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Old April 9, 2019   #1
GoDawgs
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Default Cedar Spray For Japanese Beetles?

Come May 1st I need to start watching for Japanese beetles. They mainly work on the roses, grapes and crape myrtles. I've even found one or two in the corn as the season wears on.

Poking around the internet today I found two articles advocating a spray made from pieces of Eastern Red Cedar soaked in hot water (to release the cedar oils), steeped for 36-48 hours, strained and used as a spray. Have any of you ever heard of this or tried it?

The guy in the first reference below said the beetles dropped off and flew away when he used the spray. Well, they'll do that any time you mess with them. He never provided a followup report. The second person said it did keep them away afterwards but the spray, like other stuff, needs to be reapplied after rains.

oldworldgardenfarms.com/2016/06/23/natural-japanese-beetle-spray/

www.finegardening.com/article/make-your-own-natural-spray-for-japanese-beetles

Interestingly the second reference suggests possibly using bottled cedar oil (where to find THAT?) or cedar shavings like you use for bedding in a dog house but they've not tried them.

I'm going to try this and stick with using the real cedar. It grows like a weed everywhere around here. And it ought to smell nice too!

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Old April 9, 2019   #2
Scooty
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Stuff looks expensive.... even more than the OMRI listed spinosad or pyrethrin.

Also wouldn't you need an emulsifier like a bit of soap for the oil and water to mix before you spray? Otherwise, i'd imagine it would be like the complaints often heard about neem oil..... a nice recipe to fry your plants.
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Old April 10, 2019   #3
GoDawgs
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No plans on buying cedars oil! Heaven knows I have enough red cedar around here that cutting some will be no problem.

Thanks for the reminder about the soap additive. Neither recipe calls for it but other articles promoting the use of cedar spray against brassica chewing worms do include the addition of soap. I can't imagine there will be enough "oil" from soaked wood to separate out but I will add a small bit to act as an adjuvant.
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Old April 10, 2019   #4
Scooty
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Quote:
Originally Posted by GoDawgs View Post
No plans on buying cedars oil! Heaven knows I have enough red cedar around here that cutting some will be no problem.

Thanks for the reminder about the soap additive. Neither recipe calls for it but other articles promoting the use of cedar spray against brassica chewing worms do include the addition of soap. I can't imagine there will be enough "oil" from soaked wood to separate out but I will add a small bit to act as an adjuvant.
Hmmm, I'm not sure how indicative your experiment will relate to the effectiveness of whatever compounds of ceder oil on japanese beetles. I'm assuming here, that it's probably the volatile phenols that are the principle players here, which are probably (or nearly all) fat soluble compounds. Just soaking cedar wood may get you some of the chemicals, but probably not enough in a quality to make an effective spray.

So there are four scenarios here.
1. it's all a load of hooey and you get no positive results
2. it's all a load of hooey and you get positive results (placebo effect)
3. it actually works, and you get positive results with your experiment
4. it actually works, but you get no positive results with your experiment

#4 is more what I'd be worried about. The scenario would end up with the same result as #1, but you'd never know it didn't work because its a chemical concentration issue, not because the science is bad.
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