European red mite, Panonychus ulmi (Koch) (Family Tetranych-idae), is a worldwide pest of tree fruit, with apple considered to be its most important host. Adult females are globular shaped with four rows of white hairs on their backs and change from brownish green to brownish red one to two days after molting. Adult males are smaller with a tapered abdomen and reddish yellow coloration. Eggs are orange (summer) or bright red (winter) with a long stalk protruding from the top. The six-legged larvae are pale orange but darken to pale green after feeding. Later nymphal stages have four pairs of legs and are green to reddish brown. The egg is the overwintering stage; eggs are deposited on twigs, and larvae hatch the following year to feed on foliage early in the season in apple, with adults appearing by petal fall. Up to ten generations can occur in a normal growing season. Foliar feeding results in bronzing of leaves, as chlorophyll and cell contents are destroyed. Moderate to severe infestations reduce yield by decreasing fruit size and promoting premature drop. Damaging populations also may lead to fewer and less vigorous fruit buds the following year. Monitoring involves scouting for eggs on twigs and spurs in the dormant season and foliar examinations throughout the growing season to determine the level of infestation with this species as well as twospotted spider mite. One or more prebloom oil applications along with miticide treatments have been used for control throughout the growing season. Natural enemies such as predaceous mite species and ladybird beetles can reduce populations if chemicals that are harmful to these beneficials are avoided.
Leafminer species belonging to the genus Phyllonorycter (Family Gracillariidae) can be found in fruit-growing regions of Europe, North America, and Asia and attack apples and pears, although cherries, quinces, plums, and crabapples are occasionally damaged. Phyllonorycter species are very small moths, 3 to 5 millimeters in length with 7 to 9 millimeter wingspans; forewings are heavily fringed and bronze colored with white and brown streaks. Eggs are clear to light green, flattened oval in shape, and attached to the undersides of leaves. Larvae are yellowish in color and feed within leaves between epidermal layers; early instars generally feed on sap or protoplasm of cell contents while later instars consume tissue. Pupae are brown and found within the leaf mines themselves. Pupae are the overwintering stage, and there are multiple generations per year. Pheromone and visual traps can be used to monitor flights of female-seeking adult males. However, visual inspection of leaves for mines is recommended for most species as well. Each mine can reduce effective leaf area by 4 to 5 percent. Heavy infestations can lead to complete defoliation and reduced crops and can adversely affect future fruit production. Biological control has proven effective, as 30 percent parasitism rates of first generation tissue-feeding larvae are considered to be great enough to provide effective control for the rest of the season. In secticide application to control latter generations can reduce natural enemy populations and therefore should be avoided due to the potential for greater control problems the following year.
Pear psylla, Cacopyslla pyricola (Foerster) (Family Psyllidae), is the most important pest of pears worldwide. Adults are 2 to 3 millimeters in length; summer-form adults range in color from greenish orange to reddish brown while overwintering adults are darker reddish brown to black. Eggs are 0.5 millimeter in length, oval-shaped, and change from white to yellow before hatching. Young nymphs are pale yellow with red eyes, while older nymphs develop darker coloration and distinct black wing pads. Adults overwinter in and around pear orchards. They mate in spring, and females lay eggs on or near developing buds. After eggs hatch, nymphs move to axils of leaf petioles and to stems, where they feed on sap with sucking mouthparts and surround themselves with an ever-increasing drop of honeydew, eventually leading to growth of sooty mold. Multiple generations can occur each year. Heavy infestations can cause premature leaf drop, weakened fruit buds, and reduction in shoot growth. Monitoring begins while buds are still dormant by tapping limbs to look for adults. During the summer, terminal leaves are examined. Dormant oil sprays along with synthetic insecticides, especially pyrethroids and miticides, have been traditionally used for control. Newer chemistries, including insect growth regulators, are becoming available. However, cultural control strategies, such as summer pruning and limited nitrogen applications to reduce excessive tree vigor, can aid in population reduction. Many predatory insects will feed on pear psylla, and avoiding chemical treatments that harm these beneficial insects can aid in population reduction as well.
Rosy apple aphid, Dysaphis plantaginea (Passerini) (Family Aphi-dae), is found in most apple-growing regions worldwide. Oval-shaped eggs are laid on twigs and branches in the fall; coloration of eggs changes from bright yellow to jet-black within two weeks of ovi-position. Eggs hatch into nymphs in the spring from the silver tip to one-half-inch green stage of bud development. Nymphs feed on leaves and fruit buds until leaves begin to unfold and change from a dark green to a rosy brown hue as they develop into adults. The mature adult, called a stem mother, reproduces asexually, and a second generation then matures on apple. Winged adults from third and sometimes fourth generations disperse to summer hosts such as narrow and broadleaf plantain. Multiple generations will reproduce on these hosts. Winged females return to apple trees in the fall to produce live female young who will mate with males and subsequently deposit four to six overwintering eggs. Nymphs inject a toxin as they suck sap that results in leaf curling, which may become severe and result in abscission. Furthermore, heavy infestations on apple lead to deformed and stunted fruit due to translocation of salivary toxins. Honeydew produced by colonies can lead to growth of sooty mold. Monitoring to determine the need for insecticide application requires visual inspection of clusters on susceptible apple cultivars to look for presence of aphids; monitoring should occur at pink and petal fall in apple. Predators such as ladybird beetles, syrphid flies, lacewings, and predatory midges, as well as parasitic wasps, are capable of providing effective biological control if chemicals toxic to these beneficial insects are avoided.
Twospotted spider mite (Family Tetranychidae) attacks tree fruit, ornamentals, and vegetable crops worldwide. Adults are pale and oval-shaped with two black spots located behind the eye spots; males generally are smaller than females. Eggs are clear and spherical and hatch into six-legged larvae that change from nearly transparent to dark green coloration after feeding. Later nymphal stages also are green but with four pairs of legs and more pronounced spots. Adults overwinter in orchards under bark or groundcover and become active in the spring as temperatures reach 12°C, when they disperse upward into orchard canopies to lay eggs. Females reproduce offspring of both sexes if mated, while unfertilized females produce males only. Shortly before the adult female emerges, she releases a pheromone to attract males and ensure female progeny. Up to nine generations occur throughout the season. Foliar damage caused by feeding is characterized by bronzing of leaves, as chlorophyll and cell contents are destroyed. Moderate to severe infestations reduce yield through decreased fruit size and lead to fewer and less vigorous fruit buds the following year. Regular foliar inspections can aid in determining if chemical treatment is necessary, based on percentage of leaves infested with twospotted spider mite and/or European red mite. Miti-cide treatments traditionally have been used to control this species and European red mite throughout the growing season. Natural enemies such as predaceous mite species and ladybird beetles can reduce populations if chemicals that are harmful to these beneficials are avoided.
Was this article helpful?