Pre-emergence activity

August Chlorazine was clearly recognized as an herbicide with pre-emergence activity. Its first recorded selectivity was on carrots. 

Two general questions relating to the pre-emergence activity of the TFMS herbicides have been raised—namely ... 

Figure 2a. Three-dimensional perspective plot of the Hansch equation describing pre-emergence activity of 4-sub stituted TFMS herbicides on Foxtail grass (no Tween 80 present)...

CHART 3. PRE-EMERGENCE ACTIVITY RANGE OF RACEMIC AND CHIRAL AC 233,866... 

The phenyl tetrahydrophthalimides are primarily post-emergence herbicides for the control of broadleaf weeds, though they will show pre-emergence activity at higher rates of application. Flumiclorac-pentyl is a post-emergence herbicide for the control of broadleaf weeds such as cocldebur, common lambsquarters, jimsonweed, amaranthus, prickly sida, and velvetleaf in soybean and corn at 25-... 

Du Pont started relatively late in the triketone field, and directed their efforts toward novel fused bicyclic acids. As a result of their work in this area, they discovered the broad leaf weed cereal herbicide ketospiridox [58] (62, proposed common name. Fig. 4.3.10). Ishihara, inspired by earlier work of Hokko [59], identified some new benzoyl analogues with cyclic acetal meta-substituents (63 and 64, Fig. 4.3.11) that they claim have good pre-emergent activity in flooded rice paddy fields without damaging the rice seedlings [60]. 

IIB-1 (R =Na, R =H), IIB-2 (R =Na, R =Me), IIB-3 (R =Na, R =Et), IIB-4 (R =Na, R =n-Pr) and IIB-20 (R =Na, R =fur-2-yl) with 2,4-Cl2 on the phenoxy-benzene displayed 50-75 % pre-emergence herbicidal activity against tested dicotyledons. However their corresponding (9,(9-dimethyl phosphonates had no pre-emergence activity at 450 g ai/ha. These IIB had >90 % post-emergence herbicidal activity comparable to their corresponding (9,(9-dimethyl phosphonates at the same dose. Some sodium salts of (9-methyl l-(2,4-dichlorophenoxyacet-oxy)alkylphosphonic acids were further found to be potent PDHc inhibitors (see Chap. 7). 

As shown in Table 4.25, all IIIJ had <50 % pre-emergence activity against wheat, crab grass, barnyard grass, and rape. IIU-4 and IIU-6 displayed >90 % inhibitory effect against cucumber, lettuce, or setose thistle, and IIIJ-2 showed >90 % inhibitory effect against setose thistie in pre-emergence application at 2.25 kg ai/ha. 

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