Christine A. Hoepting

Temporal Dynamics of Iris Yellow Spot Virus and Its Vector, Thrips tabaci (Thysanoptera: Thripidae), in Seeded and Transplanted Onion Fields

ABSTRACT Onion thrips, Thrips tabaci (Lindeman) (Thysanoptera: Thripidae), can reduce onion bulb yield and transmit iris yellow spot virus (IYSV) (Bunyaviridae: Tospovirus), which can cause additional yield losses. In New York, onions are planted using seeds and imported transplants. IYSV is not seed transmitted, but infected transplants have been found in other U.S. states. Transplants are also larger than seeded onions early in the season, and thrips, some of which may be viruliferous, may preferentially colonize larger plants. Limited information is available on the temporal dynamics of IYSV and its vector in onion fields. In 2007 and 2008, T. tabaci and IYSV levels were monitored in six seeded and six transplanted fields. We found significantly more thrips in transplanted fields early in the season, but by the end of the season seeded fields had higher levels of IYSV. The percentage of sample sites with IYSV-infected plants remained low (<12%) until August, when infection levels increased dramatically in some fields. The densities of adult and larval thrips in August and September were better predictors of final IYSV levels than early season thrips densities. For 2007 and 2008, the time onions were harvested may have been more important in determining IYSV levels than whether the onions were seeded or transplanted. Viruliferous thrips emigrating from harvested onion fields into nonharvested ones may be increasing the primary spread of IYSV in late-harvested onions. Managing T. tabaci populations before harvest, and manipulating the spatial arrangement of fields based on harvest date could mitigate the spread of IYSV.

Swede Midge (Diptera: Cecidomyiidae), Ten Years of Invasion of Crucifer Crops in North America

ABSTRACT The Swede midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae), a common insect pest in Europe, is a newly invasive pest in North America that constitutes a major threat to cruciferous vegetable and field crops. Since its first identification in Ontario, Canada, in 2000, it has rapidly spread to 65 counties in the provinces of Ontario and Quebec and has recently been found in canola (one of two cultivars of rapeseed, Brassica napus L. and Brassica campestris L.) in the central Prairie region where the majority of Canadas 6.5 million ha (16 million acres) of canola is grown. The first detection of Swede midge in the United States was in 2004 in New York cabbage (Brassica oleracea L.), but it has now been found in four additional states. Here, we review the biology of Swede midge, its host plant range, distribution, economic impact, pest status, and management strategies. We provide insight into this insects future potential to become an endemic pest of brassica crops in North America. We also proposed research needed to develop tactics for handling this invasive pest in brassica crops.

Sources of Iris yellow spot virus in New York

Iris yellow spot virus (IYSV) has been found consistently in commercial dry bulb onion fields throughout New York State since 2006. Yearly recurrence of IYSV may result from annual reintroductions of the virus or persistence of the virus in overwintering host plants. To identify potential sources of IYSV, we surveyed onion transplants imported into New York as well as volunteer onion plants and weeds using a double-antibody sandwich enzyme-linked immunosorbent assay. IYSV was not found in any of 1,097 transplant samples tested in 2007 but 4 of 760 (0.53%) transplant samples tested positive in 2008. IYSV was found in volunteer onion plants in 3 of 10 (30%) onion fields sampled in 2007, in 4 of 27 (15%) onion fields sampled in 2008, and in 6 of 12 (50%) onion cull piles sampled in 2008. In all, 4 of 17 weed species (i.e., chicory [Cichorium intybus], common burdock [Arctium minus], curly dock [Rumex crispus], and dandelion [Taraxacum officinale]), were confirmed to be infected with IYSV using serological and molecular testing methods. IYSV may be reintroduced annually into New York through imported onion transplants but it also persists in volunteer onion plants and selected weed species.

Consequences of co-applying insecticides and fungicides for managing Thrips tabaci (Thysanoptera: Thripidae) on onion

BACKGROUND Insecticides and fungicides are commonly co-applied in a tank mix to protect onions from onion thrips, Thrips tabaci Lindeman, and foliar pathogens. Co-applications reduce production costs, but past research shows that an insecticides performance can be reduced when co-applied with a fungicide. An evaluation was made of the effects of co-applying spinetoram, abamectin and spirotetramat with commonly used fungicides, with and without the addition of a penetrating surfactant, on onion thrips control in onion fields. RESULTS Co-applications of insecticides with chlorothalonil fungicides reduced thrips control by 25-48% compared with control levels provided by the insecticides alone in three of five trials. Inclusion of a penetrating surfactant at recommended rates with the insecticide and chlorothalonil fungicide did not consistently overcome this problem. Co-applications of insecticides with other fungicides did not interfere with thrips control. CONCLUSION Co-applications of pesticides targeting multiple organisms should be examined closely to ensure that control of each organism is not compromised. To manage onion thrips in onion most effectively, insecticides should be applied with a penetrating surfactant, and should be applied separately from chlorothalonil fungicides.