Jonathan H. Crane

Comparison of Different Sampling Methods and Effect of Pesticide Application on Spider Populations in Lime Orchards in South Florida

Abstract A survey of predatory arthropods in lime orchards at Homestead, FL, showed that spiders significantly outnumbered the other predatory arthropods (the green lacewing Chrysoperla rufilabris, coccinellid Harmonia sp., and the ant Myrmelachista sp.). The spider community consisted of nine families, 25 genera, and 15 species. The abundance and diversity of the predatory spiders in lime orchards suggests their possible role in regulating the increase of arthropod pest populations. In general, comparison of three sampling methods revealed that the visual sampling method provided the highest number of spiders collected followed by the shake-cloth method and the DVAC suction method collected the least. However, our data showed that the choice of sampling method depends on the species of interest. For instance, spider species in the hunting group were collected frequently using the visual method followed by the shake-cloth method; whereas, most of the species in the web-building group were collected by the three sampling methods with similar frequencies. The difference in the efficiency of the sampling methods may be explained by the retreating habits of the different spider species. The data gathered in sampling the predatory arthropods in sprayed and nonsprayed lime orchards demonstrated the probable nontarget effect of the different pesticides used in the orchards.

Chemical Control of the Redbay Ambrosia Beetle, Xyleborus glabratus, and Other Scolytinae (Coleoptera: Curculionidae)

ABSTRACT The redbay ambrosia beetle (RAB), Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), is an adventive pest of Lauraceae in the southeastern U.S. This wood-boring insect vectors a lethal fungus, Raffaelea lauricola T. C. Harr., Fraedrich & Aghayeva, the causal agent of laurel wilt (LW) disease. The vector-pathogen complex is responsible for extensive mortality of native Persea trees in South Carolina, Georgia, and northern Florida, and now poses an imminent threat to the avocado (Persea americana Mill.) industry in south Florida. While chemical control of the vector is not viewed as the primary solution, control tactics should be made available to Florida avocado growers. Field and laboratory tests were conducted using avocado bolts, potted avocado trees, and field grown swampbay trees (Persea palustris (Raf.) Sarg.) treated with contact and systemic insecticides. Zeta-cypermethrin + bifenthrin and lambda-cyhalothrin + thiamethoxam provided the most consistent control of Scolytinae as contact insecticides, while methomyl, malathion, bifenthrin, and endosulfan were more variable in effectiveness. Avocado trees treated with fenpropathrin, cryolite Na Al fluoride, and lambda-cyhalothrin+thiametoxam had similar numbers of beetle entrance holes on treated trees as on the untreated control trees. No statistical differences were observed in disease severity on treated versus non-treated avocados or swampbay. Linear regressions between the number of RAB entrance holes per tree (x) and LW disease severity (ya ) and between RAB entrance holes per tree (x) and recovery of R. lauricola (yb ) were both significant.

Inoculation with arbuscular mycorrhizal fungi enhances growth of Litchi chinensis Sonn. trees after propagation by air-layering

Lychee (Litchi chinensis Sonn.) is typically propagated by air-layering mature tree branches which are potted in fertilized, soil-free media after cutting. The size of these branches, low phosphorus retention by pot substrates, and fertilization all might combine to preclude benefits of arbuscular mycorrhizas to lychee. In order to examine the potential of lychee to benefit from arbuscular mycorrhizas in an agriculturally realistic context, lychee air-layers were grown for 469 days in ca. 95-l pots of soil-free substrate inoculated with field-collected arbuscular mycorrhizal roots or not at two different levels of phosphorus fertilization. High phosphorus fertilization (a one-time addition of ca. 1.32 g l−1 slow-release triple-superphosphate) had no detectable effects on mycorrhiza formation, lychee survival, net CO2 assimilation, or growth. Inoculation with indigenous South Florida arbuscular mycorrhizal fungi improved leaflet expansion as early as 120 days after inoculation, and subsequently enhanced height growth and leaf production but did not affect stem diameter growth, net CO2 assimilation, or survival. At harvest, although mycorrhizal colonization was low (average 7.4% colonized root length), mycorrhizal plants had 39% higher above-ground dry weight than control plants. Below-ground dry weights did not differ, but inoculated plants had lower fine root to leaf dry weight ratios than control plants. Leaflets of inoculated plants had higher concentrations of P, K, Cu, and Zn, and lower concentrations of Ca, Mg, and Mn than those of control plants, but total Kjeldahl nitrogen and iron concentrations did not differ significantly 10 months after inoculation. Mycorrhiza enhancement of lychee growth occurred even though phosphorus clearly was not limiting for growth. Our observations suggest that in this soil-free medium, arbuscular mycorrhizal fungus enhancement of copper and iron nutrition improved lychee growth.

Selective pruning and crop removal increase early-season fruit production of carambola (Averrhoa carambola L.)

Carambola (Averrhoa carambola L.) trees grow and bear fruit year-round in their native, tropical environment. Fruits of this species are borne mainly on the canopy periphery, and the delicate skin is easily damaged during windy conditions (wind-scar). Pruning, as well as fruit drop caused by strong winds, stimulates re-bloom of carambola trees. In subtropical southern Florida, cool temperatures and dry winds during the winter inhibit tree growth and shorten the production season to July‐February. Crop value is greatest during the early part of the season. We evaluated manual, selective pruning and crop removal as techniques for increasing production of early-season fruit in ‘Arkin’ carambola. Pruning 3‐4-year old branches to their main axes in early March (late winter in the Northern Hemisphere) resulted in flowering during mid-April (mid-spring) and a crop by the end of June (early summer), whereas harvest of intact, non-pruned trees began 4‐5 weeks later. Pruned branches produced 15 kg (November pruning) to 24 kg of fruit (July pruning). Selectively pruned branches deep within the tree canopy did not appear to be moved by wind as much as branches along the canopy periphery. Thus, fruit from pruned branches were nearly 100% free of wind-scar and had excellent appearance. In comparison, more than 58% of fruit harvested from the canopy periphery had wind-scar, with only ca. 20% free from such damage. Crop removal in November or December (mid‐late-autumn) increased early bloom and the amount of early fruit produced in the summer. De-fruited trees produced an average of 48 kg per tree of early fruit, harvested July 7, whereas non-de-fruited trees produced an average of only 5 kg per tree. # 2000 Elsevier Science B.V. All rights reserved.

Internal breakdown in mango fruit: symptomology and histology of jelly seed, soft nose and stem-end cavity

Abstract Fruit of many mango (Mangifera indica L.) cultivars are susceptible to an internal disorder often referred to as either jelly seed, soft nose, or stem-end cavity (SEC), depending on the symptoms that appear when fruit are cut open. It has not been determined if jelly seed, soft nose, and SEC are different disorders or different symptoms of the same disorder. Sections of fruit mesocarp from the cultivars Irwin, Tommy Atkins, and Van Dyke were examined by light microscopy to characterize the disorder and discern histological differences or similarities among fruit with each of the three types of symptoms. Jelly seed and SEC affected fruit during early fruit ontogeny, whereas soft nose symptoms were detected only in fully developed fruit. No major microscopic differences were detected among fruit with jelly seed, soft nose or SEC. In fruit with each type of symptom, disorganization of the cells and rupture of the cell walls were the first microscopic indicators of the disorder, followed by deterioration or dissolution of vascular connections between the stone and the mesocarp. Stem-end cavity resulted in necrosis of the mesocarp around the cavity. No cavity or tissue necrosis developed around the stone in fruit affected with jelly seed or soft nose. The presence of Ca oxalate crystals was observed only in fruit with SEC. Based on temporal and spatial differences in symptom development within the fruit, it appears that soft nose, jelly seed and SEC may be classified as separate disorders.

Potential of Contact Insecticides to Control Xyleborus glabratus (Coleoptera: Curculionidae), a Vector of Laurel Wilt Disease in Avocados

ABSTRACT Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae) is an invasive ambrosia beetle that vectors laurel wilt, a new disease that threatens avocado and other species in the Lauraceae Family. The lethal concentrations (LC50 & 90) of nine commercial insecticides to X. glabratus were determined by using a bolt-dip bioassay. Different formulations of bifenthrin, permethrin, fenpropathrin, z-cypermethrin + bifenthrin, l-cyhalothrin + thiamethoxam, malathion, chlorpyrifos, carbaryl, and methomyl were tested. Four concentrations of each insecticide were tested (0.5, 0.1, 0.03, and 0.01 of the label rate) and with water as a control. Beetles were exposed to treated bolts and mortality registered 48 h later. After 2 wk, bolts were destructively sampled to determine the number of beetles that constructed galleries and were alive inside the wood. Probit analysis was used to determine the LC50 & 90. Six pesticides were applied directly to the trunk and limbs of avocado trees in a commercial grove. Limbs of treated trees were cut weekly after the application and exposed to X. glabratus to determine the number of beetles boring into the logs. The toxicity of pesticides to X. glabratus was greatly reduced 2 wk after application. Among the tested pesticides, malathion and z-cypermethrin + bifenthrin provided the best suppression of X. glabratus. Among the insecticides registered for use in avocado, fenpropathrin and malathion were the most effective in protecting trees from attack by X. glabratus. Other pesticides that are currently not registered for use in avocados could be useful for managing this ambrosia beetle.

Water savings, nutrient leaching, and fruit yield in a young avocado orchard as affected by irrigation and nutrient management

This project was designed to determine the effect of fertilizer rate and irrigation scheduling on water use, nutrient leaching, and fruit yield of young avocado trees (Persea americana Mill. cv. Simmonds). Seven nutrient and irrigation management practices were evaluated: (1) irrigation based on crop evapotranspiration (ET) with 50% fertilizer at a standard rate (FSR); (2) ET irrigation with FSR (typical for avocado production in the area); (3) ET irrigation with 200% FSR; (4) irrigation based on exceedance of 15-kPa (SW) soil water suction with 50% FSR; (5) SW with FSR; (6) SW with 200% FSR; and (7) irrigation at a set schedule (based on timing and frequency typically used in local avocado production) with FSR. The SW with FSR treatment saved 87% of the water volume applied and reduced total phosphorus leached by 74% compared to the set schedule irrigation with FSR. The SW with FSR treatment had higher avocado fruit production, tree water-use efficiency, and fertilizer-use efficiency than the other six treatments. Thus, the use of soil water monitoring for irrigation management can substantially increase sustainability of young avocado orchards in southern Florida.

Detection of laurel wilt disease in avocado using low altitude aerial imaging.

Laurel wilt is a lethal disease of plants in the Lauraceae plant family, including avocado (Persea americana). This devastating disease has spread rapidly along the southeastern seaboard of the United States and has begun to affect commercial avocado production in Florida. The main objective of this study was to evaluate the potential to discriminate laurel wilt-affected avocado trees using aerial images taken with a modified camera during helicopter surveys at low-altitude in the commercial avocado production area. The ability to distinguish laurel wilt-affected trees from other factors that produce similar external symptoms was also studied. RmodGB digital values of healthy trees and laurel wilt-affected trees, as well as fruit stress and vines covering trees were used to calculate several vegetation indices (VIs), band ratios, and VI combinations. These indices were subjected to analysis of variance (ANOVA) and an M-statistic was performed in order to quantify the separability of those classes. Significant differences in spectral values among laurel wilt affected and healthy trees were observed in all vegetation indices calculated, although the best results were achieved with Excess Red (ExR), (Red–Green) and Combination 1 (COMB1) in all locations. B/G showed a very good potential for separate the other factors with symptoms similar to laurel wilt-affected trees, such as fruit stress and vines covering trees, from laurel wilt-affected trees. These consistent results prove the usefulness of using a modified camera (RmodGB) to discriminate laurel wilt-affected avocado trees from healthy trees, as well as from other factors that cause the same symptoms and suggest performing the classification in further research. According to our results, ExR and B/G should be utilized to develop an algorithm or decision rules to classify aerial images, since they showed the highest capacity to discriminate laurel wilt-affected trees. This methodology may allow the rapid detection of laurel wilt-affected trees using low altitude aerial images and be a valuable tool in mitigating this important threat to Florida avocado production.

Variability in reproductive traits in Jatropha curcas L. accessions during early developmental stages under warm subtropical conditions

Variability in floral, fruit, and seed characteristics, and oil content of 15 accession of Jatropha curcas during early development were assessed during two flowering periods in south Florida subtropical climate. The two flowering periods had leaf flushing in March. Field evaluation using 18 quantitative traits showed significant variation among accessions. The number of female flowers and female : male flower ratio ranged from 1 to 15 and 1 : 8.8 to 1 : 67.8, respectively. Fruit set by natural pollination was 89 and 66% during the first (1st) and second (2nd) flowering periods, respectively. A higher number of female‐type inflorescences were observed during summer. There were significant differences in seed traits, except for number of seeds per fruit. Accession TREC 31 had the highest individual seed dry weight and 100‐seed weight (0.83 g and 79.7 g, respectively). The oil content varied from 19.30% to 35.62%. Seed dry weight had positive correlation with seed fresh weight, seed length, seed thickness, seed width, and 100‐seed weight, but negative correlation with oil content. Based on the cluster analysis using 15 morphological traits, jatropha accessions were grouped into five main clusters and accessions from different geographic regions grouped together in a cluster. Principal component analyses (PCA) revealed morphological variation. The first three components explained 73.5% of the total variation and seed dry weight, 100‐seed weight, total flowers per inflorescence, male flowers per inflorescence and fruit set can be used to distinguish accessions. The PCA also indicated that flowering traits were more influenced by seed origin while seed traits were affected by flowering spans. Although evaluations were performed in plants during the juvenile phase, accessions TREC 31 and TREC 55 had superior averages for almost all characters evaluated. These results provide a preliminary assessment of the high variability in jatropha accessions evaluated and their potential for use in breeding and genetic improvement programs.

Recovery plan for laurel wilt of avocado, caused by Raffaelea lauricola

R. C. Ploetz, Tropical Research and Education Center, University of Florida, Homestead 33031; M. A. Hughes, School of Forest Resources and Conservation, University of Florida, Gainesville 32611; P. E. Kendra, USDA-ARS Subtropical Horticulture Research Station, Miami, FL 33158; S. W. Fraedrich, USDA Forest Service, Athens, GA 30602; D. Carrillo, Tropical Research and Education Center, University of Florida, Homestead 33031; L. L. Stelinski, Citrus Research and Education Center, University of Florida, Lake Alfred 33850; J. Hulcr, School of Forest Resources and Conservation and Department of Entomology and Nematology, University of Florida, Gainesville 32611; A. E. Mayfield, III, USDA Forest Service, Southern Research Station, Asheville, NC 28804; T. L. Dreaden, USDA-Forest Service, Southern Research Station, Forest Health Research and Education Center, Lexington, KY 40517; J. H. Crane, E. A. Evans, and B. A. Schaffer, Tropical Research and Education Center, University of Florida, Homestead 33031; and J. A. Rollins, Department of Plant Pathology, University of Florida, Gainesville 32611