Caterpillars and the slew of sprays that aren't working...

dorrielOctober 24, 2012

Ok. I'm sure this story has been around the block a million times. So, I have what I'm sure are striped caterpillars and cabbage loopers all over the place (cabbage, squash, turnips, lettuce, brussels, broc) and have been trying everything to get rid of them.

First round was the pepper/garlic spray concoction which was powerful! But not powerful enough for them. Second, I tried neem oil, and that seemed to do almost nothing, which I'm surprised. And lastly it was recommended to use dish soap with water, which I tried and worked great! Only problem is, it seems as though all my plants are dying! Within a day of using it, I'm getting black spots on all the leaves, and they are starting to turn brown and dry out. No bugs though!

But help! is my garden kaput? If not, what else can I use besides the previous listed that won't kill the leaves? Any suggestions?

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ken_adrian Adrian MI cold Z5

wow ...

you are in the US ... its late october..

bugs are all gone ... there is nothing to spray ...

leaves are dying due to the season ...

sooo.. whats the issue???

it might help.. if you tell us where you are.. i suppose there are one or two tropical spots in the US that are not getting ready for winter ... but it is still not time to go spewing chemicals/organics.. all over the yard.. IMHO ...


    Bookmark   October 24, 2012 at 4:45PM
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I'm in Florida (also just moved here) but I've been reading books and taking workshops on cold season vegetable gardens here, which include the things I've planted. Plants/seeds went into the ground Sept 7 and 15 for the season. And they should be doing fine. Still hits the 80s during the day and only 50s at night. The leaves began turning literally this morning, after this dish soap debacle.

I thought the bugs would be gone too...and they are probably a little better from a month ago, but I'm still getting these caterpillars on my leaves every day. I've got skeletons left for cabbages. My broccoli is almost gone due to the leaves being eaten, same with the squash. The collards didn't last three days.

In any case, I should have a healthy garden, but these damn bugs... And now this dish soap thing, I hope I didn't kill everything with it.

Should I just let it go, hoping the cooler temps will deter them?

    Bookmark   October 24, 2012 at 5:02PM
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Some of us can grow year-round and have pest issues year-round.


Try to get any bigger ones by hand. Then go to the nursery or home depot and pick up some BT -- it's organic and effective.


    Bookmark   October 24, 2012 at 9:34PM
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If a plants leaves die after being sprayed with a soap and water mixture, Insecticidal Soap, then the mixture is too strong. Soap residue, left on plant leaves, can cause problems with photosynthesis and if a plants leaves are not using sunlight to manufacture nutrients to feed the plant they are cut off and die.
Control of the moths that lay the eggs that become the Cabbage Looper or the Imported Cabbage Worm can start with Floating Row Covers, go to Insecticidal Soaps (mixed properly, like 1 teaspoon of soap per quart of water), followed with Bacillus thuringiensi, - Kurstaki strain, followed by Neem Oil products, followed by pyrethrin products, in order of broad spectrum killing power.
Sometimes a combination of these is necessary.

    Bookmark   October 25, 2012 at 6:51AM
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rhizo_1 (North AL) zone 7

Dorrie, I strongly suspect that your dish soap mixture damaged your plants. Dish soap has a lot of potential to cause problems. There are so many harsh additives to those detergents that it's surprising it doesn't happen more often. Add to that the fact that there are no directions!

I've never heard of soap residue interferring with photosynthesis, but burning and dessication of plant tissues is very possible.

I'd much rather see you make a small investment in a commercial insecticidal soap, especially formulated to be effective against arthropods while not harming plants.

Kimmsr, I'd be interested in seeing some information regarding soap residues interfering with photosynthesis. I've never heard of this problem with insecticidal soap.

    Bookmark   October 25, 2012 at 11:44AM
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Any residue left on the leaf surface has the potetntial of interfering with photosynthesis. Horticultural Oils, Powdery Mildew, etc. are known to do that so it would stand to reason that if your soap left a film you could see that would be enough to prevent the leaf from utiizing sunlight properly.

The wrong soaps, actually detergents, are known to cause burning of leaves.

    Bookmark   October 26, 2012 at 7:02AM
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rhizo_1 (North AL) zone 7

Never heard of horticultural oils causing a problem, either. The residues of properly mixed hort. oils and insecticidal soaps are extremely light and porous. For actual interference to occur, you'd have to have something obscuring the chloroplasts in the mesophyll. Even clogging the stomata could cause a problem, but neither of the above products will do that.

I recall a person who mixed about a 50:50 solution of dish soap and water, remember that? I've also seen with my own eyes the damage after someone decided that cooking oil and a little bit of water would be a good thing to try. Yikes!

Anyway, dorrie, damage from insecticidal soaps isn't very ususual...a dish soap that is too harsh, or mixed too strongly, or sprayed in the full blazing sun...all have the potential of causing problems.

    Bookmark   October 26, 2012 at 3:56PM
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Hmm. Thanks for all the info guys.

I can say that my mixture wasn't very strong, probably 2 tsp per quart, didn't look very soapy. I also put it on early in the am, and the sun isn't too blazing these days. Also, it was antibacterial soap, which I researched and didn't seem to find a reason it would kill the leaves, but perhaps the photosynthesis idea could have done it.

I also spoke to a gardener last week who spoke of microorganisms in the soil that help plants grow and thrive; so by using antibacterial soap it could have killed them and caused the leaves to dry out and brown.

Well, my squash are kaput, so is the broccoli. Strange, the brussel sprouts and carrots had virtually no response to the soap. The tomato plants are beaten up a bit, but I think they'll be ok. Lesson learned, that's for sure.

Again, thanks for the helpful suggestions. :)

    Bookmark   October 26, 2012 at 4:50PM
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The anti bacterial "soaps" are really detergents, not soaps. Using an anti bacterial in your garden most likely will not adversly affect the soil bacteria much, due to dilution, but they will allow the disease pathogens to develop immunities making those anti bacterials less effective.
The Center for Disease Control, National Institute for Health, and the Food and Drug Administration asked the manufacturers of these anti bacterials to stop making ans selling them years ago because they are allowing disease pathogens to become immune, but none have the power to prohibit that disruption of our free enterprise system.

    Bookmark   October 27, 2012 at 6:56AM
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dorriel, Bt is very effective against the caterpillars of moths and butterflies only. The product acts on the digestive system of the caterpillars and they stop feeding almost immediately.
Neem products chief characteristic is their repellant property. We used neem leaves to protect raw rice against weevils.
It also hinders the development of some insects. Presumably the product could stall the development of the caterpillar - but this could mean that the insect will continue to feed for a longer time!
Yet again it is ineffective against some species.
Pyrethrin is a very good choice for the following resons:

  1. It is very effective against insects at very low dosage rates.
  2. It is "harmless" (please pass the salt!) to mammals - at least as far as they tell us.
  3. It has almost no residual action - probably 3 days at most.
    Pyrethroids are not the same as pyrethrin.
    Scientists, as is their wont, have tweaked pyrethrin by adding a molecule (or two) here (and there). These products usually end in - thrin. The irony here is that the tweaking prolongs the residual action thereby neutralizing advantage 2; although not to the extent of say, "Dursban" "Chlordane" or "DDT".
    So what is the point of all this?
    If you can accurately identify the pest and its stage of development, you will be able to choose the most effective product to control the pest.
    Emphatically, the remedy does not have to be a product. It could be manual (picking off the caterpillars), cultural (pruning to reduce an aphid infestation) or physical (here I include traps, row covers and similar devices).
    Hopefully you will be able to choose that elusive balance of effectiveness and benignity (to the environment) in your effort to grow your plants or crops.
    Thanks also for the opportunity to do a bit of self assessment.
    Bookmark   October 27, 2012 at 8:46AM
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rhizo_1 (North AL) zone 7

Dish detergents are simply loaded with too many additives....greasebusters, anti-bacterial agents, scents, dyes and more. Organic 'real soaps ' can be found anywhere....Dr. Bonners is just one brand. But commercial insecticidal soap is nothing but a true soap.

Sensitivity can depend upon plant species....brussel sprouts have thick, waxy leaves and carrot leaves offer very little surface area. I would expect those plants to come out unscathed from a mild dish detergent application. Other plants? Not so much.

The soil theory is not a good one, unless you drenched the heck out of the soil. ( Kudos to your gardener friend for knowing the importance of soil microorganisms.) I also assure you that a problem with photosynthesis disruption is not the problem. You'll be on a very long list of gardeners who learned the hard way that strong dish detergents can cause cellular damage to plants by destroying the protective epidermis layer.

We ALL learn by making mistakes. Your experience will help others.

    Bookmark   October 27, 2012 at 8:47AM
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the line "The irony here is that the tweaking prolongs the residual action thereby neutralizing advantage 2"color> should end with 3 instead.
So much for being critical of your own work!

    Bookmark   October 27, 2012 at 8:55AM
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