Permethrin is not organic but it is far cheaper and slightly more effective than pryrethrin which is organic I believe. Diatomaceous earth is organic also and might work on flea beetles by itself if you can get good coverage. It can be applied by by dusting or by mixing it in water and straining it into your sprayer to avoid any clumps and adding a little dish washing soap to help keep it suspended and spraying all surfaces of the cucumbers with it along with the mulch under them. It will dry leaving a fine film of DE that will continue to kill until it is washed off or while it is wet. It is best to shake your sprayer every so often to keep it suspended and make sure to thoroughly wash out your sprayer. I usually use a 3/4 cup of food grade DE per gallon of water. Much more and it will clog most sprayers and too little doesn't give good coverage.
Bill
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