Pear Psylla are the most important pests of the pear orchard. They attack all types of pear tree and may attack quince. Oblong, orange-yellow eggs are laid in bark crevices, leaf creases and on stalks. The nymphs hatch and puncture leaves with their stylets, drawing out sap. Only a small portion of the sap is put to use, while the rest is secreted as sticky honeydew. The nymphs may be completely encased in globules of honeydew as they feed. There are five immature instars. After emerging from the final molt, the adult psylla is a blue-green color which darkens down to a reddish brown with black bands around the abdomen. The eyes are red. The adult is seldom larger than 2.5mm in length. The smaller males are distinguished by a hooklike projection on the upper surface of the abdomen. Females are larger with a more rounded abdomen. A female psylla may deposit up to 500 eggs in her lifetime. There are usually three or four generations of psylla per year.
Pear psylla were introduced from Europe, and along with fire blight, were responsible for the decline of pear cultivation in the eastern states. The word psylla comes from Greek for flea, although psylla are unrelated to fleas. Many dictionaries classify psylla as lice, but this is incorrect. They are in fact Homoptera, related to cicadas and aphids.
Pseudococcus maritimus (Erhorn)
The grape mealybug was originally described as a pest of grapes but has since proven to be able infest most deciduous fruit crops. Since the 1970's, it has become an ever-increasing pest of pear and apple. It is slow to spread, but once an orchard becomes infected, the infestation is difficult to clean up. It is usually only a problem on large, mature trees which are difficult to spray thoroughly and provide shelter for these pests.
The grape mealybug is white to pink in color, having a flattened ovoid shape. Filaments protrude around the perimeter, with the two longest at the rear. The mealybug's back is obviously segmented and usually covered with white, waxy secretions. There are four or five instars, depending on gender. Early-instar nymphs are smooth and shiny, but eventually develop segmentation and waxy coating. Mature females are less than half a centimeter long. Mature males are much smaller, have one pair of wings, and no mouthparts. Their adult lifespan is very brief.
Egg masses are deposited in crevices and cracks in the bark. Fresh egg masses are white, cottony and adhesive, and can be drawn out like taffy. The eggs are bright orange. First instar nymphs can overwinter inside the egg sac, emerging in April or May to feed at the base of suckers or zones of recent injury. Adults appear in late June and a second generation of egg masses is deposited under loose bark.
When disturbed, mealybugs secrete a sticky substance called hemolymph, which can gum up the mandibles of would-be predators. The ladybird beetle known as the Mealybug Destroyer (Cryptolaemus montrouzieri) dines voraciously on these pests. The beetle is a few millimeters long, shiny black with a tan front. It was originally imported from Australia in 1891 by Albert Koebele, as a control agent.
Grape Mealybug damage is primarily cosmetic. Frass and honeydew can cause unsightly russeting on pear fruit. The mealybugs can also crawl up into the pear calyx and establish a vile hive underneath.
Two-Spotted Spider Mite
Tetranychus urticae Koch
These arachnids are pests on pear and apple trees, as well as arborvitae, azalea, camellia, citrus, evergreens, hollies, ligustrum, pittosporum, pyracantha, rose, and viburnum. Fruit crops attacked include blackberries, blueberries and strawberries. A number of vegetable crops such as tomatoes, squash, eggplant, cucumber are also subject to twospotted spider mite infestations and damage. The mite may also damage maple, elm, redbud and has been reported on ash black locust and poplar. Few crops are spared the onslaught.
Tetranychid mites feed by piercing plant cells with their cheliceral stylets, and then wicking up the fluids with a grooved rostrum. The loss of chlorophyll first results in whitish or yellowish speckled areas on the upper surfaces of leaves, and eventually in a more uniformly bronzed or yellowed discoloration, defoliation, and a drop in the victim's resistance to other pathogenic organisms.
Fruit developing on heavily-infested trees is likely to be of inferior quality.
Spider Mites are difficult to spot with the naked eye. Measuring a mere 1/64" long, they have two to four spots and numerous bristles. The spots are actually aggregations of unexpelled feces. Females are larger and more rounded. Males are smaller and taper to a point. Nymphs are pale and have only six legs. Their name comes from the silk webbing a colony of mites produces on the underside of a leaf.
Females usually live 3-4 weeks and can produce up to 100 eggs.
The frenetic activity and small size of these creatures can thwart a photographer's intentions of capturing a clear image.
Although they resemble slugs, these pests are in fact the larvae of Tenthredinid wasps (sawflies.) Eggs are deposited individually through slits in the underside of the leaf. The egg is visible on the upper surface of the leaf, looking like a small bubble surrounded by dead leaf cells. The larvae are dark brown and coated in a layer of slime. They feed on pear foliage, causing skeletonization. If the infestation is severe, growth may be reduced the following year. After a few weeks the larvaeturn a lighter color and burrow into the ground to pupate. The adult is black, 4-6mm in length.
From IPM Update, Vol 2, No. 9, by Peter McGhee, WSU Dept. of Entomology:
Stink bugs have caused serious crop loss to cherry, peach, nectarine, apple and pear. Control with insecticides is difficult. Stink bugs invade orchards late in the growing season when choice of chemical controls is limited by pre-harvest interval restrictions (PHI) considerations. Repeat sprays are often required because stink bugs continue to migrate into orchards.
Stink bugs are broadly oval and shield shaped with a large triangular plate in the middle of their back. Adult stink bugs are one-half to one inch in length. At least six species of stink bugs occur in native habitats in Washington. Three of these have been observed to cause damage to tree fruit crops in north central Washington; the consperse stink bug (Euschistus conspersus), the conchuela stink bug (Chlorochroa ligata), and the green soldierbug (Acrosternum hilare). Conchuela stink bugs live in dry land habitats, green soldier stink bugs live in riparian areas, and consperse stink bugs occur in both habitats. The consperse stink bug has caused the most economic loss in apple and pears.
Adult stink bugs over-winter in brush piles, rock outcroppings, and prop stacks surrounding orchards and in native vegetation from which they emerge in the spring. Consperse and conchuela adults feed on the mullein plant and bitterbrush throughout the summer. Females lay several clutches consisting of ten to twelve barrel shaped eggs from May through early July. The first generation of stinkbugs occurs when spring conditions remain cool, and warmer conditions may result in a second generation during late August or early September.
Injury to fruit occurs when mature stink bugs pierce the skin of the fruit and suck out juice. Apples attacked by stink bugs exhibit small dark depressions, primarily confined to the upper half of the fruit. The flesh beneath these areas appears corky and white to light brown. Stink bug injury sustained to apple is often misdiagnosed as the physiological disorder bitter pit and results in downgrading of the fruit. Injury to pear is more difficult to determine from the fruit's exterior. Slight dimpling can occur where the insect has fed close to the stem where the fruit is narrow, but this symptom is not always observed. Injured areas beneath the skin are also corky and white. Often it is only the portion of the orchard where damage occurs, specifically the borders, that can provide a clue as to whether insects have caused the problem or it is the result of a physiological disorder.
Monitoring for stink bugs presents several problems. Because the insects occur on native plants outside of the orchard, it is helpful to sample in these areas to determine the stages present and to gather data on relative abundance from year to year. Near the orchard border, inspect mullein at the base and between the leaves to determine stink bug presence. A beating tray can be used to sample bitterbrush along orchard perimeters previously associated with stink bug damage. Samples taken every three weeks throughout the season will help in monitoring stink bug development. A beating tray is not a good monitoring method to use in the orchard later in the growing season. Visual inspection of trees along the border will better determine potential for damage. Inspect 50 fruit per tree from trees in the outside row; if any stink bugs are found the potential for injury exists.
High levels of fruit injury can occur on orchard borders adjacent to native habitats. Fruit injury as high as nearly 50 percent has been observed on border trees in some orchards near Chelan. In these orchards fruit injury was also found to be three to four times greater in the upper part of the tree compared with that at mid-canopy. This pattern of fruit injury strongly suggests that well-timed border sprays could prevent most damage along threatened borders.
Lesser Apple Worm
Grapholita prunivora Walsh
This Tortricid moth is a relatively minor pest. It infests only the fruits and stems of rosaceous plants. The larvae are indistinguishable from the closely related Cherry Fruitworm and Oriental Fruit Moth. The adult LAW is smaller than the adults of the other two species, approx. 7mm long with a wingspan of about 11 mm. The front wings are dark brown in color with scattered patterns of grayish orange patches and a few thin transverse bands of shining pale blue. The two largest gold areas are found in the middle of the front wing and on top of the head. When the wings are folded in the resting position, these areas form a gold band stretching across the back. Adults are crepuscular in their habits.
Japanese law forbids import of fruit from any orchard in which Lesser Apple Worms have been trapped.
Assorted Minor Pests
Bertha Armyworm - Mamestra configurata Walker
This noctuid moth larva is a pest on most fruit trees, as well as alfalfa, corn, flax, cabbage, peas, beans, turnips, beets, tobacco, and garden flowers. The greatest damage usually occurs in late August or early September.
Lacanobia cutworm - Lacanobia subjuncta
Lacanobia subjuncta occurs throughout North America and is reported feeding on a wide range of plants including several crops. In recent years larvae of this insect have become more common in commercial apple orchards and in some have caused considerable fruit injury.
There are two generations of L. subjuncta in WA. It overwinters as a pupa in the soil and adults emerge in May and June. Larvae are present in June feeding on foliage when young and on fruit and foliage when older. Larvae will remain in the tree unlike other cutworms, which return to the ground and only feed in trees at night. When larvae are young they are light green with a white stripe along the side. As larvae grow they transform into a light brown color with darker markings on the upper surface. Larvae are voracious feeders and can defoliate shoots in a few days. A second generation occurs in July and August with larvae feeding on foliage and fruit in August and September.