Weeds as alternate and alternative hosts of crop pests

Weeds pose a perpetual menace both in cropped and non-crop areas. They provide food, shelter and reproductive sites for various pest organisms (plant pathogens, insect pests, mites, nematodes, rodents and others), and thereby play a key role to serve as alternate as well as alternative hosts. Many plant pathogens (fungi, bacteria and viruses) may also have either narrow or wide host range on which they pass at least a part of their life cycle. Alternate hosts from plant families other than the family of main (primary) host help a crop pest not only to complete its life cycle, but also support the crop pest to survive under unfavourable conditions and non-availability of main host. Alternative (collateral) hosts of similar plant family as of primary host help a crop pest to survive during the periods when main hosts are not seasonally available, and while the pests subsequently migrate back onto the main host plants. Although there are some similarities, differences between alternate and alternative hosts are aptly justified, signifying the relative importance of alternative hosts over the alternate ones. There may also have the possibilities of an elevated weed status from its indirect role as alternate and alternative hosts to directly as the main host under certain circumstances. However, eliminating harmful weeds (alternate and alternative hosts) from the margins of crop fields as well as noncrop areas at the extent possible or feasible is imperative to preventing continued infection and infestation of crop plants from different pest organisms.