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Phytoseiid mites are key predators in agricultural crops. However, not all species regulate pest populations below economic thresholds, and therefore knowledge of which species are associated with particular crops aids pest control recommendations. Surveys of 12 crops across six geographical regions of California demonstrated that phytoseiid species varied by crop and geographical location, with subtropical crops exhibiting the lowest species diversity and grape the greatest. The western predatory mite, Galendromus occidentalis, long cited as a dominant species in California crops, was not found to be the major species in most situations. Euseius stipulatus, a species introduced in the 1970s, was found in the surveyed crops in many areas of the state and appears to be displacing E. hibisci along the south coast. [ABSTRACT FROM AUTHOR]

Avocado branch canker in California is caused by a complex of fungal species in the families Botryosphaeriaceae and Diaporthaceae. As the popularity of avocado fruit increases, California growers are under pressure to increase their productivity in order to compete with im-ports. One way to increase production is through high-density planting, which entails intense canopy management, possibly leaving the trees vulnerable to infection through pruning wounds. A spore trap study was undertaken to determine the seasonal spore discharge of Botry-osphaeriaceous and Diaporthaceous fungi. Based on colony counts, the highest population of Botryosphaeriaceous fungi (68%) occurred dur-ing or soon after precipitation events, which coincided with the winter months of December, January, and February. The spring and fall seasons had lower numbers of spores trapped (at 13 and 17%, respec-tively), with few spores trapped in the summer season. For members of the Diaporthaceae family, spores trapped were almost evenly split between winter and fall seasons (50 and 49%, respectively), with few to no spores trapped in the spring and summer seasons. A pathogenic-ity test of six fungi of Botryosphaeriaceae and one fungus of Di-aporthaceae was conducted in the greenhouse. Internal plant vascular lesion lengths resulting from inoculation with any of the seven fungal species differed significantly from the noninoculated control. These studies suggest that pruning during the drier parts of the year would minimize infection by fungi in the Botryosphaeriaceae and Diaporth-aceae families. [ABSTRACT FROM AUTHOR]

Optimizing 'Hass' avocado (Persea americana Mill.) tree nutrient status is essential for maximizing productivity. Leaf nutrient analysis is used to guide avocado fertilization to maintain tree nutrition. The goal of this research was to identify a 'Hass' avocado tissue with nutrient concentrations predictive of yields greater than 40 kg of fruit per tree. This threshold was specified to assist the California avocado industry to increase yields to '11,200 kg·haL1. Nutrient concentrations of cauliflower stage inflorescences (CSI) collected in March proved better predictors of yield than inflorescences collected at full bloom (FBI) in April, fruit pedicels (FP) collected at five different stages of avocado tree phenology from the end of fruit set in June through April the following spring when mature fruit enter a second period of exponential growth, or 6-month-old spring flush leaves (LF) from nonbearing vegetative shoots collected in September (California avocado industry standard). For CSI tissue, concentrations of seven nutrients, nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), sulfur (S), zinc (Zn), and copper (Cu) were predictive of trees producing greater than 40 kg of fruit annually. Conditional quantile sampling and frequency analysis were used to identify optimum nutrient concentration ranges (ONCR) for each nutrient. Optimum ratios between nutrient concentrations and yields greater than 40 kg per tree were also derived. The high nutrient concentrations characterizing CSI tissue suggest current fertilization practices (timing or amounts) might be causing nutrient imbalances at this stage of avocado tree phenology that are limiting productivity, a possibility that warrants further investigation. Because CSI samples can be collected 4-6 weeks before full bloom, nutritional problems can be addressed before they affect flower retention and fruit set to increase current crop yield, fruit size, and quality. Thus, CSI nutrient analysis warrants further research as a potential supplemental or alternative tool for diagnosing 'Hass' avocado tree nutrient status and increasing yield. [ABSTRACT FROM AUTHOR]

Cites a study which found that imported parasitic wasps helps control red gum lerp psyllid in California. Effect of this psyllid on eucalyptus species; Importation of the new parasitoid species from Australia; Approach used by researchers in finding promising parasitoids.

The rotational spectra of six isotopomers of the linear and bent isomers of HF–N2O have been collected in the 7–18 GHz region with a Fourier transform microwave spectrometer. The nuclear hyperfine structure in the spectra produced by HF spin–spin coupling interaction and nuclear quadrupole coupling interactions due to the D nucleus of DF and the 14N nuclei of N2O have been resolved and analyzed. In the linear isomer, H in HF is bonded to the terminal N in N2O. The NF bond lengths are 2.9808(2) A˚ for the HF-containing isotopomers and 2.9732(2) A˚ for the DF-containing isotopomers. The zero point angles are 23.1° for HF and 31–34° for N2O. The hyperfine constants suggest that the HF bond is lengthened by 0.0105 A˚ upon complexation and that the electric field gradients of the two nitrogen nuclei in N2O are perturbed differently in the complex. In the bent isomer, the hydrogen bond is formed between HF and O in N2O. The intermolecular distances are 3.4942(2) A˚ for the HF-containing isotopomers and 3.4436(2) A˚ for the DF-containing isotopomers, with HF and N2O forming angles of 34° and 46°, respectively, with the intermolecular axis. The nuclear quadrupole coupling constants of the two nitrogen nuclei do not indicate electric field gradient perturbation in this isomer. [Copyright &y& Elsevier]