Question. I have a family farm in central Virginia that has a major pest problem. For years, we have grown mostly potatoes for our family. However, we lose a large portion of the crop to the Colorado Potato Beetle. For years we have used liquid and powdered Sevin with 'ok' results. But I would now like to find a more healthy and natural way to fight the bugs. Can you offer any advice on what types of beneficial insects to use and where to buy them? Or is there a chemical that is safe to use? We plant about 15 acres with potatoes, tomatoes, beans, apples, pears, squash, cucumbers, and peppers; and most things do well even though we can't care for them every day as we live over two hours away in Maryland. But the potatoes get torn to shreds by those beetles. Any information would be helpful. Thank you!
- ---Rick in Louisa, Virginia
As you note in your email, the incredibly toxic and dangerous pesticide Sevin is only 'OK' at controlling the pest, and you are wise to move away from it. What's the point of growing food for your children on poisoned soil?
Now if you looked through our A to Z archives, you saw Colorado potato beetles listed as prime candidates for control by toads—so installing a few ponds and big shady areas near your potato plantings would be a good start (and toads eat a wide variety of other farm and garden pests as well). I'd put some birdbaths right in the middle of the potato patches as well, to make a nice destination for potentially hungry avian avengers.
Although I generally don't recommend tilling (because of the weed problems it can create), deep cultivation in the fall and spring is a good idea until you get the problem under control, as the last generation of adults overwinters in the soil near where the previous season's potatoes grew. Unfortunately, they go pretty deep, so you have to till down low. Crop rotation would also be a really good idea—the adults don't have a lot of energy when they emerge from the soil, so make it a long walk for them to get to this year's plants.
And if you do move your potatoes to another location (always a good idea, even without pest issues), consider surrounding them with a trench lined with plastic—this old-fashioned beetle trap can be very effective.
Because potatoes don't need pollination, row covers can provide excellent protection. These thin spun polyester blankets are a staple of organic lettuce and spinach growing—allowing light, air and rain through, but no insects; and pests can't eat plants they can't reach. Good quality row covers will last for years, and they'll improve the quality of your spuds and give you those super-tasty young 'new potatoes' much earlier in the season, thanks to the little bit of extra heat they give the plants.
Another great way to deter these (and many other) pests indirectly is with a professionally made clay spray—the biggest brand name is "Surround". A godsend for tree fruit growers, the micronized, sprayable clay is 100% natural and doesn't interfere with photosynthesis, but provides a surprisingly effective barrier to pests and disease. And it's specifically recommended for Colorado beetle control.
…As are the beneficial insects you ask about. As any spud grower can tell you, the nastiest part of this pest is its extremely grotesque immature stage—a squishy, sticky, almost formless little leaf muncher that reminds me of Slimer in the Ghostbusters films. Ah, but this soft-bodied stage is much more vulnerable to attack than the armored, somewhat ladybug-like adult. Lots of beneficial insects like to eat or parasitize such soft bodied prey, including real ladybugs, lacewings, and those amazing little mini-wasps. All are available commercially, and you can also attract local versions and get them all to breed and be happy by planting lots of small herbs around your potatoes and allowing them to flower (to provide pollen and nectar) and by filling dishes with pebbles and water (to provide safe areas for them to perch and drink without risk of drowning). Ground beetles also chow down on potato plant pests.
There IS a specific organic spray-on control for Colorado potato beetles: a version of Bt known as Bt San Diego (or Bt tenebrionis) that affects ONLY the juvenile form of the beetle. It works very well on these ugly babies, but it can be hard to find a source of this highly specialized pesticide. Note: This is not the form of Bt that controls caterpillars; all Bts are specific, and the caterpillar kind (known as Bt kurstaki; it's the original) will not harm beetle grubs (although it's an excellent caterpillar control).
Probably the best choice for an all-around organic spray-on bug killer would be one of the spinosad products, which are available under a wide variety of brand names. The effects are concentrated on pests that eat the sprayed leaves, so avoid spraying it directly on any beneficals and it should have little to no effect on your good bugs.