Thrips on Strawberry Leaves
This piece was originally posted in late November, but see updated postscript concerning the identity of the pest at the bottom:
Already giving away the punchline in the title, but I was approached yesterday by a grower experiencing an unusual problem on his strawberries. All of this has been handled remotely, so on first glance I see drying out spots of various sizes and shapes on the leaves with dark spots in the middle of many of them (Picture 1 below). Problem tends to occur and be more severe on mature leaves. Pretty inconclusive, but the gut response would be a fungal disease with the dark spots being fruiting bodies of some sort.
However, on receipt of more pictures (Picture 2 below) this morning, lo and behold I was able to discern the culprit as thrips. Note the similar sized and shaped yellow objects gathered around one of the spots in this picture.
Haven't seen this problem before, but the situation in which it is happening is also unusual. Strawberry grown in substrate under a tunnel without weed mat and consequent weed growth underneath.
Directing the grower and his support staff to our recently updated UC IPM Guidelines for strawberry for counsel on how to manage this problem:
Updated postscript: A reader in Uruguay noted that he had this sort of damage on strawberries there caused not by our typical Western flowers thrips, but a species of Caliothrips. This for sure was intriguing, so I had a sample mailed to me by the grower and my colleague Steven Koike at Trical graciously agreed to do the identification.
Just got word back and based on the sample submitted to Steve, the thrips occurring in this field are Western flowers thrips. My take on the unusual nature of the damage is that the weeds below the growing area and the higher temperatures of the tunnels must have something to do with this.
Anyway, real group effort here to get the right answer and a workable solution to the grower. Thanks everybody!!
Brown, various shaped and sized spots on strawberry leaves. Note black spots towards the middle of many of them.
Note the yellow colored thrips (circled in red) gathered around one of the spots on the top center leaf. These are clearly the cause of the issue here.