Plagues Come & Go, With Some Help, and Seattle-time

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Plague again; keep calm

Every year it seems some new plague is ready to attack plants. A few years ago, late blight of tomato moved to the fore. Emerald ash borer, threatening ash trees, was first found on our shores in 2002. (Figuratively; literally, the insect, native to Asia, was first noted in Michigan.) What’s next?

Perhaps a calmer outlook is called for. A decade or so garlic mustard seemed ready to take over our world. Not so, now, perhaps because it’s being crowded out by Japanese stilt grass, which itself seems now ready to take over our world. Garlic mustard is native over much of the northern hemisphere, except North America, and was introduced here around 1860 as a culinary herb. As for stilt grass, it hitchhiked here from China about a century ago, as packing material for porcelain. It’s deer-resistant, for what that’s worth.

Plant problems come and go. The best approach is to keep calm and, in some cases, plant something different, something plague resistant.

Bean Beetle Management

Green beans are a mainstay of my garden, of just about every garden. More than 20 years ago, Mexican bean beetles (a species of ladybug!) found my bean plants and have plagued them every year since.

The adults, with eight black spots over a red or yellow background, wake up late from winter sleep to lay eggs on bean leaves. I’ve come to despise the yellow, balled up spiny larvae that gorge on leaves and other plant parts.

Two bean beetles crawling on bean stem

Still, I have managed to grow good crops of beans over the years, not by killing the beetles or their larvae, but by growing a different plant. Sort of. Rather than grow pole beans, which reside in the garden all season long to provide a constant source of beetle food, I have been planting successive crops of bush beans. Bush bean plants tend to bear quickly and for about 3 weeks, then peter out, so a new planting in a new bed goes into the ground every 3 weeks from mid-May until late July.

Three bean beetles clustering together

Yield from a planting tapers off just as its resident beetle population is beginning a feeding frenzy. Then it’s time to pull up the plants, thoroughly clear the bed of leaves and old pods, and rush it all to the compost pile. Chopping the debris with a machete and burying it beneath straw and manure, and watering the pile, as needed, sends the temperature soaring, killing most of the beetles. Bean beetles are good fliers, so cooking the beetles in the compost pile doesn’t solve the problem, just keeps it under control.

Death to the beetles, with restraint

Something strange happened this year: As of this writing, only one beetle larvae has been seen. Last year I doused the bean plants a few times with one of two organic sprays, which gave good beetle control. It also gave me the confidence to try growing pole beans, as I did in my pre-Mexican bean beetle days. They got some bean beetles but we did harvest pole beans.

The sprays were Entrust and Azamax, both approved for organic agriculture. The active ingredient in Entrust is spinosad, a compound found in bacteria, Saccharopolyspora spinosa, that was isolated from soil collected inside an old rum still in the Virgin Islands. Although toxic to a range of insects, it is otherwise relatively benign. Still, the label requires waiting at least 3 days to harvest after spraying.Image of bean beetle larvae

Azamax is an extract of the seed of the tropical neem tree, native to the Indian subcontinent. In that part of the world, this one tree has been used as human food, insect repellant, bird repellant, and an ingredient of soap. It degrades rapidly in soil or in water, and is harmless to earthworms, honeybees, and insect predators. Food crops can be harvested right after spraying Azamax.

Still, Azamax and Entrust are pesticides. Perhaps the bean beetle cycle has been broken  here and sprays can be forgone in the future. I’ll keep calm. No sprays this year, yet.

SWD, go away

The same two organic sprays might be called upon for another pest, the spotted wing drosophila, unaffectionately known as SWD. Also an Asian import, this one has moved east since being first spotted in 2008 in California. It is hard to keep calm with this pest because it attacks blueberries, my favorite and heretofore my most reliable and abundant fruit crop. The pest is also fond of blackberries, raspberries, and — not that it matters to you or me, because we don’t eat them — honeysuckle berries.

A cluster of blueberry fruitsAgain, there are management options. Because SWD seems to blow in from more southerly locations, a fine net could exclude them. Prompt refrigeration of harvested berries for 3 days kills larvae within. Thorough harvest of sound and unsound berries also keeps populations in check.

And then there’s Entrust and Azamax (or some other neem product), any of which I consider a last resort. I’m setting up traps to monitor if and when SWD arrives. (For information on monitoring, see Till then, and after, I’ll try to remain calm. Om. Om. Ah-oh-om.

10 replies
  1. diane
    diane says:

    do you ever use Surround Kaolin clay? I have been using it on the young fruit trees last year and this year, with a bit of neem oil in it (per Michael Phillips’ book) and I have less of everything: Jbeetles, leaf curlers, fungus…. it looks funky with everything white, but I tell you, I am impressed how things are doing.

    • Lee Reich
      Lee Reich says:

      I’ve used Surround for many, many years. It is usually effective if applied before insects arrive and it’s reapplied frequently enough to maintain a dust-like coating on the plant. Nonetheless, Surround is not effective against most disease problems. Summer rots have become more severe here. As far as Neem, from my experience and reading, the jury is still out on it.

  2. Warren A. Jacobs
    Warren A. Jacobs says:

    “deer resistant, for what that’s worth” Deer resistance is probably the main factor that makes an alien plant an INVASIVE alien plant.

  3. Beth
    Beth says:

    I’ve been dealing with currant fruit fly on red and white currants here in Oregon for a few years. I’ve finally worked out an approach involving espalier (inspired by you) and covering with fine insect barrier cloth. It’s next to impossible to cover a goblet shaped bush, but with a simple t-shaped espalier I think I can cover the branches more easily. Hopefully next summer will be my first full crop of non-maggoty currants. No problems with my other berries so far though, cross-fingers and touch wood.
    Apparently spinosad is toxic to bees, but only for three hours or so or when it’s still wet. I don’t think I want to risk it though, surely bees and fruit flies are both active at the same time, when it’s sunny. If you have reassurances about spinosad use I’d be happy to hear them…..

    • Lee Reich
      Lee Reich says:

      I’m rethinking my espalier plant against imported currant worm. It doesn’t seem to work. Espalier does, as you say, make bushes easier to net, as you wrote. The currant fruit fly usually isn’t too much of a problem on currants. The main problem with using spinosad is the buildup of resistance by the target insect. So I limit its use to just when absolutely necessary, and even then not too frequently.

      • Beth
        Beth says:

        Oh the currant fruit fly is voracious here, they get every single currant. My covered ones were fine though. I’ll stay away from the spinosad then.

      • Rob Turland
        Rob Turland says:

        Lee – can you comment on the biology of the fly (when adults are active) and therefore what periods covering would be needed to be effective?

        We had terrible results about 10 years ago due to flies and so gave up on currants. But a few years ago I replanted and we are (so far) fly free. Having this tool will help us to keep our (carefully pruned!) bushes going once the fly returns.

        • Lee Reich
          Lee Reich says:

          Adults emerge from the soil soon after bud break. Translucent white eggs are laid along the leaf veins, from which the larvae hatch in 7 to 10 days. They feed on the leaves for 2 to 3 weeks and then pupate in litter on the ground. A second generation of adults appearsin midsummer, but it tends to be much lower in numbers, possibly because of predation by natural predators. This second generation overwinters as pupae.


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