Effects of fungicide residues on the survival, fecundity, and predation of the mites Tetranychus urticae (Acari: Tetranychidae) and Galendromus occidentalis (Acari: Phytoseiidae).

Representative fungicides from three or four families used for management of powdery mildew and other diseases in tree fruits were evaluated for their effects on a common spider mite and predator mite species, respectively. A modified Munger cell technique was effective in measuring the response of phytophagous and predaceous mites to fungicide residues on detached leaves in the laboratory. Demethylation-inhibiting (DMI) (imidazole [triflumazole] and triazole [myclobutanil]) and strobilurin (trifloxystrobin) fungicides were not toxic to female Tetranychus urticae Koch and Galendromus occidentalis (Nesbitt), and no sublethal effects were found on fecundity and predation rate after 3-5-d exposure to residues. Benomyl, a benzimidazole fungicide, increased adult mortality and reduced fecundity for both mite species; however, it did not alter the predation rate of G. occidentalis females on T. urticae eggs and larvae. Female G. occidentalis that survived the lethal effects of benomyl and the comparison acaricide pyridaben were unimpaired in predation. Our results for benomyl substantiate those of earlier studies and provide evidence for nontoxic effects of DMI and strobilurin fungicides on mites. We propose that DMI and strobilurin fungicides are a good fit for integrated mite management programs due to conservation of phytoseiid predatory mites.

Establishment and Dispersal of Puccinia thlaspeos in Field Populations of Dyer's Woad.

Dyer's woad rust is being intensively studied as a biocontrol agent for the noxious weed dyer's woad. These studies report on methods to establish this fungus in woad populations and to obtain information about disease incidence and dispersal of the rust subsequent to establishment. Inoculum dosages as low as 1 mg/plant established disease in dyer's woad rosettes. Dosages higher than 1 mg/plant resulted in better levels of infection, and inoculation was equally effective when the inoculum was placed directly on the plants or on the soil adjacent to the plants. The highest incidence of infection occurred when plants were inoculated in the spring, whereas summer or fall inoculations did not result in infections. Large-scale inoculation of woad was effective and resulted in significant levels of disease. However, it was not clear if artificial inoculation was effective in changing disease incidence in populations of woad where the rust was present prior to treatment because there were no significant differences between inoculated and check plots. Woad rust is systemic but apparently it is not seed dispersed, even though some infected plants occasionally produce seed. Two years after inoculation, dyer's woad rust had dispersed an average of 14.6 m from the focus of inoculation. After 3 years, the dispersal distance had not increased and infected plants averaged only 10 m from the point of inoculation. Disease was maintained naturally in woad populations after treatment, but the overall percent infection in the treated plots decreased by 3 years after inoculation.

Seasonal Infection of the Weed Dyer's Woad by a Puccinia sp. Rust Used for Biocontrol, and Effects of Temperature on Basidiospore Production.

Potted dyer's woad rosettes exposed to natural rust inoculum at field sites became infected when exposed from late April through early July, depending upon the location. The latent period between exposure and symptom expression varied from 9 to 54 weeks. The length of this latent period was unrelated to either the age of plants at exposure or the exposure period itself. The age of rosettes at the time of exposure did not affect the incidence of infection. Fall infection of potted rosettes occurred, but the incidence was low. When naturalized stands of woad were inoculated with teliosori, either fresh or dried, the incidence of infection was 58 to 76%, compared with 2 to 7% incidence in noninoculated plants. Basidiospores were readily produced from intact teliosori when suspended over water agar, with the highest rate of production between 3 and 6 h of incubation, at 10 to 20°C. The optimum temperature for basidiospore production over a 24-h period was 15°C, but they were produced at temperatures as low as 5°C, although not at 25°C. These lower-than-expected temperatures for spore production corroborate the field evidence that dyer's woad rust most actively infects in springtime, when temperatures are comparatively low and rainfall is more frequent.