Toxicity of the herbicide glufosinate-ammonium toTetranychus urticae(Acari: Tetranychidae) under laboratory and field conditions

Abstract

: The toxicity of herbicides widely used in apple orchards to the twospotted spider mite (T etranychus urticae) was evaluated in laboratory and Ðeld studies. In a laboratory study with susceptible T . urticae, glufosinate-ammonium was highly e †ective against larvae, protonymphs and adults, but non-toxic to eggs. Its efficacy was much greater than that of the commonly used acaricide azocyclotin. The immatures died within 24 h after treatment, suggesting that the nymphicidal action may be attributable to a direct e †ect rather than an inhibitory action of chitin synthesis. Glufosinate-ammonium showed a positive temperature coefficient of toxicity against T . urticae adults at six temperatures from 10 to 32¡C, being more toxic at higher temperatures. Very low levels of resistance to the herbicide were observed in the seven Ðeld-collected T . urticae populations resistant to various acaricides. Treatment with glufosinate-ammonium did not cause a repellent response from either adults or immature stages of T . urticae. Paraquat dichloride and glyphosate were ine †ective against all stages of T . urticae. In a Ðeld study of a population of T . urticae, glufosinate-ammonium when sprayed to weeds caused signiÐcant decrease in T . urticae population densities in apple trees for nine weeks after treatment, as compared with the control. Thereafter, a single application of standard acaricides to apple foliage greatly reduced population densities, although there was no di †erence in the densities between the glufosinate-ammonium-treated and control plots. Based upon laboratory and Ðeld data, two single treatments with glufosinate-ammonium to weeds in May and a selective acaricide to apple trees in July may be used to prevent damage by T . urticae.

Effects of Dispersal, Predators (Acari: Phytoseiidae), Weather, and Ground Cover Treatments on Populations of <I>Tetranychus urticae</I> (Acari: Tetranychidae) in Apple Orchards

“…In some cases, the Þrst application was tank mixed with 2,4-D amine (Estamine 600 EC, Interprovincial Cooperative Ltd., Saskatoon, SK, Canada) at 600 g ha Ϫ1 to improve control of dandelion, Taraxacum officinale Weber. With treatment 2, enhanced herbicide use in tree row, we supplemented the last glyphosate application in the tree row in July with an application of glufosinate ammonium (Ignite 15 SN, Bayer CropScience, Toronto, ON, Canada) at 500 g ha Ϫ1 because this herbicide is highly toxic, but not repellant, to T. urticae (Boller et al 1984;Ahn et al 1997Ahn et al , 2001. In 2001, terbacil (Sinbar 80 W, DuPont Canada Inc., Mississauga, ON, Canada), a residual, soil-active herbicide applied at 350 g ha Ϫ1 , was combined with glufosinate ammonium to provide an additional 4 Ð 6-wk residual control of late summer-germinating weeds.…”

“…Application of nonrepellant, strongly miticidal herbicides such as glufosinate in tree rows would kill T. urticae before they could disperse up into trees or retreat into unsprayed laneways. This approach has been successful in European vineyards (Boller et al 1984;Kreiter and le Men 1993a, b) and in a Korean apple orchard (Ahn et al 1997). In addition, application of selective herbicides in laneways would shift the ground cover away from clover and broad-leaved weeds, many of which are reproductive hosts of T. urticae, to perennial grasses, which do not support population growth (Meagher and Meyer 1990, Flexner et al 1991, Alston 1994.…”

Integration of Herbicides with Arthropod Biocontrol Agents for Weed Control

“…More recently, systematic testing of non-biocontrol agent arthropods considered to be beneficial organisms (Hassan et al , 1991(Hassan et al , , 1994Samsøe-Petersen, 1995;Sterk et al ., 1999,) has shown that most of the commonly used herbicides appear harmless, or nearly so, at field rates. One exception is glufosinate ammonium toxicity to mites, which has also been reported for pest mites (Kreiter & le Menn, 1993;Ahn et al , 1997).…”

Insecticidal activity of glufosinate through glutamine depletion in a caterpillar

“…9 Methionine sulfoximine, another GS ligand that inhibits insect fat body GS, 10 is also a potent inhibitor of mammalian and plant GS. A glufosinate-containing herbicide is reported to be acaracidal, 11 and when applied at the recommended ®eld rate acts as a feeding deterrent to the armyworm Spodoptera littoralis (Boisd). 12 GS inhibitors have not been exploited in insect control, possibly because of their non-selective properties.…”