Managing the Most Significant Biotic Challenges for Organic Onion Production across the Great Lakes Region
Project Director
Brian A. Nault
Year Funded
2017
Award Number
2017-51300-26816
Funded Institution
Cornell University, New York State Agricultural Experiment Station
Grant Program
OREI (Organic Agriculture Research and Extension Initiative)
Project Overview
Onion thrips and tne viral diseases they carry threaten organic onion production in the Great Lakes region. Thrips feeding damage increases susceptibility to fungal and bacterial diseases, especially Stemphylium leaf blight (SLB), which has a wide host range including many crops and weeds. Both SLB and thrips have developed resistance to multiple conventional crop protection chemicals. This project sought to develop an IPM strategy for onions that integrates National Organic Program (NOP)-allowed crop protectants with genetic resistance.
Onion genetics modulate both quantity and quality (chemical composition) of cuticular waxes and susceptibility to thrips. “Semi-glossy” cultivars host fewer thrips and suffer less feeding damage than “waxy” cultivars. Some waxy cultivars and breeding lines carry genes for resistance to one or more onion diseases. Plant breeders are developing and refining F1 hybrids that combine resistance to thrips, Fusarium basal rot, and pink root with desirable market traits.
Of the eight NOP-allowed fungicides tested, none reduced SLB sufficiently to benefit yields. Spinosyn (Entrust) combined with an adjuvant of neem oil (Trilogy) or potassium salts of fatty acids (M-Pede) controlled thrips sufficiently to improve yields 10-26%, though M-Pede damaged foliage if applied during hot weather. Repeated use of spinosyn poses a risk of pest resistance. One formulation of azadirachtin (Neemix 4.5) with a terpene polymer adjuvant (NuFilm) was moderately effective, while an azadirachtin-pyrethrin product (Azera) and the biopesticide fungus Isaria fumosorosea (PFR-97) were ineffective. Early planting and early-maturing cultivars avoided seasonal peaks in thrips infestation, and onions grown in UV-reflective film mulch showed a trend toward lower thrips numbers and larger bulb size.
Farmer Takeaways
(1) Spinosyn (Entrust) with neem oil (Trilogy) adjuvant is the most effective NOP-allowed pesticide against thrips, but repeated use may lead to spinosyn resistance.
(2) To reduce spinosyn use, farmers can integrate cultural controls, and use azadirachtin (Neemix 4.5) with pinene oil (NuFilm) for lighter thrips infestations.
(3) Cultural controls include semi-glossy cultivars (less attractive to thrips) and early planting of early-maturing cultivars to avoid peak thrips levels during summer.
(4) The semi-glossy yellow onion hybrid ‘USDA Maia,’ thrives in muck soils and combines resistance to pink root and Fusarium basal rot, excellent storage, and mild pungency.
(5) Bacterial bulb rot is related to excessive rainfall during onion crop maturation and may also be promoted by heavy thrips infestations.
(6) Onion breeders are developing F1 hybrids combining resistance to pink root, Fusarium basal rot, and thrips.
Project Outputs
Iglesias, L., and B. Nault. 2020. Bioinsecticides and cultural controls for onion thrips in organic onions. VegEdge, 16(11): 5-7.
Lai, P.-C., and B. Nault. 2022. Are onion thrips allies of bulb-rot causing bacteria in organic onion production? Cornell Cooperative Extension, Cornell Vegetable Program. VegEdge 18(16): 9-10.
Hay, F. S., Heck, D. W., Sharma, S., Klein, A., Hoepting, C., and Pethybridge, S. J. 2022. Stemphylium leaf blight of onion. Plant Disease Lesson. The Plant Health Instructor 22.
Marzu, J. C., E. Straley, and M. J. Havey. 2019. Genetic analyses and mapping of pink-root resistance in onion. J. Amer. Soc. Hort. Sci. 143 (6).
Munaiz, E.D., R.L. Groves, and M.J. Havey. 2020. Epicuticular leaf waxes among onion accessions selected for reduced damage by onion thrips. J. Amer. Soc. Hort. Sci. 145:30-35.
Iglesias, L., Havey, M. J., and B. A. Nault. 2021. Management of onion thrips (Thrips tabaci) in organic onion production using multiple IPM tactics. Insects. 12:207.