What does this chemical energy reaction describe? Water-hydrogen+oxygen

may be you mean water= hydrogen + oxygen, this reaction describes that water is made by the combination of hydrogen and oxygen.

the major pests we deal with are insects, weeds and fungal diseases. a pesticide is a product, whether organic or chemical, used to kill the target pest. there are other techniques gardeners should use that can prevent the severe infestations that make the use of pesticides necessary