Rosy apple aphid, Dysaphis plantaginea, is one of several species of aphids that infest commercial apple orchards and backyard apple trees in Ohio. It is the most destructive of the aphid species that feed on apple trees; other aphids found on apple are green apple aphid (see Extension Fact Sheet, HYG-2206-94) and woolly apple aphid (see Extension Fact Sheet, HYG-2208-94). Rosy apple aphid feeds on pear and hawthorn as well as apple. Because rosy apple aphid does not occur in most orchards in most years in Ohio, it is important to determine each spring whether or not this pest is present in individual orchards.
Rosy apple aphid feeding causes deformed and stunted fruit and leaves. Aphid nymphs and adults are usually found on the expanding leaf buds and fruit bud clusters, where they use their piercing-sucking mouthparts to draw sugary sap from the phloem of succulent shoots and leaves. During feeding, rosy apple aphids inject their saliva into the plant. The saliva contains chemicals that alter plant growth, and these chemicals move from leaves to fruits, causing fruits to remain small or become deformed and unmarketable. Feeding causes severe curling, stunting, and deformity of leaves, and leaves may turn bright crimson. Leaf curling is not usually noticeable until petal-fall, which is past the best time for control. Leaves may drop early, and shoot growth may be stunted or stopped completely. Golden Delicious, Ida Red, Rome, Cortland, York, and Stayman apple varieties are especially susceptible to injury.
In addition to damage caused by feeding, aphids are associated with the development of black sooty mold. As they feed, aphids excrete excess sap in a form known as honeydew. Honeydew on leaves and fruit provides a medium for growth of black sooty mold. Sooty mold on leaves can affect photosynthesis and may reduce fruit yield, while sooty mold on fruit can lower fruit quality and marketability.
|Leaves infested with rosy apple aphid (left)|
fruit affected by rosy apple aphid (right)
(From Lovett and Fulton 1920, Oregon Agric. Expt. Stn. Circ. 22)
Like other aphids, rosy apple aphid is a small, soft-bodied insect with piercing-sucking mouthparts and two cornicles (or "tailpipes") projecting from the back of the abdomen. Nymphs of rosy apple aphid are yellow or pink when first hatched; as they grow, they turn purple with a gray, waxy covering. Wingless adults are rosy or purple, and covered with a powdery, greyish-white wax; winged adults are brownish-green. The cornicles are long. They have dark legs and antennae. Nymphs are 0.4 to 2 mm long; adults are 2 to 2.5 mm long.
|Rosy apple aphid; winged female (top); summer wingless adult|
female that produces live young (left); Spring wingless female that
produces live young (right); adult female produces eggs in the fall (bottom)
Rosy apple aphid overwinters in the egg stage. In the fall, oval yellow eggs about 0.5 mm long are laid in crevices in the bark of larger branches. Eggs begin to darken, and after one to two weeks, they become shiny black and are impossible to differentiate from those of green apple aphid and apple grain aphid. In the spring, eggs hatch for about two weeks while the buds are in the silver-tip to half-inch green stage. Newly hatched nymphs feed on expanding buds and undergo five molts until they mature into wingless adult females that give birth to live young without being fertilized by males. Each female produces an average of 185 offspring, which can lead to rapid buildup of large populations. Nymphs cluster around each mother to the extent that infested leaves may be covered by more than one layer of aphids.
One generation is completed in two to three weeks. Adult aphids in a colony are generally wingless until crowded conditions induce the formation of winged individuals that can disperse to new hosts. The winged aphids often fly to a different plant species which is called the secondary host. Rosy apple aphid may remain on apple throughout the summer, but usually moves to narrow-leaf plantain or dock in early-summer. By late-July, most of the rosy apple aphids have left the apple trees.
Reproduction without mating continues on secondary hosts (plantain, dock) until late-summer or autumn when winged forms develop and return to the primary host (apple). Here a generation is produced that will develop into sexual adult males and females; these mate, then the females deposit overwintering eggs on the primary hosts.
Small parasitic wasps attack aphids; they lay their eggs in aphids by stinging with their ovipositor (egg-laying organ). The wasp egg hatches within the aphid and the young wasp larva consumes the aphid. Parasitized aphids turn brown or black. In time, the wasp larvae emerge as adults from the aphids, leaving behind empty aphid skins. These skins, called "aphid mummies," can be found attached to leaves.
Other natural enemies of apple aphids include predators such as hover fly larvae (white legless maggots), lacewing larvae, lady beetle larvae, lady beetle adults, and gall-midge larvae (orange maggots). These predators feed on many different aphid species in addition to other insect pests. A cool, wet spring favors aphid development because these conditions are unfavorable for the aphid's natural enemies.
A sample of 10 clusters from each of 10 trees should be examined for rosy apple aphid at the early pink bud stage, and insecticide applied if more than the threshold level of one colony per 100 terminals is found; this procedure was developed in New York. A sampling plan used for rosy apple aphid in Pennsylvania is to select 5 to 10 trees from each block at early pink, and count the number of fruit spurs with curled leaves on each tree for three minutes; if more than an average of 0.75 aphid-infested clusters are found per three-minute search, then an insecticide application is recommended. Varieties sensitive to rosy aphids should be sampled first.
Good control depends on proper timing of insecticide applications. Overwintering aphid eggs can be targeted with a delayed dormant spray to prevent early damage to fruit or expanding leaves, although a spray at the pink bud stage, after eggs have hatched, is usually more effective for control of rosy apple aphid.
Good control depends on choosing a material that will kill aphids but will not kill natural enemies. Systemic insecticides such as dimethoate are more effective than contact materials. After the leaves begin to curl, contact insecticides usually do not provide adequate control unless applied with large volumes of water to thoroughly cover the curled leaves. Keep in mind that use of most broad-spectrum insecticides encourages aphid outbreaks by killing predators and parasitoids.
Delayed dormant (green tip to half-inch green bud stages) Spray with superior oil plus an organophosphate such as chlorpyrifos (Lorsban) in commercial orchards. In backyard plantings, oil plus diazinon can be used. Oil alone is not effective against aphid eggs. Methidathion (Supracide) is an alternative aphicide that can be used during the delayed dormant period in commercial orchards.
Pink bud stage or post-bloom Endosulfan (Thiodan), dimethoate (Cygon), or chlorpyrifos (Lorsban) are the most effective insecticides for rosy apple aphid control. Methomyl (Lannate), oxamyl (Vydate), or pyrethroids (Ambush, Asana, Pounce) also control aphids. In backyard plantings, diazinon can be used for rosy apple aphid control.
NOTE:Disclaimer - This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.
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