A recent report of viral disease on lettuce from our neighbor (Yuma, Arizona) caught our attention since this is highly relevant to our production system (please find information on the first link below). The name of the virus is “Impatient Necrotic Sport Virus” (INSV), which is a tospovirus, similar to the virus that attacks tomato to cause tomato spotted wilt virus symptoms. This virus (INSV) was first reported affecting lettuce crops in Salinas Valley of California in 2006. Subsequently, it was reported to cause crop loss in 2012 and 2015 in the same area. This virus is transmitted by western flower thrips (Frankliniella occidentalis), which is very common and abundant in the low desert region. Early symptoms of infection by INSV are brown to dark spots and dead (necrotic) areas on leaves, which is often mistaken as chemical burn as shown in the picture below on the left-hand side (Photo Credit: Steven T. Koike, UCANR). As the disease progress, multiple leaves could be affected and result in distorted, twisted and dwarf plants (picture on the right). Most of the lettuce types are susceptible to this virus. Several weed species also believed to be the hosts of this virus. Thrips, that also feed on the alternate host weeds can facilitate INSV transmission to lettuce and other crops.
The good news is that this virus has not been reported from Imperial Valley to our best knowledge. However, we must keep an eye on anything unusual, especially the symptoms shown in the pictures below. 
If you observe similar symptoms on your lettuce or related crops, please bring to our attention, contact us at (442) 265-7700 or bring the sample to our office, 1050 E Holton Road, Holtville, CA 92250.
For more information:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=7309
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=17351
-By Apurba Barman & Oli Bachie, UC Cooperative Extension
