Crop Hygiene Research Articles

Conservation biological control of the fruit fly parasitoid Fopiusa arisanus (Hymenoptera: Braconidae)

AbstractFopius arisanus is a parasitoid of Bactrocera fruit flies. In sub‐tropical Australia, it can cause >30% parasitism of Queensland fruit fly, Bactrocera tryoni. There has been minimal research effort globally, and none in Australia, to determine how the abundance of this species can be maintained and increased through conservation biological control. We carried out three research activities aimed at conserving this species in a landscape: (i) testing mesh sizes for augmentoria, devices into which fallen fruit can be placed that capture emergent flies while allowing parasitoid release; (ii) investigation of the suitability of wild tobacco, Solanum mauritianum, and wild tobacco fly, Bactrocera cacuminata, as a non‐crop refuge for the parasitoid; and (iii) the value of floral resources for companion planting to increase carbohydrate sources. We determined that a mesh size of approximately 2 mm2 retained near 100% of fruit flies while releasing ~90% of parasitoids. A readily obtainable 50% shade cloth maintained a mesh pore of this size and was confirmed as suitable for making augmentoria. In South East Queensland, the wild tobacco/wild tobacco fly system was demonstrated to host F. arisanus continuously through the year, with an annual parasitism rate of 31%, peaking in the spring at 60%. A second fruit fly parasitoid, Diachasmimorpha kraussii, was also collected from this system, but at lower levels. Fopius arisanus were able to move >120 m from a wild tobacco patch to parasitise fruit fly‐infested fruit. None of five floral resources trialled increased wasp longevity beyond the mean of 5.3 days achieved by a water‐only control. When five additional fruit juice/fruit pulp resources were tested, only one increased wasp longevity, by 1.3 days, over the water‐only control. In contrast, wasps fed on honey and water survived for a mean of nearly 40 days. We thus concluded that in the field F. arisanus does not gain its nutritional needs from either flowers or fruit. Augmentoria offer an easily scalable tool, suitable for backyard growers through to commercial producers, which provides the control benefits of crop hygiene while not disrupting the parasitoid cycle. Where wild tobacco can be maintained without impacting the quality of farm habitat, it has great potential as a year‐round reservoir of the wasp. Companion planting to increase nectar resources is not recommended for F. arisanus conservation biological control.

Tomato brown rugose fruit disease: current distribution, knowledge and future prospects

Tomato is the most economically important fruit/vegetable crop grown worldwide. However, viral diseases remain an important factor limiting its productivity, with estimated quantitative and qualitative yield losses in tomato crops often reaching up to 100%. Many viruses infecting tomato have been reported, while new viral diseases have also emerged. The climatic changes the world is experiencing can be a contributing factor to the successful spread of newly emerging viruses, as well as the establishment of disease in areas that were previously either unfavourable or where the disease was absent. Because antiviral products are not available, strategies to mitigate viral diseases rely on genetic resistance/tolerance to infection, control of vectors, improvement in crop hygiene, roguing of infected plants and seed certification. Tomato brown rugose fruit virus (ToBRFV) is an emerging viral threat to tomato productivity and is currently spreading into new areas, which is of great concern to the growing global production in the absence of mitigation measures. This review presents the current knowledge about ToBRFV and future prospects for an improved understanding of the virus, which will be needed to support effective control and mitigation of the impact it is likely to cause.

Modeling the dynamics and transmission of cassava mosaic disease in Tanzania

Cassava mosaic disease (CMD) is caused by cassava mosaic virus (CMV) and is transmitted by the whitefly vector called Bemisia tabaci. In this paper, the deterministic model for transmission dynamics of CMD is formulated by considering the whitefly vector, cassava resistant and susceptible breeds, and infected cassava. The basic reproduction number $R_{0}$ and sensitivity index for each parameter with respect to basic reproduction number $R_{0}$ are computed to determine which parameters are sensitive to the dynamics of cassava mosaic disease. Analysis shows that the death rate of whitefly vectors, the infection rate for susceptible vectors, the number of vectors that can be supported and the rate of loss of infected cassava due to disease are the most sensitive parameters to the dynamics of cassava mosaic disease. Numerical simulation indicates that, cassava new infections increase as the number of vectors that can be supported increase and acquire cassava mosaic disease. It shows that if control measures are not considered, then the susceptible breed and cassava resistant breed will be wiped out after five and ten months respectively. To control the disease, farmers are encouraged to apply control strategies such as spraying of insecticide, using of vector-resistant varieties, phytosanitation which involve the removal of infected cassava plants from the farm, crop hygiene and the use of free stem cutting method.

Management and population dynamics of diamondback moth (Plutella xylostella): planting regimes, crop hygiene, biological control and timing of interventions.

Using an age-structured process-based simulation model for diamondback moth (DBM), we model the population dynamics of this major Brassica pest using the cropping practices and climate of Guangdong, China. The model simulates two interacting sub-populations (demes), each representing a short season crop. The simulated DBM abundance, and hence pest problems, depend on planting regime, crop hygiene and biological control. A continuous supply of hosts, a low proportion of crop harvested and long residue times between harvest and replanting each exacerbate pest levels. Biological control provided by a larval parasitoid can reduce pest problems, but not eliminate them when climate is suitable for DBM and under certain planting practices. The classic Integrated Pest Management (IPM) method of insecticide application, when pest threshold is reached, proved effective and halved the number of insecticide sprays when compared with the typical practice of weekly insecticide application.

Population dynamics of the diamondback moth, Plutella xylostella (L.), in northern China: the effects of migration, cropping patterns and climate.

The diamondback moth, Plutella xylostella (L.), is the most widely distributed pest of Brassica vegetables. Control of P. xylostella has relied on insecticides and it has developed resistance to most insecticides. Although research has clarified the resistance status of P. xylostella and the mechanisms of its resistance in northern China, little work has been conducted on long-term population dynamics in the key vegetable-growing areas of the region. We reviewed and summarized the history of P. xylostella field management practices in northern China (Haidian, Changping, Xuanhua and Zhangbei). Moths were caught in pheromone traps throughout the cropping season and P. xylostella phenology and the general trends in abundance were analysed using DYMEX modelling software. The initial input in the spring determined population size in all years. The seasonal phenology and variation in abundance in most years and sites were simulated, suggesting that the suitable climate creates the conditions for population outbreaks, and growers' actual management level (spraying and crop hygiene) influenced population abundance. Based on climate and using the timing of the initial peak in pheromone trap captures as a biofix, the timing of emergence of the next generation can be forecast, and more effective scouting and regional management strategies against this pest can be developed. © 2018 Society of Chemical Industry.

Population dynamics and management of diamondback moth (Plutella xylostella) in China: the relative contributions of climate, natural enemies and cropping patterns.

Diamondback moth or DBM is the major pest of Brassica vegetable production worldwide. Control has relied on insecticides, and DBM resistance to these compounds has evolved rapidly. We review and summarize data on DBM population dynamics across a large latitudinal gradient from southwest to northeast China: DBM is, on average, more common in southern locations than in northern locations. The species' phenology is consistent: in southern and central locations there is a decline during hot summer months, while in the north, the species can only exist in the summer following migrations from the south. A cohort-based discrete-time model, driven by daily maximum and minimum temperatures and rainfall, which was built using the DYMEX modelling software, captures the age-structured population dynamics of DBM at representative locations, with year round cropping and threshold-based insecticide applications. The scale of the simulated pest problem varies with cropping practices. Local production breaks and strict post-harvest crop hygiene are associated with lower DBM populations. Biological control appears to improve the management of DBM. Of the management strategies explored, non-threshold based applications of insecticides with reduced spray efficacy (due to poor application or resistance) appear the least effective. The model simulates the phenology and abundance patterns in the population dynamics across the climatic gradient in China reasonably well. With planned improvements, and backed by a system of field sampling and weather inputs, it should serve well as a platform for a local pest forecast system, spanning the range of DBM in China, and perhaps elsewhere.

THE OCCURRENCE OF ANTHRACNOSE DISEASE CAUSED BY COLLETOTRICHUM GLOEOSPORIOIDES ON DRAGON FRUIT (HYLOCEREUS SPP.) IN PENINSULAR MALAYSIA

This study was carried out to identify the suspected pathogenic micro-organisms associated with anthracnose disease on dragon fruit (Hylocereus spp.) and to investigate the occurrence of this disease in Peninsular Malaysia. Fifty posts of dragon fruit crops from several surveyed dragon fruit-growing areas were randomly sampled to assess the disease occurrence. The results revealed that anthracnose, caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc., was one of the main diseases on this crop. This disease not only infected the stem but also the fruit. Diseased stem and fruit had symptoms of reddish-brown lesions with chlorotic haloes. The lesion had brown centers and coalesced to rot. Identification of the isolated pathogen showed that it had a whitish-orange colony, septated hyphae and capsule-like conidia (6-10 µm × 2-2.5 µm in size). The highest disease incidence (80%) was recorded from Pekan (Pahang), a farm with unfavorable environmental condition for the optimum growth of dragon fruit crops; while the most severe disease (32.0%) was documented from a Durian Tunggal (Malacca) farm where the crop hygiene was poor. Correlation of disease incidence and severity showed a positive linear correlation with an R2 value close to 1; while regression analysis results highlighted that the occurrence and progress of disease were highly influenced by environmental conditions, alternative sources of inoculum and agricultural practices rather than by climatic factors.

The epidemiology and management of bacterial blight (Pseudomonas syringae pv. pisi) of field pea (Pisum sativum) in Australia: a review

Bacterial blight caused by Pseudomonas syringae pv. pisi is an important, but sporadic, disease of field peas (Pisum sativum) in Australia. The presence of P. syringae pv. pisi reduces the profitability of peas due to yield loss and, in some cases, it also limits Australia’s export of peas to some countries. Pseudomonoas syringae pv. pisi is primarily a seed-borne pathogen, but infected pea trash can be an important source of inoculum. Alternative hosts and soil are not regarded as epidemiologically important sources of inoculum. P. syringae pv. pisi survives, multiplies and spreads epiphytically in pea crops. Epiphytic populations of P. syringae pv. pisi only become pathogenic following crop damage caused by frost or severe weather conditions. Frost damage is especially important because the ice nucleating activity of P. syringae pv. pisi initiates frost damage at higher temperatures than occurs in the absence of the bacterium. In addition early-sown crops are more prone to damage from bacterial blight than crops sown later in the season. Pseudomonas syringae pv. pisi consists of seven identified races. One of these (Race 6) lacks all avirulence genes and is common around the world and in Australia. Globally, Race 2 and Race 6 predominate; however, in Australia, Race 3 predominates due to the widespread cultivation of cultivars susceptible to Race 3, but resistant to Race 2. Resistance to Race 6 within P. sativum has not been found but attempts are being made to incorporate a race non-specific resistance identified from P. abyssinicum into field pea. Bacterial blight can be successfully controlled using an integrated disease management strategy incorporating crop rotation, pathogen-free seed, avoidance of planting in areas prone to frequent frosts or extreme wet weather, crop hygiene and avoiding early sowing. Seed treatment and application of foliar bactericides have limited use in control of this disease.

Assessment of cocoa growers' farm management practices in Ondo State, Nigeria

This study assesses the farm management practices of cocoa growers in Ondo State, southwestern Nigeria. One hundred and twenty three farmers were selected (using simple random sampling) from the list of cocoa farmers belonging to the Cocoa Farmers' Association of Nigeria (CFAN) in Ondo State. All were asked to complete a questionnaire on the farm hygiene and management practices they followed. The majority of respondents were married men who used family labour on their farms, and who had a varying number of years of farming experience. No significant relationships were found among age, marital status, years of farming experience and gender. However, the use of farm hygiene practices showed a significant relationship with educational status and grower attitude towards the adoption of appropriate crop growing practices. The majority of respondents commonly used chemicals rather than crop growing practices to ensure crop hygiene; few undertook practices such as pruning, the removal of diseased pods and mistletoe, the application of organic fertilizers, or the breaking of pods off-farm. A limited number combined crop growing practices with the use of chemicals to control pests and diseases. The lack of credit facilities, weeds, pests, diseases, parasites and marketing difficulties were all recognised as constraints limiting production. The present findings suggest that the Cocoa Research Institute of Nigeria (CRIN), the Ministry of Agriculture, and relevant non-governmental organizations should organize a sensitisation programme/training scheme to de-emphasize the use of chemicals and encourage the use of appropriate crop growing practices for improving farm hygiene.

Incidence and distribution of viruses infecting cucurbit crops in the Northern Territory and Western Australia

During 2003–04, a survey was done to determine the incidence and distribution of virus diseases infecting cucurbit crops growing in the field at Kununurra, Broome, and Carnarvon in north-western Australia, Perth in south-western Australia, and Darwin and Katherine in the Northern Territory. Overall, 43 cucurbit-growing farms and 172 crops of susceptible cultivars were sampled. From each crop, shoot samples were collected from plants chosen at random and from symptomatic plants. Shoot samples were sometimes also collected from potential alternative virus hosts (cucurbit volunteer plants and weeds). All samples were tested by enzyme-linked immunosorbent assay (ELISA) using antibodies to Cucumber mosaic virus (CMV), Papaya ringspot virus-cucurbit strain (PRSV), Squash mosaic virus (SqMV), Watermelon mosaic virus (WMV), and Zucchini yellow mosaic virus (ZYMV). Samples from one-third of the crops were also tested by tissue blot immunosorbent assay (TBIA) using generic luteovirus antibodies. Overall, 72% of farms and 56% of crops sampled were virus-infected. The growing areas with the highest incidences of virus infection were Darwin and Carnarvon, and those with the lowest incidences were Katherine and Perth. For WA, overall 78% of farms and 56% of crops were virus-infected, and in the NT the corresponding figures were 55% of farms and 54% of crops. Overall virus incidences in individual crops sometimes reached 100% infection. Crops of cucumber, melon, pumpkin, squash, and zucchini were all infected, with squash and zucchini being the most severely affected. The most prevalent viruses were ZYMV and PRSV, each being detected in 5 and 4 of 6 cucurbit-growing areas, respectively, with infected crop incidences of <1–100%. SqMV was detected in 2 cucurbit-growing areas, sometimes reaching high incidences (<1–60%). WMV and CMV were found in 3 and 4 of 6 cucurbit-growing areas, respectively, but generally at low incidences in infected crops (<1–8%). Infection with luteovirus was found in 3 growing areas but only occurred in 16% of crops. Beet western yellows virus was detected once but at least one other luteovirus was also present. Infection of individual crops by more than 1 virus was common, with up to 4 viruses found within the same crop. Virus-resistant pumpkin cultivars (6 crops) had little infection when adjacent virus-susceptible cucurbit crops had high virus incidences. Viruses were detected in cucurbit volunteer plants and weeds, suggesting that they may act as important reservoirs for spread to nearby cucurbit crops. In general, established cucurbit-growing farms in close proximity to others and with poor crop hygiene suffered most from virus epidemics, whereas isolated farms with large-sized crops or that had only recently started growing cucurbits had less infection. The extent of infection revealed in this survey, and the financial losses to growers resulting from virus-induced yield losses and high fruit rejection rates, are cause for concern for the Australian cucurbit industry.

Organophosphorus insecticide resistance and its management in the banana weevil borer, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), in Australia

Reports of widespread failures of prothiofos, chlorpyrifos, pirimiphos-ethyl and ethoprophos to control Cosmopolites sordidus (Germar) prompted an investigation of resistance as a possible cause. Baseline response to each of these insecticides was assayed in three separate insecticide-susceptible populations by topical application, with mortality being counted 72 h post treatment. These responses were used to determine a discriminating dose for each insecticide. Full dose-response assays of several suspect resistant populations confirmed that control failures were associated with resistance. Distinct plateaus in response lines of these populations may indicate that resistance is controlled by a single genetic factor. Resistance to pirimiphos and prothiofos was almost completely suppressed with the synergist piperonyl butoxide, suggesting that an enzymic system (probably monooxygenase) is responsible for the resistance. Surveys of beetle populations from farms in both northern and southern Queensland and northern New South Wales, Australia, confirmed that resistance to all four organophosphorus insecticides was widespread. Frequency of resistant beetles in most populations ranged from 0 to about 25%. Control failures occurred when > 10% resistant phenotypes were detected in the population. There was evidence of cross-resistance to the potential alternative chemical oxamyl but not to carbofuran, isazofos or isofenphos. A system of strategic spraying based on insect population monitoring, rather than routine spraying of entire farms, is being introduced in an effort to minimize the impact of this resistance on the banana industry. Crop hygiene in association with strategic spraying is also being promoted.

Biological Methods of Bruchid Control in the Tropics: a Review

Bruchid beetles cause high losses of stored legumes in the tropics. Chemical control is inappropriate for the small scale farmer and the use of alternative measures should be encouraged. Different biological methods of control such as cultural, physical, varietal, biological, biorational and genetic control are reviewed. Cultural control techniques such as timely and frequent harvesting, legumes planted away from granaries, crop hygiene and storage in pods, are within the technical and financial means of the small scale farmer. The use of inert substances, vegetable oils and repellent plants may be cheap and effective if properly managed. The use of controlled atmosphere, vacuum, heating, cooling and sterilizing, requires relatively advanced techniques. Growth regulators and pheromones are currently not available for control. Varieties resistant to bruchids have been identified, but incorporation of resistance into suitable varieties has proven to be difficult. Biological control of bruchids should receive more attention in particular research on the introduction and conservation of natural enemies. To effectively implement control measures at farmer’s level socio-economic and cultural aspects should be taken into account. Proven appropriate techniques should be combined in an overall integrated pest management strategy.

The long-range dispersal of plant viruses by arthropod vectors

Many plant viruses have winged or otherwise windborne insect or mite vectors that can fly or be blown far, suggesting that at least some of these viruses can be transported over great distances. However, this is difficult to substantiate and the evidence is largely circumstantial and mainly derived from studies on beet curly top and a few other viruses transmitted by leafhoppers, planthoppers or aphids. This review considers the evidence for long-range dispersal of plant viruses in an overall ecological context that is also applicable to other types of host and pathogen. All the known or suspected examples are attributed to particularly active migrant forms of species that are well adapted for colonizing new habitats as the original ones deteriorate. It is concluded that distant spread occurs more frequently than is generally supposed and that it is an extreme expression of dispersive processes that occur repeatedly but over generally shorter distances. These conclusions are shown to be compatible with the view that plant viruses mainly cause ‘ crowd diseases ’ that do not spread far in any considerable amount and are amenable to control by isolation and other measures of crop hygiene.

Contamination withErwinia Carotovora andVerticillium Albo-Atrum during multiplication of pathogen-tested seed potato crops, cultivar Kennebec

Contamination withErwinia carotovora andVerticillium alboatrum (dark mycelial form) occurred rapidly in certain seasons and districts in cv. Kennebec seed potato crops which were derived from pathogen-tested stem cuttings and propagated with attention to practical procedures of crop hygiene. Only varietycarotovora ofE. carotovora was found.

The rodent problem

Loss to stored produce by rodent attack occurs more from contamination than from actual consumption. The problem of rodent damage to growing crops is both more complex and more serious. Protective methods include high standards of crop hygiene, efficient harvesting and reduction of cover and food available to the pest species. The development of warfarin and related compounds constituted a major advance in chemical control but the problem of resistance has yet to be solved.

The Biology of Soil-Borne Plant Viruses

Publisher Summary This chapter discusses the biology of soil-borne plant viruses. It lists and discusses the plant viruses that are found to be soil-borne. The viruses within each group, although presumably not related strains, have many common attributes. The modes of transmission of soil-borne viruses are discussed in the chapter. The transmission of no soil-borne virus has yet been elucidated in detail, but there is evidence that soil-inhabiting organisms transmit some. A thorough knowledge of the ecology of a disease and of its causal agent ideally should lead to the formulation of effective control measures. But only a small part of this information is available for soil-borne viruses and many of the control measures used are empirical. These measures comprise methods of preventing the introduction of viruses to new sites and of combating the viruses where they are already established. The chapter discusses the control measures on infested land that are of four types, all traditionally used to control soil-borne plant pathogens: crop hygiene, rotation of crops, soil treatment, and the use of disease-escaping varieties.

PINK ROT OF THE POTATO

SUMMARY.1. A survey of the occurrence and importance of pink rot of the potato is given. The disease is widespread in Britain, but is only occasionally of serious economic importance.2. The nature of pink rot is explained and it is shown how the disease may be caused by more than one pathogenic fungus. Phytophthora erythroseptica Pethybr. is the normal pathogene, but two other species of Phytophthora have been recorded as causing the disease in the field, viz. P. drechsleri Tucker in the U.S.A. and P. megasperma Drechsler in Northern Ireland.3. The disease may be systemic in the potato plant, causing “misses” and “pink rot wilt” in the crop; normally, however, it is of importance only as a disease of the tuber.4. Under conditions of high humidity and poor aeration the disease may cause heavy loss in an affected crop during storage.5. Under normal conditions in the field the tuber becomes infected via the mother stolon; if conditions in the field or store are sufficiently moist, however, the tuber becomes infected directly, generally through the “eyes.”6. Varietal susceptibility of the potato has been considered on the three bases: (a) artificial infection of the tuber with P. erythroseptica, (b) natural infection of the tuber when stored in contaminated soil, (c) susceptibility in the field when planted in contaminated soil. Altogether fifty‐one varieties (including nine mentioned as susceptible by Pethybridge and which were not tested) have been considered, all of which proved to be more or less suceptible. No variety was found to be particularly resistant.7. Large numbers of oospores are produced by P. erythroseptica in the haulms and stolons and also to some extent in the roots of the dead potato plant. These oospores become disseminated and greatly increase the prevalence of the fungus in the soil.8. It has been shown that, in the absence of the host plant, the fungus may persist indefinitely in the soil. This persistence is apparently principally due to the resting spores, but the fact that the fungus may exist to some extent as a saprophyte in the soil cannot be ruled out.9. The disease may be satisfactorily controlled in practice by paying attention to the general principles of crop hygiene. Satisfactory crops can be grown in contaminated soil, provided that strongly sprouted tubers are planted and that soil drainage is sufficiently good to prevent the land from becoming unduly wet in times of heavy rainfall. Early harvesting of the crop tends to secure a minimum percentage of affected tubers at the time of digging. Prevention of the spread of the disease during storage may be obtained by ensuring dry and well aerated conditions in the store.The writers wish to express their very sincere thanks to Mr A. Murray, Culnafay, Toomebridge, County Antrim, who has given every facility for the carrying out of field experiments on his farm, and to the Potato Inspectors in Northern Ireland who assisted in recording occurrences of the disease.