This 4-yr experiment was conducted to develop a profitable conservation tillage system for dryland and furrow-irrigated cotton in a winter wheat-fallow-cotton cropping system at Etter, TX. In the 2-yr cropping sequence, winter wheat was planted immediately after cotton harvest in mid-November and furrow irrigated. Three residual herbicide treatment combinations with atrazine or propazine with fluometuron, or propazine alone were sprayed on stubble after wheat harvest in late June and compared to repeated applications of glyphosate and conventional disk tillage. Glyphosate was used to control weeds that escaped residual herbicides. The following March, fluometuron, prometryn, and 2,4-D were sprayed on no-tillage treatments and trifluralin was incorporated with conventional planting. Hoeing cost ha-1 to control Palmer amaranth and kochia averaged about $13 where trifluralin was used, $38 when initial treatment included fluometuron, $63 with propazine, and $93 when glyphosate alone was used to control weeds in fallow. Lint yield on dryland was about 390 kg ha-1 with disking and when glyphosate was followed by disking in spring, and 540 kg ha-1 with no-tillage. With irrigation, lint yield was 660 kg ha-1 with disking and 759 kg ha-1 with the best no-tillage treatment. Long-term profits ha-1 on dryland ranged from $340 for disking to $524 for propazine no-tillage. With irrigation, profit ha-1 ranged from $707 for disking alone to $751 when glyphosate was used after wheat harvest and followed by disking and incorporation of trifluralin the next spring before planting cotton.

Waterhyacinths grown outdoors were treated with combinations of 0 or 22 kg ai ha-1 of the plant growth retardant paclobutrazol and 0, 25, or 250 waterhyacinth weevils per culture tank under conditions of low (25% coverage) or high (100% coverage) plant densities. The low plant density treatments simulated a regrowth or colonization situation. Weevil feeding activity, canopy height, plant volume, leaf production, and leaf mortality were monitored biweekly for 22 weeks or until all plants had died. In high plant densities, weevil infestations increased leaf mortality rates while decreasing production rates, causing eventual plant death. At low plant densities, waterhyacinth plants partially compensated for weevil feeding by increased leaf production rates, thus enabling them to survive until the end of the study. Paclobutrazol reduced canopy height for about 3 months but had little effect on weevil feeding intensities. Combinations of weevils and paclobutrazol gave complete control of waterhyacinths regardless of plant densities. The combined effects were synergistic, with accelerated leaf mortality rates exceeding production rates leading to early plant death. This study demonstrated the potential for increasing effectiveness of waterhyacinth weevils using integrated strategies.

Downy brome is a grassy weed that infests millions of acres of winter wheat in the Western United States and costs farmers millions of dollars in lost yields. It can not be controlled consistently using chemicals or cultural practices. Isolates of naturally occurring rhizobacteria have shown potential as biological control agents for downy brome. Centrifuged supernatant from aerobic shake cultures of Pseudomonas fluorescens strain D7 suppressed germination of seeds and reduced root and shoot growth of downy brome in agar diffusion assays. The present article relates to the isolation and characterization of active compounds from strain D7. The active compounds were denatured and lost activity with commonly used techniques of extraction, concentration, and purification of microbial products. Two unusual techniques for isolation and partial purification of the active compounds from supernatant of strain D7 were developed. With one technique, supernatant was concentrated at 30 to 35 C under vacuum to 10% of the initial volume. Subsequently, the concentrate was chromatographed on sephadex gels to separate the active fraction. With the second technique, cell-free supernatant was frozen, with or without prior concentration, at −12 C for 12 to 24 h. The frozen supernatant was then thawed at 2 to 4 C, resulting in precipitation and crystallization of the active fraction. The active fraction isolated with either method inhibited downy brome. Inhibition was complete at concentrations as low as 1 mg total dry matter L-1 agar. Also, the active fraction inhibited the plant pathogenic fungus Gaeumannomyces graminis var. tritici. Chemical analysis of the active fraction complex revealed the presence of chromopeptides and other peptides, fatty acid esters, and a lipopolysaccharide matrix. Separation of any of the components from the complex resulted in nearly complete loss of activity against downy brome.

Rapid biochemical tests developed for measuring viability of nondormant crop seed have been used for measuring dormant weed seed viability. The objective of this experiment was to propose and test a new method for validating one of these assays, the tetrazolium assay, for determining dormant weed seed viability. Subsamples of partially dormant jointed goatgrass seed from the same seed source were periodically subjected to sequential germination and tetrazolium assays as they afterripened until seed were completely nondormant. Changes in percent germinated, percent tetrazolium positive (presumably dormant), and percent tetrazolium negative (presumably dead) seed were graphed versus time, and compared with models of valid and invalid cases. The validation method showed that the tetrazolium assay accurately determined the viability of seed remaining after a 3-wk germination period for jointed goatgrass seed removed from joints at the start, but underestimated the viability for seed afterripened and germinated in joints. The validation method showed that additional research is needed to refine the tetrazolium assay for this latter purpose.