12 
Table 8. Frequency, canopy cover, and composition values for problem farm weeds in the study region. 







Percent Relative Percent 
Percent canopy Relative canopy species Importance 
Species and year (N = 17) frequency cover frequency cover composition value 
Annual sunflowera 
1977 3.7 0.2 0.9 0.2 0.1 1.2 
1978 0.4 T 0.1 T T 0.1 
1979 0.4 T 0.1 T iT 0.1 
Canada thistle 
1977 7.0 0.5 1.6 0.4 0.1 2.1 
1978 12.6 0.5 2.9 0.5 0.1 30 
1979 13.0 0.6 3.3 0.8 0.2 4.3 
Common milkweed 
1977 0.7 T 0.2 T fe 0.2 
1978 1.5 iT 0.3 T T 0.3 
1979 1.7 0.1 0.4 0.1 : 0.5 
Common pigweed 
1977 0.2 T T T T T 
1978 — — — = _ _ 
1979 ~ — — _ - _ 
Field bindweed 
1977 12.4 12 2.9 1.1 0.3 4.3 
1978 12.4 1.0 2.9 1.1 0,2 4,2 
1979 9.6 0.9 2.5 1.2 0.3 4.0 
Field mustard 
1977 3.2 0.1 0.7 0.1 T 0.8 
1978 0.7 x 0.2 Al T 0.2 
1979 0.6 - 0.2 T T 0.2 
Giant ragweed 
1977 = -- _ _ = = 
1978 0.1 T T T 7 T 
1979 0.1 T T Tt T T 
Kochia 
1977 3.7 0.2 0.9 0.2 0.2 1.3 
1978 2.4 0.2 0.6 0.2 0.5 1.3 
1979 0.5 T 0.1 T T 0.1 
Lamb’s quarters 
1977 15.0 0.4 3.5 0.4 0.3 4,2 
1978 2.2 0.1 0.5 0.1 T 0.6 
1979 2.7 0.1 0.7 0.1 T 0.8 
Quackgrass 
1977 28.1 11.4 6.6 10.2 11.7 28.5 
1978 41.6 11.2 9.7 12.1 17.7 39.5 
1979 38.0 9.3 9.7 12.0 18.3 40.0 
Russian thistle 
1977 7.3 0.3 1.7 0.3 0.2 2.2 
1978 0.7 al 0.2 T = 0.2 
1979 0.3 T 0.1 T T 0.1 
Showy milkweed 
1977 0.4 Z 0.1 T T 0.1 
1978 0.1 T T T T © 
1979 0.3 rE 0.1 T T 0.1 
