Herbicidal activity against dicotyledonous plants

The herbicidal activities of hydantocidin and comexistin against dicotyledonous plants are shown in Table 3. Hydantocidin and comexistin also had potent herbicidal activities against dicotyledonous plants, but the killing effects on these plants were non-selective. One notable exception was that of corn seedings which were able to tolerate comexistin. 

In lA series, optimization was focused on the modification of substituents R and Y . Most lA showed good herbicidal activity against dicotyledonous plants at 2.25 kg ai/ha. In order to examine the effect of R R and R" in flie... 

All tested compounds, such as IC-22, IG-21, and HD-10 showed much higher inhibitory potency against PDHc from dicotyledons (pea or mung bean) than their inhibitory potency against PDHc from monocotyledon (rice). They also exhibited higher herbicidal activity against dicotyledonous plants (such as pea, common amaranth, rape) than monocotyledonous plants (such as barnyard grass and rice). The data are listed in Table 7.6. 

As shown in Table 8.3, clacyfos exhibited high herbicidal activity against dicotyledonous plants, rape, and common amaranth, at all growing stages at 450 g ai/ha. 

In conclusion, hydantocidin and comexistin show non-selective, broad spectrum herbicidal activity against annual plants including mono- and dicotyledonous weeds. In addition, hydantocidin had potent herbicidal activity against perennial plants, and comexistin may be useful for postemergence weed control with selective protection of com. 

In order to confirm the pre-emergence herbicidal activity of 1-(substituted phenoxyacetoxy)alkylphosphonates, seven compounds were chosen for further herbicide activity assay at a lower rate for pre-emergence herbicidal activity. As shown in Table 2.27, they displayed very poor herbicidal activity against tested plants for pre-emergence application except IA-4 and IC-2 with 48-53 % inhibitory potency against dicotyledonous plants at 450 g ai/ha. All tested compounds had no pre-emergence herbicidal activity against tested plants at 150 or 75 g ai/ha, irrespective of difference in structure. 

As described in Chaps. 2-6, most of l-(substimted phenoxyacetoxy)alkyl-phosphonates with 2,4-Cl2 as on the phenoxy-benzene ring exhibited much better herbicidal activity against dicotyledons than monocotyledons. Therefore, some alkylphosphonates and the corresponding sodium salts with 2,4-Cl2 as were chosen to examine their inhibition against PDHc from both dicotyledons and monocotyledons plants in vitro. Mung bean (V. radiata) and pea (Pisum sativum) as representative dicotyledonous plants, rice Oryza sativa) as a representative monocotyledonous plant were used in enzyme assays. The IC50 values of the tested compounds against plant PDHc are listed in Table 7.3. 

The above observations showed that HWS had good herbicidal activity against dicotyledonous weeds, but relatively weak effects against monocotyledonous plants, indicating that HWS should be considered as an selective herbicide against dicotyledonous weeds. 

Herbimycin was found to have potent herbicidal activity against most mono- and dicotyledonous plants, especially against Cyperus microiria STEUD but strong resistance by Oryza saliva [173]. It was also reported that herbimycins showed cytocidal activity on both HeLa cells and Ehrlich cells in vitro and could convert the transformed morphology of Rous sarcoma virus-infected rat kidney cells to the normal ones [177]. However, interest in geldanamycin and herbimycin increased greatly upon the discovery of their potent antitumor activity at nanomolar concentrations [178, 179]. 

In order to make sure the weed spectrum of cyclic phosphonates IVC-IVE, seven cyclic phosphonates were chosen to test at 150 and 75 g ai/ha for postemergence herbicidal activity against twenty-one species of dicotyledonous plants including fourteen species of weeds and seven species of crops. 

As shown in Table 5.32, IVG-2, IVG-4, and IVG-6 exhibited good post-emergence herbicidal activity against tested dicotyledonous plants, especially IVG-4 displayed a 100 % inhibition effect against all tested broad-leaved weeds at 150 g ai/ ha. However, there was no activity against monocot weeds. IVG-2, IVG-4, and IVG-6 will be further tested for their post-emergence herbicidal activity at a lower rate. 

Hydantocidin. Hydantocidin (182), C7H10N2O6, is elaborated by S. hygroscopicus (278). It is unique in that the anomeric carbon of the ribosyl moiety forms the spiro bond of hydantoin (279). The ribofuranose moiety which has been reported to be in a G -endo conformation (279) has been synthesized (280,281). Hydantocidin is a herbicidal nucleoside with activity against monocotyledenous and dicotyledonous plants. 

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