Beet leafhopper (Circulifer tenellus Baker)
Pest description and crop damage The most important leafhopper for potato producers in the PNW is the beet leafhopper, due to its ability to transmit the beet leafhopper transmitted virescence agent (BLTVA) phytoplasma. This leafhopper varies in color but is always one of the smaller species and lacks prominent spots or other dorsal or head markings. Phytoplasmas can cause a wide range of symptoms in potatoes that are collectively referred to as "purple top," including leaf curling and purpling, aerial tubers, chlorosis, and early senescence. Beet leafhopper is the most important vector of BLTVA in the Columbia Basin of Oregon and Washington. Most BLTVA infection occurs early in the season, during May and June, although some evidence suggests damaging infections in July.
A wide variety of leafhoppers can be found in potato fields. At least one species of Empoasca reproduces on potatoes in the Pacific Northwest. These leafhoppers are small, pale green, and torpedo-shaped. They hold their wings roof-like over the body at rest. Empoasca leafhoppers are rarely found in significant numbers in the Pacific Northwest. Other leafhoppers usually do not reproduce in potato fields.
Biology and life history Beet leafhopper overwinters as adult females in weedy and native vegetation (mainly from the Mustard family) throughout most of the dry production areas east of the Cascade Mountains. Eggs are laid in stems of host plants, and a new spring generation begins developing in March and April. Beet leafhopper begins to move and potentially affect potatoes during the first spring generation, which matures in late May to early June. Newly emerged adults in each generation tend to migrate from their birth areas to new areas, which causes them to encounter crop fields and potentially transmit BLTVA. Not all beet leafhoppers feeding on BLTVA-infected plants carry the disease, making management challenging. Also, early beet leafhopper infestation can reduce yield. Potatoes are most seriously affected by BLTVA infections that occur early in the growing season. Beet leafhopper can remain common through the summer, during which it goes through 2 to 3 overlapping generations. The final generation for the year matures during late October, and can sometimes be the largest of the year. The favorite hosts of beet leafhopper appear to be kochia, Russian thistle, and various weedy mustard species such as tumble mustard. It seems to thrive best in marginal unirrigated situations where its host plants are small and under stress.
Scouting and thresholds For detailed information on monitoring beet leafhoppers using yellow sticky traps, see: http://www.nwpotatoresearch.com/pr/Insect-Trapping-Guides.cfm
Beet leafhoppers are preyed upon by a specific parasitoid in the fly family Pipunculidae, but little is known about the effect of this parasitoid on leafhopper populations. In potato fields, where beet leafhoppers occur almost exclusively as adults, the most likely biocontrol agents are the many species of spiders that commonly live in crops.
Controlling the favorite weed hosts of beet leafhopper is probably the most important cultural management option. Indications are that beet leafhoppers within several hundred feet of a potato field may be most important in BLTVA transmission. Therefore, controlling beet leafhopper's favorite weed hosts near potato fields may reduce BLTVA incidence.
Management-chemical control: HOME USE
- azadirachtin (neem oil)-Some formulations are OMRI-listed.
- Beauvaria bassiana-Some formulations are OMRI-listed.
- insecticidal soap-Some formulations are OMRI-listed.
- kaolin-Applied as a spray to foliage it acts to repel certain insect pests-Some formulations are OMRI-listed for organic use.
- pyrethrins (often as a mix with other ingredients)-Some formulations are OMRI-listed for organic use.
- plant essential oils (garlic, peppermint, rosemary, etc.)-Some formulations are OMRI-listed for organic use.
- spinosad-Some formulations are OMRI-listed for organic use.
Note: Pyrethroid insecticide (Group 3 in Tables 1-2) applications make aphid management more difficult and can lead to outbreaks of spider mites.
Management-chemical control: COMMERCIAL USE
The most important time to control leafhoppers that transmit BLTVA is early in the season-probably the first 2 months after emergence. Frequent applications may be necessary since the beet leafhopper vector is only a transient visitor to potato fields. One spray may kill the leafhoppers in the field as well as new invaders for a residual period, but more leafhoppers will invade from surrounding areas throughout the season. Pyrethroid insecticide (Group 3 in Tables 1-2) applications make beet leafhopper management more difficult and can lead to outbreaks of aphids and spider mites.