Table 6. Comparison of frequency, cover, and composition for three selected groups of plant species 
aggregated for 1977-79. 






Number Percent Relative Percent 
of Percent canopy Relative canopy species Importance 
Group species frequency cover frequency cover composition value 
Seeded nesting 
cover 5A 50.9 67.3 49.8 75.0 73.9 195.6 
Problem farm 
weeds 17b 27.5 16.6 28.7 17.4 18.7 64.8 
Noxious weeds 16 16.9 13.0 16.2 14.0 16.5 46.6 





Includes alfalfa, intermediate wheatgrass, tall wheatgrass, white sweet clover, and yellow sweet clover. 
bThese two groups had four species in common: quackgrass, Canada thistle, field bindweed, and sow thistle. Other species of problem 
farm weeds and noxious weeds are listed in Table 7. 
73.9% of the species composition (Table 6) and dominated 
over all other species except quackgrass. 
Problem cropland weed species. —Quackgrass, Canada 
thistle, field bindweed, and sow thistle are recognized as 
problem cropland weeds and as regulated noxious weeds 
(Table 7). The other 13 problem farm weed species that 
are not also recognized as regulated noxious weed species 
made up 5.3% or less of the relative canopy cover, 1.9% 
or less of the species composition, and 9.2% or less of the 
relative frequency (Table 8). 
Wild buckwheat, field bindweed, yellow foxtail, and 
western ragweed were problem cropland weeds that oc- 
curred commonly in SNC stands but they were not very 
obvious. Canada thistle, sow thistle, lamb’s quarters, 
kochia, and Russian thistle also occurred commonly in 
SNC stands and were very obvious. Common and showy 
milkweed, annual sunflower, giant ragweed, wild oat, 
field mustard, and common pigweed were obvious species 
in SNC stands but they accounted for very little of the 
species composition or the canopy cover. Quackgrass was 
by far the most common and predominant weed species. 
Regulated noxious weed species. —Fifteen species of 
noxious weeds are designated for legal regulation within 
the study region (Table 9). The regulated noxious weeds 
with the greatest relative values of frequency, canopy 
cover, and composition were quackgrass, Canada thistle, 
field bindweed, and sow thistle (Table 10). Quackgrass, 
which was governed by regulation only in South Dakota, 
was extremely common among these four species. Bull 
thistle was fairly common but not very obvious. Leafy 
spurge, wormwood, and plumeless thistle were not consis- 
tently present among stands but were usually dominant in 
the stands in which they occurred. 
Only 8 of the 15 noxious weed species covered by regula- 
tion occurred in quadrat samples (Table 9). Russian knap- 
weed, hoary cress, musk thistle, marijuana, horse nettle, 
perennial sow thistle, and poison ivy did not occur within 
the quadrat samples. However, musk thistle occurred in 
sample stands even though it did not occur within 
quadrats, 
With the exception of quackgrass, noxious weed species 
(Table 10) accounted for 1.2% or less of relative canopy 
cover, made up 0.3% or less of the species composition, 
and 3.0% or less of the relative frequency. These values 
should be recognized as minimum estimates becaus. sam- 
pling constraints excluded stands previously altereu by 
grazing, haying, mowing, or spraying with herbicides. 
The quantitative values for frequency, canopy cover, and 
composition of regulated noxious weed species represented 
in Minnesota, Montana, North Dakota, and South Dakota 
were closely comparable (if quackgrass were deleted from 
the data set for South Dakota) among the four States 
(Table 11). 
The cost of suppression of species of regulated noxious 
weeds and problem farm weeds is high. An example of 
such cost is given for various major land management 
agencies and for the private cropland operators for North 
Table 7. Comparison of problem cropland weeds with 
species of regulated noxious weeds in stands of seeded 
nesting cover. 


Regulated noxious 
weeds 
Problem cropland 
weeds 

Yellow foxtail 
Bull thistle 
Canada thistle 
Field bindweed 
Hoary cress 
Horse nettle 
Leafy spurge 
Annual sunflower 
Canada thistle 
Common milkweed 
Common pigweed 
Field bindweed 
Field mustard 
Giant ragweed 
Kochia Marijuana 
Lamb’s quarters Musk thistle 
Quackgrass Perennial sow thistle 
Russian thistle Plumeless thistle 
Showy milkweed Poison ivy 
Sow thistle Quackgrass 
Western ragweed Russian knapweed 
Wild buckwheat Sow thistle 
Wild oat Wormwood 

aScientific names appear in Table A-3. 
