Organic purists will blanch at this entry....sorry. In my climate/location adjacent to a 500 acre pasture on a hill in Southwest Virginia I find gardening by strict organic rules to be a non-starter although I have much sympathy for organic purism and have subscribed to OG for 37 years. The topic I wish to broach is judicious use of Bayer's Merit 75 imidacloprid insecticide on fruit and vegetable crops. For first rate information see the following Cornell U. site
While I have used Merit 75 imidacloprid to control the Japanese beetle on my roses, the horrible beasts have continued to ravage my raspberries and my grapes. A bit of simple math shows it may be OK to use Merit 75 on those grapes and raspberries. One of the first things one learns in using Merit 75 is how very little is needed for control. Merit 75 comes as a water soluble powder in a 2 oz bottle used at the rate of 1/8 tsp per gallon of water. This works out to be roughly one gram of imidacloprid in three gallons of water. A generous spraying of a half gallon mixture on a 30 foot long row of five foot high raspberries then works out to be no more than 100 mg imidacloprid on the entire row of plants. The imidacloprid is absorbed systemically so that all parts of the plant become most effectively toxic to the Japanese beetles. But the raspberry output for an excellent crop producing 10 to 15 gallons of berries is at most some 2% by mass of the plants. In the very worst case, this implies a residual of 0.2 mg imidacloprid per gallon of berries, with the chances being that there is less than 0.1 mg per gallon. Thus, we might expect a glutinous consumption of a full gallon of berries so treated might involve also ingesting about 0.1 mg imidacloprid. In tests on rats it is found that half the rats are fatally dosed (LD50) if they ingest 450 mg per killogram of body mass. Translated to a 75 kg (165 lb) person, the tests on rats suggest a 50% killing dose of 34,000 mg. Thus, to ingest a gallon of red raspberries from plants previously treated with a generous spraying of Merit 75 suggests one has ingested about 0.0003 % of an LD50 dose...at most. Similar numbers would apply to grapes. One further learns (Cornell site) that "Imidacloprid is a systemic, chloro-nicotinyl insecticide with soil, seed and foliar uses for the control of sucking insects including rice hoppers, aphids, thrips, whiteflies, termites, turf insects, soil insects and some beetles. It is most commonly used on rice, cereal, maize, potatoes, vegetables, sugar beets, fruit, cotton, hops and turf, and is especially systemic when used as a seed or soil treatment. The chemical works by interfering with the transmission of stimuli in the insect nervous system. Specifically, it causes a blockage in a type of neuronal pathway (nicotinergic) that is more abundant in insects than in warm-blooded animals (making the chemical selectively more toxic to insects than warm-blooded animals). This blockage leads to the accumulation of acetylcholine, an important neurotransmitter, resulting in the insect's paralysis, and eventually death. It is effective on contact and via stomach action (3).
The Cornell site also says: Imidacloprid is quickly and almost completely absorbed from the gastrointestinal tract, and eliminated via urine and feces (70-80% and 20-30%, respectively, of the 96% of the parent compound administered within 48 hours). and The half-life of imidacloprid in soil is 48-190 days, depending on the amount of ground cover (it breaks down faster in soils with plant ground cover than in fallow soils) (9). Organic material aging may also affect the breakdown rate of imidacloprid. Plots treated with cow manure and allowed to age before sowing showed longer persistence of imidacloprid in soils than in plots where the manure was more recently applied, and not allowed to age (10). Imidacloprid is degraded stepwise to the primary metabolite 6-chloronicotinic acid, which eventually breaks down into carbon dioxide (11). There is generally not a high risk of groundwater contamination with imidacloprid if used as directed.
As another indication of the very low toxicity of imidacloprid to warm blooded animals, one should note that your vetinarian sells monthly use vials of the stuff that you squeeze out on the spine of the dog. I don't know the dose, but it is sold in about four sizes that scale up with the weight of the dog.. It is absorbed through the dog's skin and is death to any flea or tick that bites that dog. There do not appear to be any negative consequences. A one year feeding study on dogs fed a regular diet with 1.8 parts per thousand of imidacloprid produced no observable effect. That gallon of raspberries with its
0.1 mg of possible imidacloprid corresponds to about 0.00002 parts per thousand for that one item,whereas the dogs were fed at the rate 1.8 parts per thousand on a day in day out basis for a full year.SO I SAY TO YOU, WHY NOT VERY JUDICIOUSLY USE THIS stuffto prevent our grapes and raspberries from being converted to brown lace.