Vol. 51—1997 - NorthEastern Weed Science Society

4
RESULTS ANDDISCUSSION
cal treatments significantly reduced biomass of annual weeds in 1992 relative to 2,4­
0, and the e weeder controlled weeds better than the rotary hoe (fable 2). In that year, late
planting all wed emergence of a dense cohort of green foxtail (Setaria viridis (L.) Beauv.)
synchronou ly with the crop, and this annual grass was not controlled by 2,4-0. In contrast,
annual w were less with 2,4-0 than with the mechanical treatments in 1995. In 1994, the
rotary hoei treatment had an annual weed biomass about equal to that with 2,4-0, and biomass
in the tine eeder treatment was significantly higher than in the rotary hoeing treatment.
Perennial w eds had lower biomass in the 2,4-0 treatment than in mechanical treatments in
1992, but . h variability obscured differences in the other two years.
Table2. eed biomass in mid-July, 1992, 1994 and 1995.
Rotary hoe
Tineweede
2,4-0
Untreated c eck
1992 1924 1995
Annuals Perennials Annuals Perennials Annuals Perennials
------------------------------------ g/m -------------------------------------
49 25 10 15 7 7
24 23 14 32 7 9
62 14 11 12 3 10
51 23 16 31 5 8
Untreated . others N.S. N.S. * N.S. N.S. N.S.
Mechanic v.2.4-0 + + N.S. N.S. + N.S.
Ro hoe. tine weeder + N.S. + N.S. N.S. N.S.
Statistical gnificance of orthogonal planned comparisons: +.P < 0.1; *.P < 0.05; N.S., P > 0.1
.shstudy of tine weeding of oats (12) found greater reduction in weed biomass than
In this study. many weeds survived cultivation because they had become
large to escape uprooting or burial by the time the crop was large enough to
withstand e second cultivation. On the other hand, a substantial proportion of the weeds also
escaped 2, -0, because they were not susceptible species, because they were sheltered by the
crop and 0 er weeds, or because they emerged after application (e.g. common milkweed
(Asclepias riaca L.). Overall, the three years of data indicate that the rotary hoe and tine
weeder w about equally effective. This result is interesting since (1) rotary hoes are rarely
used for w control in small grains, and (2) the rotary hoe runs 2 to 4 time faster than the tine
weeder.
hanical treatments reduced oat density relative to 2,4-0 in 1992, but not in the other
able 3). Oat density was lower in the rotary hoe treatment than in the tine weeder
treatment i 1994. These results are in accord with several previous studies indicating that crop
damage te ds to correlate with the degree of mechanical weed control in small grains (10, 12).
The crop s ived cultivation better in 1995 when it was planted at 4 em than with the 2.5 to 3
em plantin depths used in the previous years.