Plant Health Problems
Diseases caused by Fungi:
Brown rot, Monilinia fructicola.
This is the most common and destructive disease of stone fruits in Connecticut and New England. The disease is especially severe in wet, humid weather. Brown rot causes blossom blights, twig blights, twig cankers, and fruit rots. Infected blossoms wilt, shrivel, and die, becoming covered with a grayish mold. Infection can then spread to the twig and form a brownish oval canker. These cankers can expand and eventually girdle the twig, causing the terminal growth to wither and die. On fruit, this disease first appears as a small, circular brown spot that increases rapidly in size and eventually results in a soft rot of the entire fruit. Under wet, humid conditions, ash-gray, powdery tufts appear all over the surface of the fruit, a characteristic diagnostic symptom of this disease. Fruit decay is often not apparent on green fruit but becomes obvious as fruit begin to mature and ripen. Fruit which are wounded (by insects, mechanical injury, bird pecks, etc.) are more readily infected than unwounded fruit. Rotted fruit may fall to the ground or persist as mummies on the tree. The fungus overwinters in fruit mummies on the tree or ground and in twig cankers. In spring, the fungus produces two types of spores; one type is produced on the surface of cankers and mummied fruit on the tree and the other type is produced in mummied fruit on the ground. Both spore types can cause infection under warm, moist conditions.
Sanitation is essential to control of brown rot. Any mummied fruit that remain on the tree should be removed and destroyed and all dead and/or cankered twigs should be pruned and removed from the vicinity of the tree or planting. In addition, all mummied fruit on the ground should be raked and removed and/or the ground beneath the tree cultivated to prevent spores from forming on the mummies in the spring. At harvest, care should be taken to avoid bruises, punctures, or tears in the skin of mature fruit to prevent sites for potential infection. In conjunction with this sanitation program, a season-long fungicide spray program is usually necessary for effective brown rot control. Among the compounds registered for use in Connecticut are captan (found in most general tree fruit sprays), chlorothalonil, thiophanate-methyl, iprodione, and sulfur. Consult the label for dosage rates, safety precautions, and days to harvest intervals. For more information, see the fact sheet on Disease Control for the Home Peach Orchard.
Leaf curl, Taphrina deformans.
Peach leaf curl is a springtime leaf disease favored by relatively cool, wet spring weather. The fungus causes a thickened, reddish-purple discoloration of developing leaves. These leaves become puckered, primarily along the mid-vein, and appear distorted and stunted. As these symptomatic leaves age, they become yellow to brown and drop from the tree. A second crop of leaves are subsequently produced which is not affected by the disease. The fungus overwinters in the buds and infects newly developing leaves as the buds begin to swell in the spring. Infection only occurs during a relatively short time period as fungal spores are washed onto developing leaves by rain. This fungus rarely infects or causes symptoms on fruit.
It is helpful to maximize tree vigor by following good cultural practices in order to minimize the long-term effects of disease and defoliation. Leaf curl is generally not considered serious enough to warrant control. However, several years of uncontrolled heavy leaf infection can weaken the tree and effectively reduce its life span. This disease can be effectively controlled by properly selected and timed fungicide sprays. Among the compounds registered for use in Connecticut are ferbam and fixed copper. The application should be made before the buds begin to swell--this can be done in late fall after the leaves have fallen or in early spring before the buds swell. Consult the label for dosage rates, safety precautions, and days to harvest intervals. For more information, see the fact sheet on Disease Control for the Home Peach Orchard.
Scab, Cladosporium carpophyllum.
Peach scab, also known as ink spot, is most often a problem in warm, wet weather following shuck-split. Although the fungus infects leaves and twigs, disease symptoms are most often observed on the fruit. Early infection appears on the fruit as small, circular green spots concentrated at the stem end. These spots usually don't appear until the fruit are half grown. Older lesions appear as dark green-black velvety blotches that, as they coalesce, often cause cracks in the skin and flesh. Infections on twigs and leaves are inconspicuous and appear as green-brown superficial lesions. The fungus overwinters in lesions on twigs and in spring, produces spores called conidia. These conidia are washed and splashed by rain to twigs, fruit, and leaves where they cause new infections. Forty to 70 days elapse from the time the conidia land on the fruit until the disease symptoms are visible so the disease can go unnoticed until the fruit are well grown.
Sanitary practices such as pruning and removing symptomatic twigs help to reduce overwintering inoculum. Fungicide sprays are often necessary during wet years. Among the compounds registered for use in Connecticut are captan, chlorothalonil, and wettable sulfur. Consult the label for dosage rates, safety precautions, and days to harvest intervals. For more information, see the fact sheet on Disease Control for the Home Peach Orchard.
Perennial canker, Leucostoma spp.
This disease is also known as Valsa canker, Cytospora canker, and peach canker. It is particularly problematic in New England since it is more serious on trees which have been weakened or damaged by cold stress. These fungi cause cankers that first appear as sunken areas in the wood which exude considerable gum. These are oval to linear in outline and are eventually surrounded by a roll of callus at the canker margins. Cankers increase in size each year and often completely girdle a limb or an entire trunk. The fungi overwinter in cankers or on dead wood. Spores called conidia are produced and carried by splashing and wind-driven rain and/or wind. Infection requires moisture and takes place through a variety of different avenues, including winter injuries, pruning stubs, mechanical damage, insect punctures and leaf scars.
A multifaceted approach is necessary to control this disease. Pruning of trees should be delayed until March or April or later, if possible, to promote early healing of wounds. Any cankers or dead wood should be pruned and removed from the vicinity of the planting. All efforts to avoid mechanical damage, to maintain the vigor of the tree by proper application and timing of fertilization, and to protect the tree from insect and other injuries should be made. Fungicide sprays have not been found to be effective.
Diseases caused by Bacteria:
Bacterial leaf spot, Xanthomonas pruni.
The bacterium causing this disease infects the leaves, fruits and twigs, producing angular water-soaked spots on the leaves, which later turn black. Leaves eventually turn yellow and fall, even when they have only a few spots. The leaf infections are most abundant along the midrib and tip because the bacteria are washed from the twig cankers by rain and accumulate at those points. Fruit infections appear as dark angular spots. They are often concentrated near the stem end of the fruit. Cultivars vary greatly in their resistance to this disease. Some of the highly susceptible peach varieties are Elberta, Suncrest, and Redhaven; some of the susceptible nectarine varieties are Flamekist, Redgold, and Flavortop.
It is helpful to maintain adequate fertility and tree vigor by following a regular program for maintenance. Selection of resistant varieties is probably the most effective strategy for control. Among the resistant peach cultivars are Biscoe, Newhaven, and Sweethaven; resistant nectarines include Royalkist, Nectared 3, and Sweet Melody. Pesticides are generally not effective for control.
Diseases caused by Phytoplasmas:
Symptoms of this disease usually don't appear until late spring or early summer. Diffuse, yellow areas appear on the foliage scattered throughout the tree or on individual branches. The chlorotic leaves often show an upward longitudinal rolling along the mid-vein. Infected leaves also become stiff and brittle and the discolored areas turn red and usually fall out giving the leaves a characteristic tattered appearance. Symptomatic leaves often drop prematurely. However, leaves at the tips of infected branches usually remain attached, giving the branches the rat-tail symptom characteristic of X-disease. Trees that become infected after 3 years of age seldom die as a direct result of X-disease but trees under 3 years of age are frequently killed in a short time. However, the older trees soon become unproductive, because the fruit on infected branches dries up and falls off with the dropping of the leaves. When foliage symptoms appear on a branch late in the season, the fruit does not fall but develops an insipid, slightly bitter flavor as it ripens. The seed is nearly always abortive in such fruit.
The X-disease agent also infects chokecherry, Prunus virginiana. Symptoms are first evident as a slight yellowing or reddening of the foliage. Symptoms become more pronounced each year as infected plants appear vivid red or yellow and a distinct rosetting at the tips of the branches.
The X-disease phytoplasma is vectored by several species of leafhopper. Chokecherry is considered an important reservoir host and the primary source of inoculum.
The most effective and practical means of control of this disease is the eradication of chokecherry in the vicinity of the orchard. It is helpful to remove all chokecherry for a distance of 500 feet. However, this is often not practical so eradication from the fence rows immediately surrounding the planting will give satisfactory control. Leafhopper vectors are often controlled with general purpose orchard sprays. For more information, see the fact sheet on Strategies for Management of X-Disease of Stone Fruits.
Diseases caused by Physiological/Environmental Factors:
Winter injury, environmental.
Low winter temperatures, especially sudden drops to below zero temperatures or freeze-thaw cycles can damage cambial tissues, kill fruit buds, and result in tip or branch dieback. In extreme cases the wood of the entire tree can be injured. Freezing injury of the wood is characterized by an abnormal darkening of the center of the branches, extending in some cases nearly to the last ring of growth. This injury to the wood is usually followed by considerable exudation of gum the following summer.
Spray injury, pesticide sprays.
Copper sprays may cause injury to peach trees. Symptoms appear as bright red spots on the foliage followed by yellowing and dropping of the leaves.
Gumming, growth-related disorder.
Gums exude from weak areas in the bark and in developing fruit. This condition can be in response to many factors including weather cracks, insect feeding, bird pecks, and hail damage.
Several species of aphids can injure peach trees when they suck fluid from stems and leaves. Some of the more important ones are the black peach aphid, Brachycaudus persicae, the black cherry aphid, Myzus cerasi, the green peach aphid, Myzus persicae, and the rusty plum aphid, Hysteroneura setariae. The black peach aphid lives through the winter on the roots. In spring, it migrates to the leaves and tender shoots to feed.
See Cherry for the biology of the black cherry aphid. The biology of the green peach aphid is discussed below. Most aphids can be controlled with applications of malathion, diazinon, or insecticidal soap, which are among the compounds registered for use against these pests in Connecticut. Consult the labels for dosage rates and safety precautions. Often, natural enemies, such as lacewings, ladybugs, and syrphid flies, provide adequate control.
European fruit lecanium, Parthenolecanium corni.
These convex scales are considerably larger than San Jose or Forbes scales. They are rare in Connecticut and control usually is not required.
European red mite, Panonychus ulmi.
These mites attack peach, apple, and rarely other fruit trees. Large infestations of these mites may cause bronzing of foliage and premature leaf drop. Fruit on bronzed trees may be small. The mites spend the winter as red eggs on the bark of trees. Nymphs hatch from eggs about the time the shoots of apple reach the tight cluster growth stage and develop rapidly. Mites have several generations each summer, with the peak abundance in July or early August. Mite eggs are best seen with a hand magnifying lens because they are extremely small. They are slightly flattened and have a delicate central hair. The adult females are dark red with white spots. Other stages vary from red to green. Unlike the overwintering eggs, the summer ones are brown. One or more applications of horticultural oil, which is among the compounds registered for use against this pest in Connecticut, before bloom provides control by suffocating the eggs that have overwintered. To minimize the chances of foliar damage from oil, the application rates are reduced to ½ to 1% as the growing season progresses. Consult the label for dosage rates and additional safety precautions. Oil is especially effective because it does not kill the predatory mite, N. fallacis, which may assist in keeping mite populations in check.
Forbes scale, Quadraspidiotus forbesi.
Injury, life history, and control of the Forbes scale are essentially the same as that for the San Jose scale. Forbes scales differ from San Jose scales by having the center orange-red instead of yellow.
Green peach aphid, Myzus persicae.
Severe infestations of this aphid result in leaf-curling, decreased growth, and loss of tree vigor. When peach leaves begin to unfurl in spring, nymphs hatch from the eggs that have overwintered on the bark. The bodies of nymphs and adults are yellowish green with 3 darker green lines on the back of the abdomen. Nymphal and adult aphids suck fluids from leaves. Adults of the first and sometimes the second generation give birth to live young. After 2-3 generations on peach, winged adults appear and migrate to other cultivated plants in late spring. The aphids have several generations on the summer hosts. Then, in fall, females fly to peach and give birth to nymphs. These nymphs develop into adult females that mate with males that are returning from their summer hosts. The females then lay the small, shiny black, oblong eggs that will overwinter. Populations can be reduced by springtime applications of horticultural oil, azadirachtin, malathion, diazinon, or insecticidal soap, which are among the compounds registered for use against this pest in Connecticut. Consult the labels for dosage rates, safety precautions and preharvest intervals.
Lesser peachtree borer, Synanthedon pictipes.
The habits, appearance, and control of this pest are very similar to those of the peach tree borer described below.
Oak and hickory plant bugs, Lygocoris spp.
These bugs cause distortion of peaches by producing catfacing or scabby scars. They overwinter as eggs on oak, hickory, dogwood, walnut, or beech trees. The nymphs develop to adults by feeding on the same forest trees. The adults disperse to orchards a few weeks after shuck split, peaking in abundance about mid-June. They injure the peaches when they puncture the fruit to drink fluids. The adults are brown to brownish yellow and about 1/4" long. Sprays of phosmet, which is among the compounds registered for control of this pest in Connecticut, initiated several weeks after shuck fall will lessen, but probably not eliminate, injury. Consult the label for dosage rates and safety precautions.
Oriental fruit moth, Grapholita molesta.
This moth potentially is the most destructive pest of peach and quince in Connecticut. The principal damage is "wormy" fruit, but shoots may also be killed. Mature caterpillars overwinter in impervious silk cases on the bark of the trunk or upon debris in orchards. These caterpillars are pink and about 1/2" long. In spring, they form pupae in the cases, and the mostly gray adults emerge in May, starting when peaches bloom. The moths have wingspan of just less than 1/2". The females lay eggs upon the undersides of the leaves and, in some cases, on the twigs. The caterpillars of the first generation tunnel into the tender shoots early in the season, and later they leave the twigs to enter the fruit. As twig borers, the caterpillars kill the tips of shoots and cause the shoots to branch. The caterpillars of later generations go directly into the fruit after hatching. In peach orchards in Connecticut, the oriental fruit moth has three generations and sometimes a partial fourth generation. Insecticidal applications of phosmet or diazinon, which are among the compounds registered for use against this pest in Connecticut, from shuck split until four weeks before harvest control this pest. Consult the labels for dosage rates, safety precautions and preharvest intervals. Use of pheromone traps will assist in timing the sprays.
Peachtree borer, Synanthedon exitiosa.
This major pest damages the cambium of peach trees, sometimes girdling and killing young trees. The caterpillars of this moth overwinter on or under the bark of trees just below ground level. In spring, they resume feeding when the temperature reaches about 50F. The caterpillars, which are white or creamy with a yellowish brown to dark brown head, tunnel in the cambium layer just beneath the bark on the trunks. Masses of semi-transparent peach gum often exude from the wound. In mid-May and June, mature larvae make a cocoon of silken threads and bits of frass and wood, and then they form a pupa in the cocoon. The empty pupal cases often protrude from the gum exudate after the emergence of the adult moths. The wasp-like moths emerge between June and August. The moths are dark steel blue with a few white markings on the body and dark markings on the otherwise transparent wings. Often on the same day of emergence, females mate and lay eggs. The eggs hatch within 2 weeks, and the caterpillars bore into the cambium. Flights of the adult moths may be monitored with pheromone traps.
Peach twig borer, Anarsia lineatella.
Caterpillars of this insect damage peach twigs and occasionally fruit by boring into them. Unlike the larvae of the oriental fruit moth, caterpillars of the peach twig borer are reddish brown in color. Typically, the length of caterpillars is less than 1/2". Reddish-brown masses of chewed bark webbed together in the crotch indicate the presence of caterpillars in twigs. When the caterpillars mature, they construct a loose cocoon under the curled edge of the bark. The steel gray moths, which have a wingspan of about 1/2", emerge with 2 weeks. The peach twig borer has 4 generations each season. No control usually is needed.
Plum curculio, Conotrachelus nenuphar.
This beetle can destroy young peaches. See Apple or Plum. After the blossoms fall, 2-3 applications of phosmet, which is among the compounds registered for use against this pest in Connecticut, at 7-10 day intervals, provide good control. Consult the label for dosage rates and safety precautions.
Rose chafer, Macrodactylus subspinosus.
This general pest feeds on peach foliage. When very abundant, the adult beetle injures roses and many other shrubs and trees by skeletonizing the leaves. Rose chafers breed most abundantly in sandy waste land but often occur in lawns; they appear each year about June 10 to 12, and feed for about a month, though some of the beetles are present for 6 weeks. The females each lay from 24 to 36 eggs singly in the ground a few inches beneath the surface. They soon hatch and the young grubs feed upon the roots of grass and other plants, becoming full grown by late autumn when they go into the ground several inches to overwinter. The next April or May, they come near the surface and transform to pupae in earthen cells, and from 2 to 4 weeks later the beetles emerge. The adult beetle is yellowish grayish brown or clay colored and is a little over 1/3" (10-12 mm) long, with long sprawling legs. The larva is a white grub about 3/4" long when full grown. For control, see Grape, Japanese beetle.
San Jose scale, Quadraspidiotus perniciosus.
This scale often infests peach trees, sometimes causing severe injury. Large infestations of the San Jose scale can cause branch and even tree death as well as red spots on fruit. Partially-grown scales overwinter under their circular gray covering or scale on the twigs and the branches of trees. They begin to feed as the sap starts to flow. When apple trees bloom, the males emerge from under their scales to mate with the immobile females. Females are circular and cone-shaped, and their circular scales are about 1/16" in diameter, with a raised center or nipple. The males are smaller and elongate, with the nipple not centered on the scale. Females give live birth to tiny bright yellow crawlers in June, usually about 3-5 weeks after the flower petals drop. The young crawlers quickly settle, insert their long mouthparts into the twigs, and then suck sap from branches. As they grow, the crawlers secrete a waxy filament that becomes their scale or covering. This scale has multiple, overlapping generations during the growing season. Scales may be controlled by applying horticultural oil when apples are at the half-inch green growth stage. Alternatively, spraying phosmet, which is among the compounds registered for control of this pest in Connecticut, against the crawlers after bloom will also give control. Consult the labels for dosage rates and safety precautions. To detect the yellow crawlers, wrap black tape coated with Vaseline around small branches. Adult flights may be detected with pheromone traps.
Shothole borer, Scolytus rugulosus.
These beetles bore under the bark of various fruit trees, including peach. Generally, the beetles attack injured or weakened trees, further reducing their vigor. In spring, adults emerge from the bark through small circular holes similar to shot holes. The dark brown beetle is about 1/10" long. Females burrow directly into bark and sapwood to construct an egg chamber. They lay white eggs as they burrow further along the branch. After hatching, the white grubs or larvae expand the burrows further as they feed. Larval galleries may girdle a branch. Shothole borers probably have at least 2 generations annually because the life cycle can be completed in 4-6 weeks. The best way to prevent infestations of shot-hole borers is to maintain adequate vigor, especially by irrigating during serious droughts. Trunk sprays of methoxychlor or carbaryl, which are among the compounds registered for control of this pest in Connecticut, may lessen infestations. Consult the labels for dosage rates and safety precautions.
Tarnished plant bug, Lygus lineolaris.
Tarnished plant bugs feed before the flower petals fall, sometimes causing fruit to drop. Orchards near alfalfa or hay field are the most susceptible to attack. Plant bugs can cause flower abscission and fruit dimpling and scabbing. The tarnished plant bug is a mottled brownish bug about 1/5" long that hibernates in protected places and has a yellow "Y" shape on its back. Adults become active as the weather warms in spring. They inflict injury when they feed on flower buds or young fruit. In early spring, the activity of the tarnished plant bug can be monitored by placing white sticky traps at knee height near the perimeter of trees. Because tarnished plant bugs have a broad host range, their overwintering populations may be reduced by controlling broad-leaved weeds. Avoid herbicide applications or mowing from just before until just after bloom because the disturbance may drive the adults from their alternate hosts to the apple trees. An application of methoxychlor, which is among the compounds registered for use against this pest in Connecticut, before bloom may reduce injury. Consult the labels for dosage rates and safety precautions. A recently introduced parasitoid of the tarnished plant bug, Peristenus digoneutis, attacks the nymphs of the tarnished plant bug on alfalfa and may help to reduce populations moving into fruit crops.
Twospotted spider mite, Tetranychus urticae.
This mite injures the foliage of peach. Foliar damage caused by the twospotted mite is similar to that caused by the European red mite. Mature, orange females spend the winter on the lower portion of tree trunks or in the ground cover. The young nymphs feed first on cover crops, and move up the tree as the season progresses. As the common name indicates, the summer adults have a dark spot on each side of the body. Twospotted mites can develop through many generations, depending on the temperature. Their abundance usually peaks in August. Many beneficial insects and mites feed on twospotted mites. Avoid spraying carbamate or pyrethroid insecticides to peach foliage as these materials kill mite predators. When control is necessary in home orchards, a ½ to 1% rate of horticultural oil can be very effective. Consult the label for dosage rates, safety precautions and preharvest intervals.