Orchard and nursery dynamics of the effect of interplanting citrus with guava for huanglongbing,vector, and disease management

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an important pest of citrus in the United States of America primarily because it vectors ‘Candidatus Liberibacter asiaticus’, the bacterium putatively responsible for Asiatic huanglongbing (HLB). Asiatic HLB is considered one of the most serious diseases of citrus. In the United States where Asiatic HLB was first found in the state of Florida, vector control is considered an essential component to mitigate pathogen infection and spread of the disease. Therefore commercial citrus growers in Florida have adopted intensive insecticide programs to manage psyllid populations. However, the repetitive use of insecticides for ACP control is expensive and interferes with biological control of ACP and other citrus pests. As an alternative to insecticides, reports from Vietnam indicated that infestations of ACP in citrus (and consequently incidence of HLB) were reduced when citrus was interplanted with white guava, Psidium guajava L. Speculations were that guava volatiles reduced ACP infestations in citrus by either repelling ACP or interfering with ACP ability to locate and infest citrus grown next to guava. We present the results of two studies conducted in Florida (where both ACP and HLB occur) to assess ACP infestations and HLB incidence in citrus interplanted with either white or pink guava compared to infestations and disease incidence in citrus grown as a monoculture, both in orchards and nurseries. In the field study, the effect of guava on ACP infestations was assessed alone and in combination with insecticide or oil applications. Significant reductions in ACP infestations in citrus interplanted with pink guava were identified, but there was no reduction in citrus interplanted with white guava. The effect of pink guava on ACP infestations could be investigated further. However, intercropping citrus with either white or pink guava did not prevent the introduction and spread of HLB. Conclusions from field studies regarding guava as a management tactic against ACP were difficult to make due to persistent nematode problems and freeze damage to guava, which could have interfered with the production of guava volatiles responsible for deterring ACP infestations. Conversely, citrus nursery trees interspersed with guava did show reduced HLB incidence and disease progression over time. However, vector and disease reduction resulting from guava intercropping in citrus nurseries was not adequate to recommend it as a management strategy.     

Interference by Western Flower Thrips in rearing Asian citrus psyllid: Damage to host plants and facultative predation

An infestation of Western Flower Thrips (WFT), Frankliniella occidentalis (Pergande), recently developed on young citrus trees in a greenhouse devoted to rearing Asian citrus psyllid (ACP), Diaphorina citri Kuwayama. Large numbers of young flush leaves were killed which negatively impacted ACP, as ACP is dependent on flush for oviposition and nymph development. Further, WFT predated on immature ACP killing a large proportion of young nymphs. Two experiments were subsequently conducted to assess WFT damage to two ACP rearing host plants, orange jasmine [Murraya exotica (L.)] and sweet orange [Citrus sinensis (L.) Osbeck]. Direct comparisons of WFT damage to the two host plants were not made because the plants were not studied at the same time and the age of adults used in the experiments was not known. An infestation of ten adult WFT per flush shoot caused significant damage to orange jasmine: most (73%) flush shoots were killed, and shoots not killed were significantly growth retarded. Ten adult WFT per flush shoot caused little damage to sweet orange. A third experiment showed that five adult WFT per 90 ACP eggs predated on large numbers of eggs and 1st instar ACP − only 13% of the eggs hatched and developed beyond the 1st nymphal instar (WFT did not attack later instars). Predation on ACP immatures in this experiment included an evaluation of a minute pirate bug [Orius insidiosus (Say), regarded as effective against WFT] also at five adults per 90 ACP eggs. All ACP eggs were killed by this predator before eclosion. O. insidiosis might be useful for reducing infestations of WFT on citrus or other ACP host plants, but the predator would be incompatible with rearing ACP.     

Occurrence of ‘Candidatus Phytoplasma asteris’ in citrus showing Huanglongbing symptoms in Mexico

Huanglongbing (HLB), one of the most devastating citrus diseases in the world, was detected in Mexico in 2009. Currently, HLB is associated with the bacteria Candidatus Liberibacter spp., although several phytoplasmas have been found from trees showing HLB-like symptoms in Brazil and China. The aim of this study was thus to determine if, in addition to ‘Ca. L. asiaticus’ (CLas), phytoplasma species are also associated with HLB-like symptoms in citrus groves of Mexico. Citrus plants exhibiting symptoms such as diffuse chlorosis, blotchy mottle and vein yellowing were collected in the Mexican States of Nayarit, Colima and Sinaloa between August 2011 and September 2012. Samples were then evaluated for phytoplasmas and CLas by PCR, using primers that respectively target the genes for the 16S ribosomal RNA and 50S ribosomal protein of the β operon (rplA-rplJ). Out of 86 HLB-symptomatic citrus plants, 54 were positive for CLas, 20 were positive for phytoplasmas, 7 were found in mixed infections with both pathogens and 19 samples were negative for CLas and phytoplasmas. Actual and virtual RFLP analyses of the 16S rDNA sequences enabled us to classify two HLB phytoplasma strains as members of the aster yellows group (16SrI) ‘Candidatus Phytoplasma asteris’, which was confirmed by phylogenetic analysis. The HLB phytoplasma strain identified from Nayarit (HLBpc-Nay-IB) belongs to subgroup B (16SrI-B), and the strains identified from Colima (HLBpc-Col-IS) and Sinaloa (HLBpc-Sin-IS) belong to subgroup S (16SrI-S). The partial ‘Ca. L. asiaticus’ rplA-rplJ gene sequences were 100% identical to the ‘Ca. L. asiaticus’ strains isolated from several countries affected by HLB. These results confirm the association of ‘Candidatus Phytoplasma asteris’ with HLB-like symptoms in citrus groves in Mexico. Nonetheless, further studies are required to fully describe the ‘Ca. L. asiaticus’ and ‘Ca. P. asteris’ interactions in citrus, which will greatly assist the design of efficient management strategies.     

Repellency of selected biorational insecticides to potato psyllid, Bactericera cockerelli (Hemiptera: Psyllidae)

Bactericera cockerelli has recently become a major concern because of its direct feeding and vectoring of bacterial diseases in many solanaceous crops. The repellency of four biorational insecticides, MOI-201 (a Chinese medicine plant extract), Requiem (a plant extract of Chenopodium ambrosioides), BugOil (a mixture of four plant essential oils), and SunSpray oil (a mineral oil), to B. cockerelli adults was tested on tomato. In a no-choice test, all the insecticides had significant repellency to adults and deterred oviposition as compared with untreated controls. Of the four insecticides, the two oils showed a stronger repellency to adults and deterred oviposition more strongly than Requiem or MOI-201. In a choice test, all insecticides had significant repellency to adults and deterred oviposition compared to untreated controls. Of the four tested insecticides, <1 adults and no eggs were found on the leaves treated with SunSpray Oil, BugOil or Requiem 3 d after treatment. The repellency rates of these three insecticides were 77.2–95.4%. MOI-201 also repelled adults significantly and deterred oviposition compared to untreated controls even though it was the least effective insecticide among the four evaluated. In conclusion, all four insecticides tested showed significant repellency to B. cockerelli adults and deterred oviposition, especially the two oils. The overall repellency to potato psyllid adults can be arranged in a descending order of SunSpray oil > BugOil > Requiem > MOI-201. These insecticides could be used in integrated pest management programs targeted against the potato psyllid on solanaceous crops.     

Integration of soil applied neonicotinoid insecticides and acibenzolar-S-methyl for systemic acquired resistance (SAR) control of citrus canker on young citrus trees

Soil application of systemic neonicotinoid insecticides for control of psyllid vectors of Huanglongbing disease on young citrus trees also produces season-long SAR control of citrus canker caused by Xanthomonas citri subsp. citri Schaad et al. The neonicotinoids imidacloprid (IMID) and thiamethoxam (THIA) were compared with soil or sprinkler applications of the commercial SAR inducer acibenzolar-S-methyl (ASM) and foliar sprays of copper hydroxide (CH) and/or streptomycin (STREP) to evaluate their effects on the percentage of canker-infected leaves on 2-yr-old ‘Vernia’ orange and 3-yr-old ‘Ray Ruby’ grapefruit trees in Southeast Florida. All treatments significantly reduced the incidence of foliar canker compared to the untreated check. Soil drenches of ASM and season long rotations with IMID and THIA were highly effective for suppressing foliar canker on young grapefruit and orange trees under weather conditions absent of high intensity rains or tropical storms. Sprinkler application of ASM was less effective than soil drench. The level of control for SAR treatments was comparable to eleven 21-day interval sprays of CH and/or STREP. SAR induced by soil-applied insecticides provides substantial benefits for canker disease management on young citrus trees that may be augmented with ASM.     

Dormant season foliar sprays of broad-spectrum insecticides: An effective component of integrated management for Diaphorina citri (Hemiptera: Psyllidae) in citrus orchards

Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is a global pest of citrus and vector of Candidatus Liberibacter, a bacteria that causes huanglongbing or greening, a devastating disease of citrus. Mature citrus trees are dormant in winter and produce most new shoots in spring, followed by sporadic canopy growth in summer and fall. Young shoots are required for oviposition and nymphal development, but adults can survive and overwinter on hardened leaves. Surviving adults reproduce in spring shoots and their progeny are probably responsible for a large portion of disease spread as they disperse to search for food. Therefore, foliar sprays of broad-spectrum insecticides applied to mature trees in winter were evaluated in a commercial citrus orchard as tactic to reduce pest populations and insecticide use in spring and summer when beneficial insects are most active. A single spray of chlorpyrifos (2.8 kg a.i. ha⁻¹) in January 2007 reduced adult psyllids an average of 10-fold over six months compared to untreated trees. The following year, differences with the untreated control averaged 15-fold for over five months following a single spray of chlorpyrifos, fenpropathrin (0.34 kg a.i. ha⁻¹), or oxamyl (1.12 kg a.i. ha⁻¹) applied in January. Spiders, lacewings and ladybeetles were equally abundant during the growing season in both treated and untreated trees both years (P = 0.05). Thus foliar sprays of broad-spectrum insecticides before spring growth suppressed D. citri for five to six months, with no detectible impact on key natural enemies. This tactic has been widely adopted to control the psyllid in Florida, in some cases area-wide. Additional sprays during the growing season should be based on scouting and targeted at adults before anticipated new flush.     

Frequency of symptomatic trees removal in small citrus blocks on citrus huanglongbing epidemics

Among the recommended measures for citrus Huanglongbing (HLB) management, the systematic elimination of symptomatic trees is the most argued and difficult to be accepted and accomplished by citrus growers. Elimination of recently affected HLB trees represents a short term yield loss and cost increase due to the need of frequent inspections and removal operations. This work aimed to evaluate the effect of different frequencies of inoculum reduction applied at individual citrus blocks scale (or local inoculum reduction) on HLB temporal progress. Eight experiments were carried out in new planted and older citrus blocks with 504–1290 trees/plot. In all experiments, inspections to detect symptomatic trees were done in a fortnightly or monthly frequency. The treatments of frequencies of local inoculum reduction varied from fortnightly to 6 months. Annual disease progress rate was estimated by logistic model for each plot. No difference on HLB progress rates among treatments was observed, except in experiments 1 and 3 where less frequent tree removal resulted in higher disease progress rate. This ineffectiveness of local inoculum reduction on the disease progress rate was explained by the higher weight of primary spread on HLB epidemics than the secondary spread within plots associated with small size and narrow shape of treated plots (except for experiments 1 and 3), high dispersal capacity of HLB-insect vector among plots and groves, and strong control of psyllid within the plots (except for experiment 1, with poor insecticide spray program). Also, the high amount of inspections to detect symptomatic trees before the eradication treatment, which reduced the escapes (asymptomatic and non visual detectable diseased trees) contributed for these results. It is important to note that these results were obtained with only small citrus plots (0.8–2.9 ha) and they cannot be extended to larger groves and farms amenable to HLB management by the symptomatic tree removal and vector control.     

First report of the fungus Fomitiporia maxonii Murrill causing citrus wood rot in commercial orange and grapefruit groves in Cuba

Cuban citriculture has recently been affected by important pests and diseases including black citrus aphid Toxoptera citricida Kirkaldy, citrus leafminer Phyllocnistis citrella Stainton, Asiatic citrus psyllid Diaphorina citri Kuwayama, Citrus tristeza disease, and huanglongbing. This complex of ‘invasive species’ is thought to be contributing to the increasing decline of commercial citrus groves. During several surveys carried out in commercial citrus areas of several provinces in Cuba, symptoms of dieback, characterized by the presence of abundant dry branches and wood rot were detected on Criolla Valencia orange, Marsh grapefruit trees on sour orange, and Cleopatra mandarin rootstocks. Samples of branches and trunk wood were processed and a fungus was isolated from all samples. Morphological, physiological and molecular characterization demonstrated that the isolated agent is Fomitiporia maxonii Murrill. The incidence of affected trees was high in most surveyed groves, reaching 100% in old groves. Symptoms similar to the ones found in naturally infected trees were reproduced on trees inoculated with pure cultures of the fungus, and the fungus was recovered in culture from inoculated trees, thus fulfilling Koch's postulates. This is the first report of an association of F. maxonii with citrus wood rot in Cuba.     

Progress Toward an Attract-and-Kill Device for Asian Citrus Psyllid (Hemiptera: Liviidae) Using Volatile Signatures of Citrus Infected With Huanglongbing as the Attractant

Asian citrus psyllid, Diaphorina citri (Kuwayama), preferentially orient toward citrus hosts infected with the phytopathogenic bacterium, Candidatus liberibacter asiaticus (CLas) the agent of citrus greening (Huanglongbing, HLB), compared to uninfected counterparts. We investigated whether this preference for the odors of infected plants could be useful for the development of an attract-and-kill (AK) device for D. citri. Twenty-nine blends of volatile organic compounds derived from the odor of citrus infected with CLas were tested in laboratory olfactometer tests, and two blends were also assessed under field conditions. A seven component blend of tricosane: geranial: methyl salicylate: geranyl acetone: linalool: phenylacetaldehyde: (E)-β-ocimene in a 0.40: 0.06: 0.08: 0.29: 0.08: 0.06: 0.03 ratio released from a proprietary slow-release matrix attracted twice more D. citri to yellow sticky traps compared with blank control traps. The attractive blend was subsequently co-formulated with spinosad insecticide into a slow-release matrix to create a prototype AK formulation against D. citri. This formulation effectively reduced the population density of D. citri up to 84% as measured with tap counts when deployed at a density of eight 2.5 g dollops per tree as compared with untreated controls in small plot field trials conducted in citrus orchards. Psyllid populations were not statistically affected at a deployment rate of four dollops per tree. Our results indicate that an AK formulation incorporating spinosad and a volatile blend signature of citrus greening into a slow-release matrix may be useful to suppress D. citri populations.     

Monitoring of insecticide resistance in Diaphorina citri Kuwayama (Hemiptera: Psyllidae) from citrus groves of Punjab,Pakistan

The Asian citrus psyllid, Diaphorina citri Kuwayama being a vector of huanglongbing (HLB), citrus greening disease is the most destructive pest of citrus and the management of D. citri is crucial for successful control of HLB. We evaluated adult populations of D. citri from twelve districts of Punjab, Pakistan for resistance to seven different insecticides. Different levels of resistance ratios were observed for all insecticides (chlorpyrifos, bifenthrin, imidacloprid, acetamiprid, thiamethoxam, nitenpyram and chlorfenapyr). Field collected populations of D. citri were highly resistant to imidacloprid as compared to the susceptible population. The resistance ratios were in range of 236.6–759.5, 55.5–212.8, 13.1–46.4, 31.4–216.7, 8.6–89.4-fold for imidacloprid, acetamiprid, chlorfenapyr, nitenpyram, and thiamethoxam, respectively and 39.8–107.1 and 32.7–124.5-fold in case of conventional insecticides i.e., bifenthrin and chlorpyrifos, respectively. Nitenpyram and thiamethoxam, with no or very low resistance should be used in combination or in rotation with other pest management tactics for managing resistance in D. citri. The correlation analysis of the LC₅₀'s of insecticides showing positive and negative correlations among different insecticides in all tested populations, suggests mechanism of cross-resistance. Imidacloprid showed a positive correlation with acetamaprid, but a negative correlation with thiamethoxam from the neonicotenoid group, while the resistance to chlorfenpyr positively correlated with chlorpyrifos and bifenthrin in the pyrethroid group. Multiple resistance mechanisms could be the reason behind the development of such a high resistance in the D. citri.     

Potential use of selected citrus rootstocks and interstocks against HLB disease in Malaysia

Huanglongbing (HLB), also known as citrus greening disease, has spread to and is seriously threatening the citrus industry in more than 40 countries. The HLB pathogen is a phloem limited bacteria, Candidatus Liberibacter spp. There is little information pertaining to the effects of different citrus rootstocks and interstocks against HLB in Citrus reticulata. The objective of this study was to evaluate the beneficial effects of different combinations of citrus rootstocks and interstocks against HLB using side grafting. There were no symptoms of HLB when C. grandis was used as rootstock with C. hystrix as the interstock and vice versa six months after inoculation. However, C. Liberbribacter asiaticus was detected in the scion using second PCR amplification. A high rate of disease severity was observed when C. aurantum was used as rootstock and C. aurantifolia as the interstock and vice versa. This study showed that C. Liberibacter asiaticus can be detected by conventional PCR and characteristics of their detrimental effects include low rate of vegetative growth and reduction of dry matter, root dry matter, plant height and stem diameter.     

The Efficacy of Some Commercially Available Insect Repellents for Aedes aegypti (Diptera: Culicidae) and Aedes albopictus (Diptera: Culicidae)

Reducing the number of host-vector interactions is an effective way to reduce the spread of vector-borne diseases. Repellents are widely used to protect humans from a variety of protozoans, viruses, and nematodes. DEET (N,N-Diethyl-meta-toluamide), a safe and effective repellent, was developed during World War II. Fear of possible side effects of DEET has created a large market for “natural” DEET-free repellents with a variety of active ingredients. We present a comparative study on the efficacy of eight commercially available products, two fragrances, and a vitamin B patch. The products were tested using a human hand as attractant in a Y-tube olfactometer setup with Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse), both major human disease vectors. We found that Ae. albopictus were generally less attracted to the test subject’s hand compared with Ae, aegypti. Repellents with DEET as active ingredient had a prominent repellency effect over longer times and on both species. Repellents containing p-menthane-3,8-diol produced comparable results but for shorter time periods. Some of the DEET-free products containing citronella or geraniol did not have any significant repellency effect. Interestingly, the perfume we tested had a modest repellency effect early after application, and the vitamin B patch had no effect on either species. This study shows that the different active ingredients in commercially available mosquito repellent products are not equivalent in terms of duration and strength of repellency. Our results suggest that products containing DEET or p-menthane-3,8-diol have long-lasting repellent effects and therefore provide good protection from mosquito-borne diseases.     

Effect of chemical treatments on ‘Candidatus Liberibacter asiaticus’ infected pomelo (Citrus maxima)

Huanglongbing (HLB), also known as citrus greening, is one of the most destructive diseases affecting Rutaceae plants in many parts of the world. HLB is associated with three species of ‘Candidatus Liberibacter’ with ‘Ca. L. asiaticus’ (Las), being the most widely distributed bacterium in Thailand and Asia. The effectiveness of chemical treatment via trunk injection was evaluated in Las-infected pomelo (Citrus maxima) trees using quantitative real-time polymerase chain reaction. Our results demonstrated that a mixture of streptomycin (250 mg/L), ampicillin (2.5 g/L), penicillin G (2 g/L), and Bacicure^® (2 g/L) provided the highest efficiency in reducing and suppressing the Las-bacterium population indicated by the mean cycle threshold (Ct) values from 20.8 (≈7.2 × 10⁷ cells/g of plant tissue) to 36.6 (≈2140 cells/g of plant tissue) in greenhouse experiments, and from 19.4 (≈1.8 × 10⁸ cells/g of plant tissue) to 37.8 (≈969 cells/g of plant tissue) in the field experiments. In addition, our strategies remained therapeutically effective for one year. Finally, response of Las-infected pomelo to chemical treatment was elucidated using transmission electron microscopy.     

有色黏虫板对柑橘木虱的监测及防治研究进展

柑橘黄龙病是柑橘生产中的重大病害,随着其在全球范围内的传播蔓延,该病已成为近年来柑橘生产和研究中普遍关注的热点。柑橘木虱(Diaphorina citri Kuwayama)是传播柑橘黄龙病菌(Candidatus Liberibacter asiaticus)的主要虫媒,对柑橘木虱种群的准确监测与有效防控是控制柑橘木虱传播黄龙病的关键所在。有色黏虫板是一种利用昆虫趋色性,对小型飞行昆虫进行监测与诱杀的重要物理防治手段。有色黏虫板同样适用于监测和诱捕柑橘木虱,但黏虫板的颜色、光源、气候条件、悬挂黏虫板的植物种类及其挥发性信息化合物成分等都会影响黏虫板对柑橘木虱的诱集效果。本文在综合国内外柑橘木虱防控技术的基础上,将近年来利用有色黏虫板,监测与防控柑橘木虱的最新进展进行综述,并对有色黏虫板的发展前景给予展望。     

Haplotypes of the Potato Psyllid, Bactericera cockerelli, on the Wild Host Plant, Solanum dulcamara, in the Pacific Northwestern United States

‘Candidatus Liberibacter solanacearum’ (Lso) is a bacterium that infects solanaceous crops and causes plant decline and yield losses, especially in potato and tomato. Lso is transmitted to these hosts by the potato psyllid (Bactericera cockerelli Sulc) vector. B. cockerelli host plants are not limited to crop plants, but also include many wild, solanaceous weeds. These wild hosts could potentially impact overwintering and breeding of the psyllids and serve as reservoirs for Lso. In the Pacific Northwestern United States, B. cockerelli was recently reported to overwinter on bittersweet nightshade (Solanum dulcamara L.). The present study utilized high resolution melting analysis of the B. cockerelli mitochondrial cytochrome c oxidase I gene to assess the psyllid populations occurring on S. dulcamara during the summer and winter months in Washington, Oregon, and Idaho. This technique has previously been used to analyze the cytochrome c oxidase I gene of B. cockerelli, and has identified four psyllid haplotypes. Lso infection was also determined for the psyllids collected from S. dulcamara. During both the summer and the winter months in the Pacific Northwest, the Northwestern psyllid haplotype was the predominant population found living on S. dulcamara. However, low levels of the Western psyllid population were also present in Washington and Oregon during the same period. No overwintering psyllids tested were Lso-infected, suggesting that these populations do not pose an imminent threat of Lso transmission to newly emerging potatoes and other solanaceous crops in the region, unless a source of Lso becomes available.     

番石榴叶挥发油的抗菌性及优化提取研究

分别由酸疮痂链霉菌（Streptomyces acidiscabies, SA）、茄科雷尔氏菌（Ralstonia solanacearum, RS）和胡萝卜软腐欧文氏菌（Erwinia carotovora subsp. carotovora Borgey, ECCB）引起的植物疮痂病、青枯病、软腐病是农作物生产中常见多发的细菌病害。番石榴叶挥发油由多种活性物质组成，具有广谱抗微生物活性。本研究旨在提取并配置番石榴叶挥发油抗菌液，针对酸疮痂链霉菌、茄科雷尔氏菌、胡萝卜软腐欧文氏菌等3种病原菌进行挥发油的抗性研究，为农作物病害生物防治储备资源。采用添加锂盐结合微波辅助水蒸馏法提取番石榴叶挥发油，通过滤纸片扩散法和最小抑制浓度（MIC）评价了番石榴叶挥发油对3种供试菌株的抗菌效果，单因素结合响应面试验优化提取工艺，采用气相色谱-质谱联用技术（GC-MS）测定番石榴叶挥发油的化学成分。结果表明：番石榴叶挥发油对酸疮痂链霉菌、茄科雷尔氏菌、胡萝卜软腐欧文氏菌均表现出良好的抑制效果，抑菌圈直径范围为20.57～23.24 mm，抑菌率均达到60%以上，MIC值分别为3.13、1.56、3.13...     

Control of citrus postharvest penicillium molds with sodium ethylparaben

The curative antifungal activity of postharvest sodium ethylparaben (SEP) treatments against citrus green mold (GM) and blue mold (BM) was determined on different citrus species and cultivars artificially inoculated with Penicillium digitatum or Penicillium italicum and incubated at 20 °C and 90% RH for 7 d or stored at 5 °C and 90% RH for 8 weeks plus 7 d of shelf-life at 20 °C. The best concentration was selected in in vivo primary screenings with ‘Valencia’ oranges. SEP at 80 mM was tested at 20, 50 or 62 °C for 30, 60 or 150 s in small-scale trials to determine the best dip treatment conditions. Dips of 80 mM SEP at 20 °C for 60 s were selected and applied alone or in combination with 25 μL L⁻¹ of the conventional fungicide imazalil (SEP + IMZ 25). Imazalil at the very low concentrations of 25 (IMZ 25) or 50 μL L⁻¹ (IMZ 50) was also tested. Effectiveness of SEP alone at 20 °C for 60 s was significantly higher on oranges (cvs. ‘Valencia’ and ‘Lanelate’) than on mandarins (cvs. ‘Clemenules’, ‘Nadorcott’ and ‘Ortanique’), with GM and BM incidence reductions of up to 57–73% after 7 d at 20 °C. SEP was compatible with IMZ 25 and consistently improved its performance, irrespective of citrus cultivars and storage conditions. All treatments were less effective on ‘Clemenules’ mandarins. On ‘Valencia’ oranges stored for 8 weeks at 5 °C and 7 d at 20 °C, the combined treatment was significantly more effective than the single treatments (reductions of GM and BM incidence of about 96–93% and 55–39%, respectively). In additional tests, SEP, IMZ 25 and the combination applied at 20 °C for 60 s prevented GM on ‘Valencia’ oranges treated, inoculated with P. digitatum 24 h later and incubated at 20 °C for 7 d. It can be concluded from these results that SEP might be an integrating nonpollutant control alternative to be included in citrus postharvest disease control programs in the future.     

入侵植物胜红蓟精油对小贯小绿叶蝉的忌避和熏蒸活性研究

本文研究了入侵植物胜红蓟(Ageratum conyzoides L.)精油对小贯小绿叶蝉(Empoasca onukii Matsuda)的生物活性。分别使用植株选择着落法、Y形嗅觉仪和改良熏蒸法,检测不同浓度的胜红蓟精油对小贯小绿叶蝉的忌避和熏蒸活性。并且采用气质联用仪(GC-MS)分析了胜红蓟精油的化学成分,初步探讨了化学成分与活性的关系。研究结果表明:不同浓度的胜红蓟精油对小贯小绿叶蝉均具有忌避和熏蒸活性,浓度越高,效果越佳。精油含量为200μL·mL~(-1),忌避率达到100.00%;精油含量为100μL·mL~(-1)和50μL·mL~(-1)时,处理小贯小绿叶蝉5 min,忌避率分别为91.67%±1.67%和76.67%±1.67%;精油含量为5μL·mL~(-1)时熏蒸小贯小绿叶蝉12 h,死亡率为100%。并且胜红蓟精油中检测出24种化合物,其主要成分是β-石竹烯(61.53%)、早熟素I(11.09%)和早熟素II(7.79%)。胜红蓟精油对小贯小绿叶蝉的忌避和熏蒸活性可能与其主要成分的协同作用有关。研究结果证明,胜红蓟精油对小贯小绿叶蝉有明显的生物活性,具有开发成防治小贯小绿叶蝉植物源农药的潜力。     

Bioactivity of Six Plant Extracts on Adults of Demotispa neivai (Coleoptera: Chrysomelidae)

Demotispa neivai Bondar (Coleoptera: Chrysomelidae) damage oil palm fruits, which makes it necessary to develop products to control this insect. The mortality, repellency, and antifeeding effects on adults of D. neivai of six plant extracts of Azadirachta indica A. Juss. (Sapindales: Meliaceae), Ricinus communis (L.) (Malpighiaes: Euphorbiaceae), Citrus sinensis Oesbek (Sapindales: Rutaceae), Nicotiana tabacum (L.) (Slanales: Solanaceae), Capsicum annuum (L.) (Solanales: Solanaceae), and Artemisia absinthium (L.) (Asterales: Asteraceae) were determined: 1) the lethal concentration LC_50-90, lethal time of D. neivai was evaluated after spraying the fruits of oil palm; 2) repellent effects of each ingredient were evaluated by calculating the index of repellency; 3) antifeeding effects with the rate of inhibition calculated between doses of 20 and 24 g/liter. The mortality of D. neivai was higher with the extracts Ci. sinensis, R. communis, N. tabacum, and Ca. annuum. The mortality of D. neivai increased in the first 72 hr in all treatments. The extracts of N. tabacum, Ca. annuum, and A. indica were more repellent to D. neivai that those of Ci. sinensis, Ar. Absinthium, and R. communis. Antifeeding effect was higher with Ci. sinensis and R. communis. The increased mortality of D. neivai by Ci. sinensis can be explained by the effect of this compound on the respiratory system of insects. Extracts of Ci. sinensis, R. communis, N. tabacum, and Ca. annuum repelled and caused mortality of D. neivai and, thus, can be used in integrate pest management programs of this pest in oil palm plantations.     

The flavor of small immature tubers compared with mature Katahdin tubers

The flavor quality of seven immature potato samples (three varieties, four numbered selections) was found to be ‘equal to’ or ‘poorer than’ the flavor of mature Katahdin tubers stored for 10 months at 45 F (7.2 C). The samples were evaluated by a panel of 21 experienced judges.