Abnormal Weather, Temperatures, and Pests

A Year of Unusual Weather Affects Vegetable Crops

By Mikenzi Meyers, Associate Editor

A year filled with abnormal weather is starting to show its effects on vegetable crops. Tom Turini of the University of California Cooperative Extension Fresno County, who is a plant commodity specialist, shared some of the early seasonal problems he has witnessed.

“We had unusual weather this year—a very cool, late spring—and with the rains we’ve had, we expected to see some issues that are unusual. We just didn’t see the incidence of those problems that we would have expected,” Turini said.

Turini added that levels of beet curly top are relatively low and tomato spotted wilt is densely populated in some areas. He also noted that the early appearance of the consperse stink bug seems to be having a measurable impact on crops, specifically on the west side of Fresno County.

Tomato Spotted Wilt Virus Fights Back

New Strain Creates Challenges

By Mikenzi Meyers, Associate Editor

A new strain of the Tomato Spotted Wilt Virus has created a challenge among vegetable growers, making integrated pest management, or IPM, increasingly critical. Bob Gilbertson, plant pathologist at UC Davis, has insight and advice as to how farmers should tackle this new strain.

“The first thing is to know what’s out in your field. And there’s a good diagnostic test for curly top, spotted wilt, alfalfa mosaic, and other viruses,” Gilbertson said.

Bob Gilbertson

After the virus is confirmed, he encourages growers to explore their options of treatment. Prior to the new spotted wilt virus strain, growers could turn to the SW-5 resistance gene to cure their field. Unfortunately, Gilbertson explained, the new strain actually breaks that resistance, which is where IPM becomes even more important.

In the future, Gilbertson hopes to find additional resistance genes to break the new strain. Until that time comes, he wants to use good IPM to manage it.

Gilbertson further added, “Increased sanitation, removing overwintering hosts, weeds, and bridge crops like lettuce, and then timing the applications of thrips management better, to slow down the appearance of adult thrips that carry the virus,” are all examples of good IPM.

Spotted Wilt Virus Light This Season on Tomatoes

Thrips Widespread But Yields are High

By Patrick Cavanaugh, Editor

Spotted wilt virus on tomatoes was a big concern at the beginning of the season. California Ag Today spoke with Tom Turini, vegetable crops farm advisor for the University of California Cooperative Extension in Fresno County, about the topic. We caught up with him on the west side of Fresno County. He said despite the potential virus pressure, tomato yields have been very high this year.

“Thrips are the vector of tomato spotted wilt, and while the thrip distribution is much wider than it was last year, it doesn’t look like we’re seeing the level of economic damage,” Turini said.

Tom Turini

“We had had concerns initially about problems, and of course that could get worse as we get later in the season, but so far our yields have been very, very high,” Turini said.

He explained that the strong yields is in part due to the mild temperatures during the spring, so there was good early fruit set. “Even that, I would expect that now with these higher temperatures over the last six weeks, we’re going to start seeing the effects of the yield-robbing virus with a later harvest, he said.

Last year, the concern was with fresh market tomatoes.

“We had concerns late last year in the fresh market, but this year it’s at moderate levels of economic impact. “It doesn’t mean it couldn’t happen in the future, but at this point, it looks like we were spared, at least for the early season crop.

Spotted Wilt Virus Impacting Tomatoes Again

Virus has Gotten Past Resistant Gene

By Patrick Cavanaugh, Editor

Tomato spotted wilt virus is becoming big in the central San Joaquin Valley, according to Tom Turini, University of California Cooperative Extension Farm Advisor in Fresno County for vegetable crops. The virus had earlier been spotted in lettuce, and this has caused some concern in this season’s tomato crop.

Tom Turini

“We had some concerns early in the season that we might be looking at a year where it’ll become a challenge, because we were finding it in lettuce back in February and March in the Huron area,” Turini said. “And then we notice that tomatoes were showing the virus symptoms. We had been managing tomato spotted wilt in processing and fresh market tomatoes largely with a resistance gene, and it seemed that the resistance was breaking.”

The virus is spread by thrips, and the gene in the tomato was the biggest deterrent in combating thrips.

“We were also talking about an IPM program, but the industry was leaning on this gene. This gene became a big part of their spotted wilt prevention program,” Turini said. “While sanitation of weeds was practiced, and there was some thrips management, it was really dependent upon this single gene resistance in the tomatoes, and as of 2016, we saw evidence that that gene was no longer performing.”

Because the virus can wipe out entire tomato fields, researchers are scrambling to find a new way to deter the thrip spreading the virus on tomatoes.

ALERT: Immediate Action Needed for Thrips/TSWR

Source: Neil McRoberts

For those who have water and tomatoes:

 

Thrips numbers have increased rapidly in the southern arm of the Central Valley and Tomato spotted wilt virus (TSWV) has been reported in all of the areas we monitor,” according to Neil McRoberts, Assistant Professor, Plant Pathology Department, UC Davis.

There are numerous reports of TSWV symptoms in crops from Stanislaus County down to Fresno and Kings County particularly around the Huron area.

 

The current risk in Fresno County is high and we are recommending that growers who plan to use an insecticide program against thrips/TSWV take immediate action. The current mini heat wave will accelerate thrips development slightly and further bump up thrips numbers.

If you are planning to use an insecticide program against thrips/TSWV this season, you should target the next generation of thrips (generation 3).  If it is not possible to arrange for treatment in time to catch generation 3, target generation 4. Delaying treatment until later in the season will be much less effective at preventing damage from TSWV.  Coordinated spraying across large areas has an additional effect on thrips populations because it makes it difficult for them to avoid treatment by migrating.

Generation 3 adults are projected to peak on May 17th.  Sprays applied in the 14-day period before this peak date will check generation 3 and delay further population build-up and TSWV spread.  This means you need to take immediate action.

Generation 4 adults are projected to peak on June 11th.  Sprays applied in the 14-day period before this peak date will check generation 4 and delay further population build up and TSWV spread.  Treatment in the 14 days immediately following the generation 3 peak date will also be effective.

 

The current risk in the Merced area is high and we are recommending that growers who plan to use an insecticide program against thrips/TSWV take immediate action. The current mini heat wave will accelerate thrips development slightly and further bump up thrips numbers.

Generation 3 adults are projected to peak on May 22nd.  Sprays applied in the 14-day period before this peak date will check generation 3 and delay further population build-up and TSWV spread.

Generation 4 adults are projected to peak on June 16th.  Sprays applied in the 14-day period before this peak date will check generation 4 and delay further population build up and TSWV spread.  Treatment in the 14 days immediately following the generation 3 peak date will also be effective.

 

The current risk in eastern San Joaquin County is lower than in other southern Counties, but we think a precautionary approach is best. The current mini heat wave will accelerate thrips development slightly and further bump up thrips numbers.

If you are planning to use an insecticide program against thrips/TSWV this season, you should target the next generation of thrips (generation 3).  If it is not possible to arrange for treatment in time to catch generation 3, target generation 4. Delaying treatment until later in the season will be much less effective at preventing damage from TSWV.  Coordinated spraying across large areas has an additional effect on thrips populations because it makes it difficult for them to avoid treatment by migrating.

Generation 3 adults are projected to peak on May 28th.  Sprays applied in the 14-day period before this peak date will check generation 3 and delay further population build-up and TSWV spread.

Generation 4 adults are projected to peak on June 22nd.  Sprays applied in the 14-day period before this peak date will check generation 4 and delay further population build up and TSWV spread.

 

The current risk in Kings County is high and we are recommending that growers who plan to use an insecticide program against thrips/TSWV take immediate action. The current mini heat wave will accelerate thrips development slightly and further bump up thrips numbers.

If you are planning to use an insecticide program against thrips/TSWV this season, you should target the next generation of thrips (generation 3).  If it is not possible to arrange for treatment in time to catch generation 3, target generation 4. Delaying treatment until later in the season will be much less effective at preventing damage from TSWV.  Coordinated spraying across large areas has an additional effect on thrips populations because it makes it difficult for them to avoid treatment by migrating.

Generation 3 adults are projected to peak on May 22nd.  Sprays applied in the 14-day period before this peak date will check generation 3 and delay further population build-up and TSWV spread.  This means you need to take immediate action.

Generation 4 adults are projected to peak on June 14th.  Sprays applied in the 14-day period before this peak date will check generation 4 and delay further population build up and TSWV spread.  Treatment in the 14 days immediately following the generation 3 peak date will also be effective.

 

The current risk in western San Joaquin County is lower than in other southern counties, but we think a precautionary approach is best. The current mini heat wave will accelerate thrips development slightly and further bump up thrips numbers.

If you are planning to use an insecticide program against thrips/TSWV this season, you should target the next generation of thrips (generation 3).  If it is not possible to arrange for treatment in time to catch generation 3, target generation 4.

Delaying treatment until later in the season will be much less effective at preventing damage from TSWV.  Coordinated spraying across large areas has an additional effect on thrips populations because it makes it difficult for them to avoid treatment by migrating.

Generation 3 adults are projected to peak on May 28th.  Sprays applied in the 14-day period before this peak date will check generation 3 and delay further population build-up and TSWV spread.

Generation 4 adults are projected to peak on June 22nd.  Sprays applied in the 14-day period before this peak date will check generation 4 and delay further population build up and TSWV spread.

 

The web resource for integrated management of Western Flower Thrips and Tomato Spotted Wilt Virus in the California Central Valley contains two tools to help in disease risk management:  

A Field Risk Index tool uses simple information about field locations, land use, and agronomy to calculate a risk category for tomato crops.  This tool can be used before planting or early in the season to get a heads up about the general risk to a crop from TSWV.

A thrips population projection model, driven by degree-day accumulation at several Central Valley locations, aids in projecting when thrips generations are hatching, developing, and adult numbers are peaking.  This information is used to issue regular updates and provide broad guidelines for timing insecticide sprays to keep thrips numbers low enough to prevent TSWV from spreading.

The research behind these tools was supported by the California Tomato Research Institute (CTRI)

The model was developed in Collaboration with Dr. Len Coop of Oregon State University’s Integrated Plant Protection Center (IPPC).  The IPPC developed and hosts the USPEST web service which is a multi pest multi model tool that provides information on pest development and disease risk for the Contiguous 48 US states using a network of weather stations.