Spray solutions containing a cationic or a nonionic surfactant were applied to six plant species at a broad range of concentrations. The species investigated were three weeds (black nightshade, chamomile, and quackgrass) and three crops (winter wheat, pea, and tomato). The microroughness of the leaf surface as revealed by scanning electron microscopy appeared to be a relevant retention-determining factor. Plant species with crystalline epicuticular waxes (winter wheat, pea, and quackgrass) retained much less spray solution than the other species, which are characterized by a smooth cuticular surface. The two surfactants enhanced retention on species with a reflective surface, whereas retention on black nightshade, chamomile, and tomato was hardly influenced by addition of surfactants. The two surfactants had a similar influence on the retention. Surfactant at 1% (wt/v) enhanced retention on pea, winter wheat, and quackgrass by factors of twenty, six, and four, respectively, compared with retention without surfactant. A linear relation between retention and logarithm of surfactant concentration was observed. Retention of spray drops was related not to equilibrium surface tension of the spray solution but rather to dynamic surface tension.

Field and greenhouse experiments were conducted to investigate the influence of two cationic alkylamine surfactants, three nonionic surfactants, and ammonium sulfate on the performance of glyphosate (isopropylamine salt) against quackgrass. In the field experiments, the reinfestation of quackgrass in the year after treatment was zero or negligible in all plots that received the recommended rate of glyphosate (1.44 kg ae/ha). At one-fourth of the recommended rate (0.36 kg ae/ha) the glyphosate-adjuvant combinations also severely inhibited the reinfestation of quackgrass. At the low herbicide rate and without ammonium sulfate, lipophilic surfactants were less effective than more hydrophilic surfactants. In the greenhouse experiments, the glyphosate doses giving 50% response (ED50) were determined. Ranking of the surfactants according to the ED50for glyphosate demonstrated a similar result to that observed in the field experiment. Ammonium sulfate added to the glyphosate-surfactant combinations reduced the ED50for glyphosate 5-fold. The field and greenhouse experiments demonstrated that two hydrophilic nonionic surfactants enhance glyphosate efficacy against quackgrass to the same extent as the hydrophilic cationic tallowamine surfactant. These two nonionic surfactants have a relatively low toxicity to non-target organisms and may substitute the more toxic alkylamine surfactants.

No abstract

Field and growth chamber experiments were conducted to investigate the influence of emulsifiable mineral oil, emulsifiable rapeseed oil, and the emulsifier (polyoxyethylene C13/C15oxo alcohol) on the efficacy of phenmedipham and metoxuron against common lambsquarters, and of sethoxydim and the ethyl ester of quizalofop against winter wheat. In field studies, mineral oil and rapeseed oil were equally effective in increasing the efficacy of phenmedipham (0.24 and 0.48 kg ai/ha), metoxuron (0.6 and 1.2 kg ai/ha), and sethoxydim (0.05 and 0.1 kg ai/ha), but mineral oil was superior to rapeseed oil with quizalofop. In growth chamber studies, mineral oil and rapeseed oil were equally effective in increasing the efficacy of metoxuron, sethoxydim, and quizalofop-ethyl, but rapeseed oil was more effective than mineral oil with phenmedipham. Both in the field and in the growth chamber, the emulsifier was at least as effective as the oil adjuvants, when combined with all herbicides except sethoxydim. The herbicide doses giving 50% response (ED50) were determined for the growth chamber experiments. The adjuvants reduced the ED502.7-fold with phenmedipham, 51-fold with metoxuron, 2.7-fold with sethoxydim, and 6.8-fold with quizalofop when averaged over the three adjuvants. It was concluded that rapeseed oil (all tested herbicides except quizalofop) or the emulsifier (all tested herbicides except sethoxydim) can serve as a substitute for mineral oil.

The influence of calcium, iron, magnesium, other cations, and mixtures of cations on the activity of glyphosate and the interaction with pH is reviewed, discussed, and demonstrated with laboratory data. The strategy to overcome antagonistic effects of the cations via use of adjuvants is discussed and illustrated with data. The influence of calcium concentration on glyphosate efficacy was investigated on black nightshade (Solanum nigrum L.) by monitoring glyphosate activity via fluorescence technology and inhibition of growth. Giant foxtail (Setaria faberi Herrm) was also used for biological evaluation. Calcium concentrations equal to the glyphosate concentrations were most antagonistic; higher concentrations of calcium were less antagonistic. Different adjuvants were tested to overcome the antagonistic effect of calcium. Results are discussed in relation to the physical chemical properties of the adjuvants. With a more appropriate scientific base, remedial measures may protect field performance of glyphosate and reduce farm costs.