They will need to follow these directions unless there are state and local laws that are different. Have your parents call your local solid waste management authority, environmental agency or health department to find out how to properly dispose of leftover chemicals. Visit the State Contact Information on Household and Other Waste Disposal Website for additional information. I've seen a lot of weeds and insects in our garden. There are other things you can do to take care of weeds or insects in your garden besides just using a pesticide.
Some gardeners also use physical barriers to control weeds in their garden.
For example, between their rows of seeds they will put a layer of mulch or a tightly woven mesh material. Water can seep into the soil underneath these barriers but the sun can't get through, so the weeds don't grow. There are some insects that gardeners want in their garden. They eat other insects that destroy plants like aphids, mealybugs, whiteflies and mites. You can even buy these insects through some gardening catalogs.