Here's what it can do:
There is no avoiding the cucumber beetle. It overwinters in the soil, it has a broad travel range, and it affects more than just cucumbers (add squash, melons, pumpkins and gourds to the list).
So is there any good news? First, if you can get your cuke/squash/melon/pumpkin/gourd plant to a healthy size, then it can withstand having up to 50% of its leaves demolished by this beetle before the plant will call it a day. Second, there are organic ways of handling the problem.
First, try row covers. Row covers are made of special fabric which allows in sun and rain but keeps out pests. Using row covers for several weeks will give your plants time to grow and strengthen. Once the cuke starts to flower, however, you need to remove the row cover so the plant can get pollinated.
The row cover below is suspended over the plants on top of thin metal hoops. You can also drape row covers gently over your plants without hoops, securing the edges to the ground with rocks or garden staples.
Second, mulching (using an organic material as a blanket on the soil) can deter cucumber beetles from laying their eggs at the stems of your cukes. The baby beetles that come from these eggs cause the damage shown in the middle damage picture -- eating the plant roots.
Third, delay planting the cuke family. Cucumber beetles typically emerge in late May, which is usually just after we've planted our cuke family veg. Delaying planting can allow your veg to miss the first, and heaviest, wave of beetles. The problem here, though, is that you may not have enough time to get a good crop by the end of the season -- check your cuke seeds and choose a quick harvest time.
Fourth, kaolin clay is both organic and a protective film against cucumber beetles. Mixed with water, kaolin clay forms a sticky residue on the leaves, and apparently this causes "excessive grooming" for the beetles, which then have little time to chew up your plants. Kaolin clay washes off after a heavy rain, so it needs to be reapplied both every 2 weeks and/or after a heavy rain. At harvest time, kaolin clay will wash off with a little effort and is not apparently toxic for people.
Fifth, plant radishes and onions in and around your cuke. Radishes germinate really quickly, and they repel cucumber beetles, so even if you don't like to eat radishes, try tossing a bunch of seeds around your cuke (and other affected veg) plants. Onions seem to repel most insects, so it wouldn't hurt to throw them in the mix.
Sixth, sticky traps of yellow tape are a pretty effective control. You can purchase these at a nursery or make your own with yellow plastic cups and special glue for this purpose ("Stickum" or "Tangle-Trap").
Seventh, a mix of neem oil and karanja oil (both organic) have been shown to be effective sprays against cucumber beetles. I haven't found a source of this mix, though.
Eighth, pyrethrum is an extract from chrysanthemums, and it is toxic to cucumber beetles. There are two problems with it, though -- it's toxic to just about every bug as well (including beneficial insects), and it's easier to find the longer-lasting synthetic form (pyrethin) than the organic form (pyrethrum). The synthetic form is not allowed in our garden.
Remember: this is an organic garden. We're not about completely removing an entire family of insects -- we're about keeping the numbers to a controllable size and limiting the damage. It turns out that sometimes we beat the pest, sometimes the pest beats us. If you find yourself struggling against this formidable foe, maybe rethink what you want to grow in your plot, or ditch the infected plants (in your home trash, not in the compost bin) and start afresh. Seeds for these affected plants aren't expensive, and new seedlings won't set you back financially too much either.
Good luck! Please share with the rest of us if you have positive results with any of the controls mentioned above -- or other ideas!
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