I’m dealing with a major, out-of-control Harlequin bug infestation. A lot of advice I have seen recommends planting radishes to discourage them. This is blatantly false. I have observed Harlequin bugs attacking radishes of at least two varieties; Icicle and Red Cherry. The flea beetles took out the leaves and the bugs ate the sap out of the main stems. Attacks are conducted on the stems of plants. You may not see leaf damage, just a slight white discoloration on a stem. Very bushy plants give them a lot of places to hide. The orange and black bugs are colorful and very easy to spot.
With the radishes almost dead, the sunflowers have proven a major food source. 4′-5′ tall sunflowers are being leveled from the top down.
I tried old bottles of Neem oil and Garlic oil to no affect other than giving the little critters a bath. Another suggestion is dishwasher soap, which I haven’t tried.
One site mentioned the only natural predator was a praying mantis. It would have to be huge, like 3″-6″, because these aren’t tiny like flea beetles or aphids.
Normally, I would wait for a predator to appear and just damp down, but the situation is so extreme I tempted to use Sevin or something else to outright kill them. After the sunflowers, the only remaining meals are vegetables and Zinnias.