Vol. 16—1962 - NorthEastern Weed Science Society

apparently due to severe competition from the growth of corn and yellow foxtail
grass. Atrazine kept other weeds out of the corn and, combined with the corn
competition, almost entirely inhibited the nutgrass.
Table 1. Tons per acre of Penn. 600Acorn, nutgrass'count, and forage survival
in plots treated with atrazine. R.I. 1960-61
307
Atrazine
b A
Red clover
& timothy
survival
Jet
5 4.8
7t 4.5
10 4.3
l2t 4.4
2t pre-,5 post- 4.6
no chemical 4.2
2112
2496
2160
2060
1056
1584
4
1
1
1
2
21
641
777
657
633
557
620
12 30- sOIl:
10 0- 5~
5 0- 5%
3 0- 1%
12 25- 75%
17 95-10O)b
l$D at 0.05 0.4
* estimated before CUltivation by 4 random 1 foot square counts per plot.
**these counts represent plants from tubers dormant during 1960.
Scarcely any nutlets were produc.ed by the small weak plants present on 9/7/60.
The nutlets which produce next year's crop of nutgrass lie dormant in the
soil undamagedby atrazine residues which maybe strong enough to destroy a crop
of red clover and timothy. The winter rye on the areas treated with more than
5 pounds of atrazine per acre was destroyed by sprinq,196l. The count of rye
seedlings per foot of row in mid-November1960range~ from 3 from the heaviest
rate of atrazine to 17 on the checks. The area was plowed in April 1961 and
seeded to red clover and timothy. The stand was unif~rm and vigorous for about
3 weeks, when the roots of the seedlings contacted tie residual atrazine.
Estimates of forage survival in mid-June showedcomplete elimination of the
forage crop where 10 to 12 Ib/A of herbicide were applied the previous summer.
Nutgrass, however, was growing vigorously in these plots, indicating a high tolerance
to atrazine where no other competition was encountered. The numbers of .
nutgrass plants per plot ranged from 557 to 771 with no inhibition indicated
from the previous herbicide treatment.
Procedures
1961 Tests
A nearby area heavily infested with nutgrass was selected for the 1961
tests. Both Penn. 602Aand Penn. 602 dwarf silage corn were used. Therewere
3 randomized replicates of each chemical for each variety. Atrazine SOWin. 40
gallons of water per acre Ivas sprayed at rates of 2, 4 and 6 pounds, resp~c~
tively, before the corn came up. S,imilar amounts wen applied 3 weeks after'
emergence of the corn. These res~'!:ive dates were ,rune 6 and 29. Granular
preparations were also used. These,,,~terials and the, results are shown in
table 2.'