Pesticides, timing and unintended harm

The most common mistake is spraying insecticide at dusk because 'the bees have stopped flying'. Bumblebees forage until near-dark in midsummer. Solitary bees may still be active at 8 p.m. if it is warm. Spray residues on open flowers remain toxic for hours or days, depending on the active ingredient. A wet spray on a courgette flower at 9 p.m. will kill the first bee that visits at 7 a.m. the next day. If you must spray, do it after petal drop, never during flowering.

Neonicotinoids and many synthetic pyrethroids are catastrophic to bees even at sub-lethal doses — they disrupt navigation, memory and foraging efficiency. Some formulations sold as 'garden-safe' are only safe relative to agricultural concentrates, which is no reassurance. The beneficial gardener uses no routine prophylactic sprays. You tolerate aphids until ladybirds or hoverflies arrive. You hand-pick sawfly larvae. You net brassicas against cabbage white. You accept that pest control is slower and less total, but it is also cumulative and self-reinforcing.

Organic does not mean harmless. Pyrethrum (natural, derived from chrysanthemums) kills bees on contact. Insecticidal soap kills soft-bodied insects indiscriminately, including hoverfly larvae if you drench a colony. The safest approach is physical removal, water jets, companion planting to confuse scent, and patience. If you must spray, use a targeted product on a single affected plant at dusk when flowers are closed, and rinse flowers open the next morning if you can. Better: grow a garden so full of predators that you never need to.