- Author: Neil McRoberts
The warm winter and spring weather means that Western Flower Thrips (WFT) degree-days are running about one whole generation time earlier than the 30 year average. The projection model for WFT running on the Five Points CIMIS weather station shows that adult numbers for generation 1 of 2015 probably peaked around March 14th. Extensive studies over the last five years in the Central Valley have shown that the level of TSWV is very low at this time of year, so even though thrips numbers are building, the immediate risk of widespread TSWV infection in spring lettuce is low.
Because the season is warmer than usual, WFT will have another generation peak before the end of the traditional spring lettuce period in April. The projected adult peak is around April 6th. The risk of TSWV transmission by this generation will be higher than for generation 1, but still relatively low, unless there is a localized source. If thrips numbers are high enough, treatment to prevent direct feeding damage might be justified.