Reducing agroecosystem vulnerability to weed invasion

There are many agronomic variables and management strategies other than herbicides that can be manipulated to discourage weed invasion. Combining several management strategies rather than relying on one will increase the likelihood of successful weed management. Encouraging optimal crop canopy health can guide decision-making and render agricultural land less susceptible to weed invasion. Then, when necessary, herbicides can be judiciously used to supplement cultural weed management techniques. In this review we have attempted to address two of the three major habitat characteristics that influence weed invasions - disturbances and, to a lesser extent, high resource ability. The remaining habitat characteristic, low species diversity, is difficult to address in modern agriculture, but can be an avenue of defence against invading species [89]. However, even intercropping, which is an effective ecological weed management technique [90], does not approach species diversity levels in natural ecosystems. A compromise to high species diversity in space is to maximize species diversity in time; this is best accomplished by ensuring that a given field is subjected to diverse rotational crops. Diverse crop rotations are probably the most effective management tool in maintaining crop health and limiting weed invasion opportunities. In the future, very clean (near weed-free) fields may not be considered acceptable [91]. We might do well to alter our view of what is desirable: from an “ultra-clean” crop with no weeds visible to a more species-rich field with sub-threshold communities of weeds. This approach could be termed “ecological weed management” [92]. Pest management in disciplines other than weed science may benefit from a few weeds [93, 94]. For example, root maggot (Delia spp) egg deposition and larval damage were reduced in plots where weeds were left in canola longer than the period recommended for optimal yields [95]. Combining and applying the techniques discussed above, reducing herbicide use, and tolerating low infestations of weeds may be the most sustainable form of weed management over the long-term. Ignoring ecological weed management techniques and maintaining current herbicide application practices will ensure a higher frequency of weed invasions of the resistant type [96, 97].

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