- Wild proso millet (Panicum miliaceum L.) is a serious weed
recently infesting sweet corn fields in the Willamette Valley of
western Oregon. Field and greenhouse experiments were conducted to
determine the importance of seed depth in the position of the growing
point of wild proso millet seedlings and in the performance of five
herbicides. The effects of atrazine (6-chloro-N-ethyl-N'-(1-
methylethyl)-1,3,5-triazine-2,4-diamine) and tridiphane (2-(3,5-
dichloropheny1)-2-(2,2,2-trichloroethyl) oxirane) combinations and
soil placement on wild proso millet control were also studied.
Shallow seed depths (0 and 3 cm) resulted in more seedlings with
the growing point above the soil surface than deeper depths.
Mesocotyl length was also directly influenced by seed depth. Wild
proso millet emerged from the deepest seed placement which was 15 cm.
Seedlings from seeds deeper than 6 cm emerged slower than from
In the first field experiment, seed depth did not influence the
performance of alachlor, atrazine, tridiphane, pendimethalin (N-(1-
ethylpropy1)-3,4-dimethy1-2,6-dinitrobenzenamine), and EPTC (S-ethyl
dipropyl carbamothioate). In the second field experiment, seed depth
influenced the performance of these herbicides. Pendimethalin (2.0
kg/ha), atrazine + tridiphane (1.1 + 0.5 kg/ha), alachlor (2.2
kg/ha), and EPTC + dichlormid (3 kg/ha) were less effective at 1 cm
than at 6 or 11 cm wild proso millet seed depth. Higher rates of the
same herbicides were more effective on plants from seeds at 1 cm than
from either 6 or 11 cm. This suggests that higher rates are needed
to control wild proso millet from shallow seeds. Perhaps the growing
point above the soil surface is reducing the effectiveness of soil
applied herbicides on wild proso millet.
Early postemergence applications of atrazine (0.56, 0.84, 1.68,
and 2.24 kg/ha) and tridiphane (0.28, 0.56, and 0.84 kg/ha) alone and
in combinations decreased wild proso millet dry weight and height.
Plants treated with atrazine or tridiphane alone did not differ in
height or dry weight. There was synergism in the atrazinetridiphane
Shoot exposure was more damaging to wild proso millet seedlings
than root exposure at the three alachlor rates used (0.1, 0.5, and
1.0 ppm). Shoot or both shoot and root exposure caused equal
reductions in height or dry weight of wild proso millet. These
results indicate that alachlor should remain in the shoot region of
emerging seedlings for best wild proso millet control.