For the second year my hawthorn and pear have been attacked by what my horticulturally trained daughter tells me is "pear slug". The leaves look as if leaf miner is the problem but looking a little closer little black worms are visible. I used "tanglefoot" this Spring and gave the soil a good dose of marine and mine own compost. I've managed to kill, manually, (i.e. squished with my fingers) and blasted with the hose the little pests on the pear (a four in one tree) but the hawthorne is far too large to cover in that manner. Has anyone had experience with this infestation?