The neighbors keep blowing their dirt and leaves in our property?

We live in Los Angeles, own our home, the neighbors keep blowing their dirt and leaves into our property using a blowing machine, this happened right now!! I went outside and told them that when they blow their trash to our property they are blowing it into our washing machine and dryer, the husband says they don't do it that often but i said his wife does especially when I aint home she goes crazy with the blower trying to blow everything in site to our property even when she sweeps she sweeps the dirt to us, i don't understand why she just doesn't get a dust pan and throw it away, my husband says they are doing it on purpose but whats weird is because we don't have problems with the neighbors until now..can i take legal action?