1996-1997 New England Apple Pest Management Guide

Insect and Mite Pests

APHIDS. There are five species of aphids commonly found on apples: apple grain aphid, rosy apple aphid, apple aphid, spirea aphid and the woolly apple aphid. The aphid species can be identified by their color, the time of year when they are present and by differences in the cornicles, which are small paired projections from the rear of aphids. Aphids feed on foliage using needlelike mouthparts to suck out plant juices. When present in high numbers, certain species may reduce tree growth and vigor. Consult Cooperative Extension for aphid treatment thresholds. In the case of a severe fire blight outbreak, growers may wish to eradicate aphids, but controlling aphids is of little use to prevent a fire blight outbreak.

Aphids overwinter in the egg stage on twigs, around buds or in bark crevices. Apple grain aphid eggs begin to hatch when apple buds are in the green tip stage. This aphid can be identified by its green color, with a darker green stripe on its back. The apple grain aphid can become very abundant on the buds in early spring, but it causes no damage to apples, and it soon migrates to grain crops and grasses for the summer.

Rosy apple aphid eggs complete hatch soon after half-inch green. The adults are pinkish grey, and acquire a powdery white covering. Rosy apple aphids have longer cornicles ("tail-pipes") than apple aphid. Rosy apple aphids feed on fruit and leaf buds, crawling inside the leaf clusters as the buds unfold. Feeding causes leaf curling which begins to show around petal fall. They prefer fruit clusters, and feeding there causes small distorted fruits and sooty mold growth on excreted honeydew. By the time their presence is obvious, they are protected by curled leaves from contact-type insecticide spray. After three generations on apple, they move to a summer host. Narrow-leaved plantain is a key alternate host.

A cool wet spring increases the chance of a rosy apple aphid problem. Checking 10 interior fruit clusters per tree on 10 trees per block between bud break and pink can reveal the need for insecticidal control at pink. Research indicates that insecticidal control with Lorsban or Vydate is more effective at pink compared to a later date. This is probably because good coverage is needed for control. Application of Provado at petal fall against leafminers has provided excellent rosy apple aphid control. Cortland, Golden Delicious, Idared, Gravenstein, Jonagold, and possibly Red Delicious, are more prone to rosy apple aphid damage.

Apple aphid eggs complete hatch soon after half-inch green. The nymphs and adults are light green with black cornicles. Usually, they do not become abundant until July, and found primarily on the succulent foliage of water sprouts and growing terminals. If abundant, they produce large amount of honeydew which falls onto foliage and fruit. The honeydew serves as an excellent growth medium for black sooty mold fungus, which can mar and discolor the fruit surface. Aphid honeydew is relatively easy to wash off.

Commercial orchards can tolerate small to moderate populations of the apple aphid, thus there is considerable potential for integrated management of this pest. Excessive and prolonged vegetative growth can lead to an apple aphid problem. Limit nitrogen fertilization to the level necessary for optimum tree growth. Summer pruning to remove water sprouts can also prevent or reduce problems with apple aphids. Several predators destroy apple aphid colonies, and typically eliminate the need for chemical control. Syrphid and cecidomyiid fly larvae are the most important aphid predators. (See Table 7). The use of selective pesticides will allow moderate survival of predators in commercial orchards.

Spirea aphid is common on apple trees in parts of New England. Its appearance and life cycle are very similar to those of the apple aphid, but its activity may extend longer into the summer, and it may have somewhat different susceptibility to specific insecticides.

Woolly apple aphids have a complex life cycle that can involve overwintering either on apple or elm. Once on apple, they move to feeding sites on the roots or above ground. Root feeding produces knotty galls, and extensive feeding severely taxes the root system. Unfortunately, the above-ground woolly apple aphid population is not a reliable indication of the root-feeding population. Above ground, the crawlers settle in bark crevices, pruning cuts, wounds, leaf axils, and occasionally the stem or calyx of fruit. Larger nymphs have a purplish body, concealed by tufts of "wool," which are actually fine wax strands.

APPLE MAGGOT (AM). The first emergence of apple maggot flies ranges from the second week in June to the first week in July. Emergence peaks in mid-July to early August. Red ball sticky traps can indicate the timing and degree of apple maggot fly immigration into a block. The recommended treatment threshold is when an average of 5 AM flies per odor baited trap have been captured. For unbaited traps, the threshold is an average of 1 (or 2, check Extension guidelines in your state) AM flies per trap. After treatment, ignore trap captures until insecticide residue is expected to begin losing effectiveness (10-14 days after a full rate application unless there is abundant rain). Then clean the flies off the traps and begin counting from 0 to see if the threshold is reached again, indicating the need for another treatment.

The life span of a female apple maggot fly is about 30 days. They begin mating and egg-laying 7 to 10 days after emergence. Eggs are laid beneath the apple skin. The survival rate of the eggs and larvae is low in immature fruit. As apples approach maturity, the survival rate of newly laid eggs and larvae increases greatly. After tunneling for 24 weeks, larvae leave the dropped fruit and pupate in the soil.

Control measures are aimed at the adults, because eggs and larvae are protected against pesticide sprays. The adults are active and spend much of their time on leaves and fruit where they feed on honeydew. This characteristic makes AM relatively easy to control with insecticide. Guthion (and also probably Imidan) will kill AM at to º the full label rate. At an even lower rate, Guthion still effectively deters AM egglaying. Reducing the dosage will also reduce the length of residual protection, though not necessarily in direct proportion to the dosage.

Removing unsprayed apple, crabapple, and hawthorn trees that are near the orchard can help to reduce the local AM fly population.

APPLE PITH MOTH. This European insect has been found in ME, NH, MA, and CT. It overwinters as a partially grown caterpillar in a small chamber excavated beneath the bark of apple twigs. When growth resumes in the spring, the caterpillar bores into a young shoot, causing it to wilt. The pinkish caterpillar is nearly inch long when fully grown. It pupates inside the twig or shriveled shoot. Occasionally the caterpillars bore into fruit. Adult moths fly in June and July, and lay eggs on new shoots. The newly-hatched caterpillars quickly bore into twigs. They are vulnerable to insecticide at two times: prebloom and late July - early August.



BORERS. There are several species of borers that attack apple trees (especially young trees) in New England. Borers are not normally a problem in orchards where orchard grass and weed growth near the tree trunks is kept in check, close-fitting plastic spiral vole guards are removed at petal fall, and summer insecticide sprays are made for other pests. If there is need, application of Lorsban to the lower trunk in July may be effective for apple bark borer and dogwood borer. Its effectiveness against the other borers is not well understood. State laws regarding this use may vary, consult state Extension recommendations.

Roundheaded apple tree borers (RAB) are striped beetles about 5/8" long that emerge in the month after petal fall. Most egglaying occurs from late June to early August, and usually within a couple hundred yards of the tree from which the female beetles emerged. If possible, remove alternate hosts (wild and crab apple, choke cherry, hawthorn, mountain ash, shadbush) within 100 yards of the orchard.

Insecticide sprays made against plum curculio and apple maggot also help control adult RAB as they feed on apple foliage. Without summer insecticide coverage there is increased risk of RAB attack, especially to trees less than 10 years old. Eggs are laid, and larval tunnelling occurs, in the trunk from about 4 inches below ground up to one or two feet above the ground.

Brushing diluted white interior latex paint onto the lower trunk may deter egglaying. (See Trunk Painting For Bark Protection). A white coating makes it easier to detect larval tunnels. If feasible, another way to prevent damage is to ring the lower trunk with a loose fitting barrier (mosquito netting, hardware cloth, several layers of newspaper). The barrier should be closed at the bottom with mounded soil, and tied with a cord around the top. Remove barriers after harvest.

September, and again in the spring, are the best times to check trunks above and below the soil line for small pinholes exuding reddish sawdust or dark, sunken areas indicating the presence of boring larvae. Shallow larvae may be dug out with a knife. Larvae in deeper tunnels may be killed with a wire or by injecting a suitable insecticide with a grease gun. Check with local Extension for registered, effective materials.

If not removed, or eaten by woodpeckers, larvae will tunnel through the trunk until completing the 2-3 year life cycle. Affected trees have poor growth or yellow foliage, and may break off at the soil line. Trees injured beyond recovery should be removed and burned, and nearby trees checked for infestation."

The apple bark borer and the dogwood borer are both small wasp-like moths. They lay eggs in bark crevices, primarily in burr knots and callus tissue around graft unions. The caterpillars are usually less than æ inches long, with an orange tinge. They bore in the bark, not the wood. Infestation is indicated by reddish frass on the surface. Adults fly from mid-June through late August, but most activity is usually in July. The life cycle takes one year.

Trees with many burr knots (such as M9) are most heavily infested. Controlling burr knots helps prevent problems with these borers. Plant trees with the graft union not more than 1 to 2 inches above ground. Be careful not to bury scion wood. If trees are already in the ground, soil may be mounded around the trunk in a wide mound (not a narrow cone which may increase winter injury). Avoid shading and increased humidity at the trunk caused by weeds, sucker growth, opaque vole guards, or debris trapped in vole guards. Diluted interior latex paint applied to the lower trunk before egg-laying may be an effective deterrent.

Flat-headed apple tree borer adults are dark brown beetles about inch long with a metallic luster. They are primarily active in June and July, on the sunny sides of trees. Eggs are laid in bark crevices. The sinuous trails in the bark are visible without cutting into the tree. Eventually, the grubs bore into the wood, leaving tunnels that are oval in cross-section. The grubs are legless, with a broad, flattened head end, and a cylindrical body. Weakened, stressed or strongly leaning young trees are most frequently attacked.

The leopard moth lays eggs in bark crevices in July and early August. The larvae bore into the bark and quickly move into the wood. They are usually first noticed because of the moist, fibrous droppings that are pushed out of the tunnel. The caterpillars are whitish or pinkish, with a dark head and up to 2 inches long. The life cycle is reported to take 2 to 3 years.

CODLING MOTH (CM) begin flying about the time of full bloom. Peak flight is usually about 3 weeks after full bloom. First generation eggs begin hatching about the same time. Larvae search out fruit and chew through the skin. They either feed briefly beneath the fruit surface or tunnel directly to the core and feed on developing seeds. Considerable frass (excrement) is normally associated with entry hole, which is often near the calyx end. Larval "stings" result when larvae feed slightly on the fruit but do not continue burrowing. A "sting" causes a surface blemish but does not result in interior breakdown of the fruit. Tunneled fruits usually fall with the "June drop." Upon completing their development in the fruit, some larvae enter hibernation while others pupate and emerge as second generation adults in August.

Codling moths are infrequent pests in New England because the adults and larvae are killed by insecticide sprays made for other pests. Where specific codling moth treatments are needed, insecticide applied when egg hatch begins is the most effective strategy. This usually occurs about 21 days after full bloom. The specific date when this occurs can be estimated using pheromone traps to detect the beginning of adult emergence and degree day accumulation to estimate the beginning of egg hatch. Contact Cooperative Extension for more information.

Removal of unsprayed host trees (wild or abandoned apple or pear, hawthorn, stone fruit and quince trees) within 50 (preferably 100) meters of the orchard, will reduce codling moth immigration. These wild hosts are most easily located around apple bloom time, when they are also in bloom.

EUROPEAN APPLE SAWFLY (EAS) overwinters as a larva in the soil. It pupates in the spring, and adults emerge during late pink and bloom. Eggs are laid during bloom, at the calyx end of the fruit. Young larvae feed along the surface of the fruit and leave a curved feeding scar, while older larvae bore deep inside the fruit. Mature larvae drop to the soil. Insecticides applied at pink and/or petal fall control this pest. White sticky traps placed before bloom can help determine the need for EAS treatment at petal fall. Traps should be placed near blossoms at head height on the south side of at least one tree per 3 acres. If more than an average of 6 to 9 EAS per trap are captured by petal fall in a block that received prebloom insecticide (or 4 to 5 in a block that did not receive prebloom insecticide), then the cost of a petal fall insecticide is likely to be justified by improved EAS control alone.

Prebloom treatment for EAS is not needed except possibly for blocks where petal fall treatment has historically not given satisfactory control. This could be due to an unusually large EAS population where there is a mixture of early and late blooming cultivars in the block.

EUROPEAN CORN BORER larvae sometimes tunnel in current year's shoots, causing them to wilt. The caterpillars, which are light colored with a dark brown head, have also occasionally been found in the fruit. Typically, this occurs on lower limbs near groundcover, and in blocks near cornfields. Keeping groundcover mowed helps prevent damage. Several commonly used orchard pesticides, including Guthion and Lorsban, are labeled for European corn borer.

GREEN FRUITWORMS (GFW). Several species of caterpillars are called by this one name because of their similar appearance, habits and damage to deciduous fruits. Orthosia hibisci moth flight peaks around tight cluster. Green GFW larvae with narrow white stripes and speckles along the body hatch between tight cluster and pink, and begin feeding on leaves and flowers. Fruit feeding is most likely when the fruit is 6-20 mm diameter. Buds, blossoms, and fruit fed upon before petal fall abort. Damaged fruit that remain have deep corky scars and indentations at harvest. There is one generation per year.

Pink and petal fall sprays directed at other apple pests should also control GFW. Cases of GFW tolerance or resistance to organophosphate insecticides have been reported.

Research indicates that a single petal fall spray provides comparable control to a two spray program at pink and petal fall. Unless extraordinarily abundant, GFW larvae detected prebloom can be left for control at petal fall. An economic threshold is not available, but finding more than one GFW larva per tree at petal fall may be indication that the cost of treatment will be matched by the benefit of damage prevention.

LEAFHOPPERS:

White Apple Leafhopper (WAL). Leaves should be examined for leafhoppers from petal fall through August. Leafhoppers seem to increase the spread of fire blight. If fire blight infection is present, the leafhopper population should not be allowed to exceed a low level.

Adult WAL are pale yellowish-white and are about 1/8 inch long. They lay the overwintering eggs just beneath the bark surface on 1 to 5 year-old wood. Hatching begins around late pink and is completed by petal fall. The pale white nymphs complete their development on the under surface of older leaves. WAL feeding removes sap from leaves, causing stippling that may coalesce into silvery white patches. Early in the season, extensive leaf damage may affect bud formation. Extensive feeding by the second generation can cause poor fruit color and preharvest drop. Their excreted honeydew may drop onto fruit and appear as dark colored spots that are difficult to remove. Second generation nymphs appear in early August. If adult WAL are numerous at harvest, they can be a nuisance to pickers.

Rose Leafhopper (RLH). Research indicates that some New England "white apple leafhopper" populations may actually be another species, the rose leafhopper. It is difficult to distinguish between the two species. RLH nymphs have rows of small dark spots on their backs. The spots are easier to see on older nymphs, and by using a magnifying lens. WAL nymphs lack these spots. RLH have three distinct generations in New England. Many plants in the rose family are summer hosts, including apple, pear, quince, hawthorn, peach, plum, cherry, blackberry, and raspberry. Plants in other families are also hosts, but it seems that RLH overwinters only on Rosa species, such as cultivated and multiflora rose. Preliminary research in Massachusetts shows that removal of multiflora rose within 100 yards of an orchard block could substantially reduce the influx of rose leafhoppers.

First generation RLH adults immigrate into orchards form nearby multiflora rose bushes in early to mid-June. Second generation adults, present in July and August, confined egglaying largely to orchards. Third-generation adults, present in September and sometimes in very large numbers, can cause extensive excrement spotting of fruit and nuisance to pickers before emigrating to rose bushes to lays overwintering eggs.

Potato Leafhopper (PLH) nymphs and adults are pale green. When disturbed, nymphs move rapidly, often in a sideways fashion. In contrast, nymphs of the WAL and RLH move slowly and usually straight ahead. PLH feed primarily on immature leaves of actively growing shoots. Injured leaves turn yellow on the edges, cup upward, and later turn brown or scorched ("hopper burn"). PLH damage is sometimes misidentified as herbicide injury, nutrient deficiency, or the effect of overfertilization.

PLH feeding can also cause terminal growth cessation or excessive branching around the feeding point. On mature trees, PLH damage may not be significant, but heavily infested young trees can end the season with less than half their expected growth. A research-based treatment threshold is not available. New York researchers suggest a tentative threshold of an average of one PLH nymph or adult per leaf.

PLH overwinter as adults in the southern states and move northward in summer air masses. It is a sporadic pest and its time of occurrence may vary from year to year. PLH has usually been found by mid-June in Southern New England.

Leafhopper control. WAL and PLH have developed resistance to several organophosphate insecticides in many apple growing regions. Insecticides are most effective against first-generation young nymphs. Older nymphs and adults are usually less easily killed. Provado applied at petal fall or mid to late-June against leafminers has given excellent season-long control of WAL and RLH. Sevin or Thiodan is effective for control of young WAL in late May - early June and would control RLH adults and PLH if either species were present. Contact Cooperative Extension for WAL and RLH treatment thresholds.

LEAFMINERS. There are two species of leafminers commonly found in New England apple orchards: Apple blotch leafminer seems to be more common than spotted tentiform leafminer. For monitoring and management purposes, the two species can be treated as one. There are three generations of leafminers per year. They overwinter as pupae in last year's leaves. The º inch long adults emerge and mate during half-inch green to pink. Eggs are laid in the evening on the underside of leaves. The eggs hatch in 5 to 16 days depending on the temperature. In the first three instars, the larvae form "sap-feeding" mines which appear as small silvery patches on the under surface of the leaf. In the last two instars, the larvae form "tissue-feeding" mines. These are characterized by the tent shape with spots appearing on the upper surface of the leaf. Severe damage can cause fruit stunting or premature ripening, preharvest drop, or defoliation. Trees stressed by drought or other pests are more prone to these effects.

First brood larvae are present from bloom through June, second brood from July to August, and the third brood from August through September. The population can increase greatly from one generation to the next.

Red sticky traps attached near the base of the south side of the tree trunks provide information on the beginning, peak and end of flight of overwintering-generation moths during the prebloom period. Where a sufficient number of traps were used (minimum 10 traps regardless of orchard size, up to 40 traps for orchards of 100 or more acres), the red trunk traps have reliably predicted whether the number of 1^st generation sap-feeding mines in June would exceed the threshold recommended in Massachusetts. Thus, if a grower is using those threshold criteria, the red trunk traps can indicate if there is likely to be a need for a tight cluster, pink, or petal fall leafminer treatment.

Current Massachusetts thresholds for red sticky trunk traps are an average of 4 or 9 cumulative leafminer adults per trap from silver tip to tight cluster or pink, respectively, for McIntosh.; 8 or 21 cumulative adults per trap from silver tip to tight cluster or late pink, respectively, for non-McIntosh cultivars.

Sampling of leaves for leafminer eggs during pink and bloom may provide more accurate information on future abundance of larvae than trunk trap captures, contact Cooperative Extension for details on scouting for leafminer eggs.

To protect parasite and predator species that normally suppress the leafminer population below a damaging level, leafminer treatment should only be made if monitoring indicates a need. Insecticide is not effective against larvae once they have progressed to the tissue-feeding stage. Optimum control depends on monitoring to determine need and timing for treatment against either prebloom adults and eggs, first generation sap-feeding larvae, or second generation sap-feeding larvae. Control of second generation adults or sap-feeding larvae is less likely.

Scouting for first generation sap-feeding mines should begin about a week after petal fall. Use a magnifier to check for sap-feeding mines on 5 middle-aged or older fruit cluster leaves per tree on 10 trees per block. Choose fruit clusters near the trunk because leafminers are more likely to be found there. Holding the leaves up to the light can make sap-feeding mines more visible. Consult state Extension guidelines for first generation sap-feeding mine action threshold. Current thresholds for first-generation sap-feeding mines in southern New England are 714 mines per 100 leaves, depending on cultivar. First-generation leafminers exceeding this threshold range in southern New England are likely to give rise to damaging second and/or third generation populations.

If second generation sap-feeding mines (which may begin showing by early-July) exceed an average of 2 per terminal leaf, i.e. 200 mines per 100 leaves, then treatment may be needed. For trees suffering other stresses (insects, mites, disease, drought, chemical leaf burn, or trunk injury), the second generation treatment threshold may be as low as an average of 1 sap-feeding mine per leaf.

If there is a leafminer problem, it is far better to control it in the first or second generation, so that third generation leafminers will not be a problem. By the third generation, the population is spread among all lifestages and thorough spray coverage is difficult because of thick foliage. Treatment is not likely to be effective against the leafminers, but beneficial species will be vulnerable. Because the third generation occurs late in the season, unless the cumulative number of mines reaches or exceeds approximately 300 per 100 leaves, it is not likely to affect the crop.

Leafminer populations have already developed resistance to the common organophosphate insecticides, and could also become resistant to other types.

Leafminer management: There are several choices of pesticide for leafminer control. Ambush, Pounce, Asana, Vydate, or Thiodan can be applied prebloom against adults or eggs. Provado can be applied at petal fall against first generation sap-feeding mines, or in late June or early July against second-generation sap-feeding mines. Provado is most effective against eggs and newly hatched leafminer larvae. Lannate can be applied in June when first-generation sap-feeding mines are visible, or in July against second-generation sap-feeding mines.

Each of these insecticides has its own specific advantages and disadvantages in terms of effectiveness for control of leafminers and other pests, harmful effects on beneficial natural enemies, and timing allowance for degree of assurance that treatment is necessary. For example, insecticides for prebloom use merit application only if there is good evidence that adults or eggs have exceeded threshold levels. The same is true for Provado application at petal fall. Monitoring adults or eggs is not as reliable an indicator of potentially damaging populations as monitoring sap-feeding mines. Hence, a Lannate application against first-generation sap-feeding miners; or use of Provado or Lannate against second-generation sap-feeding miners; offers greater reliability in determining need for treatment. But other aforementioned considerations may argue in favor of prebloom or petal fall treatment.

LEAFROLLERS. The most common leafrollers found in New England orchards are the oblique banded leafroller (OBLR), and the redbanded leafroller (RBLR). These insects are not usually major pests, but they do cause serious fruit injury in some locations, and may become a problem in very low-spray blocks. Leafrollers are named because of the larval habit of rolling, folding or attaching leaves together.

Adult RBLR emerge in the spring before or soon after green tip, and continue to fly until around bloom. By petal fall, young green or pale yellow larvae begin feeding on the underside of leaves within a web; later they are more likely to move about and feed on fruit. Second flight adults emerge in mid-June to mid-July, with larvae feeding in July and August. There may be a partial third generation in early fall.

Damage on leaves is not significant except as evidence that larval feeding is occurring. RBLR larvae produce a skeletonized band near the leaf midrib or veins. First brood larvae may also web two apples together, causing deep, corked-over scars and deformed fruit. Later broods of RBLR tend to tie a leaf to an apple and feed on the apple under its protection, in a shallow irregular pattern. Damage by the summer broods can be late enough in the season that corking may not occur, leaving exposed tissue which will result in the fruit being discarded. Yellowish green OBLR larvae emerge and begin feeding on fruit and leaf buds around early tight cluster. Larvae continue to feed and grow through petal fall, with first generation adult flight occurring in mid-June to early July. Eggs appear as greenish-yellow masses laid on the upper surfaces of leaves, measuring about º by inches. First brood larvae feed on tender terminal growth, water sprouts or developing fruit. As the larvae grow, they are more likely to damage fruit. Second generation adults fly in August, giving rise to larvae which feed on leaves and occasionally fruit before seeking overwintering sites.


Foliar feeding by OBLR is characterized by rolled leaves with feeding evident on surrounding foliage. Early-season fruit injury usually causes the fruit to abort, but those that remain have will deep corky scars and severe fruit deformation, similar to green fruitworm injury. Later-season injury is similar to the injury caused by RBLR, but is generally deeper and smoother. OBLR has developed resistance to insecticides in NY and elsewhere, and has become a major pest in areas where it has done so.

In New England, leafrollers are usually controlled by insecticides directed at other pests such as plum curculio and apple maggot. Leafroller problems may increase with reduced summer spraying or with pesticide resistance in leafroller populations.

MULLEIN PLANT BUG (MPB). Small, green, fast-moving MPB nymphs emerge during or shortly after bloom. Red Delicious, Northern Spy and, especially Golden Delicious, are much more susceptible to MPB damage than McIntosh. Damage is sporadic, but can be extensive when it does occur. On Red Delicious, damage appears shortly after petal fall as small depressed corky areas, raised dark pimples or misshapen fruit. MPB damage can be distinguished from tarnished plant bug injury by there being more extensive damage on Delicious, multiple wounds per fruit, raised bumps, and less of a conical dimple. Knowing block history is a key factor in managing MPB. MPB damage in the block last year is cause to be concerned this year.

A high aphid population in the block during the previous late summer and fall, and the presence of numerous mullein plants near the orchard, are two factors that may increase the local MPB population.

MPB are not well controlled by the insecticides usually used at petal fall: Imidan or azinphosmethyl (Guthion). Where there is a chance of MPB damage, monitoring is advised. There is only a short period when it is possible to assess the number of MPB in the block before the damage occurs.

A limb-tap sample taken just before the petal fall spray may be late enough for most of the MPB nymphs to have emerged (and late enough so that the number of petals falling onto the collection sheet will be minimized), yet early enough so that, if necessary, MPB can be factored into the petal fall spray decision. By the time a first cover spray is applied, much of the damage may have already occurred. Alternatively, with cool weather, the optimum sample date may occur well after petal fall. There are degree day models that estimate the optimum sampling date, though they have not been validated in New England.

The limb-tap sample method is to jar a minimum of 20 limbs per block over a tapping tray. A piece of cloth, two feet on a side with cuffs in the corners, can be spread by two crossed wood slats to make a light and portable tapping tray. Trays are available from IPM suppliers. The MPB nymphs are roughly the same size and shape as green aphids, but they much more mobile than aphids. MPB can be distinguished from aphids with a hand lens by looking for their wing pads and four jointed antennae.

The action threshold used in Nova Scotia (where MPB and brown apple bug are major pests) is to treat if there are more than 8 MPB nymphs dislodged per 20 limbs tapped. It is not possible to directly translate this threshold for New England because of the need for plum curculio control (which is not a problem in Nova Scotia). The choice in New England is likely to be about which insecticide to use at petal fall instead of choosing whether to use an insecticide or not. Lorsban, Lannate, Digon (dimethoate), diazinon, Carzol, and Asana are reported by various sources to effectively control MPB. Of these choices, Lorsban may be the best choice for controlling both MPB and plum curculio with the minimum detriment to beneficial arthropods. Lorsban used as the petal fall insecticide may not provide protection against plum curculio for as long a residual period as azinphosmethyl (Guthion) or Imidan. But New York researchers rate Lorsban 50 WP for plum curculio control as equal to the best of the other options. Ironically, MPB itself is a mite predator and not a pest after fruit swell.

PLUM CURCULIO (PC) weevils are about 3/16 inch long, have a long snout. They are dark brown-black with flecks of grey on a bumpy back. The adults overwinter in leaf debris in nearby woods and hedgerows, and in the orchard. They may begin migrating to apple trees during bloom, but peak migration usually occurs from petal fall to 14 days after petal fall. Egglaying and feeding damage can occur as soon as the fruit begins to form, continuing until the apples are about 1.5 inches in diameter. Most infested fruits drop in June. Fully grown larvae leave fruit and enter soil to depth of 1 inch and pupate. Adults of the next generation emerge about 50 days after the eggs were laid in June. The adults feed on maturing apples until they seek hibernation sites.

Plum curculio often move down to the orchard floor during the day and during cool, windy weather. Thus, limb tapping that finds no weevils does not guarantee that they are not present. To monitor the beginning and continuation of plum curculio damage, check fruit on border row trees (especially near woods) for fresh damage. Damage appears as small crescent-shaped egglaying cuts and small hollowed-out feeding cavities. Fresh scars show no shriveling of the skin edges, no browning of the flesh at the cut, and no crusty exudate. Search as high as is practical in the tree. Damage may be heavier in trees pruned in April or May, compared to trees pruned earlier or not at all. Removing unsprayed plum, hawthorn, and native crabapple trees from near the orchard will reduce the threat of plum curculio damage, especially the threat of egglaying damage 3 weeks or more after petal fall.

Insecticide for plum curculio control is typically applied at petal fall, first cover, and (depending on block history, scouting, and weather) second cover. Even if tarnished plant bug and leafminers are under threshold before bloom, growers may consider using a pyrethroid at pink as preliminary protection against plum curculio damage. The long- term negative effects of pyrethroid use (destruction and repellence of predators and parasites, increased potential for pyrethroid-resistant pests) argue against this tactic. Research trials have found that adding a pyrethroid application at pink did not reduce plum curculio fruit damage as compared to the normal postbloom-only treatments.

Different petal fall dates among cultivars in a mixed block can complicate the timing of the first spray to prevent plum curculio damage. If populations of other pests at petal fall are below threshold, and if there is not a history of high plum curculio immigration, it may be possible to delay the first postbloom spray and still prevent plum curculio damage. Unusually cool weather during bloom and petal fall can delay the peak threat from plum curculio, and extend the duration of the threat. Not using a petal fall spray requires careful daily monitoring of plum curculio activity and the weather forecast. Plum curculio damage to fruit can begin abruptly, and extensive damage can occur in a single night. If the temperature exceeds 70^oF for 2 days before petal fall, females may be ready to lay eggs at petal fall. Humid, calm, warm evenings (especially if the temperature is above 70^oF), pose the greatest risk. The risk of plum curculio damage increases after there have been a 3-4 days of average temperature of 55-60^oF, or 2 days with maximum temperatures above 75^oF, after petal fall.

If you are uncertain about the need for an initial full block spray against plum curculio, an alternative is to treat only two rows around the perimeter of the block, or to treat only those trees that are expected to be at significant risk, based on block history. This also applies to the end of the plum curculio egg-laying period. See Spray Strategies: Border Row Spraying for precautions before using this method.

Research in New York indicates that degree day accumulation is a useful predictor of how long protection is needed against plum curculio. The model is based on field trials that found negligible plum curculio egglaying damage where insecticide protection was maintained from petal fall until 340 DD (Baskerville-Emin method, base 50^o F) had accumulated after petal fall. This gives growers a guideline for making decisions about a final insecticide spray for plum curculio protection.

SAN JOSE SCALE (SJS) is most commonly a problem on trees which do not get proper spray coverage. SJS overwinter under protective scales on twigs and branches. At bloom, the males emerge and fly to the females, which remain immobile. Tiny bright yellow oval crawlers hatch roughly 3 to 5 weeks after petal fall. There are 2 or 3 generations a year. SJS infestations are easily detected by examining the fruit at harvest. SJS on the fruit are surrounded by reddish rings. Heavy infestation can stress the tree, causing thin foliage, dying branches, and eventually tree death. The most effective control program includes an oil spray at half-inch green, and an insecticide directed against the postbloom crawlers. Guthion (azinphosmethyl), Imidan, Lorsban 50WP, and Penncap-M are effective against SJS crawlers. Black tape, wrapped around infested limbs (sticky side out, or covered with a thin layer of Vaseline) is an effective tool for monitoring SJS crawler activity.

TARNISHED PLANT BUG (TPB) overwinters as an adult and becomes active as the weather warms in the spring. It feeds on the buds or fruit from the time of bud swell until about petal fall, but research has shown that fruit dimpling and scabbing is caused primarily from tight cluster to petal fall. Feeding before tight cluster results in abscission of one or more of the developing flowers. If bud abscission is not a concern, but control is needed to prevent dimpling, control may be enhanced by spraying on a warm sunny day when TPB are most active.

TPB populations vary considerably between blocks. White sticky traps placed at silver tip can help determine the need for prebloom TPB treatment. Traps should be hung at knee height (no higher) near the tree perimeter at a density of at least one trap per 3 acres. If an average of more than 3-5 adults per trap are captured by tight cluster, or an average of more than 5-8 per trap by pink, the cost of a prebloom treatment against TPB is likely to be justified.

Destroying broad leaf weed hosts (such as mullein, pigweed, and golden rod) in and around the orchard in the fall may decrease the overwintering TPB population. To improve TPB control, avoid mowing or using herbicide between pink and petal fall because disturbance of alternate hosts in the groundcover may cause TPB to move up into apple trees. If dandelion removal before bloom is necessary, applying insecticide application at pink immediately before the dandelion removal may effectively control TPB that are flushed up into the trees.

A non-pyrethroid insecticide rated as poor for TPB control may nevertheless provide adequate control of a moderate TPB population. Pyrethroids are rated as good for TPB control, but pyrethroid use is likely to have a long lasting devastating effect on mite predators. The eventual disadvantage in terms of mite outbreaks can be greater than the benefit from improved TPB control. For this reason, the use of pyrethroids in apple orchards is discouraged.

Digon (dimethoate) is very effective against TPB, but is also harmful to mite predators and bees. The detrimental effect can be minimized if it is used no later than half-inch green. Apparently because of local systemic activity, Digon used at half-inch green prevents fruit injury by later-feeding TPB, and can be an effective control where TPB damage has repeatedly been a significant problem.

MITE PESTS

EUROPEAN RED MITE (ERM) overwinter as eggs on rough bark areas of small limbs and fruit spurs. Egg hatch begins at tight cluster, is about half complete by pink, and is complete by petal fall.

TWOSPOTTED SPIDER MITES (TSM) overwinter as mature females on the lower portion of the tree trunks or in orchard groundcover. First immature stages of each species have only 6 legs, but all other stages are 8-legged. TSM become active before bloom but usually remain on bindweed and other weed hosts beneath the trees into June. As the TSM population increases and host quality declines, or is disrupted by groundcover management, TSM begin moving into apple trees.

There are multiple ERM and TSM generations per year. The number within a season varies with temperatures. ERM require 40 days to complete a generation at an average temperature of 55^oF, but only 10 days at 75^oF.

Both ERM and TSM are indirect pests that feed by extracting leaf sap. A severe infestation can cause leaf bronzing, reduced photosynthesis, fruit size reduction, preharvest drop, poor fruit coloring, and reduced crop potential for the next year.

There are many beneficial insect and mite species that prey on pest mites (see Table 8). Because ERM and TSM are foliar feeders and do not damage fruit directly, low populations can be tolerated. This creates an opportunity to benefit from biological control, and to limit miticide use to situations where ERM or TSM have become too numerous for timely control by their natural enemies.

Minimizing the use of pesticides that are harmful to mite predators is critically important in order to conserve and benefit from biological mite control. Until research demonstrates the efficacy of mite predators purchased for release, it is recommended that growers rely only on naturally occurring populations.

MITE THRESHOLDS: Mite injury is most likely to be significant in the weeks following petal fall. It is critical that mites not be allowed to build up during May and June, when the trees are most sensitive to even relatively low numbers of mites (2 to 5 per leaf). Thorough application of prebloom oil, Apollo, or Savey should keep mites below damaging levels during this critical period.

From July on, apple trees can withstand much higher levels of mite activity. Accumulations of 500 to 750 mite days (1 mite day = 1 mite per leaf for 1 day) have not caused any apparent damage to fruit in field experiments. This would be the equivalent of 5 mites per leaf for 100 days or 20 mites per leaf for 25 days. In many cases, this summer injury threshold will not be reached. It may be best to wait until it is clear that withholding a miticide will result in a buildup of mites over the injury threshold before taking action. Often, mite predators or rainy cool weather will help keep mite populations below the injury threshold.

Consult your state Cooperative Extension guidelines on mite monitoring and action thresholds. If the threshold is reached, but there are more eggs than active mites present, it may be better to delay application until 50% of the eggs have hatched. Miticide application is more effective if most of the mites are in the immature nymph stage. Adults and eggs are harder to kill. In addition to assessing the need for treatment, regular mite monitoring can help determine the timing for optimum control.

MITE RESISTANCE can develop to all currently registered miticides, except possibly oil. Growers can reduce the chance of resistance in their blocks by conserving biological control species, using miticide only when the economic threshold is exceeded, and by switching to a different miticide for each application.

MITE MANAGEMENT

A variety of pesticide-use strategies for mite control is available. Prebloom application of two oil sprays (one at half-inch green and another at tight cluster) or an oil spray at half-inch green and Apollo at tight cluster or Savey at pink can provide effective mite suppression through June or mid-July. If mite predators have been conserved through minimized and selective use of insecticide, by the time prebloom suppression treatments lose their effect predator populations may be high enough to maintain mite suppression.

Beginning at petal fall, a succession of two or three sprays of summer oil alone, or summer oil and Vendex combination, may furnish reasonable season-long suppression provided mite populations are not too high at petal fall and if the mite predator population has not been decimated by insecticide sprays.

Kelthane and Carzol are the two remaining options for summer treatments to reduce an established over-threshold mite population. The continued registration of Kelthane for use on apples is uncertain. Pest mites in some orchards have developed reduced susceptibility or resistance to either or both of these chemicals. Kelthane, and especially Carzol, are detrimental to beneficial mite predators. Vydate is not as effective on mites as these materials, but paired Vydate applications can also provide mite suppression. However, Vydate is also detrimental to beneficial insects and is not a preferred choice.

The limitations and undesirable attributes of summer mite treatments have increased the importance of a management approach to pest mites that

Maximizes the benefit of early season mite suppression tactics.

Maintains groundcover, tree, and fruit condition to reduce susceptibility to the negative effects of mite feeding on foliage.

Makes use of available cultural and biological controls for orchard pests. Restricts pesticide applications to situations where scouting observations or other information indicates that pesticide use is required. Makes use of spot or border treatments where feasible.

Includes frequent and structured mite scouting to detect a mite problem as soon as it develops, and to allow possibility for treatment to be made before the majority of the pest mites become fully mature and less susceptible, and before they can lay a full batch of eggs for the next generation

When pesticide is needed, gives preference to materials with low hazard to beneficial insect and mite species that provide biological control of European red mite and twospotted spider mite.

When miticide applications are needed, they are performed in a manner that maximizes the likelihood of successful mite suppression: high volume/low concentrate sprays from accurately calibrated equipment, weather conditions and tractor speed that favor good coverage, proper chemical rates, appropriate use of adjuvants and attention to potential effects of other materials in the tank on miticide performance.