动态第790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13日

Leaves with gray-brown areas surrounded by a dark or yellowish margin are one of the early symptoms of this fungal disease. These discolored areas lack the concentric rings characteristic of early blight, but they may be filled with many small, black spores. Symptoms generally appear on lower leaves first. The fungus can infect a wide variety of plants. In a severe outbreak, septoria leaf spot fungi may also attack seedlings. [图片]The disease is most problematic in cool, wet weather. The fungus overwinters on plant debris in the soil and on weeds such as jimsonweed, horsenettle and nightshade. [图片]Prevention and Control Plant disease-free seed. Rotate crops to avoid growing susceptible plants in the same area year after year. Pick off and destroy any infected leaves. Mulch around the plants to reduce soil splashing, which can spread the disease. Use drip irrigation or soaker hoses rather than overhead watering. In the fall, remove any diseased plant material and destroy it.

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2017年09月13日

A powdery white growth on leaves is the first evidence of this fungal disease, which affects beans, cucumbers, squash, pumpkins, lettuce, peas and many other kinds of plants. The fungus can spread to flowers and fruit. New growth and succulent plant tissues are particularly vulnerable to infection. Infected areas eventually turn yellow and dry up; severe infection can weaken or even kill entire plants. [图片].jpg"> Unlike other fungal diseases, powdery mildew does not require wet foliage for infection to occur, although it does require high humidity. It can spread quickly in warm, dry climates. The fungus overwinters on plant debris. [图片]Prevention and Control Plant powdery mildew-resistant varieties, such as Super Sugar Snap pea. Water plants as needed to prevent moisture stress. Keep plants well spaced and weeded to optimize air flow around the leaves. Avoid excess nitrogen fertilizer, especially late in the growing season.

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2017年09月13日

Early symptoms of late blight infection include irregular olive or gray water-soaked lesions on the leaves and stems of tomatoes and potatoes. Both crops are vulnerable to this fungal disease at every stage of their growth cycle. A mildew-like white mold may also develop on or near these lesions. The disease spreads rapidly and can kill crops within a week of infection. (Late blight fungus, Phytophthora infestans, was the cause of the potato famine in Ireland in the 1850s.) [图片]Unlike early blight, late blight does not cause the plant’s leaves to drop off; leaves usually remain attached even after they’ve turned brown and dried up. On tomato plants, infected fruits develop large sunken areas. These may not appear until after harvest. On potato plants, infection of leaves doesn't necessarily mean that tubers will be diseased. Tubers become infected by late blight when fungal spores wash down through the soil or tubers come in contact with foliage at harvest. [图片]To prevent this from happening, remove and destroy all potato foliage and wait a week before harvesting to allow the tuber skins to cure. Monitor potatoes in storage for dry brownish rotted areas; disease symptoms may not appear until after harvest. [图片]Wet weather with cool nights and warm days favors the spread of late blight. In warm parts of the United States, the pathogen can overwinter in soil and plant debris. In cold-winter areas, it survives only in potato tubers left in the soil, though the fungal spores move easily and quickly on the wind, spreading northward each growing season. [图片]Prevention and Control As a preventive measure, use Actinovate®, an organic fungicide. Add a copper-based product, such as our ready-to-spray Copper Fungicide, when late blight is present. Buy certified disease-free seed and transplants. Seek out late blight-resistant varieties of tomatoes and potatoes. Keep plant foliage as dry as possible; use drip irrigation or soaker hoses rather than overhead watering. Space plants generously to ensure good air circulation. Uproot and destroy any volunteer tomato or potato plants that sprout in your garden. Plants that become infected with late blight can rarely be saved. As the disease advances, the number of fungal spores produced multiplies rapidly. Remove infected plants from your garden as soon as possible. Bury deeply in the soil or put them in a plastic bag for disposal. Be thorough when harvesting potatoes. Destroy any infected tubers that you find.

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2017年09月13日

This common fungal disease of tomatoes and potatoes first appears as dark brown spots on leaves. On close examination, the spots show a pattern of concentric brown rings. Spots may enlarge and merge, and the leaves will turn yellow and die. Infected plants slowly lose leaves from the bottom up as the disease progresses. Tomato plant stems may also be infected, and eventually tomato fruit will display leathery black lesions. If the disease progresses relatively slowly, gardeners can usually expect to harvest usable fruit, but the quality and yield will be reduced. When potatoes suffer from early blight, their leaves display similar black spots and the tubers become covered with brown, corky spots. [图片]The early blight fungus overwinters in plant residues in the soil; the disease spreads rapidly in warm, humid conditions. [图片]Prevention and Control Grow blight-tolerant tomato varieties and purchase disease-free seeds and plants. If space allows, rotate susceptible crops. Destroy any volunteer potato or tomato plants that sprout in your garden, as they may already be infected. Keep foliage as dry as possible. Use drip irrigation or soaker hoses rather than overhead watering. Keep tomato plants staked to encourage good air circulation and minimize contact between plants and soil. Mulch tomato plants early in the season to slow the disease spread. Pick off and destroy infected leaves. If the disease continues to spread, uproot and destroy or deeply bury the diseased plants. After harvest, remove all potentially infected plant debris from the garden and destroy it. Compost the material only if you maintain a “hot” compost pile that will reach 150 degrees F for several days.

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2017年09月13日

Irregular brown or yellow spots on leaves are an early symptom of this fungal disease, which can infect many vegetable crops. Check the undersides of affected leaves; presence of a hairy white or purple mold confirms the diagnosis. Severely infected leaves may die, and the disease can eventually spread to stems, flowers, and fruit. [图片]The fungus overwinters on plant debris. Downy mildew is a host-specific disease. Thus, if your cucumber plants become infected, that doesn’t necessarily mean your onions will succumb. [图片]Prevention and Control Grow mildew-resistant varieties such as Fanfare cucumber and Allstar melon. Late-season crops tend to be more vulnerable to downy mildew. Plant disease-free seeds and plants. Space plants widely to promote good air circulation. This will help leaf surfaces stay dry, which inhibits infection. Keep foliage as dry as possible by using drip irrigation or soaker hoses rather than overhead watering. Control weeds, such as wild mustard, that can harbor the disease.

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2017年09月13日

Northern corn leaf blight appears on corn leaves as distinct, grayish green to tan blotches or streaks up to 6″ long. Southern corn leaf blight causes smaller tan spots with reddish brown borders. Young corn plants are most susceptible to these fungal diseases, and if the infection is severe the plants may die. [图片]Corn leaf blight is usually associated with commercial corn plantings. Wet, humid weather favors the spread of the disease and under these conditions corn leaf blight may also infect backyard corn plantings. The fungus overwinters on infected plant debris in the soil. [图片]Prevention and Control Plant blight-resistant varieties, such as Sugar Buns. Purchase only certified disease-free seed. Rotate corn to avoid planting it in the same location more than once every three years. Clean up the garden at the end of the growing season Compost infected cornstalks in a hot compost pile (material must reach the disease-killing temperature of 150 degrees F for several days) or destroy them.

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2017年09月13日

An early symptom of bacterial wilt is drooping leaves on squash or cucumber vines — even when the plants have been well watered. This happens because the wilt bacteria clog the vascular systems of plants, blocking the flow of water and nutrients from the roots to the leaves. If infected stems are cut open, they may release a milky sap. As the disease spreads, leaves turn brown. Eventually the entire plant shrivels and dies. [图片]Bacterial wilt can occur in all plants in the squash family except watermelons; another type of bacterial wilt can infect tomatoes and beans. There’s a direct link between bacterial wilt and insects. The bacterium overwinters in the gut of cucumber beetles and grasshoppers; when these insects emerge the following spring, they spread the bacterium as they feed. The severity of disease is typically proportional to the amount of feeding by the host insects. [图片]Prevention and Control Plant disease-free seed, and choose wilt-resistant cucumber varieties such as County Fair. Prevent cucumber beetle from feeding on susceptible plants. Keep plants in good health; cucumber beetles are more likely to target weakened plants. Uproot and destroy infected plants or add them to a hot compost pile.

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2017年09月13日

This disease produces small, dark irregular spots on tomato and pepper leaves; leaves eventually turn yellow and drop off. This defoliation weakens plants and exposes developing fruits to sunscald. Small, dark, wartlike raised spots with slightly sunken centers may appear on green fruits. Rot organisms are able to enter the fruit at these spots and cause decay. Bacterial spot symptoms are similar to, and often indistinguishable from, bacterial speck. [图片]Very warm, wet weather encourages the development of the disease. The bacteria overwinter in plant residues. This disease is a problem mainly in the East and Midwest. [图片]Prevention and Control Purchase certified disease-free seeds. Remove volunteer tomato and pepper plants, which may harbor the bacteria. Use a three- to four-year crop rotation for susceptible crops. Space plants well apart and support vines to ensure good air circulation. Use drip irrigation or soaker hoses instead of overhead watering to keep foliage as dry as possible. Keep the soil surface covered with mulch to prevent spores from splashing up from the soil surface. Remove infected plant parts from the garden and destroy them or add them to a hot compost pile.

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2017年09月13日

In the vegetable garden, bacterial blight is most often a problem on snap beans and lima beans. (Note that other crops also suffer from bacterial diseases that may be called bacterial blight.) Symptoms of infection are large, water-soaked, pale green spots on leaves that later turn brown. These spots may also appear on pods and can produce a yellowish ooze in wet weather. Leaves infected with halo bacterial blight develop many small dead spots with yellow halos around them; spots on pods produce a cream-colored ooze. [图片]The bacterium overwinters on plant debris and in the soil. High humidity and wet weather promote the spread of the disease. [图片]Prevention and Control Use a three-year crop rotation for beans. Space rows and seeds more widely than usual to allow good air circulation among plants. Don't work in the garden when plants are wet. Splashing water spreads bacteria among plants. Use drip irrigation or soaker hoses rather than overhead watering. Uproot infected plants and destroy them. Do not save and plant seeds from infected plants.

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2017年09月13日

Water-soaked lesions between the veins of leaves are a telltale symptom of this bacterial disease, which infects cucumbers, summer squash, and melons. Symptoms often first appear on the underside of leaves. As infected areas in the leaf die, the tissue becomes brittle and those leaf parts fall away, giving afflicted leaves a ragged appearance. Angular leaf spot lesions may exude a milky fluid that dries on leaf surfaces. In severe outbreaks, lesions may also develop on stems and fruit. [图片]The bacterium overwinters in the soil on seeds and plant residues, and is spread by rain splash and wind. Angular leaf spot is especially prevalent in warm, humid climates. [图片]Prevention and Control Plant vegetable varieties that are well-suited to your particular climate, and when possible, choose varieties such as Olympian cucumber that are resistant to angular leaf spot. Practice a two- or three-year crop rotation of cucumbers and other squash-family crops to break the disease cycle. Prevent the spread of disease by destroying infected plants and any that are in close proximity to them. Splashing water spreads bacteria. Avoid overhead watering and use drip irrigation or soaker hoses to keep foliage as dry as possible. Avoid working in garden when plants are wet. Avoid overfertilizing; excess nitrogen produces tender growth that is more vulnerable to infection

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