GSA’s INSV/PW Task Force, Impacts On Lettuce Supply

There has been recent attention on the limited supplies of lettuce and leafy greens. The supply issue has been largely attributed to crop damage associated with an aggressive pest and disease complex of INSV and soil-borne diseases.

What is INSV or thrips-vectored Impatiens Necrotic Spot Virus? Lettuce fields are infected by INSV via thrips migrating from infected host plants. Plants infected by INSV can have dark spotting and yellowing, which resembles the effects of sunburn on the leaves. Another plant disease, Pythium wilt (PW), often accompanies INSV infections and causes the plant to wilt or collapse making this truly a complicated pest/disease issue for farmers.

In 2022, disease pressure was exacerbated by unseasonably warm weather stretches which caused prolonged stress on the plant making the lettuce more susceptible to disease impacts.

But there is hope for solutions. Through the Grower Shipper Association’s (GSA) INSV/PW Task Force established in 2021, scientists, farm advisors and farmers are working jointly to learn more about this disease complex and determine preventative and curative control methods. And the results so far seem encouraging.

One of the best ways to control plant diseases is via varietal tolerance. Through the GSA Task Force, researchers are assessing disease resistance of lettuce and some initial findings were presented at an industry forum on November 3. Early data revealed that while Pythium Wilt was present in all 53 lettuce varieties studied in the trial, approximately 20% were asymptomatic with no discernable damages to the plant above the soil surface. And 7.5% of the varieties assessed were asymptomatic, showing no signs of discoloration or wilting. Researchers shared that when there is a co-infection, namely the plant is infected with both Pythium Wilt and INSV, the lettuce plant will almost always show symptoms.

However, the overall conclusion that some currently available varieties performed relatively well when judged for tolerance against wilting from Pythium Wilt and browning and yellowing from INSV suggests that when farmers are making planting selections (especially for late season romaine crops) there are better performing varieties for mitigating disease effects.

Another area of importance in combating INSV is thrips control through cultural practices. Farmers are encouraged to reduce weed pressure in around their farms since weeds are hosts and provide harborage for thrips. State and local agencies are also needed to lower thrips populations by controlling weeds along highways and roadways. And residents and business owners in our community can help reduce disease incidence too by controlling weeds in their yards and landscaping areas.

In addition to varietal assessment and identification of cultural prevention practices, the GSA Task Force is also examining treatment strategies and treatment efficacy trials and will continue to conduct grower education and outreach programs specific to these diseases.

We understand frustration concerning recent limitations on lettuce supplies originating from the Salinas region. However, GSA wants to reassure consumers that farmers are resilient and they have consistently found solutions to the production challenges Mother Nature often presents. While we have already seen progress, through the combined knowledge of farmers and scientists, we are optimistic that successful strategies will be found to combat this pest/disease complex to ensure lettuce supplies reach consumers.