A week ago I planted out a lot of young module-grown brassica plants in a new bed created out of long-standing meadow land. Three days later a large number of quite big black shiny flea beetles had landed on several of the weaker plants and were fast reducing them to lacy thinness. I tried a soapy spray and diatomaceous earth but to no avail. I read that talcum powder can deter flea beetle so I liberally dusted the plants with Johnson's Baby Powder. Having hopped away, the beetles regrouped within an hour or so of my treatments and moved on to slightly stronger plants. A day or so later I resorted to a pyrethrum based spray which advertised itself as killing beetles. The attack remains unabated and it look as though within a few days the whole planting of about 70 or so plants will have been finished off.
I've never encountered flea beetle on this scale before and wondered whether there's any explanation for this sudden onslaught and whether anyone else has had similar experience