Abstract
The juglone (5-hydroxy-1,4-naphthalenedione) can be found in the leaves and fruits of the black walnut (Juglans nigra L.). This
substance has an inhibitory effect on the growth of the vegetal species, phenomenon which is named allelopathy. The inhibitory
effect of the 50-100% concentration of this water extract, prepared from the black walnut fruits, on the seeds germination,
plantlets growth and peroxidasic activity – registered in the seedlings roots – was poor, compared to the allelopatic action of the
extract obtained from de black walnut young leaves, inhibition that was much stronger. Thus, the allelopathic phenomenon can
be used as a natural pesticides in the vegetal world, which limit the negative effects of the synthetic pesticides on soil. The
strongest negative reaction – the two types of aqueous extracts undergo tests – was highlighted on the red clover seedlings,
lettuce, while on the awnless brome, ray grass, while the peas, cucumbers and wheat the inhibitory effect was lower.