- Author: Richard Smith
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.
- Author: Alejandro Del Pozo-Valdivia
This will be a ZOOM Webinar
When? Thursday August 6th
At what time? From 10:00 –11:15 am
If interested in participating, please register at:
http://ucanr.edu/survey/survey.cfm?surveynumber=31781
We will send the ZOOM link 24 hours before the event
/span>- Author: Alejandro Del Pozo-Valdivia
Please, fill up the registration and survey form at:
- Author: Steven T. Koike
Beginning in early April, 2012, the UC Cooperative Extension diagnostic lab in Salinas began to receive lettuce samples exhibiting obvious symptoms of a virus problem. Samples continued to be submitted throughout the month. All samples tested positive for the thrips-vectored Impatiens necrotic spot virus (INSV). This virus first began to cause damage to California lettuce in 2006. Since that time, INSV has occurred to a greater or lesser degree every season. However, significant INSV outbreaks usually are found beginning in late May or early June. Seeing INSV on lettuce in April is therefore unusual and growers and pest control advisors should carefully monitor these situations.
INSV-infected plants have leaves with brown to dark brown spots and dead (necrotic) areas; this necrotic tissue can resemble burn damage caused by pesticide or fertilizer applications (see photos below). Affected leaves can be distorted and twisted. Extensive necrosis can cause much of the leaf to become brown, dry, and dead. Some leaf yellowing can also be observed. Yellowing and the brown spotting tend to be observed on the newer leaves near the center of the plant’s growing point. If plants are affected with INSV early in their development, growth may be stunted. All lettuce types are susceptible, and INSV has been confirmed on iceberg, butterhead, romaine, and leaf lettuces. INSV can infect many other crops and weed species; the virus is vectored by the Western flower thrips (Frankliniella occidentalis).
Growers, PCAs, and other field personnel should exercise caution in diagnosing INSV disease because the lettuce dieback viruses cause very similar symptoms (see table below). Lettuce dieback is caused by two pathogens: Lettuce necrotic stunt virus (LNSV) and Tomato bushy stunt virus (TBSV). Infected lettuce can be severely stunted, especially if infected early in plant development. The oldest, outer leaves can be severely yellowed. Brown, necrotic spots and lesions later develop in these outer leaves. The younger, inner leaves remain dark green in color, but can be rough and leathery. LNSV/TBSV infects only romaine, butterhead, and leaf lettuces; modern cultivars of iceberg lettuce are immune. The LNSV/TBSV virus complex is a soilborne problem and no vector (insect, nematode, fungus) is known to spread these viruses.
For help in diagnosing these and other plant problems, submit samples to the UC Cooperative Extension diagnostic lab in Salinas.
Photos: Impatiens necrotic spot virus (INSV) on lettuce.
- Author: Steven T. Koike
As the coastal California lettuce crop heads into the ending fall season and as the inland county region initiates its fall lettuce cycle, both crops are being affected by Tomato spotted wilt virus (TSWV). Diseased plants have leaves with irregularly shaped, brown to dark brown lesions and dead (necrotic) areas (Photo 1); this necrotic tissue can resemble burn damage caused by pesticide or fertilizer applications. Chlorosis (yellowing) can also be observed. Depending on the age of the plant when first infected, these necrotic and chlorotic symptoms can occur on both the older, outer foliage as well as the younger, inner leaves. If plants are affected with TSWV early in their development, growth may be severely stunted. The virus is vectored by thrips and in California is primarily spread by the western flower thrips (Frankliniella occidentalis) (Photo 2).
All lettuce types are susceptible, and TSWV has been identified in iceberg, butterhead, romaine, and leaf lettuces. TSWV has an extremely wide host range that includes over 500 crop and weed species. Vegetable crop hosts include basil, bean, celery, cucumber, eggplant, endive, escarole, fava bean, lettuce, pea, pepper, potato, radicchio, spinach, and tomato. This host range may explain, in part, why TSWV has been observed in a number of lettuce fields in the San Joaquin Valley. The relatively cool summer temperatures have resulted in delayed tomato harvests, causing an overlap of the summer tomato and fall lettuce crops. Thrips vectoring TSWV are therefore able to readily move from the late tomato plantings and into the lettuce fields. (For related information see research conducted by the Gilbertson team (UC Davis) and sponsored by the California Processing Tomato group.)
Growers and pest control advisors should exercise caution if attempting to identify TSWV in the field and without testing. In the coastal region, symptoms caused by the very closely related, thrips-vectored Impatiens necrotic spot virus (INSV) are identical to those caused by TSWV. Romaine and leaf lettuces are susceptible to the lettuce dieback virus complex (Lettuce necrotic stunt virus [LNSV] and Tomato bushy stunt virus [TBSV]) which is also common on the coast.
Photo 1: Tomato spotted wilt virus (TSWV) on lettuce.
Photo 2: Western flower thrips, vector of TSWV.