Controlling Potato Leafhopper To Reduce Fireblight and Maintain Growth on Young Apple Trees

To optimize growth of newly planted trees, protection of the terminal shoot is essential for economic return within the first three to five years. Browsing by white tail deer is the most common form of damage to newly developing apple, with yearly feeding on apple by white tail managed successfully using orchard perimeter fencing.

Potato leafhoppers (Empoasca fabae)(PLH): We are seeing the onset of damage to newly planted apple by two arthropod pests this week in the form of Potato Leafhopper and European Corn Borer. Typical examples of ECB feeding on apple is similar to that of Oriental Fruit Moth on apple with frass and entry under petiole or side shoot of new shoots.Delegate 25WG and Dipel 10.3DF are labeled and very effective against ECB on newly planted trees.

With very high incidence of fire blight this season, controlling Potato leafhoppers, a known vector of the fire blight bacterium, Erwinia amylovora (EA), should be a strong consideration. In apples, PLH may also be a threat to the tender foliage of young fruit trees, leading to reduced terminal growth and vigor. This year is no exception as PLH nymph feeding gives rise to leaf curl observed this week. The injury to fruit trees is similar to that found on other host plants of the potato leafhopper. Injured foliage has the characteristic V-shaped “hopper burn,” severe injury may cause the entire leaf margin to be affected. Injured leaf margins generally curl downward with associated reduction in shoot extension growth. Other leafhoppers that may be present in orchards include the white apple leafhopper and rose leafhopper, which cause stippling that under high populations can lead to reduced loss of photosynthesis and carbohydrate development.

Potato leafhoppers cannot survive the winter in New York. The infestations we are seeing arise from spring migration from southern Gulf Coast States where the insect reproduces throughout the winter. The potato leafhopper females live approximately one month, ovipositing two to three eggs daily into the stems and larger leaf veins of suitable plants.
Injury: Nymphs hatch occurs in 7 to 10 days with immature developing through five nymphal ‘instars’, each instar stage taking about 2 weeks. The entire life cycle requires about 1 month to complete with three to four generations of leafhoppers observed each year in New York. During the summer months, it is common for generations to overlap. Potato leafhoppers can be found in orchards until the first killing frost.

Products containing the neonicotinoid active ingredients (Actara, Admire Pro, Assail, Calypso and some pre-mix formulations), have both contact and translaminar activity, moving into leaf tissue for uptake during feeding. Excellent control of the PLH, using reduced rates of the neonicotinoid product immidacloprid at 7d intervals, can reduce LH populations and maintain continued predation by coccinellid beetle adults and larvae. Contact insecticides such as the carbamates (methomyl-Lannate; Oxamyl-Vydate; carbaryl-Sevin), and the pyrethroid group should be applied on a tight 3-7d period during active periods of flush growth. Aza-Direct, Portal, and Centaur shold be applied at the early stage of nymph development for greatest efficacy.

With regards to the spread of the fire blight Dr. David Rosenberger writes “The predominant sucking insects present on terminals in early summer in apple orchards are aphids and leafhoppers. The role of aphids has been evaluated in two studies, and both reported that aphids were incapable of vectoring or facilitating spread of fire blight (Plurad et al., 1967, Clarke et al., 1992). Pfeiffer et al. (1999), using caged insects, showed white apple leafhoppers caused no increase in fire blight incidence or severity.

Potato leafhoppers (Empoasca fabae, formerly E. mali), were implicated in some of the earliest studies of potential insect vectors/facilitators of fire blight (Brooks, 1926; Burrill, 1915; Gossard and Walton, 1922; Miller, 1929; Stewart and Leonard, 1916). Unlike aphids and white apple leafhoppers, potato leafhoppers (PLH) feed primarily in the phloem and their feeding injury causes physiological changes in the host. In a study with caged insects, Pfeiffer et al. (1999) reported that PLH caused a highly significant increase in fire blight in two out of the three years they conducted trials. They postulated that PLH facilitated bacterial entry through feeding wounds. Dissemination of bacteria by leafhoppers moving from tree to tree was not examined.

None of the published studies have provided definitive evidence that PLH actually transmits EA from plant to plant, nor has anyone proposed a threshold level of PLH that may be required before these insects impact the incidence of shoot blight during summer.

Nevertheless, given the tremendous losses that fire blight can cause if it spreads during summer, it may be prudent to apply insecticide treatments to control PLH in orchards that have active fire blight.”

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