When is a plant considered a weed?Experts at Penn State University have a simple answer:When the undesirable qualities outweigh the good qualities.Consider the fact that crops generally produceseveral hundred seeds from each plant.By comparison, each weed plant can produce tensor even hundreds of thousands of seeds.And some buried seeds can survive up to forty years-- or even longer.Eradicating weeds means that you have to removeall the seeds and roots so the plants will not grow back.But birds or the wind can reintroduce them to the land.A more common way to deal with weedsis to control them enoughso that the land can be used for planting.Experts advise using twoor more control methods to deal with weeds.Chemical weed killers or natural treatmentslike corn gluten can suppress weed growth.Dense planting of a crop can also act as a natural control.Bill Curran is a professor of weed scienceat Penn State, in University Park, Pennsylvania.He says one of the most common methodsfor suppressing weeds is dense planting.He says a dense, competitive cropthat quickly shades the soil will help suppress many weeds.The seeds need light to grow,so blocking the sun will reduce weed growth.Other controls include turning over the soil,pulling the weeds or covering themwith mulch made of shredded wood,garden waste or other material.But even mulch has its limits.Natural resource specialists point outthat weeds can be transported in mulch.This is also true of soil, grain, hay and animals.Yet animals like sheep or goats eat weeds,so they can provide a biological control.Insects and other organismscan also act as biological controls.Preventing the spread of weedsis an important part of weed management.Farm vehicles should be kept out of areas with weeds.If that is not possible,then clean off the equipment and your shoes when leaving.Some people burn weeds or bury them deeplyor make them into mulch.Professor Curran says another wayto make use of weeds is to compost them.Heat is produced in the process of makingorganically rich compost to improve soil.The heat will kill many, though not all, weed seeds.The same is true for seedsthat pass through animals that graze on weeds.And that's the VOA Special English Agriculture Report,written by Jerilyn Watson.Tell us about your own fight against weeds.Share your stories at 51voa.com.