Experiments were conducted to evaluate a biotype of smooth pigweed that had survived applications of sulfonylurea (SU) and imidazolinone (IMI) herbicides in a single season. The source field had a history of repeated acetolactate synthase (ALS)-inhibiting herbicide use over several years. Whole-plant response experiments evaluated the resistant (R11) biotype and an ALS-inhibitor susceptible (S) smooth pigweed biotype to herbicides from the SU, IMI, pyrimidinylthiobenzoate (PTB), and triazolopyrimidine sulfonanilide (TP) chemical families. The R11 biotype exhibited 60- to 3,200-fold resistance to all four ALS-Inhibiting herbicide chemistries compared with the S biotype. Nucleotide sequence comparison ofALSgenes from R11 and S biotypes revealed a single nucleotide difference that resulted in R11 having an amino acid substitution of aspartate to glutamate at position 376, as numbered relative to the protein sequence of mouseearcress. This is the first report of an amino acid substitution at this position of anALSgene isolated from a field-selected weed biotype. To verify the role of this mutation in herbicide resistance, theALSgene was cloned and expressed inArabidopsis. TransgenicArabidopsisexpressing thisALSgene exhibited resistance to SU, IMI, PTB, TP, and sulfonylaminocarbonyltriazolinone ALS-Inhibiting herbicide classes.
Studies were conducted to determine if mesotrione alone or in mixtures with low rates of atrazine would control Canada thistle. In the field, mesotrione applied alone did not adequately control Canada thistle, although smaller plants in the rosette stage of growth were more susceptible than plants in the bolting stage. A mixture of mesotrione at 105 g ai ha−1 and atrazine at 280 g ai ha−1 improved control of Canada thistle over that with mesotrione alone. In the greenhouse, mixtures of mesotrione plus atrazine at 560 g ha−1 reduced Canada thistle regrowth more than mesotrione alone or mesotrione plus 280 g ha−1 atrazine. Mesotrione plus atrazine mixtures increased the rate of tissue necrosis compared with the slower development of bleaching symptoms normally associated with mesotrione alone. Uptake, translocation, and metabolism of 14C-mesotrione in Canada thistle were generally slow, and results did not explain the increased control associated with mesotrione plus atrazine mixtures. However, higher levels of absorption and translocation and reduced root metabolism of mesotrione in rosette stage plants compared with bolting plants may explain the greater susceptibility to mesotrione in the rosette stage. The changes in symptomology and increased control with mixtures of mesotrione and atrazine were likely due to the interrelationship between the modes of action of these herbicides.
Field studies were conducted in 1999, 2000, and 2001 to investigate weed control and crop safety with preemergence (PRE) and postemergence (POST) applications of mesotrione alone and in tank mixtures with acetochlor and atrazine. Corn injury was less than 4% with all mesotrione treatments in 1999 and 2001, but it was 8 to 20% in 2000, when rainfall was 3.1 cm 7 d after PRE applications. Mesotrione PRE at 0.16 and 0.24 kg ai/ha did not adequately control most broadleaf weeds or giant foxtail. Tank mixtures of mesotrione plus acetochlor controlled smooth pigweed and giant foxtail but did not adequately control common ragweed, common lambsquarters, or morningglory species. Control by tank mixtures of mesotrione plus atrazine at 0.56 kg ai/ha was frequently low and varied with rainfall after PRE applications. All weed species were controlled 80% or more by mesotrione plus acetochlor PRE or atrazine plus acetochlor PRE followed by mesotrione POST at 0.11 kg/ha.
Several 7-hydroxypyrazolo[1,5-a]pyrimidines (1-21), 7-mercaptopyrazolo[1,5-a]pyrimidines (37-49), and 4-alkylpyrazolo[1,5-a]pyrimidin-7-ones (50-55) and the corresponding 4-alkylpyrazolo[1,5-a]pyrimidine-7-thiones (56-60) were synthesized and tested for antischistosomal activity against Schistosoma mansoni. Of the compounds examined, the greatest degree of activity in vitro was found with the 7-mercaptopyrazolo[1,5-a]pyrimidines. In particular, compounds 37 and 47 proved lethal at 100 micrograms/mL after an exposure of only 1 h. The 7-hydroxypyrazolo[1,5-a]-pyrimidines were not as active. None of the compounds exhibiting in vitro activity were active against S. mansoni in vivo.
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