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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
The spotted wing drosophila (SWD), Drosophila suzukii, is a small fruit fly (vinegar fly) native to Japan. It was first discovered in the western United States in 2008 and has quickly moved through the Pacific Northwest into other parts of the US and northward into Canada. It has been reported in Illinois and Missouri. It is a serious pest of most berry crops, cherries, grapes and other tree fruits, with a preference for softer-fleshed fruit, such as raspberries, blackberries, strawberries and blueberries. Unlike most fruit flies it lays eggs in undamaged, healthy fruit as well as damaged or rotting fruit. (Other species lay eggs only in already-damaged and rotting fruit.) The adult flies have been transported by man far and wide.
Symptoms and Diagnosis Adult male flies are only 1/16 to 1/8 inch long and have red eyes. They have two distinctive dots on the wings (females do not have the wing spots). Male flies also have two dark bands on the forelegs. On the female SWD, the large serrated ovipositor is a distinctive morphological feature, longer than other fruit and vinegar fly species and with two rows of serrations. Infested fruit do not show obvious symptoms of infestation at first with only a small pin-prick visible from egg-laying. Within a few days, however, the fruit flesh will start to break down leading to discolored regions and eventual collapse of the tissues. By this point, the white larvae, about 1/8 inch long, can be relatively easy to detect. By being able to insert eggs into healthy, undamaged fruit the larvae of SWD can be present during ripening on the plant but only detected after harvest. During egg-laying, sour rot and fungal diseases can also be introduced, further affecting fruit quality. There is a greater risk of fruit contamination at harvest from SWD compared with native species that lay eggs only in already-damaged and rotting fruit.
Life Cycle Adults live about two weeks to over a month depending upon climatic conditions and can lay more than 100 eggs a day. In Missouri they will complete multiple generations a year. This demonstrates their high potential for fruit infestation and spreading if not controlled. Females cut into intact fruit using their serrated ovipositor to insert 1-2 eggs under the skin. The larvae (maggots) hatch in a few days and begin feeding. The maggots pupate either on the fruit, or fall to the ground, where they emerge as adults. A complete life cycle can take between 10-20 days. Integrated Pest Management Strategies 1. Practice strict sanitation. Collect and dispose of any and all damaged and fallen fruit. Do not compost. Place in a sealed plastic bag to prevent adults from emerging and dispose in the trash. Also, keep the surrounding area free of weed host plants, such as, wild blackberries and other plants with soft fruit that could harbor the pest. Increase air circulation around plants as SWD prefers sheltered areas with high humidity as in dense foliage cover.
2. Harvest early. Harvest fruit when it first begins to turn color and allow the fruit to ripen off the plant reducing its attractiveness to the fruit fly. 3. Exclude adult flies. The use of very fine netting (less than 0.98 mm, 18 mesh or finer) applied before the fruit starts to begin to ripen can exclude the adults. Be sure and apply before the first fruit start to ripen or flies can be trapped inside the netting. Exclusion, however, can have the adverse effect of excluding pollinators from crops, such as, everbearing strawberries.
4. Use insecticides. Sprays of spinosad, malathion or pyrethrins can be effective if applied early before adult females have laid eggs in the fruit. Some resistance to natural pyrethrins has been noted. Malathion is very toxic to bees and natural predators. Make sure the crop you are spraying is listed on the pesticide label and follow all directions including those for the waiting time before the crop can be harvested. SWD prefers high humidity so will be found in dense foliage areas. Good coverage is essential to be effective.
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
Plum curculio, a snout beetle, is an important pest on stone fruits like plums, cherries, and peaches. Plum curculio is one of the most serious pests of peach trees; they lay eggs within the fruit and both adults and larvae feed on the fruit, causing brown rot of the fruit. On apples, plum curculio is considered the second most damaging pest after codling moth.
Symptoms and Diagnosis Plum curculio beetles, Conotrachelus nenuphar, can be found on plum, cherry, peach, and apple trees, less commonly on nectarine and pear trees. Fruit may fall prematurely, in late May and June. The skin of infected fruit has small crescent-shaped blemishes that eventually become swollen and knotted. Upon closer examination, larvae may be seen feeding near the blemishes. Infested fruit is often hard and misshapen. The larvae create holes in the fruit skin when they leave the fruit to pupate. These holes are clean-cut and free of frass or webbing.
Life Cycle Plum curculio beetles are dark brown, about 1/4 inch long, and have a prominent snout, measuring about 1/3 the length of their bodies. They have four characteristic humps on their wing covers. Adults may overwinter in the soil or in hedgerows near host trees. These adults emerge from their overwintering sites to feed on trees in early spring. Females lay eggs within the fruit. The larvae that emerge from the developing fruit have grayish-white, worm-like bodies with brown heads and can be seen on infested trees in late summer. Larvae may feed on the fruit for 2–3 weeks before they burrow into the ground to pupate. Adults emerge in mid- to latesummer to cause more feeding damage on mature fruit before they overwinter.
Integrated Pest Management Strategies 1. Shake infested trees. In backyards with only a handful of infested trees, plum curculios may be shaken out of infested trees. This technique works best early in the day when the beetles are sluggish. Lay paper or cloth underneath the trees to collect the beetles. Destroy the collected beetles. 2. Clean up fallen fruit in which eggs or larvae may be developing. 3. Cultivate the soil surrounding infested trees in late spring or early summer to destroy pupating larvae that may have fallen to the ground with the fruit or pupae that may be developing in burrows in the ground.
4. Apply insecticides when populations of adult beetles are severe. Apply carbaryl (Sevin) spray to curb feeding damage and prevent beetles from laying eggs. It is important to delay application of the pesticide until after flower petals drop to avoid harming pollinating insects. Reapply pesticides two more times, at 10–14 day intervals. Other pesticides registered for use include azadirachtin (Bio-Neem, Margosan-O), Beauvaria bassiana, malathion, and pyrethrins.
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
The fall webworm, Hyphantria cunea, is a general feeder on nearly all trees except conifers. While this native North American insect attacks over 100 different tree species, it tends to prefer mulberry, walnut, hickory, elm, sweetgum, poplar, willow, oak, linden, ash, apple, and other fruit trees. The insect makes webs at branch tips and is harmful mainly to the beauty of the host. It is considered to be more of a nuisance than a threat to the health of the tree.
Symptoms and Diagnosis A distinctive web of silk, containing many caterpillars, is constructed around leaves at branch ends. Each "nest" may contain hundreds of larvae that feed together for a while. By late summer, the unsightly nest may measure three feet across and, in addition to the growing larvae, contains excrement, dried leaf fragments, and cast skins. An unusual characteristic of fall webworm caterpillars is that if alarmed, all the caterpillars in a nest make jerking movements in unison. It is thought that this is a potential defensive mechanism to startle and deter predators. Another tent-forming caterpillar is the eastern tent caterpillar, Malacosoma americanum. However, eastern tent caterpillars make webbed silk nests in a fork of a branch or tree trunk and leave the nest to feed. Fall webworm caterpillars have nests at branch tips and feed inside the webbing.
Life Cycle In late spring or early summer, adults emerge from overwintering pupal cases and lay hair-covered masses of several hundred eggs on the underside of leaves. The larvae that emerge can be either yellowish green with a black head or tan with a red head. Both color forms have many long, gray hairs and pairs of wart-like black spots running down their backs. Once feeding begins, the larvae congregate in masses and produce the silky web that surrounds the entire colony. Larvae feed inside the web and expand it as they grow. Larvae stay in the colony until their last molt after which they may be found crawling anywhere on the host plant. The larvae crawl to a protected place to spin a flimsy cocoon and pupate. The adults emerging from pupation have two color forms: either all white or white with black spots. There are two generations a year.
Integrated Pest Management Strategies 1. Live with the problem and let nature take its course. Hosts are seldom seriously harmed because defoliation usually occurs later in summer rather than during a period of active growth and not enough terminal growth is consumed to affect tree growth. In addition, more than 75 natural enemies parasitize and prey on the fall webworm. 2. Prune out webs. Branches that have active webs ("nests") may be cut out and destroyed. Webs are always on branch ends and are easier to remove when they are small. Pole pruners are helpful for reaching into trees.
3. Apply insecticidal sprays. If chemical control is truly necessary, treatment is recommended when webs first appear. This is because the smaller caterpillars are more susceptible to insecticides and, secondly, the webbed nests are somewhat waterproof and can be difficult to penetrate with sprays. The microbial insecticide Bt (Bacillus thuringiensis) is available as Dipel or Thuricide and can be used on the small caterpillars. Other pesticides registered for use include acephate (Orthene), carbaryl (Sevin), pyrethrins and spinosad.
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
The eastern tent caterpillar, Malacosoma americanum, is a native species that occurs throughout the eastern United States and westward to the Rocky Mountains. Before the outbreak of the gypsy moth, the eastern tent caterpillar was considered by many authorities to be the most widespread and destructive defoliating pest of deciduous trees in the eastern United States. Its favorite host trees include apple, wild cherry, and crabapple. However, the caterpillars will also attack ash, birch, maple, oak, poplar, cherry, and plum. Populations fluctuate greatly because of factors such as unfavorable weather and natural enemies.
Symptoms and Diagnosis Eggs are laid in distinctive masses encircling the twigs of the host plant. The egg masses are about 3/4 of an inch long and are covered with a dark substance that makes them appear varnished. The egg mass has the consistency of styrofoam. Eggs hatch and the caterpillars gather at a nearby branch fork where they begin to build a silk webbed tent. As the caterpillars grow, they build new tents in the larger forks of trees. Webbed tents are the most obvious sign of the caterpillars. Another tent-forming caterpillar is the fall webworm, Hyphantria cunea. However, fall webworm caterpillars make webbed silk nests at the ends of branches and feed inside the nest. Eastern tent caterpillars have tents in a fork of a branch or tree trunk and they leave the nest to feed.
Life Cycle Tent caterpillars overwinter as eggs in an egg mass. The eggs hatch in the spring, about the time wild cherry leaves begin to unfold. The young caterpillars quickly gather at a branch fork or crotch and begin to build a silk web. The larvae leave their tent to feed on foliage. Young caterpillars feed during the day and remain in the tent at night; older (and larger) caterpillars feed at night and remain in the tent during the day. Mature larvae can reach a length of about 2 inches. They are generally black with a white stripe down the back and have a series of blue spots between yellow lines that run lengthwise down the back. They also have long, fine hairs all over their body. This is the only common caterpillar with a white stripe down the back. At maturity, a caterpillar will leave the host tree and search for a place to spin a cocoon (fence post, tree trunks, debris on the ground, sides of buildings, etc.). Adult moths emerge in two weeks, mate, and lay eggs that overwinter. Moths have reddish-brown wings with two white diagonal stripes on each front wing. There is one generation per year with about 9 months spent in the egg stage.
Integrated Pest Management Strategies 1. Live with the problem. It is not necessary to spray insecticides to control the eastern tent caterpillar. Healthy defoliated trees will grow new leaves. Infested trees can be unsightly and are less vigorous than attacked trees, but they are seldom killed. Typical natural controls include birds, predaceous and parasitic insects (especially wasps), and disease organisms. Caterpillars with white eggs or cocoons attached to their back should not be destroyed because they are being hosts for native parasites. 2. Handpick egg masses. Future damage on small trees can be reduced by locating and removing egg masses during winter because they are most obvious at that time. They can be scraped off with a thumbnail or pruned out.
3. Manual removal of tents or caterpillars. Start looking for tents when service berries (Amelanchier laevis) or sugar maples (Acer saccharum) are blooming or when silver maples (Acer saccharinum) have leaves about 1 to 2 inches long. Tents can be pruned off if small, because they are usually located in small branch forks. They can also be removed by winding them around the end of a broomstick or pole that has a small brush or nails mounted on the end. It is most effective to do this at night or on cloudy, rainy days because the young caterpillars are gathered in the tent for protection and aren't venturing out to feed. Caterpillars can also be handpicked and dropped into soapy water.
4. Apply insecticides. If insecticide sprays are necessary, they should be applied when the tents are first noticed. Caterpillars leave the tents to feed so thorough coverage of the foliage with the insecticidal spray will provide control. Tents are water repellent so spraying them with water based insecticides is not very effective. Insecticides that can be used include Bacillus thuringiensis (Bt, Dipel or Thuricide), carbaryl (Sevin), pyrethrins, acephate (Orthene) or spinosad.
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
Steneotarsonemus pallidus, or cyclamen mites, can be major pests on strawberries. Plants they infest are chlorotic and sickly looking because mites extract chlorophyll from the plants.
Symptoms and Diagnosis Yellow or white stippling appears on leaves. New growth is stunted and older growth becomes distorted and curled. Flower buds may drop. Fruit that develops from infected buds are small and dry. Whole plants may have a bronze cast.
Life Cycle Mites are minute arachnids, only measuring up to 1/25 inch. Under a magnifying lens, you will find that adults are red-orange and immature stages are somewhat translucent. The distorted growth and bronze cast of the plant occur due to toxins injected by the mites. They overwinter in the crowns of strawberry plants. Mites can do serious damage to strawberry plantings because they can reproduce and spread quickly; a new generation may be produced every 14 days.
Integrated Pest Management Strategies 1. Apply insecticidal soap weekly until control is achieved to rid plants of mites. Make sure to cover the undersides of leaves because that is where these pests tend to be found feeding. 2. Remove and destroy infested plants. 3. Apply insecticides. Pesticides registered for use include dicofol (Kelthane and endosulfan (Thiodan).
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
The two most destructive species of cankerworms (a kind of inchworm) in the St. Louis area are the fall cankerworm and the spring cankerworm, both of which feed in the spring. They attack many different species of trees and shrubs.
Symptoms and Diagnosis Leaves are chewed. Complete defoliation and crop loss may occur; or after repeated damage, less and less fruit is produced until little, if any, fruit matures. Damage is first evident in the early spring or summer after trees have fully leafed out. This is about the time that larvae of both species emerge and begin to feed. Life Cycle Cankerworms are small caterpillars, only getting up to an inch long. Adult males are small, gray moths with a wingspan reaching only 1 inch long. The females of both species are wingless.
FALL CANKERWORM: The adult fall cankerworm, Alsophila pometaria, emerges from the ground in late November or early December. The wingless adult females climb up the trunk of the host tree and lay barrel-shaped eggs in masses on twigs and branches. The eggs hatch and larvae begin feeding about the same time leaves begin to emerge. The larvae drop down and dangle on silken threads until swept away by a breeze. The ballooning larvae may travel from plant to plant until a suitable host plant is found. The larvae feed for about a month before they fall to the ground to pupate. The worms have brown backs with white stripes running lengthwise down their backs. The fall cankerworm has three sets of prolegs with the foremost proleg severely stunted. This distinguishes it from the spring cankerworm that has only two pairs of prolegs.
SPRING CANKERWORM: The adult spring cankerworm, Paleacrita vernata, emerges in late February or early March. The wingless adult females climb up the trunk of the tree and lay barrel-shaped eggs in cracks in the bark and underneath the bark and bud scales. Yellow-striped green worms hatch at the same time as fall cankerworm larvae and follow the same general feeding pattern. They too drop to the ground where the larvae overwinter in a protective cell. Spring cankerworm larvae have only two pairs of prolegs. Integrated Pest Management Strategies 1. Sticky barriers may be banded around tree trunks. Apply a band of a sticky material, such as Tanglefoot, around the trunks of trees in October. The sticky material will trap the wingless females of the fall cankerworm moths as they crawl up the tree trunk to lay eggs in late November or early December. Renew the traps in February to trap the emerging female adults of the spring cankerworm that climb the trunk to lay eggs in late February or early March.
2. Prevent larvae from emerging. In the spring apply a horticultural oil spray on the tree before the larvae hatch, about the time trees just begin to leaf out in the spring. 3. Spray Bt (Bacillus thuringiensis) or Sevin after leaves are fully expanded and flowering is finished. Repeat this application two more times, at 14-day intervals. Sevin is very toxic to bees, hence spraying should be delayed until after flowering to limit damage to these beneficial insects.
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
Two different cane boring beetles, raspberry cane borer and red-necked cane borer, can cause damage on brambles such as raspberry and blackberry. Occasionally, the raspberry cane borer may also cause damage on roses.
Symptoms and Diagnosis RASPBERRY CANE BORER: Twigs are girdled causing younger shoot tips to wilt and eventually die. The bases of girdled areas show a purple discoloration. RED-NECKED CANE BORER: Random areas on branches may become swollen or enlarged. These areas can be several inches long and at least 1/2 inch diameter. Sometimes branches may break off where swelling has occurred. Holes in leaves caused by the feeding of the adult beetles should also be evident.
Life Cycle RASPBERRY CANE BORER: Raspberry cane borers, Oberea bimaculata, are long-horned beetles. Their black bodies are about 1/2 inch long, and they have prominent antennae that may be as long as, or longer than, their bodies. They have a yellow prothorax with two black dots. Adults emerge in June. Females will insert single eggs into punctures that they make in the twigs; twigs may be girdled above and below these punctures. Larvae girdle the trunks from the inside and remain to bore downward through the trunks for two winters before pupating and finally emerging as adults. RED-NECKED CANE BORER: The red-necked cane borer beetle, Agrilus ruficollis, has a blue-black metallic body with a copper-red thorax. Females lay their eggs on the bark of the canes, near the base of a leaf. The white grubs are 1/2 inch long and can be found feeding within the canes, near the swollen and discolored areas. Adult borers can be found feeding on the foliage in late spring or summer. There is one generation per year.
Integrated Pest Management Strategies 1. Prune all canes that show signs of infestation. If you prune after wilting first occurs, you only need to prune about an inch below the wilted part; if you wait to prune a wilted cane, a longer cut must be made to insure that you remove the feeding larva. Prune girdled canes the first winter after observing damage in order to kill raspberry cane borer larvae. Otherwise, they will continue to feed and bore through until they have completely destroyed the cane and reached the ground to pupate the next winter. Remove canes after red-necked borer damage has been observed by late spring the next year so that adults don't get a chance to emerge.
2. Destroy any wild brambles that may be bordering your property. They may also be hosting cane borers. 3. Apply insecticides. Both adults and larvae can be controlled with insecticides. Apply an approved insecticide when adult beetles are most active prior to bloom in order to achieve the most success. If needed, apply a second spray once petals have fallen. Spray or paint trunks and branches of infected bushes with pyrethrins so that larvae are destroyed before they have a chance to burrow into the wood.
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
The brown marmorated stink bug (Halyomorpha halys) is an Asian species that was introduced into Allentown, Pennsylvania around 1996 from China or Japan. In 2015 it was found in 42 states including Missouri. Its range is increasing in Missouri and is projected to be a major pest of vegetable and fruit crops including apples, peaches and blackberries, as well as, a nuisance in homes where it can overwinter. However, it will not reproduce inside homes or cause structural damage. It can be confused with other stink bugs, notably the brown stink bug, which is smaller and less destructive.
Symptoms and Diagnosis Brown marmorated stink bugs (BMSB), like other stink bugs, feed by inserting their mouth parts into the leaves, flowers, buds, fruits, and seeds of host plants and sucking plant sap. Large infestations of stink bugs may cause plants, especially small plants and young tender growth, to wilt, become stunted and misshapen, or die. Other damage includes yellow or white blotches on leaves; misshapen or aborted fruits, seeds, and buds; calluses, blemishes or depressions; and black pits on nuts. Tomatoes exhibit a condition called cloudy spot (pale yellow spots and a white pithy area just under the skin at the puncture site). Peaches and other fruits may develop scarring and dimpling resulting in cat-facing or a pitted appearance. The seeds in soybean pods may be deformed, small, discolored, or shriveled.
Life Cycle Adult brown marmorated stink bugs are about ½ inch long and have the characteristic “shield” shape of stink bugs. They are mottled brownish grey in color with a white or pale gray underside. The antennae and legs have light bands. The edges of the abdomen that extend beyond the sides of the wings have brown and white bands. The native brown stink bug is smaller and has a light green underside. It lacks the bands on the antennae and legs. Adults overwinter outdoors and in buildings and emerge in late March through April when they mate and lay eggs on the underside of leaves May through August. The eggs (about 1/16 inch in size) are light yellow, yellow-red or green and are laid up against each other in clusters of 20 to 30 eggs. The eggs hatch in 1-3 weeks into brightly colored red and black nymphs with banded legs and antennae. They have a “tick-like” appearance. The nymphs begin feeding and progress through 5 instars to adulthood. By the second instar the banded abdominal extension has clearly begun to develop. In northern areas there may be only one generation a year but in warmer, southern states there may be up to three generations a year. In Missouri, there may be two generations a year.
In late September into mid-October adults seek protected areas for overwintering. They can gain access into homes through cracks and opening around windows, doors, siding, fascia boards, chimneys, attics or window air conditioners where they overwinter in walls and other locations. In spring, they can be found in interior spaces as they look for ways to reach the outdoor. Integrated Pest Management Strategies There are no easy controls for the brown marmorated stink bug, but here are some suggestions for management. Outdoors 1. Sanitation. Control weeds in susceptible crops and in areas adjacent to gardens to decrease breeding and overwintering habitat. It is important to remove weeds early in the growing season before stink bug populations increase or the loss of habitat may force pests to move into the garden. 2. Collect insects. Hand pick and destroy eggs and bugs. When hand picking, use gloves as dermatitis at the point of contact can occur. Some individuals are also allergic to the smell of stink bugs. Indoors, use a shop vacuum to vacuum up the overwintered adults.
3. Use natural controls. Although there are currently no known natural predators, it is always wise to encourage other natural predators such as parasitic wasps and flies by growing small-flowered plants. The unpleasant odor produced by stink bugs deters many predators but several bird species do consume these pests. 4. Use insecticides. Control with pesticides is short-lived and difficult. Also, resistance to some pesticides has already been observed. If damage is severe and there is a need to save a crop, you can try sabadilla, pyrethrin or permethrin (Eight). Check label directions for suitability with your crop before using.
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
Many ornamental trees and shrubs are susceptible to Phytophthora root rot and can develop root and crown rot, particularly if the soil around the base of the plant remains wet for long periods of time. Typical symptoms of a root disease are apparent on infected plants. The leaves will appear droughtstressed and may die quickly as the weather warms in late spring or early summer. Trees that are especially susceptible include oak and dogwood.
Symptoms and Diagnosis Leaves will appear drought stressed, sometimes turning dull green, yellow, red, or purple as they wilt. Infected trees may survive a few years before the disease kills the whole plant. The bark around the soil-line may appear darkened. Cutting away some bark should reveal red-brown discoloration in the wood underneath it. Disease symptoms are distinguishable from Armillaria root rot because mycelial mats do not develop in tissues infected with Phytophthora root rot.
Life Cycle Root rot-causing Phytophthora species can survive in the soil for years, as long as moist conditions persist. It can spread through splashing rain, irrigation water, and runoff water. Disease fungi can spread through contaminated soil and garden equipment as well. Rot is more likely to spread in early spring and late fall during cool, rainy weather. But symptoms are more likely during stress periods of low rainfall. Flooded and saturated soil conditions for 6–8 hours are especially conducive to the spread of root rots. Wounds are not required for infection.
Integrated Pest Management Strategies 1. Improve water drainage. Prior to planting, make amendments to the soil composition to help manage drainage away from tree roots. Don’t allow water to pool around the collar or root system. Core aerate to improve drainage and lessen compaction. 2. Raise the planting site to avoid poor drainage and prevent pools of standing water from forming around valuable ornamentals. Plant on mounds of soil. Never plant trees deeper than they were planted at the nursery. 3. Separate plants, shrubs, and trees according to their irrigation needs, and avoid overwatering.
4. Remove soil. If soil has been piled up over the crown, remove it carefully to expose root flare. This is where fungal infection is likely to occur. 5. Plant resistant or less susceptible varieties. Consider replanting with tolerant plants after Phytophthora root rot has been diagnosed. Trees that are tolerant to Phytophthora root rot include white cedar and American arborvitae.
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Dummer. ゛☀
2017年09月17日
Dummer. ゛☀
Peach leaf curl is a springtime disease caused by the fungus, Taphrina deformans. It infects the leaves and shoots of peaches and nectarines. Apricots are immune. It is one of the most common diseases of these fruits. It causes the leaves to curl and turn reddish in color. A severe infection can cause reduced yields.
Symptoms and Diagnosis Symptoms first appear in spring. New leaves become curled and develop reddish areas. The reddish areas become thickened and puckered resulting in severely distorted leaves. As the disease progresses, the thickened areas turn yellowish gray and become covered with velvety spores. Affected leaves turn yellow or brown and fall prematurely. Affected shoots usually send out new leaves which often are unaffected by the disease unless rainy weather ensues. In more severe infections, shoots may become thickened and die.
Aphids can also cause leaves to curl. If present, the insects or cast skins will be evident to the naked eye. Life Cycle The fungus overwinters on bud scales, on twigs, and on fallen infected leaves. In spring the fungal spores are splashed onto newly developing leaves. During cool, wet weather the spores germinate on the young leaves and initiate infection. Development of the disease slows as temperatures increase. Older leaves are resistant to infection. Consequently, the disease is most prevalent in the spring.
Integrated Pest Management Strategies 1. Keep plant healthy — avoid excess fertilization. A healthy plant can better withstand the loss of leaves, but excess fertilization can cause succulent tissue that is very susceptible to infection. 2. Clean up diseased leaves. Raking up and disposing of diseased leaves can't hurt, but its value in controlling the disease is slight. 3. Don't panic.Once infection has occurred fungicidal sprays are not effective. A healthy plant should refoliate. Because refoliation normally occurs during warmer, dryer weather, re-infection is usually not a problem. Thinning the fruit crop in years of severe infection can also help maintain plant vigor. To limit damage the year after a moderate to severe infection, follow the protective spray program below.
4. Use properly timed protective fungicidal sprays. If leaf curl was a problem in the spring, apply a protective fungicidal spray after leaf fall in October or November or before bud break in late winter, January through February. After buds have begun to swell fungicidal sprays are not satisfactory. Do not apply to foliage. Chemicals effective in controlling leaf curl include copper-based fungicides like Bordeaux mixture, Bravo, lime-sulfur spray, or other brands that list the control of peach leaf curl on their label.
5. Replace the tree with a more disease tolerant variety. If you want to avoid using fungicidal sprays, consider replacing the tree with a more tolerant variety. ‘Redhaven’ and cultivars derived from ‘Redhaven’ have greater tolerance to peach leaf curl disease.
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