White apple leafhopper and potato leafhopper
Excerpt from Publication 310, Integrated Pest Management
Table of Contents
Although many species of leafhopper feed on apple, only two are of economic importance in Ontario. The white apple leafhopper, Typhlocyba pomaria (McAtee), is a native pest found in all apple-growing areas. The potato leafhopper, Empoasca fabae (Harris), is an occasional pest on apple, especially young non-bearing trees.
The white apple leafhopper is native to North America and found in most apple-growing regions in Canada and the United States. Apple trees are probably the only host that white apple leafhopper overwinters on, but during the growing season it may also infest peach, plum, cherry and hawthorn. The insect feeds on foliage and does not attack the fruit directly.
The egg is less than 1 mm in length, cylindrical with tapering ends and creamy white in colour. There are five nymphal instars. Young nymphs (first and second instar) are pale whitish with dull red eyes, and about 1.0-1.5 mm in length (Figure 4-22). During the third instar, wing pads and dull white eyes develop. The fourth and fifth instar nymphs are similar in appearance to the third instar, but are larger in size (Figure 4-23). White apple leafhopper nymphs are differentiated from potato leafhopper nymphs by the way they walk when disturbed - white apple leafhoppers walk forward and backward, while potato leafhoppers walk sideways in a crab-like fashion. Adults are creamy white, about 3 mm in length and hold their wings over their back when resting (Figure 4-24).
Figure 4-22. White apple leafhopper young nymph
White apple leafhopper overwinters as an oblong egg about 1 mm in length, inserted beneath the bark and producing blisters on the twigs. Overwintering eggs are most often present on two-year-old wood, and are also found on wood three to five years of age. These eggs begin to hatch prior to bloom, and continue hatching through petal fall. After emerging, nymphs move to foliage and complete their development on the underside on a single leaf or cluster of leaves. Nymphs are seldom seen on the upper surfaces of leaves. Nymphs of the first generation are found on cluster leaves close to the main trunk or large limbs of the tree, and not often found on actively growing terminal shoots. Nymphs develop into adults in early summer. Mating usually occurs early in the morning and oviposition (egg laying) follows about 14 days later. Eggs are laid in the petioles, midribs and large secondary veins on the undersurface of leaves. The oviposition period lasts approximately three weeks and each female can deposit 50-60 eggs. The total lifespan of first generation adults is five to six weeks. Second generation nymphs appear in early August and adults are present from mid to late August, until the first hard frost. This second generation is less synchronized and more difficult to control. In Ontario, there are two generations per year.
White apple leafhopper damage causes stippling of the leaves and fruit spotting. Both nymph and adult white apple leafhopper insert sucking mouth parts into plant cells to remove the contents. This feeding leaves pale green or whitish stipples on the leaf where cells have been damaged (Figure 4-25). Leaf stippling reduces the photosynthetic area of the leaf, affecting fruit size, colour, maturity and winter hardiness of the tree. Leaf stippling appears more prevalent during the first generation in June and July.
Figure 4-25. Severe stippling injury from white apple leafhopper feeding
As white apple leafhopper feed, they deposit excrement on fruit which dries into dark brown spots (Figure 4-26). These marks are unacceptable on apples destined for fresh market sales, especially cultivars with light-coloured skin. Fruit spotting is more prevalent during the leafhoppers' second generation, beginning in August. Dried spots normally wash off with water and brushes on packing lines. White apple leafhopper droppings can be confused with a fungal disease called flyspeck - affecting apples late in the summer. In contrast to leafhopper spots, flyspeck spots are charcoal gray to black in colour and cannot be washed off. Flyspeck usually occurs as a circle of evenly spaced spots - while leafhopper droppings are randomly spaced all over fruit.
Figure 4-26. Leafhopper excrement causing speckling on mature fruit
In heavily infested orchards, white apple leafhopper adults are a nuisance to orchard workers during summer pruning and harvest operations. When disturbed, they fly up in clouds into pickers' eyes, ears, noses and mouths. This irritation can reduce worker efficiency and pose a safety threat if workers are distracted when operating equipment or climbing ladders.
Leafhoppers and other sucking insects can transfer diseases (such as fire blight) from one plant to another, however the importance of leafhoppers in the dispersal of this bacterial disease is unknown.
Check the undersides of 5 leaves from each of 20 randomly selected trees in an orchard block (for a total of 100 leaves). Select older and mid age leaves - located near the trunk area - for the first generation. Observe second generation leafhopper nymphs at arm's length into the canopy, roughly midway into the radius of the tree. Examine leaves in the orchard by carefully observing the undersides for presence of nymphs. Newly hatched nymphs are difficult to see, and a hand lens is recommended.
Initiate monitoring for first generation nymphs by late bloom or petal fall and continue for several weeks. Second generation nymphs are more difficult to monitor due to expanded foliage and a prolonged hatch beginning in late July and continuing well into August. White cast skins left over from nymphs moulting are often seen on leaves and terminals.
Low numbers of white apple leafhopper are not of economic concern. An insecticide treatment is only necessary when a spray threshold of 2-5 nymphs per leaf is observed in a 100 leaf sample.
There are a few parasitoids or predators that attack white apple leafhopper, but none provide biological control. Mullein bugs are sometimes observed feeding on leafhopper nymphs.
Insecticides are most effective on younger nymphal stages during the first generation, and second generation control is not often required. Where late season populations surpass threshold levels, insecticide timing can be difficult due to the extended hatch.
The white apple leafhopper is resistant to organophosphate insecticides. For recommended materials, see OMAFRA Publication 360, Fruit Production Recommendations.
The potato leafhopper, Empoasca fabae (Harris), has a much broader host range than the white apple leafhopper, feeding on apple, grapes, strawberry, potato, many other vegetable crops, beans, alfalfa and approximately 200 other species of plants. The potato leafhopper's toxic saliva causes considerably more damage in orchards.
Young nymphs are yellowish-green (Figure 4-27), and move very quickly on the underside of leaves. Older nymphs develop "wing pads" that distinguish them from the fully winged adults. Nymphs have the curious ability to walk sideways or backwards, and rapidly move to the underside of the leaf if disturbed. Adults are light green, wedge-shaped insects about 3 mm long (Figure 4-28). They have sucking mouth parts and can fly, walk and hop. Their body structure resembles a grasshopper with well developed back legs and wings that fold tent-like across their back.
Figure 4-27. Potato leafhopper nymph (NRAES-75,
Mid Atlantic Orchard Monitoring Guide. Edited by Henry Hogmire)
Potato leafhoppers do not overwinter in Ontario. Each spring adults are carried by wind currents from southern Gulf states and across the Great Lakes into Ontario. The first adults arrive as early as mid May and continue to arrive well into June. Adults are first noticed in apple orchards in early or mid June, generally just after the first cut of hay in the area. The removal of the food source (alfalfa) usually causes potato leafhoppers to migrate to nearby alternate host crops, including apple. Adults mate and females deposit two to three eggs per day throughout their life span. Eggs are laid on leaves or stems in the upper part of the canopy and hatch in about 10 days. Potato leafhopper nymphs take about 25 days to pass through five life stages (instars), each larger than the previous stage. Only the last three instars possess visible wing pads, which become wings in the adult. As the insects molt from one instar to the next, they leave behind white cast skins. Three or four generations are produced each year and remain active until killed by a hard frost. In hot, dry summer weather, leafhopper populations can build to tremendous numbers and insecticide treatments may be necessary.
Adults and nymphs feed by sucking plant juices from leaves. They inject a toxin into the plant while feeding, blocking vascular system flow. Feeding reduces plant vigour and plugs off the vascular system, preventing normal movement of water and nutrients to the affected area of the plant. Leaves turn pale green and curl downward at the margins (Figure 4-29). Leaf margins eventually turn brittle and brown - known as hopperburn - and exhibit symptoms resembling aphid injury (Figure 4-30). However, it takes dozens of aphids on a leaf to cause it to curl, whereas the same curling will occur with only two or three potato leafhoppers. Some research suggests potato leafhoppers are involved in the transmission of fire blight through orchards.
Figure 4-29. Leaf curling on terminal due to feeding
Potato leafhoppers are most often found in tree nurseries and non-bearing orchard blocks, in part because they prefer young, vigorously growing leaves. More importantly, non-bearing plantings have a lighter insecticide spray program than the rest of the orchard, and leafhoppers are able to survive better.
Check for potato leafhopper during weekly orchard monitoring beginning in early June. Look for curled leaves and shoots that are not growing as vigorously as they should. Check the undersides of leaves for nymphs and adults.
Assess leafhoppers in the field as they are easily disturbed and move off the leaf. Turn the leaf over slowly when monitoring to assess how many leafhoppers are on the lower leaf surface.
There are no spray thresholds established for potato leafhopper in Ontario. It has been documented on other crops that potato leafhopper feeding can affect the rate of photosynthesis, yield and crop quality at fairly low populations, and before leaf symptoms occur. In apples, one or two nymphs per leaf cause leaf curling if allowed to feed for a prolonged period of time (four to seven days).
Insecticides - particularly on nursery trees and in non-bearing blocks - are recommended at the first sign of injury.
There are no parasitoids or predators that provide biological control. If feasible, do not plant alfalfa or establish hay fields near orchards.
For recommended materials, see OMAFRA Publication 360: Fruit Production Recommendations.
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