Profitability of farm-scale management strategies against the boll weevil in the tropics: case study from the Colombian Caribbean

Decision making in pest management is a challenging task. While pest dynamics are often quite uncertain, such decisions are often based on tenuous assumptions of certainty (economic injury levels and marginal utility approximations). To overcome such assumptions and adequately consider uncertainty, we apply decision analysis to evaluate management strategies used by farmers in the Colombian Caribbean against the boll weevil (BW). We represent the decision to protect the crop using partial budget analysis. This allows us to capture key properties of BW control strategies, while accounting for uncertainty about pest infestation pressure, control effectiveness and cotton yield and price. Our results indicate that proactive pest management is more efficient than reactive control given the current BW infestation pressure. However, farmers may prefer the reactive strategy, since they have experienced seasons with low infestation pressure where no insecticide applications were required. The proactive strategy, in contrast, requires scheduled pesticide applications in all years. Results show that in seasons with high infestation pressure the expected revenues of the reactive strategy tend to decrease, mainly because more spray applications are required when fields are heavily infested by the weevil. Value of information analysis revealed that uncertainties related to the start of the infestation, loss damage rate and attainable yield have the greatest influence on the decision recommendation for crop protection. Narrowing these key knowledge gaps may offer additional clarity on the performance of the current management strategies and provide guidance for the development of strategies to reduce insecticide use. This is particularly important for the promotion of the proactive strategy, which, under the current infestation pressure, has potential to reduce insecticide use. While economic injury levels can only be applied to responsive measures, our approach of partial budget analysis under uncertainty allows us to assess and compare both responsive and preventive measures in the same methodological framework. This framework can be extended to non-pesticide control measures.

Field management of Taro (Colocasia esculenta (L.) Schott) leaf blight via fungicidal spray of foliage

Taro leaf blight (TLB) epidemic hit Cameroon for the first time in 2009. Since then, the disease is persistent and its typical devastating legacy is threatening Taro (Colocasia esculenta) in the North and South West Regions of Cameroon. This study was initiated with the objective to determine the potentials of some fungicides to control TLB. The experimental design was completely randomized with a 3x15x2 factorial, including 3 treatments: T1 (Callomil plus72WP), T2 (Mancoxyl plus 720WP) and T3, 1:1 ratio T1 + T2 all applied at concentrations of 4g/L; 15 repetitions and 2 planting seasons (dry season i.e. October 2014 – March 2015 and rainy season i.e. April-October 2015). Disease incidence and disease severity were used to evaluate the disease progression while corm yield was used to appraise the economic injury. The results revealed disease incidence of 0% during the dry season and 18.2%, 27.3% and 100%, for T1, T2 and T3 and control during rainy season respectively. Disease severity was 75% in control and only 1% for the different treatments. Corm yield in the rainy season was 17.4kg, 15.08kg, 14.27kg and 5.89kg for T1, T2, T3 and control respectively. This study suggests that TLB epidemic can effectively be managed by foliage spray with Metalaxyl containing fungicides at a weekly dosage of 4g/L. Key words: Chemical control, Colocasia esculenta, Epidemic, Phytopathology, Phytophthora colocasiae

Idioscopus clypealis (mango leafhopper).

Mango leafhoppers are major pests in the Indian subcontinent. The major damage caused is at the flowering stage and several studies have highlighted the reduction of yield which may be between 20 and 100% depending on population size. Verghese and Rao (1987) examined the critical infestation stages of I. clypealis in Uttar Pradesh, India. The mean density of cicadellids was 0.54-20.64 per panicle in 1983 and 0-6.03 per panicle in 1984. In both years, the peak population occurred when the fruit was pea sized. At the post-bloom stage a population of two adults per panicle was sufficient to cause yield reduction. It is suggested that the critical infestation stages are at post-bloom, when the fruit is marble sized, and 1 month before harvest, with corresponding critical population levels of two adults, 6-21 nymphs and 4-11 hoppers per panicle. In the Philippines, Corey et al. (1989) found that the economic injury levels for I. clypealis on two croppings of mangoes averaged 4.21, 4.30, 4.45 and 4.55 adults per panicle at 2, 10, 18 and 26 days, respectively, after flower bud break for the first cropping, and 4.79, 4.88, 5.06 and 5.18 adults per panicle for the second cropping.

Knowledge-Based System for Crop Pests and Diseases Recognition

With the rapid increase in the world’s population, there is an ever-growing need for a sustainable food supply. Agriculture is one of the pillars for worldwide food provisioning, with fruits and vegetables being essential for a healthy diet. However, in the last few years the worldwide dispersion of virulent plant pests and diseases has caused significant decreases in the yield and quality of crops, in particular fruit, cereal and vegetables. Climate change and the intensification of global trade flows further accentuate the issue. Integrated Pest Management (IPM) is an approach to pest control that aims at maintaining pest insects at tolerable levels, keeping pest populations below an economic injury level. Under these circumstances, the early identification of pests and diseases becomes crucial. In this work, we present the first step towards a fully fledged, semantically enhanced decision support system for IPM. The ultimate goal is to build a complete agricultural knowledge base by gathering data from multiple, heterogeneous sources and to develop a system to assist farmers in decision making concerning the control of pests and diseases. The pest classifier framework has been evaluated in a simulated environment, obtaining an aggregated accuracy of 98.8%.

Idioscopus nitidulus (mango leafhopper).

According to Viraktamath (1989), 14 idiocerine species in three genera (Amritodus, Busoniomimus and Idioscopus) breed on mango, and of these only six are of economic importance. Mango leafhoppers are major pests in the Indian subcontinent. The major damage caused is at the flowering stage and several studies have highlighted the reduction of yield which may be between 20 and 100% depending on population size. Verghese and Rao (1987) examined the critical infestation stages of the related species I. clypealis in Uttar Pradesh, India. The mean density of cicadellids was 0.54-20.64 per panicle in 1983 and 0-6.03 per panicle in 1984. In both years, the peak population occurred when the fruit was pea sized. At the post-bloom stage a population of two adults per panicle was sufficient to cause yield reduction. It is suggested that the critical infestation stages are at post-bloom, when the fruit is marble sized, and 1 month before harvest, with corresponding critical population levels of two adults, 6-21 nymphs and 4-11 hoppers per panicle. In the Philippines, Corey et al. (1989) found that the economic injury levels for I. clypealis on two croppings of mangoes averaged 4.21, 4.30, 4.45 and 4.55 adults per panicle at 2, 10, 18 and 26 days, respectively, after flower bud break for the first cropping, and 4.79, 4.88, 5.06 and 5.18 adults per panicle for the second cropping.

Idioscopus nagpurensis (mango leafhopper).

Mango leafhoppers are major pests in the Indian subcontinent. The major damage is caused at the flowering stage and several studies have highlighted the reduction of yield which may be between 20 and 100% depending on population size. Verghese and Rao (1987) examined the critical infestation stages of the related species I. clypealis in Uttar Pradesh, India. The mean density of cicadellids was 0.54-20.64 per panicle in 1983 and 0-6.03 per panicle in 1984. In both years, the peak population occurred when the fruit was pea sized. At the post-bloom stage a population of two adults per panicle was sufficient to cause yield reduction. It is suggested that the critical infestation stages are at post-bloom, when the fruit is marble sized, and 1 month before harvest, with corresponding critical population levels of two adults, 6-21 nymphs and 4-11 hoppers per panicle. In the Philippines, Corey et al. (1989) found that the economic injury levels for I. clypealis on two croppings of mangoes averaged 4.21, 4.30, 4.45 and 4.55 adults per panicle at 2, 10, 18 and 26 days, respectively, after flower bud break for the first cropping, and 4.79, 4.88, 5.06 and 5.18 adults per panicle for the second cropping.

Aphis glycines (soyabean aphid).

A. glycines is distributed throughout eastern Asia, principally in China, Japan, Indonesia, Thailand, Korea, far eastern Russia, North Borneo, peninsular Malaysia and the Philippines (Blackman and Easop, 2000). It is a major pest of soyabean in China, causing particularly severe economic losses in the regions of Jilin, Liaoning, Heilongjiang and Neimenggu (Wang et al., 1962). It attacks soyabeans and is also a minor pest on other leguminous crops. It has recently been introduced into Australia, Canada and the USA (Fletcher and Desborough, 2000; Edwards et al., 2001; Michelutti et al., 2002). It has quickly become a soyabean pest in North America, where aphids had previously not attacked soyabeans (Ragsdale et al., 2011). A. glycines causes economic injury due to direct feeding, and indirect injury due to the spread of viruses, in particular Soybean mosaic virus (SMV).

Economic Injury Levels for Bt-resistant Helicoverpa zea (Lepidoptera: Noctuidae) in Cotton

Thresholds for Helicoverpa zea (Boddie) in cotton Gossypium hirsutum L. have been understudied since the widespread adoption of Bt cotton in the United States. Our study was possible due to the widespread presence of H. zea populations with Cry-toxin resistance. We initiated progressive spray timing experiments using three Bt cotton brands (Deltapine, Stoneville, and Phytogen) widely planted across the U.S. Cotton Belt expressing pyramided toxins in the Cry1A, Cry2, and Vip3Aa19 families. We timed foliar insecticide treatments based on week of bloom to manipulate H. zea populations in tandem with crop development during 2017 and 2018. We hypothesized that non-Bt cotton, cotton expressing Cry toxins alone, and cotton expressing Cry and Vip3Aa19 toxins would respond differently to H. zea feeding. We calculated economic injury levels to support the development of economic thresholds from significant responses. Pressure from H. zea was high during both years. Squares and bolls damaged by H. zea had the strongest negative yield associations, followed by larval number on squares. There were fewer yield associations with larval number on bolls and with number of H. zea eggs on the plant. Larval population levels were very low on varieties expressing Vip3Aa19. Yield response varied across experiments and varieties, suggesting that it is difficult to pinpoint precise economic injury levels. Nonetheless, our results generally suggest that current economic thresholds for H. zea in cotton are too high. Economic injury levels from comparisons between non-Bt varieties and those expressing only Cry toxins could inform future thresholds once H. zea evolves resistance to Vip3Aa19.