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White Apple Leafhopper
family: cicadellidae |
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White Apple Leaf Hopper Typhlocyba pomaria McAtee Leafhoppers which attack apples are found across Canada. They include the apple, the white apple, the rose and the potato leafhopper.
The nymphs and adults feed on the sap in the underside of leaves, resulting in diminished plant vigor. Infested foliage becomes pale in color, with white spots on the underside. Potato leafhoppers often feed on apple tree nursery stock, producing hopper burn which results in curled leaves. The fruit may also be damaged, the result of spotting caused by the insects' excrement.
Apple leafhoppers do not survive the winter in Canada and the northern United States, but migrate from southern areas where they overwinter in the egg stage or as hibernating adults. Adults become active early in the spring and mate soon after. When the leaves appear on the trees, the females lay their eggs in the veins and stems of the leaves. First-generation nymphs appear about the time the foliage becomes full-grown and, along with the adults, feed on the sap in the underside of the leaves. The greenish-white and wingless nymphs mature about midsummer, molt and become adults. The females then deposit their eggs for the second generation, which becomes full-grown during early autumn.
Spraying is advisable if there are 50 or more nymphs per 100 leaves. For recommendations on control, consult your provincial agricultural representative.
Three batches of eggs laid beneath leaves throughout summer, development is 980 D days (of 50.5 degrees). The limitation on the wasp population is overwintering since the wasp has no food over the winter (since the hopper lays no eggs then). Blackberries (riparian habitats) or prunes are the refugia for hopper eggs and therefore wasp population. Generalist predators (lady beetles, spiders, mites, pirate bugs, and lacewings).
Subject: White Apple Leafhopper (Typhlocyba pomaria) WHITE APPLE
LEAFHOPPER, (Typhlocyba
pomaria) White apple leafhopper adults are a pale yellow color and about 3 mm in length. This pest primarily attacks apple, but can occasionally be found on cherry and plum. It is only an economically important pest of apple.
The white apple leafhopper has two generations per year and overwinters on tree limbs in the egg stage. The overwintering eggs are deposited by the second brood females just beneath the bark surface on one to five-year old wood. These egg laying sites appear as elongate, oval, blister-like swellings, measuring about 1.5 mm in length. Overwintered eggs begin hatching about late pink, and newly hatched 1st instar nymphs can be found in the orchard beginning in late-April to early-May. White apple leafhopper has five nymphal stages or instars. Nymphs can be found feeding on the undersides of leaves. As the nymphs pass through progressively larger stages, the development of their wing pads becomes noticeable by the 3rd instar (see diagram). As they grow, they go through a "molting" process where the old "skins" are cast off. These skins appear white and can frequently be seen hanging from the undersurface of leaves. First generation adults begin appearing in late-May or early-June. This first generation is usually small and peaks in early- to mid- June. Adult females begin producing eggs about 10 days after emergence for a three-week period. Summer eggs are laid in leaf petioles and veins and begin hatching in July. Second generation nymphs and adults can be found in orchards through the remainder of the season, often peaking at high numbers (much higher than 1st generation densities) around apple harvest time.
It is usually the 2nd generation that causes the most problems for apple growers. White apple leafhopper can cause three general types of injury: 1) feeding injury which causes a white speckling or mottling of leaves (leaves with a heavy infestation can become almost completely white), 2) feeding nymphs and adults excrete a sticky honeydew which can cause black spots on leaves and fruit, and promote growth of sooty mold, and 3) large 2nd generation populations in orchards at harvest time can create a nuisance problem to apple pickers. Although severe injury caused by leaf feeding has been associated with a slight reduction in tree health, fruit size and quality, it is the nuisance problem to pickers at harvest caused by large numbers of flying adults that can be the most serious.
The key to management of white apple leafhopper is to prevent the 2nd generation from reaching nuisance levels by controlling the first generation. Although the 1st generation population may be small and not seem threatening at the time, we found that even very low numbers of young nymphs at petal fall (<0.4 nymphs/terminal (terminals are the tight cluster of leaves at the tips of branches)) resulted in populations considered to be an interference to pickers by harvest. Growers that wait to control the leafhopper until late in the season may end up applying several sprays and never achieve good control of adults. The winged adults fly quickly when disturbed and then come back to haunt you again later, laying more eggs that will overwinter and contribute to next year's problem. Also, timing of late season sprays may be more difficult because of pre-harvest intervals that must be observed and chemical residue concerns. White apple leafhopper is best controlled around petal fall when the majority of nymphs are still small (instars 2-4), and egg hatch is nearly complete. The early nymphal stages are the most easily controlled, and so should be the main target for control action. Larger nymphs are progressively more difficult to control and adults often escape sprays because of their mobility. Careful scouting for young leafhopper nymphs should begin at late pink and continue through petal fall. When scouting, 100 terminals per 10 acres should be examined. The action thresholds for first and second generations are given below.
If 1st generation control is required, a spray at this time will minimize later damage and may prevent later season build up of the population. (follow provincial or state control guidelines.) White apple leafhopper populations should again be monitored in the 2nd generation by inspection of terminals and/or leaves. Adults can be sampled with a beating tray. Orchards with nearby sources of white apple leafhopper (e.g., unsprayed orchards, backyard trees) should especially be monitored for reinfestation by adults. Optimum timing for 2nd generation is generally more difficult because the vulnerable stages are more spread out over time. Control can be achieved by a split application: one timed for first emergence of the 2nd generation nymphs, the second spray two weeks later. However, this is an expensive option. If only one spray is to be applied, then it should be timed for about two weeks after the emergence of 2nd generation nymphs. Caution should be given against using Sevin or Carzol for 2nd generation control, as they may be toxic to predatory mites and disruptive to an IPM program. *See "Apple Spray Guide" in "Utah Fruit Pest Control Handbook" for more details. Written under contract to the BC Ministry of Environment, Lands and Parks (now Ministry of Water, Land and Air Protection ) by: D.E. Henderson, E.S. Cropconsult Ltd., Vancouver, British Columbia in collaboration with D.A. Raworth, Research Station, Vancouver, British Columbia:
Leafhoppers, which attack raspberry, and spittlebugs, which can
be a problem on strawberry, are related to aphids and damage plants
in much the same way, by sucking plant juices. Leafhoppers are
3 mm long, active, slender insects, which usually jump when disturbed.
They vary in color from pale white to brownish green and feed on
the underside of young raspberry leaves. Their feeding causes yellow
areas along the veins and at the edges of the leaves, giving the
leaf a mottled appearance. Some will also feed on berries. Leafhoppers
appear in late May in some regions, and in June and July in others.
Like aphids, they excrete honeydew, which contaminates the plant
or berry with a shiny, sticky substance. Black sooty mold can develop
on this substance. Also like aphids, they are attacked by a variety
of predators such as lacewings, ladybird beetles, some rove beetles,
damsel bugs, assassin bugs, and ground beetles. |
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