Graduate Thesis Or Dissertation
 

Seed depth influence on position of the growing point and chemical control of wild proso Millet (Panicum miliaceum L.)

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  • 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 alachlor (2-chloro-N-(2,6-diethylphenyl-N-(methoxymethyl)acetamide) 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 shallower seeds. 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 combinations. 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.
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