Some species shed seed from the plant before it is fully mature , requiring an after-ripening period before germination can occur. Seeds of certain species have been shown to survive in soil for long periods of time. Lotus seeds, found in a lakebed in Manchuria, were approximately 2000 years old, still viable and capable of germinating. Several turf weeds, such as green foxtail and curly dock, have germinated after 38 years of dormancy. The greatest influence weeds exhibit on turf is through direct competition for water, light, space, and nutrients.
Weeds also influence turf in other important ways.
Turf injured from insects or other animals, diseases, excessive wear, compaction, or misuse of fertilizers or pesticides results in weakened turf and thin or bare areas. Weeds often occupy these areas more rapidly than the desired turfgrass. Loss of turf cover greatly reduces overall quality and the turf's ability to compete. Weeds, during normal development, can produce chemicals which, when exuded into the soil solution, are toxic to surrounding turfgrass plants. These allelopathic compounds can have a tremendous impact on the balance of plant species in a given area.