From BASF: The Chemical Company Website
By Paul Pilon
Each year many growers produce a large quantity of their perennials for summer and fall sales in outdoor production sites. There are many advantages to producing plants outside; however, in some situations certain insect pests can cause serious damage to ornamental crops. Leafhoppers are commonly observed in outside production areas and have been known to cause serious injury to crops. They feed on a wide variety of herbaceous perennials including Anemone, Aster, Bellis, Campanula, Chrysanthemum, Coreopsis, Delphinium, Echinacea, Gaillardia, Liatris, Phlox, Rudbeckia, Salvia, Scabiosa and Veronica to name a few.
Of the numerous species of leafhoppers out there, the aster leafhopper (Macrosteles fascifron) and potato leafhopper (Empoasca fabae) are two species that are the most problematic for growers. Leafhoppers can be easily spotted as they quickly leap from plant to plant or scurry behind plant stems as you walk through the crops.
Most leafhopper species are wedge shaped and vary in coloration and size. They are usually slender, yellow to light green, measure 3 to 5 mm in length and hold their wings roof-like over their body. Both the nymph and adult stages actively move from plant to plant and potentially from crop to crop. They initially move into production sites from adjacent fields or weeded areas and with air currents.
Leafhopper feeding causes a stippling of the foliage (similar to injury caused by two spotted spider mite feeding) and may result in some curling and distortion of the new growth. Extensive feeding damage may cause the plants to appear scorched, chlorotic, or stunted.
Besides symptoms of normal feeding activity, the aster leafhopper also transmits a disease called aster yellows. Aster yellows, also referred to as witches broom, is an irreversible viral-like disease that causes plants to appear and grow very abnormally, often forming a massed appearance or brush-like development of numerous weak shoots. Some plants, such as Echinacea and Veronica, produce deformed, yellowish green flower heads (or flower spikes) after they are infected with aster yellows. Plants infected with aster yellows should be removed from the production site and destroyed.
To reduce the entry of leafhoppers into production areas, it is beneficial to control and/or remove weeds within and surrounding the production site as many weeds serve as a reservoir for leafhoppers. Many weeds are also symptom-less hosts of aster yellows which can easily get introduced into crop areas by movement of leafhoppers and their subsequent feeding activities.
It is beneficial to control the weeds around the perimeters of structures, in driveways, in the seams and rips in ground mat, as well as to maintain a weed-free zone (30 to 50 feet) surrounding the production area (all sides).
The best strategy is to control leafhopper populations and keep them from reaching excessive levels. If leafhoppers have been problematic in the past and aster yellows has been observed, it may be best to produce susceptible crops within enclosed structures or cold frames covered with shade fabric to prevent leafhoppers from entering the site. In most cases, shade cloths that provide less than 30% shade will have minimal, if any, affects on plant appearance and quality (providing shade will actually be beneficial in many instances).
Leafhoppers can be controlled to some extent using contact insecticides, such as bifenthrin, carbaryl, insecticidal soaps, lambda-cyhalothrin, and petroleum oil (horticultural oil). Control of leafhoppers with contact insecticides can be difficult as leafhoppers are very mobile and new leafhoppers often enter the treated area after the sprays have dried. Several systemic products containing the active ingredients imidacloprid, thiamethoxam, and acetamiprid are effective and offer extended control with less frequent applications.
The mention of specific active ingredients does not constitute an endorsement or recommendation of, or discrimination against similar products not mentioned. ALWAYS READ PRODUCT LABELS AND USE THEM AS DIRECTED ON THE LABEL.