White Apple Leafhopper and Potato Leafhopper

Table of Contents

1. Introduction
2. White Apple Leafhopper
3. Description
4. Biology
5. Damage
   • Stippling or Mottling of the Leaf
   • Fruit Spotting or Speckling
   • Nuisance to Orchard Workers
   • Disease Vector
6. Monitoring and Management
7. Potato Leafhopper
8. Description
9. Biology
10. Damage
11. Monitoring and Management
12. Table 1. Differences Between the White Apple Leafhopper and Potato Leafhopper

Introduction

Although many species of leafhopper will feed on apply, 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.

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White Apple Leafhopper

The white apple leafhopper is native to North America and is found in most of the apple-growing regions in Canada and the United States.

Apple trees are probably the only host on which white apple leafhopper overwinters, but during the growing season it may also invest peach, plum, cherry and hawthorn. The insect feeds on foliage and does not attack the fruit directly. In Ontario, there are two well defined generations per year: one in June and one in late August.

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Description

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 (1st and 2nd instar) are pale whitish in colour with dull red eyes, and are about 1.0 to 1.5 mm in length (Figure 1). The third instar is characterized by the development of wing pads and dull white eyes. The fourth and fifth instar nymphs are similar in appearance to the third instar, but are of increased size (Figure 2). The adults are creamy white in colour, about 3 mm in length and hold their wings over their back when resting (Figure 3).

Figure 1. Young instar of white apple leafhopper.

Figure 2. Older instar of while apple leafhopper - note wing pads.

Figure 3. Adult white apple leafhopper.

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Biology

The white apple leafhopper overwinters as an egg under the bark of twigs measuring approximately 1.25 cm in diameter. The eggs appear as blister-like swellings about 1.5 mm in length. Overwintering eggs are most often present on two-year-old wood, but can also be found on wood three to five year of age.

The overwintering eggs begin to hatch prior to bloom, sometime in early May. Hatch is usually complete by petal fall. After hatching the nymph moves to the foliage and completes its development on the underside of a singe leaf. 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, but are not often found on actively growing terminal shoots. They are generally most numerous in late May to early June when adults of the first generation begin to appear.

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 the 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 (summer) 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 therefore more difficult to control.

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Damage

The white apple leafhopper causes four types of damage:

Stippling or Mottling of the Leaf

Both nymph and adult white apple leafhopper have sucking mouth-parts, which they insert 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).

Figure 4. Severe stippling injury from white apple leafhopper feeding.

Leaf stippling reduces the photosynthetic area of the leaf and can affect fruit size, fruit colour, fruit maturity, and winter hardiness of the tree. Leaf stippling seems to be more prevalent during the insects first generation in June and July.

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Fruit Spotting or Speckling

As white apple leafhoppers feed, they deposit their excrement on the fruit which dries into dark brown spots (Figure 5). These marks are unacceptable on apples destined for fresh market sales especially those cultivar with light-coloured skin.

Figure 5. Leafhopper excrement causing speckling on mature fruit.

Fruit spotting is more prevalent during the leafhoppers' second generation, beginning in August. Normally the dried spots are washed off by water and brushes used on packing lines.

White apple leafhopper droppings can be confused with a fungal disease called flyspeck, which often affects apple late in the summer. In contrast to leafhopper spots, the spots caused by flyspeck are charcoal gray to black in colour and they cannot be washed off (Figure 6).

Figure 6. Flyspeck on fruit.

Flyspeck usually occurs as a circle of evenly spaced spots, whereas leafhopper droppings are usually randomly spaced all over the fruit.

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Nuisance to Orchard Workers

In heavily infested orchards, white apple leafhopper adults can be a nuisance to orchard workers during summer pruning and harvest operations. They fly up in clouds when disturbed and enter pickers' eyes, ears, noses and mouths. The irritation can result in reduced worker efficiency and may pose a safety threat if workers are distracted when operating equipment, climbing ladders, etc.

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Disease Vector

There are indications that insects may be vectors (transfer disease from one plant to another) of fireblight. Leafhoppers have sucking mouth-parts to extract juice from leaves and therefore have the potential of being fireblight vectors. The importance of leafhoppers in the dispersal of this bacterial disease is unknown.

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Monitoring and Management

Monitoring consists of checking the undersides of five leaves from each of 20 randomly selected trees in an orchard block (for a total of 100 leaves). Older and mid-age leaves, located near the trunk area, should be selected for the first generation. Second generation leafhopper nymphs are observed arm's length into the canopy, roughly midway into the radius of the tree.

Leaves are examined in the orchard by carefully observing the undersides for presence of nymphs. Newly hatched nymphs can be quite difficult to see, therefore a hand lens is recommended.

Monitoring for first generation nymphs should be initiated 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.

Low numbers of white apple leafhopper are not of economic concern. An insecticide treatment is only necessary when a spray threshold of two to five nymphs per leaf is observed in a 100 leaf sample. Insecticides are most effective on younger nymphal stages.

Control of the second generation is not often required. Where populations do build to spray threshold levels insecticide timing can be difficult due to the extended hatch.

The while apple leafhopper is resistant to organophosphate insecticides. Refer to the Pest Management Decision Guidelines in Chapter Five of Publication 310: Integrated Pest Management for Ontario Apple Orchards for recommended materials.

There are a few parasitoids or predators that attack white apple leafhopper, but none provides biological control Mullein bug are sometimes observed feeding on leafhopper nymphs.

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Potato Leafhopper

The potato leafhopper has a much broader host range than the white apple leafhopper feeding on apple, grape, strawberry, potato, many other vegetable crops, beans, alfalfa, and approximately 200 other species of plants.

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Description

The adults are light green, wedge-shaped insects about 3 mm long (Figure 7). They have sucking mouth-parts and can fly, walk and hop. Their body structure resembles that of a grasshopper with well developed back-legs and wings that fold tent-like across their back.

Figure 7. Potato leafhopper adult.

Eggs are laid on leaves or stems in the upper part of the canopy and hatch in about 10 days. The young nymphs are yellowish-green (Figure 8), and move very quickly on the under-side of leaves. Older nymphs develop "wing pads" that distinguish them from The fully winged adults. The nymphs have the curious ability to walk sideways or backwards, and they rapidly move to the underside of the leaf if disturbed.

Figure 8. Potato leafhopper nymph.

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Biology

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 the province. The first adults arrive as early as mid-May and continue to arrive well into June. The insect is first noticed in apple orchards in early or mid-June, generally just after the first cut of hay in the area. The removal of that rood source (alfalfa) usually means a migration of potato leafhoppers to nearby alternate host crops, including apple.

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 before they are destroyed by frost under Ontario conditions.

In a summer during hot dry weather, leafhopper populations can build to tremendous number and insecticide treatments may be necessary.

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Damage

The adults and nymphs feed by sucking the plant juices from the leaves. While feeding they inject a toxin into the plant, which blocks vascular system flow. Feeding reduces the vigour of the plant while plugging off the vascular system prevents normal movement of water and nutrients to the affected area of the plant. The apple leaves turn pale green and curl downward at the margins (Figure 9). Leaf margins eventually turn brittle and brown, symptoms resembling aphid injury (Figure 10). 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.

Figure 9. Leaf curling on terminal due to feeding.

Figure 10. "Hopper burn" on leaf edges.

Potato leafhoppers are most often found in tree nurseries and non-bearing orchard blocks. Partly this is because they prefer young, vigorously growing leaves. The more important reason though is that non-bearing plantings usually have a lighter insecticide spray program than the rest of the orchard, and the leafhoppers are able to survive better.

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Monitoring and Management

Apple growers should 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.

As leafhoppers are easily disturbed, and move off the leaf, it is important to do assessments in the field. Turn the leaf over slowly when monitoring to assess how many leafhoppers are on the lower leaf surface.

There have been 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 can cause leaf curling if they are 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. Refer to the Pest Management Decision Guidelines in Chapter Five of Publication 310: Integrated Pest Management for Ontario Apple Orchards for recommended materials.

There are no parasitoids or predators that provide biological control. If feasible do not plant alfalfa or establish hay fields near orchards.

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Table 1. Differences Between White Apple Leafhopper and Potato Leafhopper

Category	White Apple Leafhopper	Potato Leafhopper
Appearance of insect	Pale whitish-yellow	Light green to lime green
Size	Adult: 3 mm long	Adult: 3 mm long
Host preference	Apple, peach, plum, cherry, Hawthorne	Apple, grape, strawberry, potato, alfalfa, beans and over 200 other species.
Overwintering stage and site	Eggs under the bark of apple trees	Die after severe frost in Ontario; reinfest each spring from southern states.
Number of generations/season	2 generations	3 to 4 generations
Visual symptoms of leaf	White stippling on leaf surface	Leaves curled downward, with pale green edges
Economic impact on tree health	Lowers rate of photosynthesis and production of sugars (results in weaker leaf canopy)	Lowers rate of photosynthesis and production of sugars. Injects toxins into leaf which blocks vascular tissue and transport of water and nutrients. Overall effect of slowing growth of young plants and new leaves.
Behaviour when disturbed	Forward or backward movement	Sideways "scuttling"
Monitoring technique	Examine leaves by turning them over slowly to observe nymphs on lower leaf surface, beginning during bloom.	Examine leaves by turning them over slowly for nymphs on lower leaf surface, beginning in early June.
Monitoring frequency	Once per week.	Once or twice per week.
Economic thresholds trees.	2 - 5 active per leaf	At first sign of injury, particularly on young

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