By K. F. Ward, L. du Toit, and C. M. Ocamb
Cause Beet curly top virus (BCTV) which can affect a wide range of crops including beet, tomato, cucurbits, beans, etc. and non-crop plants. Symptomatic buckwheat crops have been observed in Washington for several years, and have tested positive for BCTV based on polymerase chain reaction (PCR) assays. It is transmitted by beet leafhopper feeding on plants, so it is not uncommon to observe healthy plants next to severely affected plants. Because the beet leafhopper feeds preferentially on other crops and weeds, the virus appears randomly through buckwheat crops but a higher incidence of infection may occur on field margins.
Symptoms Infected plants initially show unthrifty growth and small, misshapen leaves at the stem terminals. Plants become stunted and leaves become chlorotic and/or red. Stem terminals may lose leaves and become necrotic and shriveled, which can be mistaken for a fungal or bacterial infection. In severe cases, infected plants lose all leaves, leaving only the shriveled brown stem. The root system may decline and roots may rot from secondary fungal infections, but BCTV infection alone does not cause root rot. Severity of symptoms depends on how young plants are once they become infected. Plants infected at a more mature growth stage may show only yellowing or reddening of the leaves. Once infected, plants stop growing, produce no seed, and may die prematurely.
Cultural control
- Sow new plantings in early spring or later season so seedling stage occurs before or after peak beet leafhopper migration.
- No buckwheat varieties have been evaluated for curly top resistance but when Fagopyrum tataricum and F. esculentum were planted side-by-side, symptoms were worse in F. esculentum.
Chemical control BCTV cannot be controlled directly in buckwheat plants and controlling beet leafhopper ingress into buckwheat is difficult.