The flea beetles were so small that it was hard to see them with the naked eye. Under a magnifying glass, they were easy to watch: shiny, elongated, black insects, marching around on the surface of the broccoli foliage, munching as they went. But no such proof was needed. The damage was unmistakable — leaves stippled with holes so numerous that some were more hole than leaf.
Touch a flea beetle with your finger and it will disappear like magic, launching itself into the air with its strong hind legs — the leap that gives it its name — only to return and continue the business at hand. This pest is mostly a spring visitor that emerges from its winter home in the soil to gorge, then returns to the soil to lay eggs. These hatch into soil-dwelling larvae, but it’s the adult beetle stage that gives gardeners fits. (The larvae might nibble on the plants’ roots, but only with a root crop, chiefly the potato, is this a problem.) An attack on young seedlings, however, can do them in, because they have little foliage to spare. Some recover, some don’t, and for our broccoli the future did not look bright.
There are many species of flea beetles, and most favor a particular vegetable or vegetable family. Among plants in the nightshade family (potatoes and their relatives), we’ve consistently had trouble with flea beetles on eggplants. Among the brassicas, arugula is the most susceptible. Broccoli had never been a major target before.
So we’re focusing on prevention. Apart from basic common-sense maneuvers such as good soil fertility, irrigation and crop rotation, there are strategies a gardener can try. A mulch that reduces access to the soil might help break the egg-laying cycle. Plant populations with umbel-shaped flowers, such as fennel and Queen Anne’s lace, will attract braconid wasps and syrphid flies, both of which parasitize flea beetles. Growing a trap crop of something the beetles prefer, such as the Chinese mustard Southern Giant, works for some people.
But we find that timing a planting can be the biggest help. The first generation of beetles, in spring, tends to be the most damaging. Fall plantings of arugula are beetle-free. It also helps to sow arugula in a greenhouse, where the beetles seldom go.
With the other brassicas, and with eggplants, we grow them from transplants, whose larger size gives them a better chance of outgrowing an attack. We’re hoping that a second, slightly later planting will do the trick for our broccoli. As a precaution, we’ve set out the transplants under floating row covers, to screen out the pest altogether. This must be done immediately after planting, with the sides well weighted down to prevent beetle entry, and in a spot where that plant family has not previously grown.
As for the first planting, things are still hopping in that row, but a number of plants are showing healthy new green growth, and we’re rooting for that, as summer sets in.
Damrosch’s latest book is “The Four Season Farm Gardener’s Cookbook.”
Roses that have flowered should be pruned to promote reblooming and general health. Use hand pruners to remove flower clusters back to just above a lower leaf, and take out suckers and wayward stems. Any leaves showing signs of blackspot also should be removed. Wear thorn-proof gloves and a long-sleeved shirt.
— Adrian Higgins