Copyright (c) 2013 California Polytechnic State University All rights reserved. http://digitalcommons.calpoly.edu/hcs_fac Recent documents in Horticulture and Crop Science en-us Wed, 01 May 2013 13:15:27 PDT 3600 http://digitalcommons.calpoly.edu/hcs_fac/41 http://digitalcommons.calpoly.edu/hcs_fac/41 Fri, 17 Feb 2012 12:24:13 PST Despite problems of low fruit set, small fruit size and alternate bearing, the Hass cultivar dominates commercial avocado production worldwide. To increase yield and fruit size, gibberellic acid (GA₃) (25 mg L⁻¹) was applied at different stages of ‘Hass’ avocado tree phenology: (i) mid–late April (flower abscission), end of June–beginning of July (fruit abscission and beginning of the exponential phase of fruit growth), and mid-January (beginning of pre-harvest fruit drop); (ii) end of June–beginning of July; and (iii) mid-September (near the end of the major fruit abscission period; period of exponential fruit growth). In both years of the research, applications of GA₃ in April and June–July were within the periods of intense flower and fruit abscission, respectively; fruit abscission was low in September and January. Maximum air temperature was not related to flower or fruit abscission. In the on-crop year (391 fruit per untreated control tree), a single application of GA₃ at the end of June–beginning of July significantly increased total yield (kilograms only) and yield of commercially valuable fruit (178–325 g/fruit) (as kilograms and number per tree) compared with the control (P < 0.0001). GA₃ applied in September increased total yield (kilograms only) and yield of commercially valuable fruit (kilograms and number per tree) to values intermediate to and not significantly different from all other treatments, except trees receiving multiple applications of GA₃. This treatment reduced total yield and yield of commercially valuable fruit (kilograms and number per tree) relative to all treatments (P ≤ 0.0002). In contrast, during the off-crop year (32 fruit per control tree), no GA₃ treatment had a significant effect on yield or fruit size compared with the control and all other GA₃ treatments. For ‘Hass’ avocado, there was no negative effect from applying GA₃ at the end of June–beginning of July in both the off- and on-crop years; 2-year cumulative total yield and yield of commercially valuable fruit were increased by 27 kg (128 fruit) and 22 kg (101 fruit) per tree, respectively, above the yield of untreated control trees (P < 0.0001).

]]> Lauren C. Garner et al. http://digitalcommons.calpoly.edu/hcs_fac/40 http://digitalcommons.calpoly.edu/hcs_fac/40 Wed, 21 Dec 2011 14:23:31 PST The developmental thresholds for Marmara gulosa Guillen & Davis (Lepidoptera: Gracillariidae) were investigated in the laboratory by using 17, 21, 25, 29, and 33°C. The lowest mortality occurred in cohorts exposed to 25 and 29°C. Other temperatures caused >10% mortality primarily in egg and Þrst and second instar sap-feeding larvae. Linear regression analysis approximated the lower developmental threshold at 12.2°C. High mortality and slow developmental rate at 33°C indicate the upper developmental threshold is near this temperature. The degree-day (DD) model indicated that a generation requires an accumulation of 322 DD for development from egg to adult emergence. Average daily temperatures in the San Joaquin Valley could produce up to seven generations of M. gulosa per year. Field studies documented two, Þve, and three overlapping generations of M. gulosa in walnuts (Juglans regia L.; Juglandaceae), pummelos (Citrus maxima (Burm.) Merr.; Rutaceae), and oranges (Citrus sinensis (L.) Osbeck; Rutaceae), for a total of seven observed peelminer generations. Degree-day units between generations averaged 375 DD for larvae infesting walnut twigs; however, availability of green wood probably affected timing of infestations. Degree-day units between larval generations averaged 322 for pummelos and 309 for oranges, conÞrming the laboratory estimation. First infestation of citrus occurred in June in pummelo fruit and August in orange fruit when fruit neared 60 mm in diameter. Fruit size and degree-day units could be used as management tools to more precisely time insecticide treatments to target the egg stage and prevent rind damage to citrus. Degree-day units also could be used to more precisely time natural enemy releases to target larval instars that are preferred for oviposition.

]]> M. J. O'Neal et al. http://digitalcommons.calpoly.edu/hcs_fac/39 http://digitalcommons.calpoly.edu/hcs_fac/39 Wed, 04 May 2011 11:17:11 PDT Undergraduate students enrolled in the introductory pomology course at California Polytechnic State University, San Luis Obispo, CA, from 2007 to 2010, participated in a service-learning project. Students helped the community organization, the California Rare Fruit Growers (CRFG), teach grafting skills to San Louis Obispo County high school students and community members. At the end of each quarter, pomology students completed evaluations of their experience. Results of these evaluations were used to improve teaching methodology and the experience in which the students participated. Self-reported and instructor evaluations of the service-learning project demonstrated that students increased their grafting knowledge and skills, their confidence in learning new skills, and their interest in fruit science and community involvement. The service-learning project enabled students to meet course learning objectives of understanding and becoming experienced in horticultural techniques, such as grafting, and to meet university learning objectives of developing critical thinking and communication skills and increasing community involvement.

]]> Lauren C. Garner http://digitalcommons.calpoly.edu/hcs_fac/38 http://digitalcommons.calpoly.edu/hcs_fac/38 Thu, 15 Jul 2010 17:05:55 PDT The commercial use of mechanical stimulation to control transplant growth is quite limited. To be commercially successful, the technique must be simple and flexible, and must not reduce plant quality. Brushing was applied to tomato (Lycopersicon esculentum) seedlings growing at a density of 2100 plants m^-2 by daily stroking with a piece of polystyrene. Ten or twenty daily strokes typically provided significant height control without plant damage. Increasing the interval between strokes to up to 10 minutes resulted in the same amount of height control as continuous brushing. There were typically no differences between treating the plants at 0800 or at 1700 hours. Significant height control was achieved if treatments were begun at the first or second true leaf stage, but treatments begun at a later stage of development resulted in leaf damage. Brushing before transplanting to the field resulted in a significant decrease in stem elongation (~20%). However, there were no significant differences between brushed and unbrushed plants in long-term growth or final fruit yield after transplanting to the field. Preliminary studies were also conducted on four bedding plant species: geranium (Pelargonium x hortorum), impatiens (Impatiens holstii), petunia (Petunia hybrida) and pansy (Viola tricolor). Brushing was applied to seedlings growing at a density of 1500 plants m^-2 using either polythene or plastic netting. For geranium and impatiens, any reductions in plant stature were associated with significant plant damage. Brushing induced a prostrate growth habit and leaf distortion in petunia and significantly reduced leaf area and shoot dry weight. Pansy plants were undamaged by 10 or 20 brush strokes per day and showed a significant (17–22%) decrease in petiole length, typically without significant effects on leaf area, dry weight or days to flower. Brushing provides a flexible, effective method for controlling tomato and pansy transplant size without adversely affecting quality or long-term growth.

]]> Lauren C. Garner et al. http://digitalcommons.calpoly.edu/hcs_fac/36 http://digitalcommons.calpoly.edu/hcs_fac/36 Thu, 15 Jul 2010 17:05:54 PDT Though brushing is an effective method for controlling excessive elongation in many species, its adoption by the commercial plug transplant industry will depend on the ease and flexibility of its application. Brushing was applied to pansy (Viola tricolor L.) seedlings growing at a density of 1500 plants m^-2 by daily stroking with 20/20 gauge netting. In dose response experiments, final petiole length appeared to approach a lower asymptote as number of brush strokes increased, and the number of strokes required to give near full reduction in length increased under environmental conditions favouring extension growth. Ten or 20 daily strokes, typically gave a 25-30% reduction in petiole elongation without causing plant damage or affecting subsequent flowering. Reductions in shoot dry weight tended to parallel those for petiole length. Increasing the interval between strokes by up to 10 rain resulted in similar reductions as continuous brushing. There was no difference between brushing the plants at 09:00 or 16:00 h, or between brushing 1 or 2 times day^-1. Plants required at least 5 days treatment week^-1 for significant size control. Brushing is an effective, flexible method for controlling petiole length in pansy and it should find application in the commercial transplant industry.

]]> Lauren C. Garner et al. http://digitalcommons.calpoly.edu/hcs_fac/37 http://digitalcommons.calpoly.edu/hcs_fac/37 Thu, 15 Jul 2010 17:05:54 PDT Nutrient film technique (NFT) and deep water culture (DWC) hydroponic systems were used in a split-root study of the effect of four treatments on sweetpotato yield, the translocation of assimilates, and microbial population count. ‘TU-155’ cuttings (15 cm) were prerooted for 30 days in sand using deionized water and a modified half-Hoagland (MHH) solution. After 30 days, the plants were removed, and the roots of each were cleaned and split evenly between two sides of a channel (each 15 cm deep by 15 cm wide by 1.2 m long), four plants per channel. Replicated treatments were: MHH/MHH; MHH/Air, MHH/deionized water (DIW); and monovalent/divalent anions and cations (Mono/Dival). The entire experiment was repeated. Plants were harvested after growing for 120 days in a glasshouse. Storage roots, when produced, were similar in nutritive components. However, no storage roots were produced in Air or Mono channels and only a few in DIW suggesting inhibition of assimilate translocation. Fresh and dry weights for storage roots and foliage were highest in MHH/MHH in both NFT and DWC in both experiments. Solution samples were collected at 14-day intervals for microbial population profiling. Microbial counts (4.20–7.49 log cfu/ml) were highest in Dival channels. The counts indicated that solution composition influenced population size, and they were relatively high in both systems.

]]> M. A. Sherif et al. http://digitalcommons.calpoly.edu/hcs_fac/35 http://digitalcommons.calpoly.edu/hcs_fac/35 Thu, 15 Jul 2010 17:05:52 PDT The closest wild relatives of maize, Zea mays ssp. mays are various Zea taxa known as ‘‘teosinte.’’ Hybrids between maize and the teosinte taxon, Zea mays ssp. mexicana, often occur when the 2 are sympatric in Mexico. Measuring the spontaneous hybridization rate of the 2 taxa would shed light on the mechanisms contributing to the evolution and persistence of these hybrid swarms. We conducted a series of field experiments in Riverside, CA, to measure the natural hybridization rates between maize and 2 teosinte taxa, Z. m. ssp. mexicana and Zea mays ssp. parviglumis. We planted teosinte within and near maize plantations. Hybrids were identified by progeny testing for a maize-specific herbicide resistance allele and a teosinte-specific allozyme allele. Hybridity was confirmed by growing putative hybrid progeny to maturity to evaluate whether they had the characteristic morphology of maize X teosinte hybrids.We found that maize and Z. m. ssp. mexicana naturally hybridize at a low rate (m. ssp. parviglumis hybridizes with the crop at a high rate (>>50%).

]]> Norman C. Ellstrand et al. http://digitalcommons.calpoly.edu/hcs_fac/34 http://digitalcommons.calpoly.edu/hcs_fac/34 Mon, 12 Jul 2010 16:38:43 PDT A living mulch combines an annual crop with a cover crop to provide pest control and soil protection. Results of a study in the Salinas Valley show cabbage aphid infestation can be lowered on broccoli grown in living mulches compared to clean cultivation, possible because light reflectance patterns are less attractive to incoming aphids. Early and intense mowing of the cover crop and adequate irrigation maintained broccoli yield in living mulches relative to clean cultivation. Lack of specialized equipment is the main limitation to the commercial application of living mulches at this time.

]]> Michael J. Costello et al. http://digitalcommons.calpoly.edu/hcs_fac/32 http://digitalcommons.calpoly.edu/hcs_fac/32 Mon, 12 Jul 2010 16:38:42 PDT Light reflectance in five wavebands of the spectrum was measured from broccoli (Brassicae oleracea var.botrytis [L].) interplanted with leguminous cover crops (cover crop background) or broccoli grown as monoculture (bare soil background), and fertilized with compost or synthetic fertilizer. Alate Brevicoryne brassicae (L.) and Myzus persicae (Sulzer) (Homoptera: Aphididae) were monitored in yellow pan water traps and on broccoli leaves. Reflectance intensity was higher with a background of bare soil at all wavebands except blue (400–455 nm) in the early-season. Intensity decreased as broccoli canopy cover increased at all wavebands except blue and green (515–550 nm), declining-most dramatically in the yellow (550–590 nm). Highest late-season intensities were in plots with bare soil background and fertilized with compost (those stressed for nitrogen). Few differences in spectral composition, expressed for each waveband as a percentage of total intensity, were recorded. Numbers of alatae were lowest in cover crop background plots in the early season, reached equivalency with bare soil background by mid-season, and showed highest positive correlations with intensity in the yellow (550–590 nm). Results correspond to laboratory findings that aphids are attracted to higher intensity light, especially in the yellow waveband, and support a phototactic explanation for aphid orientation in the field.

]]> Michael J. Costello http://digitalcommons.calpoly.edu/hcs_fac/33 http://digitalcommons.calpoly.edu/hcs_fac/33 Mon, 12 Jul 2010 16:38:42 PDT In 1990 and 1991, populations of the cabbage aphid, Brevicoryne brassicae, and the green peach aphid, Myzus persicae, were monitored on broccoli interplanted with three leguminous cover crops (the living mulches) and compared with broccoli without cover crop (clean cultivation). The cover crops used were white clover (Trifolium repens L.), strawberry clover (Trifolium fragiferum L.) and a mixture of birdsfoot trefoil (Lotus corniculatus L.) and red clover (Trifolium praetense L.). Fertilizer was applied as compost or synthetic fertilizer crossed with cropping system regime. Brevicoryne brassicae can reach pest status in Brassica cropping systems, whereas M. persicae is generally innocuous. Both aphids are attacked by the parasitoid Diaeretiella rapae. Seasonal aphid abundance, parasitism and population growth rates were analyzed. No significant effect of fertilizer was found for any of the parameters analyzed. The living mulches had lower aphid populations overall, although differences with clean cultivation were greatest early in the season for M. persicae and diminished over time. No effect of cropping system on population growth rate was seen for Brevicoryne brassicae, but for M. persicae growth rates were higher in living mulches compared with clean cultivation. Parasitism was highest on clean cultivated broccoli for both aphid species in 1990 and for M. persicae in 1991, but no differences were found for Brevicoryne brassicae in 1991. This suggests that differential population growth rates and parasitism seen for M. persicae are a result of inhibition of D. rapae in the living mulches. Possible reasons for differences in parasitism between the two aphid species in living mulches and clean cultivation are discussed.

]]> Michael J. Costello et al. http://digitalcommons.calpoly.edu/hcs_fac/31 http://digitalcommons.calpoly.edu/hcs_fac/31 Mon, 12 Jul 2010 16:38:41 PDT As part of an investigation to estimate the effect of resident spider populations on Erythroneura variabilis Beamer, spider species composition, relative abundance, and seasonal occurrence were determined. Spiders were sampled monthly during the 1992 and 1993 growing seasons; their numbers were pooled and analyzed for species diversity using the Renkonen index of similarity and cluster analysis. Twenty-seven species of spiders were recorded, representing 14 families. The most common species were Cheiracanthium inclusum (Hentz), Trachelas pacificus (Chamberlin and Ivie), Theridion dilutum Levi, Theridion melanurum Hahn, Oxyopes scalaris Hentz, Oxyopes salticus Hentz, Hololena nedra Chamberlin and Ivie, and Metaphidippus vitis (Cockerell). Three species (C. inclusum, T. dilutum, and T. melanurum) constituted >30% of all spiders collected; however, species diversity varied among vineyard sites. In 4 vineyard sites, hunting spiders (C. inclusum, T. pacificus, Oxyopes spp., and M. vitis) dominated the fauna, representing an average of 79.7% of the specimens collected. In the other 3 vineyards, hunting and web-weaving spiders were more equally represented, averaging 43.5 and 50.0%, respectively,of all spiders collected. Species similarity between vineyards from both years ranged from 19 to 73% based on the Renkonen index. Similarly, cluster analysis showed a wide separation in species composition among sampled vineyards. The discrepancy in species similarity among sampled vineyards is discussed in reference to potential prey density and vineyard cultural practices. Seasonal abundance patterns of the 8 most common species are presented and discussed in reference to their respective phenologies.

]]> Michael J. Costello et al. http://digitalcommons.calpoly.edu/hcs_fac/30 http://digitalcommons.calpoly.edu/hcs_fac/30 Mon, 12 Jul 2010 16:38:40 PDT The effectiveness of 3 methods for sampling spiders in grape vineyards was tested. The sampling methods were as follows: (1) a drop-cloth method in which spiders were dislodged from a 5.1-m2 area of grapevine onto a drop cloth, (2) a funnel method in which spiders were dislodged into a 0.74-m2 funnel, and (3) a D-vac method in which 50 sections of grapevine (30-cm sections, total area of 5.4 m2) were suctioned with a gasoline-powered vacuum. Data from all sampling methods were adjusted for area sampled and compared with an absolute control, in which foliage from an entire vine was removed and searched for spiders. Analyses were made on the following 8 most abundant spider species: Allyphaella pacifica Banks, Metaphidippus vitis (Cockerell), Theridion dilutum Levi and Theridion melanurum Hahn (grouped as Theridion spp.), Cheiracanthium inclusum (Hentz), Hololena nedra Chamberlin & Ivie, Trachelas pacificus (Chamberlin & Ivie), and Erigone dentosa (O.P.-Cambridge). Mean spider abundance from each sampling method differed significantly from the absolute control in (≥1) species. The funnel method often overestimated spider abundance while the drop-cloth and D-vac methods often underestimated spider abundance. Estimates of spider species composition were most accurately measured by the drop-cloth method and were significantly altered by the D-vac method. We tested 3 data transformations (ln[x + 1], √ [x + 0.5], and x^1-b/2) to stabilize the variance and satisfy the requirements of analysis of variance (ANOVA). No single transformation uncoupled the mean and variance for all spider species over the 3 sampling methods. Using mean and variance of mean spider abundance, sample size and dispersion parameters were created by way of the Taylor power law. Sample sizes were determined for each sampling method; estimates of sample size and sampling costs varied considerably among spider species and sampling methods. All but 1 spider species collected with the drop-cloth method had a clumped distribution, the funnel method produced variable dispersion indexes, and all spider species collected with the D-vac method had a random distribution pattern. Whereas no single sampling method was best for all spider species, the funnel method is favored because of its efficiency in estimating spider densities and its reduced cost.

]]> Michael J. Costello et al. http://digitalcommons.calpoly.edu/hcs_fac/29 http://digitalcommons.calpoly.edu/hcs_fac/29 Mon, 12 Jul 2010 16:38:39 PDT In 3 of 4 vineyards we studied, late-season leafhopper density was lower on vines in cover cropped plots than in plots with no cover crops. However, the level of leafhopper reduction (about 15%) was rarely economically important and the mechanisms leading to reduction were not clear. For example, there were few differences in the number of leaf hopper predators or parasitoids on the vines in cover cropped versus no cover plots. However, there were significant between-treatment differences in vine growth. Plots with seasonwide maintenance of a cover crop and resident grasses had a reduction in vine vigor. Lower vine vigor has been associated with lower leafhopper densities and, in our studies conducted from 1993 to 1996, those plots with reduced vine vigor often had the greatest reduction in late-season leafhopper density.

]]> Kent M. Daane et al. http://digitalcommons.calpoly.edu/hcs_fac/28 http://digitalcommons.calpoly.edu/hcs_fac/28 Mon, 12 Jul 2010 16:38:39 PDT 1. Cover crops and/or resident ground vegetation have been used in California vineyards to increase the number of predators and decrease the number of pestiferous herbivores. The most common resident predators in vineyards are spiders (Araneae). Several observational studies suggest that the addition of cover crops results in an increase in spider density and a decrease in insect pest densities. 2. To test experimentally the effects of cover crops and/or resident ground vegetation (hereafter collectively referred to as ground cover) on spider populations, a 3-year study was undertaken in a commercial vineyard. Large, replicated plots were established with and without ground cover during the growing season. Spider species diversity was analysed on the vines and on the ground cover. 3. On the vines, there was no significant difference in spider species richness or the total number of spiders in plots with and without ground cover. There were differences in the relative abundance of two spiders between treatments, with one species (Trachelas pacificus [Chamberlin & Ivie]) more abundant in plots with ground cover and another (Hololena nedra Chamberlin & Ivie) more common on vines in plots with no ground cover. Annual variation in spider abundance was greater than variation due to ground cover treatment. 4. On the ground cover, the spider species diversity was considerably different from that found on the vines above, suggesting that there is little movement of spiders between the ground cover and the vines. Enhancement of T. pacificus populations on vines with ground covers may be a result of prey species movement between the ground cover and the vines. Spider abundance was sparse on the bare ground. 5. The maintenance of ground cover increased spider species diversity in the vineyard as a whole (vine and ground cover). However, the relatively small changes in spider abundance on the vines indicate there are limitations in the use of ground covers for pest management with respect to generalist predators.

]]> Michael J. Costello et al. http://digitalcommons.calpoly.edu/hcs_fac/27 http://digitalcommons.calpoly.edu/hcs_fac/27 Mon, 12 Jul 2010 16:38:38 PDT We compared the abundance of spiders and predaceous insects in five central California vineyards. Spiders constituted 98.1% of all predators collected. More than 90% of all spiders collected were from eight species of spiders, representing six families. Two theridiids (Theridion dilutum and T. melanurum) were the most abundant, followed by a miturgid (Cheiracanthium inclusum) and an agelinid (Hololena nedra). Predaceous insects comprised 1.6% of all predators collected, and were represented by six genera in five families. Nabis americoferis (Heteroptera, Nabidae) was the most common predaceous insect, with its densities highest late in the growing season. Chrysoperla carnea, Chrysoperla comanche and Chrysopa oculata (Neuroptera, Chrysopidae) and Hippodamia convergens (Coleoptera, Coccinellidae) were most abundant early in the season. The dominance of spiders may be due to their more stable position in the vineyard predator community compared to predaceous insects. We also suggest that the low percentage of predaceous insects (e.g., lacewings) may reflect the lack of preferred prey (e.g., aphids) on grapevines.

]]> Michael J. Costello et al. http://digitalcommons.calpoly.edu/hcs_fac/26 http://digitalcommons.calpoly.edu/hcs_fac/26 Mon, 12 Jul 2010 16:38:37 PDT Ground cover is used in some vineyards to improve soil structure and help manage insect pests; previous studies have shown lower leafhopper (Erythroneura spp.) densities on vines grown with ground cover. We undertook a 2-yr study to determine why ground cover is associated with reduced leafhopper densities. Ground cover consisted of a fall-planted cover crop of purple vetch (Vicia benghalensis) and barley (Hordeum vulgare), which senesced in May and was replaced by a complex of resident vegetation comprised primarily of the grasses Echinochloa spp., Digitaria sanguinalis, and Setaria spp., as well as common knotweed (Polygonum aviculare). We compared three treatments during the growing season: Cover, No Cover, and Cover/Exclusion. Cover/Exclusion was similar to Cover treatment but with barriers to impede arthropod movement between ground cover and vines. We measured leafhopper density and egg parasitism, spider density and diversity, and grapevine vigor, and found that mid- and late-season leafhopper densities were significantly lower in Cover versus No Cover. Neither leafhopper egg parasitism nor spider density on the vines or ground cover could explain these differences; however, grapevine vigor was significantly lower in Cover than No Cover, and provides the best correlation to leafhopper density. Late-season leafhopper density was highest in the Exclusion treatment but cannot be explained by changes in grapevine vigor. Individual spider species composition and density on the grapevine canopy varied significantly among treatments: Trachelas pacificus (Chamberlin and Ivie) was higher in the Cover treatment, Hololena nedra Chamberlin and Ivie, Cheiracanthium inclusum (Hentz), and Neoscona oaxacensis (Keyserling) were lower in the Exclusion treatment, and Oxyopes spp. was higher in the Exclusion treatment. We suggest the lower densities of leafhoppers in the Cover treatment resulted from poorer host plant quality because of the competition between ground cover and grapevines. The higher late-season leafhopper densities in the Exclusion treatment may be due to changes in spider species composition, and subsequently, differences in rates of predation on leafhopper nymphs.

]]> Michael J. Costello et al. http://digitalcommons.calpoly.edu/hcs_fac/24 http://digitalcommons.calpoly.edu/hcs_fac/24 Mon, 12 Jul 2010 16:38:36 PDT Sulfur is the oldest and most widely used fungicide in the vineyards of California, where it is used for control of powdery mildew (Uncinula necator [Schw.] Burr). For decades, sulfur use has been associated with outbreaks of Tetranychus pacificus McGregor (Acari: Tetranychidae) on cultivated grapes in the San Joaquin Valley. I undertook large-scale field studies to test this association, to evaluate the impact of sulfur on Galendromus occidentalis (Nesbit) (Acari: Phytoseiidae), a major predator of T. pacificus, and to determine if timing of sulfur applications with respect to grape bloom has an impact on T. pacificus density. The studies took place in a 32 ha vineyard in Fresno County, and all fungicide applications were made with commercial-scale equipment. In 1998 a ‘high sulfur’ treatment, a combination of wettable sulfur and sulfur dust, was compared to ‘low sulfur,’ in which demethylation inhibitor (DMI) fungicides partially substituted for sulfur. In 1999 treatments were ‘sulfur,’ ‘DMI,’ ‘sulfur pre-bloom’ (here sulfur was applied prior to grape bloom, in late May, and then DMIs were applied until mid-season) and ‘sulfur post-bloom’ (the reverse of ‘sulfur pre-bloom’). In each year, the T. pacificus population increase came after the end of fungicide applications, and results clearly show a relationship between sulfur use and T. pacificus density. In 1998, mean T. pacificus density was 2.7 times higher and mean G. occidentalis density 2.5 times higher in ‘high sulfur’ compared to ‘low sulfur.’ In 1999, the highest T. pacificus counts were in the ‘sulfur’ and ‘sulfur pre-bloom’ treatments, 4.8 times higher than ‘sulfur post-bloom’ and 2 times higher than ‘DMIs.’ Density of G. occidentalis was 2.3 times as high in ‘sulfur’ or ‘sulfur pre-bloom’ than ‘DMIs.’ The predator/prey ratio was not significantly different among treatments in 1998, but in 1999 it was highest in the ‘sulfur pre-bloom’ treatment. In 1999, density of Homeopronematus anconai (Baker) (Acari: Tydeidae) was 2.7 times higher in ‘sulfur pre-bloom’ compared to ‘sulfur,’ and higher by 2.7 times in ‘DMI’ compared to ‘sulfur post-bloom,’ suggesting a negative effect of sulfur on this tydeid. These results do not support the hypotheses that the cause of the increase in T. pacificus density is due to negative effects of sulfur on phytoseiids or tydeids. Rather, it appears that a plant-based explanation is likely, first, because of the differences in pre-bloom versus post-bloom sulfuring, and second, because of the long lag time between the end of the sulfur applications and the corresponding increase in spider mite density.

]]> Michael J. Costello http://digitalcommons.calpoly.edu/hcs_fac/25 http://digitalcommons.calpoly.edu/hcs_fac/25 Mon, 12 Jul 2010 16:38:36 PDT We compared day sampling (between 0700 and 1100) and night sampling (between 1900 and 2300) of spiders on grapevines in a California vineyard in 1993 and 1994, shaking spiders from the vines onto a drop cloth and vacuuming them up. Pooled density of the seven most abundant spider species did not differ significantly between day and night sampling, nor did density of Cheiracanthium inclusum (Miturgidae), Trachelas pacificus (Corrinidae), Oxyopes spp. (Oxyopidae) or Neoscona oaxacensis (Araneidae). Under day sampling Metaphidippus vitis (Salticidae) was 60% more abundant and Hololena nedra (Agelenidae) more than 2.5 fold more abundant than under night sampling. Daytime sampling generally resulted in a higher percentage of capture for each spider taxa analyzed, but neither of the diversity indices (Shannon-Wiener, Simpson or Bray-Curtis) showed any difference between day and night sampling. Parameters generated by Taylor’s power law indicate a uniform distribution for most spider taxa, which was not affected by sampling time with the exception of H. nedra. We suggest that at vineyard sites in California with a similar spider community, sampling can be limited to daylight hours if a sampling method is used which is sufficiently vigorous to dislodge spiders from their resting places.

]]> Michael J. Costello et al. http://digitalcommons.calpoly.edu/hcs_fac/23 http://digitalcommons.calpoly.edu/hcs_fac/23 Mon, 12 Jul 2010 16:38:35 PDT This study looked at regulated deficit irrigation (RDI) on leafhoppers in the genus Erythroneura (Erythroneura elegantula Osborn, or western grape leafhopper, and Erythroneura variabilis Beamer) (Hemiptera: Cicadellidae), which are serious pests of cultivated grape (Vitis vinifera L.) in California. RDI is an irrigation strategy that reduces irrigation during a critical point in the phenology of a cultivated perennial crop, to improve vegetative balance and crop quality. Erythroneura spp. are known to respond negatively to vine water stress, and the second generation of leafhoppers begins during a potential RDI initiation period, between berry set and veraison (beginning of fruit maturation). In experiments at commercial wine grape vineyards, I imposed deficits of between 25 and 50% of crop full evapotranspiration (ETc) between berry set and veraison, with control treatments based on the growers’ standard irrigations (typically between 0.8 and 1.0 ETc), and then we counted leafhopper nymphs weekly, and leafhopper eggs after the second generation. Results show a consistent reduction of second generation nymphal density with this type of RDI, with average density ≈50% lower under deficit treatments in all three studies. Deficit irrigation reduced second generation egg density by 54% at one site and by 29.9% at another. These results confirm previous studies regarding the sensitivity of Erythroneura spp. to grapevine water stress, and, in addition, they show that a season-wide irrigation deficit is not necessary for reduction in leafhopper density. Results suggest that lower oviposition at least partly explains the lower nymphal density in the deficit treatments.

]]> Michael J. Costello http://digitalcommons.calpoly.edu/hcs_fac/22 http://digitalcommons.calpoly.edu/hcs_fac/22 Thu, 08 Apr 2010 08:55:46 PDT The thrips-attacking Eulophidae (subfamily Entedoninae) known from the Nearctic region are reviewed. One new species, Ceranisus loomansi, is described. Four other species of Ceranisus are redescribed and illustrated based mainly on a study of their type specimens as well as on additional material from Arizona, California, Hawaii, Mississippi and Japan. Lectotypes are designated for Ceranisus americensis (Girault), C. nubilipennis (Williams) and C. russelli (Crawford). A key to eight species belonging to four entedonine thrips-attacking genera is given, and host associations are indicated for those species.

]]> S. V. Triapitsyn et al.