American black walnut tress contain a tannic acid chemistscall juglone. The reddish yellow substance leaches fromleaves, and some believe exudes from roots, or transfersfrom branches and foliage to the roots. Tree physiologistsagree that roots of other plants that come in contact withthose black walnut tree roots die--even other black walnutseedlings.
Juglone is sometimes washed out of the still green walnutsduring late summer or even autumn rains. The growth ofplants 60 to 80 feet away are inhibited by the juglone. Thesubstance affects plants of various families. Studies havefound that tomatoes, alfalfa, potatoes, apples,blackberries, rhododendron, mountain laurel and pine treesare all affected.
According to a professor and extension forester at IowaState University, juglone is known to repel various gardeninsects. Just by placing branches of the tree around thehouse and under furniture dog and cat owners are amazed tofind that their pets have fewer fleas.
For more information on natural flea control:
http://www.apluswriting.net/onlynaturalpetstore/fleacontrol.htm
For more information on natural garden products:
http://www.apluswriting.net/garden/gardensalive.htm