Weed intrusion into grasslands has usually been considered to be by forceful, aggressive, invader plants that become established by dislodging the desirable native grass plants.
Except, the invasion of these problematical unwanted weeds cannot occur without the previous creation of open spaces in grasslands from poor antagonistic management practices that causes great reductions in native grass herbage biomass production and causes decreases in grass density (basal cover).
The presence of weedy plants in grasslands are the visual symptoms of degraded grassland ecosystems; invading weeds are not the cause of degradation of the grasslands.
Prescribed control treatments designed only to reduce the weedy species can temporarily decrease the quantity of weeds, but weed reduction cannot restore the problems of deteriorated ecosystems.
Degraded grassland ecosystems continue to remain susceptible to reinfestation of undesirable weeds. Restoration of the degraded grassland ecosystems requires a change in management practices.
The open spaces are ideal habitat for invasion of opportunistic introduced grasses, weedy forbs, and woody shrubs and trees.
The rate of weed expansion within degraded communities progresses at different rates depending on the characteristics of the weeds intrinsic mechanisms to compete with degraded grass plants for sunlight, belowground nutrients, and soil water.
Noxious weeds advance rapidly in degraded communities because they produce numerous seeds with long distance distributions, have high germination rates and remain viable for long periods, the mature plants develop long lived subterranean caudex that produce large quantities of dense aerial stems that shade the grass understory, and produce extensive aggressive lateral roots and rhizomes with high numbers of vegetative buds that are easily activated. All of the noxious weeds have recently been introduced by human activity from other continents. Noxious weeds mandate obligatory prescribed treatments where ever they occur.
Aggressive weeds advance quickly in degraded communities because they produce large quantities of seeds that can be transported long distances, that readily germinate producing large dense patches that shade the grass understory. The perennial plants produce subterranean crowns that produce aggressive roots and rhizomes with numerous vegetative buds. The aggressive weeds have recently been introduced by human activity from other continents.
The prescribed treatments for the noxious and aggressive introduced weeds would include herbicides used as directed from this list: 2,4-D, dicamba (Banvel), picloram (Tordon), aminopyralid (Milestone), metsulfuron (Escort), imazapic (Plateau), triclopyr (Garlon), chlorsulfuron (Telar), and imazapyr (Arsenal). Please refer to the NDSU Weed Control Guide for more information on herbicides https://www.ndsu.edu/agriculture/ag-hub/publications/north-dakota-weed-control-guide.
Woody species that have originated in other regional floras have encroached into grasslands primarily during the 160 years after the implementation of the Homestead Acts of the United States and Canada.
Large trees reproduce by seed forming single stem plants usually long lived for 100's of years. Coniferous trees have no vegetative buds. Deciduous trees have vegetative buds on base of trunk, root crown, and lateral roots but have no rhizomes.
Small trees reproduce by seed and vegetative buds forming multi-stem thickets of aerial stems usually short lived for 10's of years. The perennating belowground structures are usually long lived for 100's of years.
Coniferous shrubs reproduce by seed forming numerous branches from a stem and have no vegetative buds.
Deciduous shrubs form dense or loose clonal colonies with multiple aerial stems arising from numerous vegetative buds on extensive rhizome systems.
Subshrubs have persistent perennial woody subterranean caudex or rhizome system with numerous vegetative buds which produce multiple annual herbaceous aerial stems that die back at the end of the growing season.
Succulent cacti have extensive shallow lateral root systems from which numerous jointed stems covered with barbed spines arise. Stem segments are readily detachable and transported, then develop roots and form new clumps.
The prescribed treatment for the woody trees, woody shrubs, woody subshrubs, and succulent cactuses would include application of tebuthiuron pellets (Spike 20P) at the rate of 0.5 lb ai tebuthiuron (2.5 lb product) per acre which is one pellet per square foot of land occupied by woody species. One application of tebuthiuron recycles the active chemical through the plant and soil for 5 to 6 years with some decrease in quantity each cycle. Several woody species may have stored greater quantities of carbohydrates than can be reduced during the active period of one application. A second application at half rate of 0.25 lb ai tebuthiuron (1.25 lb product) per acre would be necessary to deplete remaining carbohydrates. Rates greater than 0.75 lb ai tebuthiuron (3.75 lb product) per acre cause severe injury to perennial grasses. It is very important to read and follow label instructions before making a herbicide application.
The grasslands have a low number of grass weeds. These grass weeds have been introduced from other continents.
Perennial grass weeds produce numerous viable seeds, plants develop large mats with long branching rhizomes that have many vegetative buds that are easily activated.
Winter annual grass weeds grow from seeds, produce very small quantities of forage during a short period before flower stalks develop.
Poisonous grass weed is an introduced bunch grass with short rhizomes, and contains an endophytic fungus who’s toxins can cause four nasty degenerative diseases in livestock.
Removal or reduction of introduced noxious and aggressive weeds, encroached woody trees and shrubs, and introduced weedy grasses by prescribed control treatments from degraded grassland ecosystems does not recuperate the problems of deteriorated grassland ecosystems.
The open spaces that invited intrusion of the weeds still exist, retaining the grassland’s susceptibility for reinfestation of undesirable weeds. This evidence strongly shows that the previous and current grassland management practices are not ecologically sound and necessitates change of the management practices.
Grasslands that require prescribed control treatments to reduce or remove undesirable weeds also require change of the grassland management practices.
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