The Garden Pests And Diseases In Wallflowers

What is causing these tiny, near-circular holes on the leaves of my rocket and radish plants? Something similar seems to have attacked aubretia, alyssum, wallflowers and nasturtiums, but all is sure these tiny beetles are flea beetles, a species of Phyllotreta. They measure in length and are most commonly very shiny and black, but occasionally have a bright-yellow stripe; or they can be yellowy brown or metallic blue, depending on the species. These beetles eat the tiny rounded holes in the upper surface of the leaf, and you may have noticed that sometimes they don't actually eat right the way through the leaf, but leave a brownish-white spot of dry leaf tissue. On older plants these pests may have little effect or just check the growth slightly, but they can sometimes kill seedlings, if they do a lot of damage. There are lots of different types of flea beetle and the damage is most commonly seen on brassicas, including those you described, but also Swedes and turnips. There is another type of flea beetle that will also attack the foliage of potatoes and the Chilean potato vine. Flea beetles will feed between the middle of spring and the end of summer, and in bad years the injury they cause can set plants back quite a bit.

Control is difficult, but you should do everything you can to encourage seedlings to grow strongly, so that they can compensate for any damage that occurs. This includes keeping plants well watered and only sowing seeds at a time when you think germination and early growth will be rapid and vigorous. You could also consider using pesticides such as Derris, Politest and Sybol. I have heard people suggest that you can trap flea beetles by disturbing the foliage and at the same time holding a batten of wood covered in non-setting glue just above the leaves. The idea is that the beetles jump in the air and get stuck to the adhesive surface. An interesting idea, but I suspect that it is rather too time-consuming and a bit too unreliable for me but that's up to you.The damage is typical of that caused by capsid bugs or plant bugs. The common species of both are in length when fully grown and they feed by sucking the plant's sap. As they do this they produce a toxin that kills off the plant cells in the area penetrated by the insects' mouth parts. This causes the brown spots to develop and the leaves or shoot tips.