The Effect of Formulation, Dose, and Adjuvants on Uptake of Phosphite Into Pine Foliage.

The aim of this investigation was to determine the effect of dose and adjuvant on uptake of two phosphite products (Phos-A and Phos-B) into Pinus radiata needles. In experiment 1, uptake of 6 kg ha-1 phosphite, applied as Phos-A, in 100 liters of water, together with an organosilicone superspreader (0.2%), was high (>60%). Uptake at doses greater than 6 kg ha-1 (12, 15, 18, and 24 kg ha-1) and applied in volumes less than 100 liters of water (75 and 50 liters) was poor (1 to 30%). Using stability tests and NMR spectroscopy in experiment 2, this appeared to be linked to a concentration dependent reaction resulting in the degradation of the organosilicone adjuvant that facilitated uptake of Phos-A. In experiment 3, uptake of phosphite applied as Phos-B, between 6 and 24 kg ha-1 in 100 liters of water, was tested alone and with four adjuvants (an organosilicone, alcohol ethoxylate, lecithin, and esterified seed oil). Uptake of Phos-B without any adjuvant was high (>50%) across all doses, indicating the formulation was optimized for P. radiata needles. Uptake of Phos-B increased with concentration up to 72% at 24 kg ha-1 in 100 liters of water. Symptoms of phytotoxicity were observed at rates of ≥12 kg ha-1. This study highlighted the effect of formulation, dose, concentration, and adjuvant on the uptake of phosphite into P. radiata needles.

Effect of dose and adjuvant on uptake of triclopyr and dicamba into Pinus contorta needles.

Management of dense infestations of wilding Pinus contorta in New Zealand requires high doses of herbicides; 18 kg active ingredient (a.i.) ha-1 triclopyr and 5 kg a.i. ha-1 dicamba are used in combination with a complex mix of adjuvants (methylated seed oil, non-ionic surfactant and ammonium sulfate) and other active ingredients. From the perspective of cost and environmental impact there is a need to reduce the complexity of this tank mix and the rates of active ingredients. Using radiolabelled herbicides, this study evaluated the effect of dose and adjuvants (crop oils, non-ionic surfactants, and organosilicones) on needle injury and uptake of triclopyr and dicamba into P. contorta needles at 24 hr or 7 days after treatment (DAT). The uptake of triclopyr decreased significantly with increasing concentration (0.75%-6%) resulting in the highest uptake dose at the equivalent of 18 kg a.i. ha-1 triclopyr at 7 DAT. When applied at 18 kg a.i. ha-1, none of the adjuvants tested significantly increased the uptake of triclopyr (applied as Grazon®), with ~50% uptake occurring at 7 DAT. The uptake of dicamba (applied as Kamba® at 5 kg a.i. and 10 kg a.i. ha-1) was significantly affected by dose and adjuvants. The uptake of dicamba applied at 5 kg a.i. ha-1 was low at 7 DAT with no adjuvant (31%); however, use of a methylated seed oil doubled the uptake. When triclopyr and dicamba were applied together, there was no evidence that either active ingredient negatively affected uptake of the other, with triclopyr enhancing uptake of dicamba. These results show potential to reduce the amount of herbicide used for conifer control without compromising efficacy.

Visualisation of the uptake of two model xenobiotics into bean leaves by confocal laser scanning microscopy: diffusion pathways and implication in phloem translocation.

The diffusion of two fluorescent dyes, Oregon Green 488 (Oregon Green) and Rhodamine B into the leaves of broad bean (Vicia faba L) plants was studied to simulate the foliar uptake process of pesticides. The uptake rate of these model xenobiotics into bean foliage was measured using a standard leaf surface wash-off method. Diffusion into leaf tissues was visualised in vivo by confocal laser scanning microscopy (CLSM). The moderately lipophilic dye (Rhodamine B) showed faster uptake than the hydrophilic one (Oregon Green), despite the former being a larger molecule. While no distinct channels or domains for preferential entry of any of the dyes could be detected in the cuticle layer by CLSM, two different diffusion patterns were identified for the movement of these two dyes after traversing the cuticle. Upon desorption from the cuticle, Rhodamine B diffused extensively into the vacuole of the epidermal cells. Further transport of this dye from the epidermal cells to the mesophyll cells was not observed. In contrast, Oregon Green was found in the epidermal cell walls and cytoplasm, and was also present in the mesophyll cells. Examination of the petioles of the treated leaves revealed that, once absorbed, Oregon Green moved readily out of the treated leaf, whereas Rhodamine B did not show any phloem translocation. It is proposed that these two different diffusion characters may be responsible for the contrasting phloem mobility of the two xenobiotics. The results are discussed in relation to the current knowledge on the uptake, translocation and efficacy of pesticides as influenced by their properties.