powdery mildew, sowbug and pillbug infestation, fungicides on tomatoes, garlic bloat nematode: q&a with ken druse

MORE URGENT GARDEN QUESTIONS: In the July edition of Ken Druse’s and my monthly Q&A radio podcast, we tackled listener questions about powdery mildew prevention and aftercare, and what to do when an abundance of roly-poly or sowbugs and pillbugs has descend on the garden. Also: Should you use copper-based fungicides against tomato blight—and what to do after an infestation by the garlic bloat nematode?

In Part 1 (a transcript of which is at this link) we talked with a caller curious about the wonderful tree called Stewartia and how to make it happy—plus Ken recommended other garden-sized, multi-season trees to consider adding to your landscape, including dogwoods, redbuds, and tree lilacs.

Ken, of Ken Druse dot com, is a longtime garden writer, author and photographer and all-around great gardener—and great friend. If you have a question for a future show, you can submit it in the comments on either of our websites, or use the contact form to send us an email from either site, or ask us on my Facebook page.

Read along as you listen to the July 10, 2107 edition of my public-radio show and podcast using the player below. This is Part 2 of the two-part show, beginning at 24:48 in the audio.

You can subscribe to all future editions on <a href=”https://itunes.apple.com/us/podcast/a-way-to-garden-with-margaret/id370801678″>iTunes</a> or <a href=”https://www.stitcher.com/podcast/whdd/a-way-to-garden-with-margaret-roach”>Stitcher</a> (and browse my <a href=”https://awaytogarden.com/category/etcetera/radio-podcasts/”>archive of podcasts here</a>).

And a small apology: The sound, especially in Part 1, is a little uneven; we had an electrical brownout in the area while taping and lost our master audio file. The backup that survived this unique power event was not ideal, but the transcript is thorough.

part 2 of the july q&a with ken druse


Image from Missouri Botanical Gardentackling powdery mildew

Q. I have a question I suspect others are having at this moment, from Zoe on email via the contact form on my website:

“Help! Several of my peonies have powdery mildew. From what I’ve read, it’s best to prevent early on, but now that the blooms have passed what, if any, action should I take to clean/remove the mildew.”

Did you know that there are like 11,000 species of powdery mildew organisms on ornamental plants? [Above, mildew on peony foliage, from Missouri Botanical Garden.]

Ken. I don’t doubt it for a minute—there are like 12 growing on the sponge in the kitchen.

Q. So the basic thing is when you get warm days and cool nights, it can be good conditions for it, and the spores exist—that’s what happened to Zoe. My understanding is that once it happens you don’t get rid of it, right?

Ken. It doesn’t seem to ever really be…

Q. It doesn’t kill it.

Ken. It’s not terminal, it’s just unsightly. It’s very unsightly, and the lilacs always seem to get it at the end of the summer, but it doesn’t seem to kill them.

Q. And really, it’s fungal—and really when she said peonies…

Ken. Botrytis…

Q. Yes, so you like to check because peonies get other fungal diseases, so you want to check. It’s great to go to Missouri Botanical Garden website, or Cornell—or if you live in a different region, pick a different botanical garden website. Look at some pictures of the different fungal diseases of the plant, so you can be sure. I think she is sure; she knows what it is.

So really with these fungal diseases, prevention is the thing—but those fungicides that were used for prevention, I don’t want to be spraying that stuff.

Ken. I’d like to go back in time; I’d like to be 26. But that’s another story.

Q. OK. [Laughter.]

Ken. You said prevention, and I would say especially with peonies, if you see any kind of disease on them, in the fall when things are quieting down and everything’s turning brown, that’s one plant I would cut the foliage off and discard; put it in the garbage. Don’t compost it.

Q. I agree; anything with a mildew situation or let alone botrytis—the fungal diseases. A really, really good cleanup in fall, including raking up under the plants. If it’s really disfigured or discolored—besmirched! [laughter]—you can even cut off some of the worst so that you can limit the number of spores that are flying around, but you don’t want to defoliate the plant entirely early in the season. That’s a judgment call, I think.

Since roses get fungal diseases, too, rosarians have looked for what’s natural, safe antifungal preventive thing instead of [chemical] fungicides. Isn’t there a baking soda recipe?

Ken. I used to use that, something like a tablespoon to a gallon of water, and then you need something for a spreader-sticker, a surfactant, like dish soap or better would be some kind of sun oil, some kind of natural oil spray so it spreads over the leaves. But a lot of people, especially rose people, really had not as much success as Napalm, but a lot of success with baking soda—and of course it’s perfectly safe.

Q. I looked up Cornell’s recipe, because I remember it was like the late 80s or 90s when they did some testing. It was like you said, but they used a little extra baking soda—like 4 teaspoons instead of a tablespoon, and a gallon of water, and they put a couple of teaspoons of Sunspray or one of the other ultrafine, year-round horticultural oils (again, not toxic). And they put it in a no-clog kind of hose-end sprayer, and then they sprayed them prophylactically—not once they had an outbreak—every three to fours days, and had tremendous results.

[Vintage-2001 pdf on baking soda recipes for fungicidal use, from National Sustainable Agriculture Information Service.]

Armadillidium vulgare pillbug from Wikipedia pillbugs and sowbugs

Q. I think we have a caller on the line named Lynda. Where are you calling from?

Lynda. I’m calling from Lilburn, Georgia, which is just outside Atlanta—northeast of Atlanta. It’s kind of hot and steamy here, as opposed to what you guys have.

Q. We actually are having a break from the humidity, which we are very thankful for, but I guess you are not.

Lynda. No, full-tilt. We were in Maine and Canada recently and enjoyed it, and came back and walked into a wall of humidity that hasn’t left since we got home.

Q. My goodness. So what’s your question?

Lynda. Well part of it is because of all the rain we’ve had, but I seem to be overrun with the little pillbugs and sowbugs—both kinds. I do kind of know what they are. [Above, the pillbug called Armadillidium vulgare, from Wikipedia.]

They’re everywhere. They’re in my planters, they’re under my planters. I picked up a stick out of the garden, a rotting stick—I know that’s what they eat—and it was covered, literally, from one end to the other.

We’ve gotten maybe two strawberries this summer because they crawl up onto them. Any little ding in the strawberry and they’re on it; there will be two or three on it, just chomping away. I know they are detritus eaters, but it feels like they are actually eating the stems of some of the plants in my planters, where it stays moist, and I know that’s what they like. What can I do? Help!

Q. Ken, do you get them?

Ken. Yes, but I have never heard of that. I’ll lift a pot and they’ll be under the pot. And as you say Lynda they eat decayed stuff, like a fallen leaf, but I’ve never had them attack nice live growth.

Lynda. That was my understanding, too, but the fact that they are so thick on my planters and the strawberry plants—and they are out in the sun, too, which surprises me because I know they don’t like that. They just seem to be everywhere and it’s kind of overwhelming, and it’s kind of gross. [Laughter.]

Q. There are two kind of these creatures that are related, and one thing that’s super-interesting about them since we have to put a positive spin: They’re more closely related to Crustaceans than they are to insects. They have seven pairs of legs.

There are sowbugs and pillbugs, and the pillbugs are the roly-polys, and the sowbugs have those two little appendages at the rear end that you can see.

You’re right—they’re detritivores, and they recycle stuff, and they normally feed at night or in the evening. But the tricky thing I’ve read is that apparently when there is a big population of them, they will also eat seedlings, for instance, or fruit—tender bits of things. So they will do that, because it’s soft, kind of the way decaying debris is soft.

Lynda. That makes sense. So I am not completely crazy on that. [Laughter.]

Q. Normally the experts say, “No, that’s not who’s eating the stuff. You probably have slugs as well, but you’re just not seeing the slugs, and only seeing the roly-polys.” But sometimes they can in fact eat tender shoots and are known to do that.

And the thing to do—and it’s not easy to do—but how do you limit moist, dark hiding spaces? I find that flower pots can’t be on the ground, they have to be raised. When you have a profusion of them, anything that’s in contact with the ground creating that moist, dark place is tricky.

Water early in the day, not later in the day—so that it’s not moist when they are active. Some people I’ve read about say they elevate strawberry plants and other things up off the ground on screens or frames—but it gets to be crazy, right?

Lynda. It does. Most of my pots are on feet, but I was out digging around in the two planters by the porch yesterday and they are just crawling with them. Everywhere.

Q. You could try to trap or attract them in least-toxic ways. One would be to roll up newspaper tubes on the soil surface, hopefully attracting them—it’s there, it’s moist along the ground, so maybe they go in when they are done feeding. And then obviously you’re going to destroy the ones that you catch.

People have used, with varying results, diatomaceous earth—a thin layer of that fine, sharp powder. You can’t put a thick layer on or it gets like goo, like plaster. That’s what people do when they have a problem with them and are planting seedlings and don’t want them to eat them, similar to a cutworm [or slug]. They use the diatomaceous earth like a row on either side of the seedlings to protect them—as a barrier.

I’ve read about people trying non-toxic slug bait—a lot of experimentation—but mostly it’s about trapping to reduce the population and getting the area as dry in the later part of the day as possible and eliminating the hiding places, or using the hiding places as traps.

Lynda. I hadn’t thought about the traps; I’d thought about the slug bait. I had not tried that yet, but that’s on my list. I hadn’t thought about the diatomaceous earth, but that’s probably a good idea with their little crustacean bodies.

Ken. Maybe wear a mask or bandana if you are going to use that, because they really are sharp barbed things, and you don’t want to be inhaling that.

Lynda. That’s a good reminder.

Ken. And as Margaret said, just a dusting.

Q. Following the package directions carefully. I’ll be interested to hear what happens. [Laughter.]

Lynda. I’ll let you know if I knock them down some.

By Dr. Meg McGrath Cornellcopper fungicides on tomatoes?

Q. I have a question from Facebook, from Susan:

“Typically I treat my tomatoes with copper for blight…”

Ken. Oooh!

Q. “… but the tomatoes look great this year,” she says. “No signs of spots on leaves. Should I treat them anyway?” [Above, late blight photo from Cornell, by Dr. Meg McGrath.]

Ken. No!

Q. I know, I am not a copper person; I’m not into the copper thing. What people don’t know is that there are fungicides containing copper that are approved for organic farming, such as organic apple farming (or tomatoes). But copper’s residual in the soil—it doesn’t go away—and I don’t want to participate in that. [More on copper fungicides and on cooper and late blight specifically.]

Ken. Right. It’s funny, we’re talking about the sowbugs with Lynda and we’re talking about prophylactic measures. But we tend not to want to take prophylactic measures and not treat a problem that we don’t have. If she’s got nice-looking tomatoes this year, that’s that. And I wouldn’t use copper for the same reasons that you said.

Q. For people who want an organic solution, I’ve read about this other substance and have never tried it, for people who want a non-chemical fungicide. It’s called Actinovate; I’m interested to learn about what people are coming up with, because obviously these are problems in agriculture where they need an alternative in order to produce a crop in an agricultural situation, a large-scale situation.

[Actinovate is a biological fungicide containing beneficial bacterium, and used as a foliar spray or soil drench to prevent various issues.]

Keep the plants clean, spacing them well, lots of air circulation, clean mulch or a black plastic layer to prevent fungal spores from splashing up from the soil—all those things are super important, and theoretically Susan’s already doing that.  But I’m just not a copper person.

Ken. [Laughter.]

'German Extra Hardy' has few cloves, each very largegarlic bloat nematode

Q. Have you ever heard of garlic bloat nematode?

Ken. No, do I want it? [Above, healthy garlic bulbs.]

Q. I don’t think you want it. You definitely do not want to get this. There was a question on Facebook, from Camille, about garlic, who says:

 “I have been very successful with garlic. Last year however, I think a great majority got hit by the garlic nematode. I didn’t have the soil tested, but was wondering if you have a thought on using the spot next year. I planted elsewhere last October.”

I would not have even known what that meant [laughter], although I grow garlic every year, but I had been to an organic farming conference in my region, the Northeast, and they had a panel about it.

It’s apparently been around maybe since the 1800s; in the US it was first reported in the 1920s or something. It affects the various Allium, but also other things from hydrangea, to alfalfa, to  parsley, Canada thistle…. It’s a tricky thing, a nematode, a microscopic parasitic nematode, and it disfigures the bulbs and weakens them

But her question is about how long to wait, and this is the bad news [laughter]: It’s a super-long rotation if you have had an outbreak like that. It’s four to five years not planting in the same area. What’s also recommended is an organic approach to help reduce the nematodes is a cover crop that is then turned in, that’s a natural soil fumigant, like mustard, rapeseed, or oilseed radish, or even that sorghum-sudangrass hybrid that’s used as a cover crop. So cover cropping with one of these natural biofumigants and then turning that in. But even then, it’s a four- or five-year rotation, I am sorry to tell her.  I’m sorry Camille.

[More on garlic bloat nematode from the Ontario Ministry of Agriculture, from “Growing” magazine and from High Mowing Organic Seeds.]

Ken. There are two things: One is that there are good nematodes and bad nematodes, and that’s confusing enough. But I think the idea that if you have a problem, like Fusarium wilt or something, it’s a good idea not to plant in the same place if you can help it, in all cases. And I guess to see if the nematodes are gone she could wait four or five years and then do a little bit of a test, but if she’s got the space: move the garlic.

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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the July 10, 2017 show right here. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

      1. margaret says:

        Hi, Gail. I have read various recommendations, from as low as 1:9 milk: water (10 percent milk) to 4:6 (40 percent milk). I suspect it’s more preventive (like a baking soda solution — another home remedy idea) that curative, so you start before the issue arises, and have to coat all parts including undersides of leaves. Have never tried it and don’t have a goo authority to quote for you with details.

  1. Jane in So Cal mts says:

    Ditto! I have also had good luck with a water and milk (4:1 skim) solution sprayed every 7-10 days. And yes, it works as preventative rather than a cure.
    Thank you again Margaret and Ken for another informative and enjoyable podcast!
    Jane in So Cal mts

  2. Dianne says:

    I can relate to Lynda and her pill/sow bugs. I have them but not in the quantities I used to. Mine started mainly when I was putting leafy kitchen scraps in the compost. Then when I dumped the compost into my beds I realized it was teeming with pill bugs, only after I’d filled all three of my raised vegetable beds. After that I could not direct sow seeds because the seedlings were eaten immediately as they emerged. I researched and tried everything mentioned above to virtually no avail. They too ate my strawberries. I found out that a real cold winter will cut back on the population, say below 20 degrees, which doesn’t happen often here in TN, probably like Lynda in GA. Could be that’s why folks in the north can’t understand pill/sow bug infestations and constantly are saying that they are good. Yes, good in moderation. I immediately quit using kitchen scraps in the compost and only use shredded leaves, coffee grounds and eggshells. Virtually no pillbugs now. I propped up all the strawberry plants off the ground with cedar mulch which helped. I put DE around all my tender transplants. I could only put out transplants and never direct sow. So after one or two cold winters, correcting the compost and using DE and cedar mulch, the population is now under control and I can actually direct seed!!! Oh, the pill/sow bugs still eat the bottom cabbage leaves, but I figure if they concentrate there the tender little lettuce sprouting won’t get their attention.

    1. margaret says:

      Thanks, Dianne. I shared your feedback with Lynda as well. I hadn’t thought about the regional differences, but of course! Wonderful insights.

  3. Margaret Clarson says:

    Powdery Mildew : My cure is to 1 gal of water 2 Tbs vinegar , 1 tsp of dish soap , 1 tsp of neem oil and 2 tbs of potassium bicarbonate ( Nuts.com) as you don’t won’t a salt build up in the garden. One spray every week for 3 weeks usually cures it.

  4. Marie says:

    Mites and more mites! – Since I transitioned seven years ago to a totally organic gardening approach here on my quarter acre city home the ornamental gardens bordering the house have had an increasing number of mites … boxwood mites, spider mites, and possibly others? I have learned to identify their presence as I recognize the damage and occasionlly use a lens to gauge the population. I have tried managing this challenge over the last five years with good cultural practices (thoughtful watering, feeding the soil, monitoring the health of the plants) and tried many of the solutions found on the web (such as repeated strong sprays of water on the leaves, pruning to increase air circulation, dust reduction with mulching, releasing beneficial predators, introducing plants to provide food & habitat for the beneficials) … but all to no avail. This pest population keeps growing and have now disfigured all of the leaves on the boxwood, defoliated the clematis vines, etc., etc. Our Virginia Extension Service suggested changing the plantings to those which might be more drought tolerant, but I am uncertain new plants would be more water wise than the existing established ones which do not have high water consumption needs. I would appreciate your insights and advice.

    1. margaret says:

      Hi, Marie. I will put this on our list for the next Q&A session. I know about spider mites but not lots of others, so I will have to ask some more expert friends and do some homework. From what I know you have as you say followed all the usual recommendations. Hmmm…

  5. Liane says:

    Lynda and I share the same problem (and live in the same area). I have never seen pill and sow bugs like this year. Two warm winters that allowed tropicals like Tibouchina to overwinter apparently were also a boon for the bugs. My beer and yeast baits for slugs caught far more sow and pill bugs than slugs. The putrid smell of those traps (and necessity to empty nearly daily) reluctantly led me to just invest in a large shaker jug of Sluggo Plus. It has made an immediate difference, although frequent rain requires reapplication. I try to only use it where something precious or young is at stake. I know it isn’t slugs doing the damage in the rock garden. Maybe someone needs to study if the southern pill and sow bugs have expanded their diet!

  6. Jane in So Cal mts says:

    Whoops! Correction on the water and skim milk ratio…. 3:1 rather than 4:1. It may not be the perfect preventative, but it did do the trick when applied regularly to my peach tree (including the peaches themselves) just this past summer. And of course there are more details online. ????…
    Jane in So Cal mts

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