Weed, Disease, and Nematode Management in Onions with Biofumigants and Metam Sodium

Abstract

Onions (Allium cepa) are a high-value crop in the Treasure Valley of eastern Oregon and western Idaho. To grow quality bulbs, growers use fumigants and pesticides to control weed, pathogen, and nematode pests. Metam sodium and other commonly used pesticides are considered effective in controlling onion pests but also pose a wide range of problematic issues related to the environment, human health, and economic profitability. Biofumigant crops ‘Idagold’ mustard (Sinapis alba) and ‘Colonel’ oil seed radish (Raphanus sativus) were evaluated as substitutes for commercial fumigants in controlling soil-borne pests. During some years of this study, there was limited control of a few weed species based on visual and biomass data for metam sodium and biofumigant treatments, but the weed control was not consistent or acceptable. The severity of pink root (Phoma terrestris), a major fungal onion root pathogen, was significantly lower with metam sodium in most comparisons with other treatments. Biofumigants showed limited effects on pink root severity and are not a viable option for pink root control. Nematode damage or populations were not high enough to determine if the biofumigant and metam sodium treatments influenced their control. In some years, biofumigants reduced onion yield. The influence of these biofumigants on onion pest control was limited and their use in onion production is not warranted without significant nutrient recycling or soil quality benefits.