MANAGING CURLY TOP IN SOUTHERN IDAHO

Curly top of sugarbeets caused by Beet curly top virus (BCTV) was widespread from southeastern Oregon to southcentral Idaho in 2004. Curly top first became a serious threat to sugarbeet production in southern Idaho in 1919. By the time the first resistant variety was released in 1935, BCTV had almost eliminated the sugarbeet industry (2). Today this disease is largely managed through the use of resistant varieties. Early planting and the use of systemic insecticides (phorate, aldicarb, and imidicloprid) will also help limit curly top (1,2,4). The virus is transmitted by the beet leaf hopper, Circulifer tenellus, and overwinters in host plants or adult females that survive on mustard species (1). The coldest southern Idaho winters will not eliminate the leaf hoppers. Eggs are laid on leaves and stems in the spring which leads to three broods per year in Idaho. The first brood occurs in the desert prior to spring migration. In southcentral Idaho, migration occurs from May 12 to June 5 with the average peak migration occurring on May 25 (1). The second and third broods occur on sugarbeets and other hosts. Brood development normally takes 1 to 2 months depending on temperature. The leaf hoppers can survive on plants from 19 families and 106 species (1). In the spring the most important hosts are tansy mustard (flixweed) and tumble mustard (Jim Hill mustard). Summer weed hosts include halogeton, kochia, Russian thistle, and bassia. In the fall, the primary weed hosts include Russian thistle and red orache (saltbush). Russian thistle is particularly important since it determines the size of the hibernating population which will survive over the winter on mustards. Leaf hoppers acquire BCTV by feeding on infected plants. Studies (1) indicate that the percentage of a population of leaf hoppers that will acquire and transmit BTCV increases as feeding time increases (acquisition percentage): 1 min (1.4 – 3.3 %), 2 min (6.7 %), 5 min (26.5 %), 30 min (28 %), 1 hr (44 %), and 4 hr (76 %).