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Leafminer, Synthetic Pyrethrum
I've been told last year's damage to my Swiss chard leaves was from leafminer, though my source didn't indicate fly or moth type. I'd like to treat this chard food crop this season. I have seen a product containing "canola oil with pyrethrins" for leafminer. Since pyrethrins are toxic to humans, at least when first applied, I'm wondering if there is also residual toxicity on leaves that I will be eating weeks after spraying. I eat only organic produce. If it is toxic residually, can you suggest a way to prevent leafminer damage other than floating row covers. A birch tree adjacent to the chard bed also sustained significant leafminer damage. Since spray applied to it would float down onto the chard bed, can you suggest a way to also treat it without risking toxicity upon ingesting the chard?
If the leafminer larva has no legs it is the maggot of a fly, if it has six legs at the front it is the larvae of a moth/butterfly. Synthetic Pyrethrins are not allowed under any NZ organic standard because they are too toxic. Early detection/anticipation and sprays with Pyrethrum should help. Crop rotation is also important.