Hi.

We've been a bit slow getting the thrips risk and TSWV updates up and running this year.  We hope you are all safe and well.  We also want to say thank you to everyone involved in food production and agriculture in general for keeping the food chain flowing during the COVID-19 epidemic.

Current outlook After a warm, dry winter we're expecting thrips pupal survival over the winter to have been high and the numbers to pick up quickly.  The recent late season cold/rain system that passed through over the weekend will have checked them somewhat.  Based on the Davis weather station, we're currently projecting generation 1 adults to peak in the middle of April, with generation 2 in the first week of May and generation 3 in the first week of June.

Generally, generation 1 doesn't present much of a risk for carrying TSWV into processing tomato.  In recent years, TSWV hasn't been present until generation 3 or 4, but we will gather up status report before our next update in case there's any virus out there early this year and action is needed on generation 2.

NOTE:  The dataset for the Five Points CIMIS station (which we've been using for several years) is currently corrupted so we've switched to Stratford CIMIS station in the meantime.

As ever, if you're seeing high thrips counts or obvious signs of TSWV we'd like to hear from you via your local UCCE adviser.  Best wishes for a good growing season and for as much normality as possible in these difficult times.

Weather outlook:  After further atypical cool, showery weather over the last week or so, the forecast for the next ten days shows a more settled period of dry weather with partial cloud cover and daytime highs increasing towards the mid 90'sF.  Thrips population development can be expected to be steady over this period.

Thrips population timings: In our last update on 4/16 we projected Generation 3 adults to peak on May 27th and Generation 4 to peak on June 21st.  The period of cool weather has slowed development somewhat, delaying the projected generation times.  The projected peak date for Generation 3 is now June 1st, with Generation 4 now projected to peak on June 24th.  There are reports of low TSWV incidence in the area.  We also detected SW-5 resistance-breaking strains of TSWV earlier in the season, but the overall risk level remains low to moderate at this time.  Depending on crop development stage we recommend targeting Generation 4 for any intended thrips treatments if they have not already been made. Later planted crops may still be at early, vulnerable growth stages as Generations 3 and 4 emerge; stay on top of the situation and check in with your UCCE adviser to find out if TSWV is being reported as the season progresses. 

Weather outlook  The next 10 days will see consistent warm, dry weather in the San Joaqin Valley. Highs in the upper 70's to upper 80's and overnight lows in the mid to low 50's will allow steady thrips development, and we should see numbers starting to build up.

Generation peak timings  since our last update a couple of weeks ago our predicted peak date for generation 3 has moved forward by one day to May 27th, and generation 4 has advanced by one day June 21st.  If you are concerned about TSWV risk these are the two generations where control will have the biggest impact.  Knocking thrips numbers down while the populations are still relatively small and while the crop is still small enough to allow good penetration of sprays is a good tactic.  Keeping thrips under control at this stage also allows the crop to grow past the really vulnerable stage before and during flowering before there is much TSWV around and helps to reduce the yield impact if the virus does show up.  The UC IPM guidelines for thrips control can be found by following this link.  Further advice on treatments is available from your local UCCE adviser.

Resistance-breaking TSWV Strains of TSWV that can break the SW5 virus resistance in both processing and fresh market tomatoes have been found in Fresno county for the last couple of years.  It would not be advisable to rely on this resistance to keep TSWV at bay, and a disease management plan should be followed to reduce the risk of yield loss.  Contact your local UCCE farm adviser for more information. 

General situation After a dry and warmer weekend, the weather will return to a slightly cooler, unsettled pattern next week, with temperatures in the mid-to-high 70's and slight chance of  rain showers on several days.  This pattern will prolong the slow start to the season, with thrips developing relatively slowly at the forecast temperatures.  We have projected thrips development out to the end of June, based on current conditions. This takes in the first four generations of thrips and covers the period we would typically think of as the most critical for controlling thrips numbers.  Because we are projecting ahead by two to three months, based on relatively cool early season conditions, we can expect the projected dates for generations to peak to vary by a few days as we settle in to the summer season.

Specific details Generation 2 adults probably peaked a few days ago but a few will still be emerging.  Since there are no significant sources of TSWV this early in the season, thrips are not a risk at the moment.  We are expecting to see Generation 3 adult numbers peak around May 30^th with Generation 4 peaking around June 22^nd.  Given the slow start to the season, at this stage we would expect Generation 4 to be the key generation to target to suppress TSWV until the pre-flowering high risk period is past.  We will be actively monitoring the TSWV situation and will be posting updates, especially if anything happens to change our current advice.