Non- Impatiens Necrotic Spot Virus (INSV) Plants for Habitat Plantings

Richard Smith¹, Daniel Hasegawa², Kirsten Pearsons¹ and Yu-Chen Wang¹

1 - UCCE Monterey County and 2 - USDA ARS, Salinas

Growers plant habitat plantings to provide various benefits on the farm. Insectaries and hedge rows provide a food source and habitat for beneficial insects that can prey upon insect pests of crops. Plantings that occur on slopes and berms can also help stabilize the soil and compete with weeds. Additionally, cover crops provide numerous benefits to the soil and help cycle nutrients, but also provide habitat for beneficial insects.

However, given the wide host range of impatiens necrotic spot virus (INSV), it is critical to avoid planting species of habitat plants that serve as a host for INSV or the thrips that spread this virus. Over the past three years, Smith and Hasegawa have tested numerous plant species to address whether they can serve as a host for INSV. Table 1 shows results of a survey of plants in the Salinas Valley near areas affected by INSV. The greater the number of samples with a negative test provides greater confidence that that plant is not a host. Not all potential habitat plants have been tested to date and more sampling of other species needs to be carried out. However, given our current understanding, the plants shown in Table 1 would be the best candidate species to use as habitat plantings to avoid introducing a known host for INSV. Additional thrips transmission experiments to each of the described plant species will also help resolve their status as hosts for INSV.

Table 1. Recommended non-hosts species of INSV for use as habitat plantings on vegetable farms.

1 - The mustards used for cover crops (Brassica juncea and Sinapis alba) were not tested in the survey. The related weedy mustard species (B. rapa and B. nigra) both tested negative for INSV; however, Short pod mustard (Hirshfeldia incana) had 4% infected plants. Clearly, evaluations of cover crop mustards as hosts for INSV needs to be carried out to clarify their status

2 - There are numerous other species used in hedgerow plantings, but they have not been tested as hosts of INSV at this time.