A lot of growers already know this, but here we have a clear (no pun intended) demonstration that the thin colored plastics deployed as mulch in our strawberries are not as opaque as one would think. Today I discovered several plants and mosses green and bright under some colored plastic I had peeled back to do some work, meaning plenty of sunshine is getting through.
We've got some dataloggers buried at various depths underneath this, it will be an interesting comparison to the data being collected under the clear plastic laid out close by.
Some weeds and moss doing quite well under a plastic most people think of as opaque.
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.
During a tour yesterday with our new small fruit plant pathologist Akif Eskalen and Tom Gordon we happened into some blackberry canes hollowed out by sphecid wasps, most likely of the genus Pemphredon.
As one can see from the photo below, as is typical with these wasps the pith of the cane is hollowed out and the pupae lined up within. While this particular cane didn't seem to be dying back too much from this activity (since the vascular elements of the plant are in the surrounding stem and not the pith), it's still interesting to see this. As I've written before, these wasps are aphid feeders and their incidence in the field is sort of rare here (and hence cause for excitement with our group on their discovery!), I wouldn't consider doing control measures and indeed the grower echoed this.
Several Pemphredon pupae nestled with a blackberry cane. Note that the excavation begins at the point of pruning.
A closer look. Note that the frass from larval feeding seems to be sectioning each pupa off from the other.
I know I pull too much from the Wall Street Journal, but I just can't not share this beautifully phrased paragraph that distills current political streams and what they could mean for the continuing integration of markets and labor across international borders.
Think here about the expansion of export markets for California produce and our continuing need for people to do the work of agriculture, many of whom come from outside of the US.
"But the economic benefits of integration must be weighed against the political loss of sovereignty. You could almost certainly integrate the entire world economically and achieve massive economies of scale and integration. Efficiencies in product, service and labor markets would improve productivity and generate higher overall income levels. But most people in the world wouldn't tolerate the political implications, including free mass integration and steady erosion of cultural identities through universally applied regulations." - Gerard Baker, "The Great Brexit Breakdown", Wall Street Journal, Dec 8, 2018.
My take? If one views the current political state of many of the world's well developed and internationally integrated economies through the lens of the preceding paragraph, a lot of what is happening right now makes sense. With this in mind, the question which follows then would be are we at this time striking the political upper limit to the integration of markets and labor across international borders?
I had a pretty sharp eyed PCA stop by my office just this morning with a sizable sample of what turned out to be Lewis mite from a newly planted field of strawberries. To this savvy individual, something about the mites he was looking at didn't seem right, and sure enough inspection under the scope at our office proved him right - they were Lewis mites.
The key point here is that Lewis mite doesn't necessarily respond to the same control tactics that twospotted spider mite does, in particular Phytoseiulus persimilis doesn't like to eat it. Which means that treating every mite population that one sees in the field this winter as twospotted spider mite could be a painful mistake.
Up to date information on managing Lewis mite is right here, courtesy your friendly scientists at UC Cooperative Extension:
Lewis mite. Photo courtesy Anna Howell, UCCE