Weeds can negatively affect quality, especially in the case of noxious weeds. Insect pests can lower forage quality, particularly if they cause significant leaf loss. Plant diseases can affect quality when they result in a shift in the species present in the field and when they promote leaf senescence. Insects and diseases generally have their greatest impact on yield and persistence of forages. Exceptions to the ranking Forage crops that accumulate a significant quantity of grain may increase slightly in overall quality with maturity as grain content increases in the plant.
Some species contain antiquality factors that can lower animal performance.
Variety can become the most important forage quality factor in cases where varieties are developed to significantly reduce or eliminate species antiquality factors, as in low-alkaloid varieties of reed canarygrass. Harvest and storage of a forage crop at a moisture content leading to spontaneous combustion would plainly become a most important factor. Or, if prolonged flooding or drought threatens a forage crop, environment becomes as important as any of the other factors. Certain soil fertility conditions, such as a very low pH, could eliminate alfalfa from a mixed seeding, thereby changing the species composition of the stand and greatly diminishing its quality. Significance of Factors that Influence Forage Quality All of the ranked factors above can be controlled to some extent through proper management.