Interesting case here of calyx browning caused by spider mites.  Most strawberry industry people normally will correctly associate calyx browning with a lack of water or plant physiological issues, but this case of calyx browning is clearly being caused by spider mites.

As one can see from the series of pictures below, brown and spotted patches are all associated with mites and webbing.

The grower reports that the rest of the plant is fine and very few leaves are affected anywhere.  It does beg the question why the mites would be specifically infesting the fruit calyces only, but control will be the same as for foliar infesting mites.