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Potato Leafhopper Management: Reducing Fireblight Risk & Maintaining Growth on Young Apple Trees. June 18th

Synopsis: The arrival of potato leafhopper, Empoasca fabae (PLH) occurred late last week. Monday we observed early stages of leaf necrosis or ‘hopper burn’ on terminal leaves, resulting from adult foliar feeding. PLH nymphs are now present from 1st to 3rd instar in the mid-Hudson Valley. Increasing damage from PHL will significantly stunt growth in young plantings if left unmanaged. Wounding and transmission of fireblight bacteria by PLH to young trees is also a concern. Couple this with terminal leader shoot damage from European corn borer injury and upcoming warm weather, intermittent rains and lingering fireblight strikes, scouting for and treating these pests should be a management concern in new orchard plantings over the next few weeks.

To support newly planted tree vigor and growth, reduce the risk of fireblight by managing PLH and ECB in newly planted orchards. Uninterrupted tree growth in new plantings is essential for highest economic returns over the next few years.

Deer damage to young apple. Image: P. Curtis

Deer damage to young apple. Image: P. Curtis

Growing 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. Yearly feeding on apple by white tail can be managed successfully using orchard perimeter fencing. Fencing deer out of the orchard is the most efficient way to reduce damage when deer density is high and damage extensive. The conventional 8-foot woven-wire fence effectively excludes deer by forming a barrier around the orchard. The fence consists of two widths of 4-foot woven wire and 12-foot posts. To prevent deer from crawling under, keep the wire close to ground level. Unfortunately, deer-proof fencing is expensive, but it is effective, long lasting, and requires little maintenance. High tensile wire is recommended.

Damage to newly planted apple shoots by arthropod pests is occurring this week. They include Potato Leafhopper and European Corn Borer.

Adult potato Leafhopper

Adult potato Leafhopper

Potato leafhoppers (Empoasca fabae)(PLH): 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.

With incidence of fire blight this season, controlling Potato leafhoppers, a potential vector of the fire blight bacterium, Erwinia amylovora (EA), should be a management consideration in young establishing orchards.

PLH nymph

PLH nymph

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.

PLH damage to growing shoot.

PLH damage to growing shoot.

Shoot blight. Image: D.A.Rosenberger

Shoot blight. Image: D.A.Rosenberger

Fireblight: 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.

Management: Contact and translaminar insecticides labeled for Leafhopper.

Growing terminal shoots during late May and through June will quickly outgrow insecticide residue. That said, 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. Be advised that Imidacloprid (*Admire Pro, *Leverage) has caused mite flare-ups during summer during HVRL efficacy studies.

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 should be applied at the early stage of nymph development for greatest efficacy.

ECB larva on apple

ECB larva on apple

European corn borer, Ostrinia nubilalis: 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 terminal growth. Rick Weires and Richard Straub had shown in previous studies that in some years damage from ECB can exceed 8% infestation of terminal shoots in new plantings. The injury consists of a tunneling into the succulent portion of the current season’s growth, causing either the death of the portion distal of the feeding site or predisposing the shoot to breakage at this point. Use of apple shoots by ECB larvae is often attributed to unusually hot, dry summer weather, which adversely affected the number of preferred weed hosts. Loss of the terminal growth in central leader shoots creates economic losses in newly planted young apple trees.

Management: Delegate 25WG and Dipel 10.3DF are labeled and very effective against ECB on newly planted trees.

ECB Frass, Infestation of Young Apple

ECB Frass, Infestation of Young Apple

References:
Brooks, A.N. 1926. Studies of the epidemiology and control of fire blight of apple. Phytopathology 16:665-696.

Burrill, A.C. 1915. Insect control important in checking fire blight. Phytopathology 5:343-347.

Clarke, G.G., Hickey, K.D., and Travis, J.W. 1992. Fire blight management: evaluation of the role of aphids in transmission of bacteria and development of a computerized management system for growers. Penna. Fruit News 72(2):30-33.

Delong, D.M. 1934. The relative value of Bordeaux mixture, sulphur and pyrethrum products in reducing populations of the potato leafhopper (Empoasca fabae Harris). J. Econ. Ent. 27:525-533.

Gossard, H. A., and Walton, R.C. 1922. Dissemination of fire Blight. Ohio Agric. Expt. Sta. Bull. 357:83-126.

McManus, P.S., and Jones, A.L. 1994. Role of wind-driven rain, aerosols and contaminated budwood in incidence and spatial pattern of fire blight in an apple nursery. Plant Dis. 78:1059-1066.

Menusan, H, Jr. 1938. Results of potato dusting experiments on organic soils. J. Econ. Ent. 31:259-262

Miller, L.I. 1942. Peanut leafspot and leafhopper control. Bull. Va. Agric. Exp. Sta. 338:21.

Miller, P.W. 1929. Studies of fire blight of apple in Wisconsin. Jour. Agr. Res. 39:579-621.

Pfeiffer, D.G., Killian, J.C., and Yoder, K.S. 1999. Clarifying the roles of white apple leafhopper and potato leafhopper (Homoptera: Cicadellidae) in fire blight transmission in apple. Journal of Entomological Science 34(3):314-321.

Plurad, S. B., Goodman, R. N., and Enns, W. R. 1967. Factors influencing the efficacy of Aphis pomi as a potential vector for Erwinia amylovora. Phytopathology 57:1060-1063.

Stewart, V.B., and Leonard, M.D. 1916. Further studies in the role of insects in the dissemination of fire blight bacteria. Phytopathology 6:152-158.

Weires, R. W., Straub R. W. 1982. European Corn Borer Infestation of Newly Planted Apple Trees
Environmental Entomology, Volume 11, Issue 3, 1 June 1982, Pages 645–647, https://doi.org/10.1093/ee/11.3.645