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

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 IYS

Using NEWA Internet Resources and Scouting to Improve Pest Management in Onions

Much information is available through Northeast Weather Association (NEWA), an on-line resource that plugs into local weather stations to model/forecast disease and insect activity/pressure.  This information in combination with scouting has great potential to be used in an Integrated Pest Management (IPM) strategy in onions, but both require in-depth training before it may readily be used by onion growers.  In this project, we worked with seven onion growers and taught them how to use scouting information and weather and disease model information provided in NEWA to make fine-tuned, effective and economical crop protection decisions.  We also trained two grower’s teenage children to scout onions and to retrieve the information provided in NEWA.  Of the information provided by NEWA, the downy mildew disease model appears to be the most useful, followed by the Michigan Botrytis Leaf Blight model while the Purple Blotch model had the least practical application.  Having an unbiased skilled onion scout appears to be critical to an onion IPM program.  In this study, weekly monitoring of pest pressure allowed one grower to delay both his first fungicide and insecticide sprays two and three weeks, respectively, a total savings of $125 per acre.  The grower’s teenage children still require more training, but show great promise in being a relatively inexpensive means for their onion grower parents to obtain scouting information that will save them money in pesticide sprays while maintaining high quality of their crops

Detection of Systemic and Latent Presense of Botrytis allii in Onion Transplants

In New York, major outbreaks of Botrytis neck rot of onion, caused by Botrytis allii have occurred in association with the recent increases in growing onions from transplants.  It has been suspected that bare-root transplants grown in Arizona could be infected withB. allii before they are transplanted in New York.  The present study conducted during 2006 endeavored to survey onion transplants for B. allii contamination, to elucidate the main source of this contamination and its role in Botrytis neck rot loss in storage, and to compare the data with that developed from a preliminary and similar study conducted during 2005.  In the present study which involved 50 entries (variety by grower), 81.3% of the bare-root transplants had some level of latent B. allii, compared to 0% for plug transplants and 0% for direct seeded seedlings.  Raw and treated seed, bare-root transplants, and direct seeded seedlings, all of the same lot number, had 71.4%, 0%, 90% (of the bundles) and 0% B. allii, respectively.  In the 2005 study which involved 35 entries, 77.8% of the bare-root transplants had some level of latent B. allii.  The feasibilities of growing bare-root transplants free of B. allii, thereby preventing spread ofB. allii from contaminated transplants, and using plug transplants free of B. allii as an alternative to the bare-root transplants should be considered by New York onion growers and could be utilized as procedures to reduce and hopefully eliminate the occurrence of Botrytis neck rot of onion bulbs in storage

Detection of Swede Midge in Western New York Crucifer Fields

The swede midge (Contarinia nasturtii) is a tiny insect whose larvae feed on and destroy the growing tips of cruciferous plants such as broccoli, cauliflower, and cabbage. The pest was not known in North America until it was identified in Ontario, Canada in 2000. A 2002 survey conducted by the Canadian Food Inspection Agency (CFIA), confirmed the presence of swede midge in eight Ontario counties, where it has caused serious losses in crop yield and marketability. Neighboring New York State leads the United States in cabbage production with a crop valued at $87 million per year that could be at risk should swede midge infestation occur. There was a need to educate the NY agricultural industry about this potential pest and to determine its presence in NYS

Organic Management of Swede Midge

NYS IPM Type: Vegetables IPM Fact SheetSwede midge (Contarinia nasturtii) is a small (1/16” long) invasive fly that is a serious pest of Brassica (cruciferous) vegetable crops, including broccoli, cabbage, and kale. The insect was named for one of its hosts in Europe, the “swede,” a type of forage turnip. Management of swede midge is particularly challenging because of its small size, hidden feeding behavior, low damage threshold, and life cycle consisting of multiple overlapping generations during the growing season. Small-scale organic growers with insufficient space for crop rotation to break the swede midge life cycle are especially at risk for economic losses from this pest