Controlling flea beetles in the fall garden (help wanted)

I didn’t get row cover on my beans in time this spring, and the flea beetles found me.

tired beans

Flea beetle is something of a catch-all term used to describe several species of beetles (not all of the same genera), all of which are tiny (1/16 to 1/10 of an inch long), that live in the soil and cause mayhem in North American gardens. They adore feeding on your vegetable plants, and can reduce a favorite crop to smithereens if not dealt with promptly. One treatment won’t suffice: They can produce four generations or so in a warm-climate growing season. Overwintering adults typically emerge when temperatures hit about 50 degrees (10 C). In recent years, it’s been 50 degrees at Christmas.

Here is my quandary: Their preferred cuisine is cruciferous, which happens to be what I need to get planted soon. Most winters are mild enough here that greens and root crops may be harvested year-round if grown under horticultural fabric, but that means getting seedlings and transplants off to a good start, starting now.

Row covers can be effectively employed to exclude flea beetles from pristine soil, but (clearly) that’s not what I have. Installing row cover where an infestation has already occurred just traps the beetles inside, keeping them safe from predators while they devour your spinach. Row cover must be sealed tightly all the way around to be effective, by the way.

Trap crops come highly recommended. “Plant a crop of mustard greens!” the gardening literature exhorts. Alas, the trap crops are what I want to eat this winter. Kale, collards, mustard greens, broccolini, radishes, tatsoi, arugula. These are the seed packets sitting on my desk, awaiting my decision. I fear that planting a trap crop, even far away (relatively speaking) from the vegetable bed, will only encourage more of the little punks to move in and feast upon everything in sight.

The garden literature also recommends scouting newly planted beds and counting the beetles as they arrive. This presumes the gardener can count insects best differentiated from dirt with a hand lens before they jump to the safety of the earth. Anyone who has brushed against a plant infested with flea beetles has seen a spray of tiny bugs fleeing the scene of the crime. Who can possibly count them in situ? Even if the gardener manages to hunker silently down and get a view of the action, must she hold her breath to avoid disturbing them? What if she needs to sneeze? (It’s fall pollen season, you know.)

Flea Beetle Management for Canola, Rapeseed, and Mustard in the Canadian Northern Great Plains. Graphic by the Government of Saskatchewan.

I don’t want to spray if I can avoid it. I have been known to pull out the neem oil from time to time, but it’s only moderately effective against flea beetles.

What to do, then?

Possible solutions to flea beetle infestation

I’m tempted to try one or a combination of the following. Have you had success with any of these?

1. Diatomaceous earth. DE is a fine powder made of fossilized remains of diatoms, a kind of algae. When used as an insecticide, the powder absorbs components of the waxy coating of insects’ exoskeletons and causes them to dehydrate. It’s critical to obtain food-grade DE for this application to be effective.

2. Interplanting with garlic. Garlic is a moderately effective insect repellant when sprayed on plant surfaces. I have to plant my garlic somewhere; I suppose it may as well go between my rows of kale.

3. Parasitic nematodes. To read about parasitic nematodes is to discover another of Mother Nature’s horror shows. Employing them can be a bit tricky, because the gardener must get the correct kinds of nematodes (families Steinernematidae and Heterorhabditidae, and some species are picky about who they infect); time the application to coincide with a larval stage of the target species; and keep the soil moist, not too hot, and not too cold.  On the plus side, they don’t infect birds or mammals.

Parasitic nematodes. Photo by Penn State University Extension.

Given my warm climate, and extrapolating unscientifically from the graphic above, I guess I might be able to interrupt a larval cycle if I went out tomorrow and applied the nematodes…maybe?

Please send your advice, post-haste.

Dear Friend and Gardener: June 27, 2014

Dear Friend and Gardener,

It was another hot and dry week in the garden. I fed the beans with some nettle tea to perk them up. I’m starting to see flea beetle damage but the plants are big enough to be able to withstand it, I think. I have also sown a second crop elsewhere in the garden in case these do surrender their fight before long.

The tomatoes are showing signs of ripening, particularly the Principe Borgheses. I am so ready for them! I love dried tomatoes, particularly in the dead of winter, but have never tried drying any of my own. Another kitchen adventure awaits. The basil tastes splendid and there is plenty of it.

I noticed a little mildew on one of my honeyberries the other day. I shall spray it with a little milk spray if it gets truly bad, but I’m willing to let a lot go for the sake of avoiding toxic sprays. It doesn’t look terrible unless you get up close, and if you get that close, well, you shouldn’t be walking on my garden beds to begin with.

I transplanted a few Blue Hubbard squash seedlings sown from the packets I got at the seed library. I have heard that nasturtiums planted with squash will help deter squash bugs. Do you know if this is true?

Hope your garden is giving you joy and lots of tomatoes.

Best,

Amy

 

 

 

Wood sorrel: Turning my garden into public grazing lands?

Waiting for the school bus a couple of weeks ago, my neighbor’s son wandered over to a patch of weeds and plucked up a handful.

“What are you doing?” my daughter asked. “Are you eating weeds?!”

“It’s wood sorrel,” said the boy. “It’s good. It tastes sour, kind of lemony.”

Wood sorrel

Wood sorrel, Oxalis stricta

Wood sorrel is a member of the genus Oxalis. It is edible, if you go for that sort of thing. The leaves, seed pods, and flowers are all safe to eat raw or cooked. My neighbor’s son likes the seed pods especially: “We call them sour bananas.”

The plant is high in vitamin C. It also has diuretic properties and is high in potassium oxalate and oxalic acid. Oxalic acid is a compound also found in grapefruit, parsley, broccoli, spinach, and many other vegetables. While it’s unlikely that anyone would consume enough wood sorrel to suffer any toxic effects from the oxalic acid, people with kidney disorders, rheumatoid arthritis, and gout should avoid consuming oxalis until they consult with a medical professional.

Have I stumbled upon a new means of organic weed management? I envision herds of grazing children, replacing their favorite Sour Patch Kids with this weed that proliferates in my garden. More likely, I’ve found a new phenological cue: “When you see the children grazing, the sorrel is setting seed.” This reminds me that I had clearly better get to the weeding, unless I hope to find even more of the stuff in my garden beds next year.

By the way, my daughter knows not to eat anything in the garden without first checking with me. Encourage your kids to check with you before eating wild plants–even if their friends do it.

For more information:

Know thine enemy: Common weeds to know

Here’s a terrific chart of common weeds, by the Missouri Botanical Garden. Get to know the weeds that make their homes in your garden. The more you know about them, including their life cycles and reproductive habits, the more weapons you have with which to thwart them.

And please, avoid using chemical weed controls. They can be toxic to pollinators, including bees and butterflies, and can persist in the soil for very long periods of time. Mulch and other methods of weed control are more sustainable, and healthier for you, your family, your pets, and the environment over the long term.

 

Joe Pye weed, Eupatorium fistulosum

Know thine enemy: Oxalis sp., or wood sorrel

Continuing in my quest to learn my weeds, I am getting better acquainted with the most prolific of my weeds, Oxalis stricta, or wood sorrel.

Oxalis stricta

Copyright © 2005 by Robbin Moran, [ref. DOL15341].

This one is so common it’s almost difficult to see. It has a shallow taproot, but its extensive rhizome system also has lots of fibrous roots to support it. And those rhizomes go everywhere.

Unlike the other weeds I’ve examined to date, this one is a perennial. It also is apparently difficult to control with herbicides, not that I like to go that route. So the best approach to controlling it seems to be to dig it up, taproot, rhizomes, and all, and mulch heavily after digging to prevent seeds from germinating.

Growing up, we called almost anything with a three-part (tripartite–another Scrabble word) leaf a “clover.” But clover is a different plant from wood sorrel. How to tell the difference?

Oxalis leaves are heart or spade-shaped and partly folded. Their leaf margins are smooth. Clovers, on the other hand, have oval-shaped leaves with finely serrated margins and prominent veins. Oxalis species have five-petaled yellow flowers at maturity.

Red clover

Red clover (Trifolium pratense) by masaki ikeda, 22 May 2010, via Wikipedia and Creative Commons 3.0 http://creativecommons.org/licenses/by-sa/3.0/deed.en

Oxalis corniculata, or creeping woodsorrel, is a related perennial weed that grows low to the ground and roots where it establishes ground contact. Its leaves, shaped like other Oxalis species, fold downward in intense sunlight. When removing this weed, take care to dig the whole plant. If portions of the taproot or stolons are left in the ground, the plant can quickly reestablish.