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.

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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.

Know thine enemy: The weed battles begin

Last summer and fall, I endeavored to learn a bit about the weeds that persist in my garden, to better understand how to combat them effectively.

One of the worst offenders in my garden is hairy bittercress, or Cardamine hirsuta. It is a rapidly growing winter or summer annual, which begins its life innocently enough as a petite rosette of arugula-like leaves. Overnight, apparently, it sends up a flower stalk, pollinates itself, and sets tiny explosive seed capsules that spring open when they are touched, flinging seed (the average plant contains 600, by the way) for what feels like acres. If only I were so resilient.

On the way to the mailbox, I noticed a greenish mat in the midst of a stretch of mud. The knavish fellows are back, unthwarted by polar vortices, uncurbed dogs, and rapacious squirrels.

hairy bittercress cardamine hirsuta weed seedling

But this year, I come to the battle armed with a tiny bit of knowledge (yes, indeed, a dangerous thing!). I know not to turn my back on these wolves-in-sheep’s-clothing of the weed world, or they’ll have propagated themselves before I can say “Well, [redacted].” I’m heading out this minute to pull these impish devils (they come up quite easily). And I shall add a generous helping of mulch in case their evil little siblings are getting ideas.

Don’t be too tidy: Good garden practices to bring birds to your winter garden

Where I live, we haven’t yet been hit by snow or ice, so it’s time to focus on garden clean-up.

In addition to raking and shredding oak leaves, I’ve been cutting back dead stems and diseased leaves of perennials and picking out twigs that have fallen in the heavy rains. But I try to remember not to be too thorough. Leaving some plants with decorative seed heads or berries allows birds to find food easily in the winter. 

Berry cluster of Nandina domestica

Berry cluster of Nandina domestica

Like the rest of us, birds need some variety in their diets. While many of us enjoy setting out bird feeders in the winter, encouraging them to forage in our gardens is both healthy for them and good for our gardens. If birds become accustomed to finding food and shelter sources in your garden in the winter, you can be assured they will return in warmer seasons to help you control your insect populations.

Additional tips for encouraging birds to your winter garden:

  • If you have native perennial plants or grasses in your yard, don’t be too hasty to cut them back. Native plants provide especially good food sources for local bird populations.

    echinacea seed heads

    Seed heads of Echinacea purpurea

  • Leave a bit of leaf litter in your garden. Leaf litter attracts insects, another important food source for birds.
  • Provide fresh water: If you have a bird bath, keep it clean. Wash it weekly using mild soap, and rinse well.
  • Give them shelter: Any dead or pruned limbs may be stacked or piled in the garden to provide cover for birds in your garden. Establishing bird feeders near brush piles or dense evergreen shrubs like hollies, cedars, or most conifers, allows small birds to take shelter quickly if hawks or other predators make appearances.

O water, where art thou?

A brief tutorial on water gardening for the novice:

Do: Add plants to your water garden.

Don’t: Forget to prune them occasionally.

runaway pond plants

Do: Use bricks to support planted baskets.

Don’t: Forget to prune, such that the roots envelop the bricks and make the plants very hard to remove from the pond.

bricks rescued from water iris roots

Those brick fragments are enjoying their first taste of freedom after spending at least a year in captivity of vigorous iris roots.

Do: Plant a variety of species.

Don’t: (ahem.) Let them grow together. They’re really hard to separate. But if you forget,

Do: Keep a sturdy garden knife around. Or a chainsaw.

DSC_0003

Do: Add fish to the garden to control mosquito larvae.

Don’t: Ask to see what happened to the fish in this garden. Basically, the plant roots grew together, creating an impenetrable mat. The water above the mat evaporated in three weeks of dry fall weather, and he couldn’t break through to the shallow water beneath the plants.

He was worth every penny of the dime I paid for him, though. He lived for two, or maybe three years. He now sleeps with the anemones. I feel terrible.

Do: Try again.

Know thine enemy: Learning about weeds

I listen to Margaret Roach‘s excellent podcast, A Way to Garden, and read her website of the same name. This year Margaret has been seeking to identify the weeds in her garden, to better understand their life cycles and ultimately get the upper hand on them.

This is wise advice, and I am hoping to (gradually) acquire this knowledge of the plants in my own garden with which I wage perpetual battle. Today I am starting with an easy one: spotted spurge, known also as Euphorbia maculata or Chamaesyce maculata.

spotted spurge, photo courtesy wikipedia

Although it grows from a taproot, I have always found spotted spurge fairly easy to pull up with a hand rake. But maybe this is my problem: Perhaps my technique yields the topgrowth, but part of the taproot remains, leaving a source from which it can regrow. Or my problem could be that I have a lot of it and don’t get around to eradicating it, so it multiplies.

This is a summer annual weed, which means that if I can get to it early (and get that taproot!), before it sets seed, I should be able to get it under control. It emerges in mid-summer, and can flower within 3 to 4 weeks according to NC Turffiles, so that time before flowering is the critical window in which I need to act. I fear the ship may have sailed, but I may still be able to row after it. Summer lasts a long time where I live.

Also, like many Euphorbias, its stems contain a sap that can be irritating to sensitive skin. Must remember to get out the gloves.

If you have spotted spurge in your lawn, you can help control it by raising the cutting height of your lawn mower. Higher-standing grass cuts down on the amount of light reaching the weed seeds in the soil. As it happens, I don’t have a lawn to mow. But I do have plenty of spots that could use a good top-up with mulch, which is also an effective control.

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Camellia leaf gall treatment

Every year, my Camellia sasanquas get leaf gall.

camellia funk

This disease is caused by a fungus, Exobasidium camelliae. Infected leaves become fleshy, thick, and discolored.

camellia petal funk

While disgusting to look at, the misshapen leaves don’t do any serious harm. The disease may be controlled by removing the infected pieces and disposing of them in the trash (not the compost). It’s best to do this as soon as you spot them, before the galls have a chance to fully develop and release their spores.

Moist and humid weather produces favorable conditions for camellia leaf gall to develop. We have certainly met those criteria this spring. I have never seen the disease on my japonicas (the spring bloomers); only on the sasanquas (fall bloomers). Take a look at your camellias and if you spot the problem, don’t reach for a spray. Just nip off the swollen leaves, clean up any that have dropped, and your plants will be happy again.