Biological weed management tactics rely on biological forces and factors to provide
weed control. These kinds of tactics fall into several groups including tactics
encouraging crop competition, the biological control of weeds, and crop management
cultural practices
Crop Competition Tactics
The primary source of weed control is crop competition with weeds. Tactics in this area
include anything that results in vigorous crop emergence and growth.
-manage crop habitat for maximum advantage to crop
-vigorous crop selection, vigorous varietal selection
-competitive plant seeding rates, crop populations and row spacing
Weed control can also be gained by tactics that discourage weed growth
-allelopathy and allelopathic crops
-cover and nurse crops
-smother crops
-mulching
-manipulate water supply, irrigation
-residue management
Biological Weed Control Tactics
Classical biological weed control uses natural enemies of weeds to kill or inhibit or
reduce thier impact. These natural enemies include insect predators, microflora like
bacteria and viruses, and fungi or plant pathogens. Pasturing by vertebrates (cattle,
goats, chickens, geese, etc.) in terrestrial habitats, and fish and aquatic mammals (e.g.
sea manatee) in aquatic habitats are also used.
Often these types of tactics are more difficult to use in annual cropping systems because:
-the host sources for the natural enemies are not present year round, and thier
populations can be eliminated from a field or reduced to such a point there is not enough
left to innoculate a field in the future. As such they often work best in large continuous
fields with large weed infestations, often monocultures of weeds.
-host specificity: the weed must be recognized and acceptable to the predator
-risk of introduction to non-target organisms must be avoided
Crop Production Cultural Tactics
Delayed planting can reduce weed problems. It can allow destruction of earlier emerging
weeds, possibly reducing populations that year. In Iowa this often works best in soybeans
as their is less yield penalty with a delay in planting than with corn.
Crop rotation reduces likelihood of buildup of particular weed species. Rotating to crops
with life cycles different than corn or soybeans is especially beneficial. Crop rotation
provides more flexibility in herbicide selectio. In some cropping systems fallowing can be
used to advantage.
Herbicide resistant crops may increase the selection of herbicides available for use in
that crop and improve control of certain weeds. Conversely, it may also lock-in and
decrease herbicide and cultivar selection (esp. if herbicide carryover is present). These
types of cultivars can minimize herbicide injury, or mask injury, from direct herbicide
applications. It can also be used to hide herbicide carryover.
Other crop cultural tactics that may provide weed control include:
-fertility manipulation: nutrients, lime and soil pH
-seed bank management
