Flea Beetle Controls for Organic Gardeners

, written by us flag

Flea beetle damage on arugula leaves

It happens every year. Your beautiful spring greens and radishes are coming along nicely, and then little round holes start appearing in the leaves. The most likely culprits are tiny flea beetles the size of a pinhead that jump away and hide at the slightest disturbance. Holes made by slugs are larger, with smooth edges, while those caused by diseases feature discolored patches or contrasting margins. Flea beetle holes are round, resembling tiny pits.

“Eggplant
Flea beetles are tiny and hard to identify

Spring Flea Beetles

Flea beetles are so small that identifying them is tricky, though you can certainly catch a few with a yellow or white sticky trap and look at them with a magnifying glass. Of the springtime flea beetles that dine on garden crops, the most common species are crucifer flea beetles (Phyllotreta cruciferae), striped flea beetles (P. striolata), or the western black flea beetle (P. pusilla) in Western US.

These crucifer flea beetles are among the first garden pests to appear in spring, with young seedlings of arugula, bok choy, Chinese cabbage, mustard, radishes and turnips at high risk for damage. Crucifer flea beetles prefer hairy or glossy leaves from plants in the mustard family, though they also can damage young broccoli or cabbage plants. A few flea beetles on fast-growing plants can be ignored, but unprotected seedlings can be so heavily damaged that the leaves appear to have been scorched.

Flea beetles overwinter as adults, which emerge in early spring and lay eggs at the base of host plants, including wild mustard. By early May, garden plants are being threatened by overwintered flea beetles and a new generation, too.

“Crucifer
Crucifer flea beetles reach peak populations in late spring

Quite a bit of research has been done in search of reliable organic controls for crucifer flea beetles. Row covers are the best defense, though a few may emerge from the soil under the tightest covers. Do not waste your time applying neem, pyrethrum, or using a vacuum, which don’t work for this pest. Row covers are the best control, followed by the biopesticide spinosad (available in organic formulations) or fungal agents containing Beauveria bassiana and Metarhizium brunneum, which cause flea beetles to dry out and die.

Ready for some good news? Crucifer flea beetle populations fall off in midsummer, with most of them resting in their winter hideouts by September. So, the same leafy greens that are riddled with flea beetle holes in spring may be clean as a whistle when grown as an autumn crop.

“Flea
Vigorous potato growth outpaces light damage done by potato flea beetles

Summer Flea Beetles

In American gardens, crucifer flea beetles are replaced in summer by species that feed on solanaceous crops, including potatoes, eggplant, tomatoes and tobacco. Feeding by the potato flea beetle (Epitrix cucumeris) results in potato or tomato leaves that look like they have been shot through with tiny holes amidst numerous smaller brown pinpricks.

Potato flea beetles have numerous natural enemies and seldom reach damaging numbers in a diversified organic garden. Ground beetles consume the tiny larvae, and spiders harvest many adults. Yet unexpected population spikes can occur, with the organic control method of choice being an organic spinosad spray.

“Row
Lightweight row covers protect plants from most eggplant flea beetles, which will appear quickly after the covers are removed

Eggplant flea beetles (Epitrix fuscula and E. hirtipennis) are present in most American gardens, ready to descend on eggplant seedlings within days after they are set out. To sidestep trouble, I like to grow eggplant seedlings in containers on my deck for as long as possible, or you could use a high outdoor table; eggplant flea beetles jump fast, but not very high. I install wedding net (tulle) row covers the day the plants go into the ground, which buys them more trouble-free growing time. The plants are so big and healthy by the time the covers are removed to admit pollinators that they can tolerate light flea beetle feeding.

In many cases flea beetle damage is cosmetic. Simply cooking greens with a few holes in them, like the arugula at the top of the page, makes the blemishes disappear. With big, robust potato and tomato plants, flea beetles seldom come close to damaging 30 percent of the plants’ leaf cover, the damage level needed to reduce yields.

Bugs, Beneficial Insects and Plant Diseases

< All Guides

Garden Planning Apps

If you need help designing your vegetable garden, try our Vegetable Garden Planner.
Garden Planning Apps and Software

Vegetable Garden Pest Warnings

Want to Receive Alerts When Pests are Heading Your Way?

If you've seen any pests or beneficial insects in your garden in the past few days please report them to The Big Bug Hunt and help create a warning system to alert you when bugs are heading your way.

Show Comments



Comments

 
"I would love to know where to get a lightweight row cover. "
Nicole on Friday 15 May 2020

Add a Comment

Add your own thoughts on the subject of this article:
(If you have difficulty using this form, please use our Contact Form to send us your comment, along with the title of this article.)

 
   
(We won't display this on the website or use it for marketing)



Captcha


(Please enter the code above to help prevent spam on this article)



By clicking 'Add Comment' you agree to our Terms and Conditions