Evaluation of mustard biofumigation for management of stem nematode (Ditylenchus dipsaci) and clover root curculio (Sitona hispidulus) in alfalfa

Alfalfa stem nematode (ASN) and clover root curculio (CRC) are soil-dwelling pests of alfalfa whose recent increase in abundance and damage has been contingently linked to the ban of carbofuran. Few alternative management options are available for these soil pests outside of multi-year, non-host crop rotation. Mustard biofumigation, that is soil incorporation of plants containing volatile glucosinolate compounds, has received increased implementation within other cropping systems to suppress soil-borne pests. However, it is unknown whether similar suppressive effects on ASN or CRC occur. This study examined the effects of mustard plant extracts on ASN mortality and leaf feeding damage by CRC. In the lab, ASN were immersed in three extracts of mustards containing increasing levels of glucosinolates, Centennial (low), Adante (moderate), and Caliente 199 (high) varieties, as well as non-biofumigant controls of either oats, alfalfa, or water. ASN mortality and behavior was recorded. In microcosms, a single adult CRC was placed on alfalfa leaves while being exposed to extracts of Centennial, Caliente 199, or control treatments as previously described. CRC feeding over 4 days was recorded and analyzed using imaging software. ASN mortality was not seen with mustard extracts but exhibited variable mobility. Moreover, CRC showed decreased feeding in the presence of mustard extracts compared to alfalfa extracts. These data suggest that mustard biofumigants may play a role as an alternative management strategy against soil pests in alfalfa.