A. Sundaram

Solubility products of six metal‐glyphosate complexes in water and forestry soils, and their influence on glyphosate toxicity to plants

Abstract The solubility products (Ksp) of 1:1 complexes of glyphosate, [N‐(phosphonomethyl)glycine], with Mg2+, Ca2+, Mn2+, Zn2+, Cu2+ and Fe3+, were determined in buffered (pH 7.0) distilled water, moist Ottawa sand, sandy loam and clay loam soils, each adjusted to 0.02 M with respect to KNO3. The Ksp values decreased in the order of Mg ≍ Ca > Mn > Zn > Cu > Fe, regardless of the medium in which they were determined. The constants measured in Ottawa sand were similar to those in water, but those in the forestry soils depended upon the type of metal ion involved. The values for the Mg, Ca, Mn and Zn complexes were about 2 to 3 times lower in sandy loam soil than those in water, but those in clay loam were about 3 to 10 times lower. The Ksp of the Cu and Fe complexes were similar to those in water regardless of the soil type used. In a bioassay experiment using tomato plants, immersed in the saturated solutions of the complexes or planted in the sand and soils containing saturated solutions of the complexe...

Foliar persistence and residual activity of tebufenozide against spruce budworm larvae

A field study was conducted to investigate the persistence of tebufenozide in white spruce foliage. An aqueous suspension concentrate formulation, RH-5992 2F, was sprayed over single trees at three dosage rates, 35, 70 and 140 g of the active ingredient (AI), in 2.0 litre ha -1 , using ground application equipment. Foliage was collected at different intervals of time up to 64 days after treatment and tebufenozide residues were measured by high-performance liquid chromatography. Foliage was also fed to laboratory-reared 4th- and 6th-instar spruce budworm (Choristoneura fumiferana Clemens). The data indicated that tebufenozide residues in foliage declined with time according to first-order kinetics. The average rate-constant and half-life of disappearance (DT 50 ) were 0.0340 and 20.45 days, respectively. Larval mortality declined gradually, corresponding to the residues, but was still appreciable (49 to 70%) when the larvae were fed with foliage collected 64 days after treatment. The amount of foliage consumed by the larvae decreased when foliar residues of tebufenozide increased, thus indicating anti-feedant activity of the chemical. The LD 50 values for both instars were similar and averaged c.25 ng per insect, but the LD 90 values were significantly lower for 4th-instar than for 6th-instar, at 63.6 and 96.1 ng per insect respectively. This implies that, theoretically, at a foliar concentration of 1.0 μg tebufenozide g -1 foliage (fresh wt), the spruce budworm larva needs to consume 65 to 100 mg of foliage in 10 days to cause mortality in about 90% of a population of the insect.

Formulation selection, and investigation of azadirachtin‐A persistence in some terrestrial and aquatic components of a forest environment

Five commercial formulations of azadirachtin-A (AZ-A) Margosan-O®, Azatin-EC®, Neem-EC®, RH-9999 and Neemix® 4.5, were investigated for their volatilization and washoff potential in laboratory studies. Prior to the investigation, RH-9999 (a wettable powder) was mixed with water to provide an end-use formulation containing 35.6 g AZ-A kg -1 , while the remaining four formulations were investigated without dilution. Volatilization and washoff of AZ-A occurred more from white spruce foliage than from wax-coated glass plates. Neem-EC provided the lowest amount of loss, whereas Margosan-O provided the highest. Physical properties and atomization behaviour of the five formulations indicated that Azatin-EC was highly viscous and caused phase separation in droplets collected on glass plates after atomization in a rotary atomizer. RH-9999, despite its low viscosity, caused phase separation in droplets because of the heterogeneity of the wettable powder formulation. Based on the minimum loss of AZ-A due to volatilization and washoff from spruce foliage, and on the minimum potential for phase separation in droplets after atomization in a rotary atomizer, Neem-EC was considered to be the most appropriate choice for use in field studies to investigate environmental persistence and fate of AZ-A in terrestrial and aquatic matrices of a forest ecosystem. The Neem-EC formulation was sprayed at 40 and 80 g AI ha -1 over single spruce trees and on litter and soil plots selected in a mixed-wood boreal forest in Ontario, Canada. In addition, outdoor aquaria containing stream water and sediment were also fortified with the formulation at 400 and 800 g AI ha -1 . Persistence of AZ-A was evaluated using one-year-old spruce needles, current-year shoots, spruce bark, litter, soil, stream water and sediment. The duration of persistence varied from 3 to 6 days in terrestrial matrices, whereas it ranged from 8 to 13 days in water, and 2 to 3 days in sediment. The half-life (DT 50 ) values ranged from 10.7 h (for soil) to 71.6 h (for spruce bark) at the lower dosage rate, and from 18.8 h (for litter) to 76.2 h (for bark) at the higher dosage rate. The DT 50 value for stream water was about 35 h regardless of the dosage rate applied. The data indicated that AZ-A was appreciably labile and short-lived in different forestry matrices, with low DT 50 values.

Dissipation kinetics of azadirachtin in some forest matrices and its systemic translocation in conifers for spruce budworm control

Abstract Field microcosm studies were conducted to investigate the deposition, persistence, translocation and bioactivity of the botanical insecticide azadirachtin‐A (AZ‐A) in young spruce trees. The deposition and persistence of AZ‐A in aspen foliage, forest soil and litter were also studied. AZ‐A residues in the different matrices were monitored at intervals of time after spray application of Neemix® 4.5 formulation at 100 g AZ‐A in 2.3 L/ha. The dissipation half‐lives in the matrices ranged from 16.9 to 33.6 h. AZ‐A was translocated and concentrated in the growing parts (especially the shoots) of spruce trees, after treatment by trunk injection (Tl), basal bark painting (BBP) and foliar painting (FP) of the Neemix 4.5 formulation. Systemically translocated and accumulated AZ‐A residues in the shoots after Tl and FP were found to be effective against spruce budworm (Choristoneura fumiferana Clemens.) larvae. Results suggest that Tl may be a useful way of using neem insecticide to protect high value tree...

Spread factor, penetration depth and stain height of drops of aqueous pesticide mixes on kromekote® cards

Abstract Spreading behaviour of water‐based pesticide drops ranging from 50 to 450 μm in diameter was studied on Kromekote® cards (K‐cards), using spray mixes of five chemical insecticides, and three commercial formulations of Bacillus thuringiensis var. kurstaki (BTK). Spread factors (SF, the ratio of the stain diameter ‘D’ of a drop on the card to the spherical diameter ‘d’ of the drop making the stain) ranged from 1.0 to 4.5. The investigation on the role of drop size on SF, hp (the penetration depth) and hE (the stain height), showed that drops of the chemical insecticides underwent complete spreading and penetration into the card with no hE above the card surface, and that both SF and hp increased with drop size. The mixes of BTK underwent only partial spreading. The smaller drops (50 to 150 μm) of Dipel® 6AF and Thuricide® 48LV, were spherical, but the medium, ones (150 to 300 μm) provided spherical segments, and the larger drops (300 to 450 μm) formed flattened cylinders. All BTK drops showed hE bu...

Persistence of Bacillus thuringiensis deposits in a hardwood forest, after aerial application of a commercial formulation at two dosage rates

Abstract A commercial formulation of Bacillus thuringiensis Berliner var. kurstaki (BTK), Foray® 48B, was sprayed aerially over four blocks B13, B14, B15A and B15B in an oak forest in Wayne County, Pennsylvania during May 1990. B13 and B14 were sprayed at 75 billion international units (BIU) in 5.91 litres/ha and the other two at 50 BIU in 3.94 litres/ha. Oak foliage was collected at different intervals of time after treatment. Three types of bioassays were conducted against fourth instar gypsy moth larvae, viz., direct feeding of sprayed foliage, feeding on diet containing homogenized foliage, and force‐feeding of foliar extracts. Larval mortalities were converted into international units of BTK activity per unit area (IU/cm2) of foliage. Foliar extracts were also subjected to enzyme‐linked immunosorbent assay (ELISA) to determine the concentration of delta‐endotoxin protein. Regardless of the type of bioassay used, bioactivity of BTK persisted in foliage for about a week in all the blocks. The half‐life...

Spray deposition and persistence of a Bacillus thuringiensis formulation (Foray® 76B) on spruce foliage, following aerial application over a northern ontario forest

Abstract A commercial formulation of Bacillus thuringiensis Berliner subspp. kurstaki, Foray® 76B, was sprayed aerially at a dosage rate of 30 BIU in 1.5 L per ha, over a 500‐ha block in a mixed spruce‐fir forest in northern Ontario, Canada, using two fixed‐wing aircrafts equipped with rotary atomizers. Droplet size spectra were determined on Kromekote® cards at ground level, and spray deposit recovery was assessed on glass plates. Initial deposits and persistence of different components of the formulation were determined on canopy foliage by bioassay using spruce budworm (Choristoneura fumiferana Clem.) larvae as the indicator species, and by different quantification techniques that were newly developed in this study. For quantification of foliar deposits, the total protein content was determined and foliar residues were expressed in ng per g foliage (fresh weight). Foliar extracts were acidified to precipitate the protein. The supernatant was subjected sequentially to n‐hexane and n‐octanol extraction, ...

Rain‐washing of foliar deposits of Dimilin®WP‐25 formulated in four different carrier liquids

Abstract Dimilin® WP‐25, a wettable powder formulation of diflubenzuron (DFB) [1‐(4‐chlorophenyl)‐3‐(2,6‐difluorobenzoyl) urea], was formulated in four different carrier liquids, viz., water; a light petroleum paraffinic oil, ID 585; a heavy paraffinic oil, Sunspray® 7N; and a 1:2 mixture of a light petroleum aromatic solvent (Cyclosol® 63) and canola oil; to provide four end‐use mixtures, Dim‐W, Dim‐585, Dim‐7N and Dim‐Cy‐C respectively, each containing 28 g of DFB per litre. Balsam fir branch tips clipped from greenhouse‐grown seedlings, and sugar maple branch tips clipped from field‐grown young trees, were exposed to uniform‐sized droplets (ranging in diameters from 135 to 190 μm) of the four end‐use mixtures which were atomized using a monodispersed droplet generator. Droplets were collected on the fir and maple branch tips and the initial residue per g fresh weight of foliage was determined by high‐performance liquid chromatography (HPLC). The branch tips were exposed to cumulative rainfall of 3, 6 a...

Persistence of bacillus thuringiensis deposits in oak foliage, after aerial application of foray® 48b using rotary and pressure atomizers

Abstract A commercial formulation of Bacillus thuringiensis var. kurstaki (Btk), Foray® 48B, was sprayed aerially over blocks selected in a hardwood forest in the USA at the rate of 90 billion international units in 7.0 L/ha, using a helicopter and a fixed‐wing aircraft, each fitted with pressure or rotary cage atomizers. Droplet size spectra were assessed on foliage using two new parameters, viz., droplet‐spot number median diameter (S‐DN.5) and protein mass median diameter (S‐DM.5). The data indicated that when rotary cage atomizers were used, the droplet spectra were narrow with smaller S‐DN.5 and S‐DM.5 values, than when pressure atomizers were used. The protein mass deposits corresponded with the droplet sizes, i.e., the larger the droplet sizes, the greater the deposits. The initial bioactivity did not correspond with the deposits, because the greater the deposits the lower the activity. Persistence of bioactivity also showed irregularities, indicating the role of environmental transformation of for...

Effect of tracer dyes on initial deposits and persistence of bacillus thuringiensis subsp. kurstaki toxin after application of two commercial formulations onto spruce trees

Abstract The effect of two tracer dyes [Erio Acid Red (EAR) and Acid Black 48 (AB‐48)] on initial deposits and persistence of Bacillus thuringiensis subsp. kurstaki (Btk) toxin (delta‐endotoxin) was studied after spraying two commercial formulations, Foray® 48B and Foray® 76B, over potted white spruce [Picea glauca (Moench) Voss] seedlings, at a dosage rate of 30 billion international units (BIU) per ha. Spray was applied using a spinning disc atomizer calibrated to deliver droplet sizes similar to those utilized in ultra‐low‐volume (ULV) treatments in operational insect control programs. The sprayed seedlings were left outdoors at the Sault Ste. Marie laboratory for 18 days under natural conditions of sunlight, wind and rainfall. Initial deposits and persistence of delta‐endotoxin protein in spruce foliage were determined by immunoassay [enzyme linked immunosorbent assay (ELISA)] quantification of the delta‐endotoxin. The total protein (inactive plus active) and delta‐endotoxin (active protein) concentra...