Ben Faber

Zinc uptake by corn as affected by vesicular-arbuscular mycorrhizae

Pot-grown mycorrhizal and non-mycorrhizal sweet corn were grown in a low Zn soil. All treatments received a complete nutrient solution with or without Zn. Treatments were harvested sequentially to detemine temporal mycorrhizal effects on: (a) tissue and water soluble Zn and (b) differential uptake of P and Zn. Plants grown with supplemental Zn had greater growth and Zn tissue concentration than those not receiving Zn. With no supplemental Zn, mycorrhizal treatments had greater growth and Zn concentration than non-mycorrhizal treatments. There was no indication of nutrient interaction between Zn and P. Over the range of tissue Zn found, there appeared to be no advantage to water soluble Zn analysis over total Zn in assessing plant Zn status.

Effects of Aerial Spray Volume, Coverage, and Abamectin on Scirtothrips perseae (Thysanoptera: Thripidae)

Abstract Helicopter applications using abamectin in different spray volumes were made against Scirtothrips perseae Nakahara in Ventura County, CA. On small (2.2 m tall) trees, spray coverage on water-sensitive papers was 24–48% and 43–97% for 468 and 935 liter/ha volume treatments, respectively. On large (6.2–8.1 m tall) trees, spray coverage was lower and quite variable, from 1 to 28% and 10 to 70% for 468 and 935 liter/ha treatments, respectively. On small trees, 468, 701, and 935 liter/ha with a high abamectin rate (26 g [AI]/ha) were equally effective against larvae from 13 to 27 d after treatment (DAT). On medium (4.2 m tall) trees, 468 and 935 liter/ha with the high rate were equally effective from 23 to 113 DAT. On large (6.5–8.1 m tall) trees, 468 and 935 liter/ha with a low abamectin rate (13 g [AI]/ha) were ineffective in three tests. In a fourth large (6.8 m tall) tree test, 468 and 935 liter/ha with the high rate were effective at 3 and 37 DAT. In a fifth large (6.2 m tall) tree test, 468-1, 403 liter/ha with the high and 935 liter/ha with the low rate were equally effective 2-22 DAT. After all effective treatments, thrips numbers were lower than in controls for 1–3 mo. However, stable and highest reductions in populations were sometimes delayed until 20–23 DAT even when coverage was high. The variability in spray coverage on the lower levels of large trees and the delayed effect may explain inconsistencies in the reporting of or in actual aerial application results.

Phenology of Arthropod Pests and Associated Natural Predators on Avocado Leaves, Fruit, and in Leaf Litter in Southern California

Abstract Abundance of Scirtothrips perseae Nakahara (Thysanoptera: Thripidae), Oligonychus perseae Tuttle, Baker & Abbatiello (Acari: Tetranychidae), predators, and associations among their population trends on avocado leaves and fruit were determined in three untreated avocado orchards in Ventura and Santa Barbara Counties, CA, from 1998 to 2000. Objectives were to understand pest-predator dynamics and to assess which predators have potential as biological control agents. Numbers of S. perseae and predators from leaf litter/soil were also determined in one orchard from 1998 to 2000. On leaves, O. perseae was the most abundant pest, followed by S. perseae, and Oligonychus puniciae (Hirst) (Acari: Tetranychidae). Phytoseiid mites and spiders were the most abundant predators. The predatory thrips Franklinothrips orizabensis Johansen and Aeolothrips kuwanaii Moulton (Thysanoptera: Aeolothripidae) were also relatively abundant compared with at least 13 other species of predators on leaves. On immature avocado fruit, S. perseae was the most abundant pest and phytoseiid mites, F. orizabensis, and A. kuwanaii were the three most abundant predators. No consistent positive associations between pests and predators were seen on leaves, but F. orizabensis, A. kuwanaii, and phytoseiid numbers on fruit and S. perseae numbers on fruit were positively and significantly associated in all three orchards. In addition, there were significant positive associations between S. perseae and predatory thrips populations from leaf litter in two of the 3 yr. These pest-predator interactions may play a role in developing new control strategies and the importance of these relationships needs to be experimentally investigated.

Relationships Between Scirtothrips perseae (Thysanoptera: Thripidae) Populations on Avocado Leaves, Fruit, and Scarring Damage on Fruit

Abstract Scirtothrips perseae Nakahara causes significant scarring of avocado fruit and is the most serious pest of avocado in southern California. Because it was described only in 1997, no information that can be used for its control exists, including the relationships between its densities on leaves and fruit and scarring damage on fruit. To determine these relationships, percentages of scarring damage on avocado fruit were regressed against thrips numbers/leaf and numbers/fruit using data collected from three orchards in Ventura and Santa Barbara Counties, CA, from 1997 through 1999. Thrips population increases were positively related to leaf growth flushes. Numbers of first and second instars, total larvae, and adults/leaf were all predictive of scarring on fruit. Peaks of three to five larvae/leaf before and during fruit set predicted 6–15% economic scarring damage on fruit from October through December, whereas means of 0.5–1.5 larvae/small fruit predicted 22–51% scarring. Fruit were most susceptible to damage within a 2-wk period during and shortly after fruit set when they measured 0.53–1.42 cm long. Results suggest S. perseae numbers on leaves during fruit set can be used to predict scarring damage on fruit, and that damage thresholds may be ≤5 larvae/leaf during this time. Because low numbers of larvae on fruit within a 2-wk period can result in high scarring damage, early treatments when thrips are on leaves, just before they move onto fruit, may help prevent damage to fruit.

Survival of plant pathogens in static piles of ground green waste.

Ground green waste is used as mulch in ornamental landscapes and for tree crops such as avocados. Survival of Armillaria mellea, Phytophthora cinnamomi, Sclerotinia sclerotiorum, and Tylenchulus semipenetrans was assessed for 8 weeks within unturned piles of either recently ground or partially composted green waste. S. sclerotiorum survived at the pile surface and at 10, 30, and 100 cm within the pile for the entire 8 weeks in both fresh green waste (FGW) and aged green waste (AGW). A. mellea and T. semipenetrans did not survive more than 2 days in FGW, while P. cinnamomi persisted for over 21 days in FGW. AGW was less effective in reducing pathogen viability than FGW, most likely because temperatures in AGW peaked at 45 degrees C compared with 70 degrees C in FGW. Survival modeling curves based on pile temperatures indicate the time to inactivate 10 propagules of pathogens was 11, 30, 363, and 50 days for A. mellea, P. cinnamomi, S. sclerotiorum, and T. semipenetrans, respectively. Sclerotia-forming pathogens pose the greatest risk for escape; to ensure eradication of persistent fungi, green waste stockpiles should be turned intermittently to mix pile contents and move pathogen propagules to a location within the pile where they are more likely to be killed by heat, microbial attack, or chemical degradation.

Spore Trapping and Pathogenicity of Fungi in the Botryosphaeriaceae and Diaporthaceae Associated with Avocado Branch Canker in California

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 imports. 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 Botryosphaeriaceous and Diaporthaceous fungi. Based on colony counts, the highest population of Botryosphaeriaceous fungi (68%) occurred during 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%, respectively), 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 pathogenicity test of six fungi of Botryosphaeriaceae and one fungus of Diaporthaceae 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 Diaporthaceae families.

Captures of Wild Ceratitis capitata, Bactrocera dorsalis, and Bactrocera cucurbitae (Diptera: Tephritidae) in Traps with Improved Multilure TMR Dispensers Weathered in California

Abstract During 2012–2013, solid Mallet TMR (trimedlure [TML], methyl eugenol [ME], raspberry ketone [RK]) wafers impregnated with DDVP (2, 2-dichlorovinyl dimethyl phosphate) insecticide were weathered during summer (8 wk) and winter (12 wk) in five California citrus-growing counties (Kern, Ventura, Orange, Tulare, and Riverside). In addition, TMR wafers without DDVP and with a Hercon Vaportape II insecticidal strip were compared with TMR dispensers with DDVP at Exeter and Riverside. Weathered treatments were shipped every week (overnight delivery) to Hawaii and frozen for a later bioassay in a 1,335-ha coffee plantation near Numila, Kauai Island, HI, where Mediterranean fruit fly, Ceratitis capitata (Wiedemann), oriental fruit fly, Bactrocera dorsalis Hendel, and melon fly, Bactrocera cucurbitae Coquillett, were all present. We compared trap captures of the three species, C. capitata, B. dorsalis, and B. cucurbitae, for the five different weathering locations. Captures of C. capitata, B. dorsalis, and B. cucurbitae with Mallet TMR dispensers (with DDVP) were not significantly different for the five locations. Captures with the Mallet TMR dispenser without DDVP and Vaportape were similar to those for Mallet TMR with DDVP, although there were some slight location differences. In conclusion, based on these results, the Mallet TMR dispenser could potentially be used in California habitats where large numbers of detection traps are currently deployed. Use of Vaportape with dispensers would not require them to be registered with US Environmental Protection Agency (EPA). Dispensers for use as Male Annihilation Technique (MAT) devices will be tested further in Hawaii.

Re-evaluation of the roles of honeybees and wind on pollination in avocado.

Summary Avocado (Persea americana Mill.) flowers, with their synchronously dichogamous behaviour, are considered to be pollinated by honeybees, despite the lack of any direct evidence. Results in southern Florida showed that avocado pollen was transferable by wind, and was dispersed over a brief period of time (15 – 60 min) each day. Ten ‘Hass’ avocado orchards in the Santa Clara River Valley, CA, USA, planted far from any known ‘Zutano’ polliniser trees, were selected to investigate the impact of honeybees on pollen transfer. ‘Zutano’ pollen (5 g per insert) was placed at the entry to beehives (approx. eight beehives per orchard) and refreshed four-to-five times during the flowering season. Successful pollinations were determined by parental analysis of harvested ‘Hass’ fruit from trees located at various distances from the beehives, and at three different stages of fruit development, using microsatellite DNA markers. The results showed no significant difference in the proportions of ‘Zutano’-pollinated fruit with respect to distance and/or development stage between orchards provided with beehives containing ‘Zutano’ pollen and those without supplemented pollen. This strongly suggests that honeybees are not the major pollinators of avocado, and that most avocado flowers are self-pollinated by wind.

Chemical Degradation of TMR Multilure Dispensers for Fruit Fly Detection Weathered Under California Climatic Conditions

Abstract Degradation models for multilure fruit fly trap dispensers were analyzed to determine their potential for use in large California detection programs. Solid three-component male lure TMR (trimedlure [TML], methyl eugenol [ME], raspberry ketone [RK]) dispensers impregnated with DDVP (2, 2-dichlorovinyl dimethyl phosphate) insecticide placed inside Jackson traps were weathered during summer (8 wk) and winter (12 wk) in five citrus-growing areas. Additionally, TMR wafers without DDVP, but with an insecticidal strip, were compared to TMR dispensers with DDVP. Weathered dispensers were sampled weekly and chemically analyzed. Percent loss of TML, the male lure for Ceratitis capitata (Wiedemann) Mediterranean fruit fly; ME, the male lure for Bactrocera dorsalis (Hendel), oriental fruit fly; RK, the male lure for Bactrocera cucurbitae (Coquillett), melon fly; and DDVP was measured. Based on regression analyses for the male lures, TML degraded the fastest followed by ME. Degradation of the more chemically stable RK was discontinuous, did not fit a regression model, but followed similar seasonal patterns. There were few location differences for all three male lures and DDVP. Dispensers degraded faster during summer than winter. An asymptotic regression model provided a good fit for % loss (ME, TML, and DDVP) for summer data. Degradation of DDVP in TMR dispensers was similar to degradation of DDVP in insecticidal strips. Based on these chemical analyses and prior bioassay results with wild flies, TMR dispensers could potentially be used in place of three individual male lure traps, reducing costs of fruit fly survey programs. Use of an insecticidal tape would not require TMR dispensers without DDVP to be registered with US-EPA.

Micropropagation of Banana

Banana (Musa spp. AAA) is propagated vegetatively and can be rapidly and efficiently propagated by micropropagation. Conventional micropropagation techniques, however, may be too costly for commercial purposes. Our laboratory has found that depending on the combination of culture vessel and gelling agent more economic methods can be chosen for successfully micropropagating banana.