- Author: Neil McRoberts
General Situation Maximum temperatures over the coming week are forecast to be in the low to mid 90's F, which is ideal for thrips development. Over the last seven to ten days TSWV has started to appear in tomato fields in Yolo, Colusa and eastern Solano counties. In most cases disease incidence is still low (i.e. mostly 1% or less) but with increasing thrips activity there is potential for rapid increase in TSWV.
There are many late-planted crops in this region which are yet to set fruit or are in the early stages of fruit set. These crops are at greatest risk from TSWV attack and should be treated as soon as possible to limit new infections and spread from existing infections.
From now, through to the end of the cropping season, thrips generation peaks will be three to four weeks apart. Crops which do not carry the SW5 gene for TSWV resistance should be protected until fruit set is complete, bearing in mind that a new wave of thrips adults which can spread the virus will build up and decline roughly on a three to four week cycle.
Generation 3 was projected to peak on May 25 and will have mostly produced eggs and a new generation of larvae. Immediate spraying will reduce the number of these juveniles and reduce the numbers of adults in Generation 4.
Generation 4 is projected to peak on June 19th. Early adults from this generation may already be appearing. Spraying between now and June 19th will knock down the number of adults which are able to breed and lay the eggs which will give rise to generation 5. Because there is some TSWV present in the region generations 4 and 5 adults may well contain infected adult thrips that will spread the virus. Concerted effort to reduce these generations will limit the effects of disease on late planted crops.
Generation 5 is projected to peak on July 12th. This may be the last generation of thrips for 2014 that can cause serious damage to processing tomato because most crops should be past the very sensitive stage by that time. Particularly on late planted and late developing crops, consider maintaining an active control program for thrips through to mid July.