What concerns should I have using systemic pestisides on fruit trees?
Are there any special concerns associated with the use of systemic pesticides ( i.e. imidacloprid) on fruit trees from which fruit is going to be consumed this season? I know "read and follow label directions" and it says it's ok but seems like something I need to double check on as obviously I have concerns or I wouldn't be asking.
Houghton County Michigan
You can get a sense of the toxicity of imidacloprid by looking at the published lethal dose 50 for it. The lower the number, the more toxic it is. Imidacloprid has a LD50 oral of >4000 and dermal LD50 is >2000
Asprin has a oral LD50 of 1,000, salt is 3,320, antifreeze is 460. So these three would be considered more toxic than equal amounts of imidacloprid.
Typical application rate is 8 oz of imidacloprid per acre, which translates to 4 grams of active ingredient per acre. Typical yields are 50,000 apples per acre. Most of the spray misses the apple fruit during spraying. Say 10% reaches the apples. So this is 0.4 g of active ingredient spread over 50,000 apples. Minimum interval before spraying and harvest is 7 days. A rough guess is that 50% breakdown occurs before harvesting. So we are down to 0.2 g active ingredient spread over 50,000 apples. For a size comparison, a typical vitamin pill is about 0.5 g.
So, In my opinion there are a lot bigger things to worry about than fruit treated with imidacloprid.
See the following links for more details.