, producing short, intensely red shoots. The disease causes the plant to be exceptionally susceptible to freeze damage. Symptoms on cultivated roses are typically less severe than on multiflora rose. Cultivated roses show symptoms of thickened, succulent stems and a proliferation of thorns. Symptoms can mimic some forms of herbicide damage.[图片]Life Cycle The disease is transmitted by an eriophyid mite, a wingless mite that can travel passively in the wind as well as on contaminated clothing and equipment. The mites are most prevalent in the apex of the rose shoots where they feed and reproduce. Females overwinter under bark or on bud scales of living roses. The females move to newly developing shoots where they lay one egg a day for about 30 days. The young hatch in 3-4 days. They can reach adulthood in about a week depending upon temperatures. Multiple generations occur each year until fall when females seek overwintering sites. The mites are hampered by low humidity and can only survive about 8 hours without being on a host plant. Virus transmission occurs most readily between the months of May through mid-July when plants are making active growth. Symptoms from new infections usually start appearing in mid-July. In general, smaller plants go through the disease stages more quickly than larger plants. Small plants are usually killed in about 2 years, while a large plant may survive for five years in a deteriorated condition.[图片]Integrated Pest Management Strategies 1. Remove ornamental roses with symptoms. The entire plant including the roots should be removed and destroyed by burning or placing in a plastic bag. Care must be taken when working with diseased plants as you can facilitate spread of the mites that spreads the disease. Bag the plant before removal, cut it at ground level and then dig out the plant’s roots. Soil need not be removed. Clean tools and put on fresh clothing before moving to a disease-free plant or area. 2. Plant ornamental roses as far away as possible from known stands of multiflora rose. The general recommendation is maintain at least 300 feet between your roses and any stands of multiflora rose. Even greater distance is preferred especially if they are upwind of your desirable rose plants.[图片]3. Control the disease by controlling the mite. Start mite control early by pruning your roses hard in late winter (back by 2/3) to remove as many overwintering mites as possible and then spray with horticultural oil to kill any remaining mites. Organic pesticides such as horticultural oils and insecticidal soap are recommended over other pesticides as these organic pesticides are less harmful to natural predators that feed on the problem mites. Apply weekly during the months of June and July paying particular attention to the new growing tips where the mites will congregate. Refrain from using leaf blowers around roses as they can spread mites.[图片]4. Help to isolate your roses. Do not plant roses too close together. With extra space between the plants mite movement can be reduced. Also, consider interplanting roses with other ornamental plants. 5. Using rose rosette disease as an IPM strategy. The multiflora rose is an exotic invasive species that is responsible for the degradation of millions of acres of farmland and recreational areas. Using the disease to control this invasive weed can cut costs and be considered environmentally friendly for reducing the amount of synthetic chemicals used. However, the disease also affects cultivated roses. One should be extremely cautious and good neighbor-minded when it comes to rose rosette disease.[图片]6. Plant a resistant cultivar. Rose breeders have been working to develop new rose cultivars that are resistant to rose rosette. The first, 'Top Gun', is a shrub rose that is scheduled to be released in 2018. 'Top Gun' is also reportedly resistant to most other common rose diseases. Others cultivars are planned to follow.

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