Climate change & plant health

Irmgard Hoeschle-Zeledon*, i.zeledon@cgiar.org or sp-ipm@cgiar.org
*Coordinator of the CGIAR Systemwide Program on Integrated Pest Management (SP-IPM) convened by IITA

Diverse crop production system. Photo by IITA.
Diverse crop production system. Photo by IITA.

The discussion on the impact of climate change (CC) on agriculture has often focused on how changes in temperature, rainfall, and CO2 concentrations will affect the suitability of temperate regions for crop production and how crops will react in terms of yields. The effects of climate change on biotic factors in the tropics, such as weeds, pests, and pathogens (hereafter referred to as pests), have not received much attention.

Empirical data exist, however, to show that these biotic factors have major effects in determining productivity in the tropics. For instance, during the 1997 El Niño phenomenon, the mean temperature on the Peruvian coast increased by about 5 °C above the annual average, causing a decrease in potato infestation by the leafminer fly Liriomyza hydobrensis, which otherwise was a major pest. However, the abundance and infestation severity of all other pests increased in all crops, including potato (Kroschel et al. 2010). The complex consequences of CC particularly on pests and pathogens are still only imperfectly understood (Gregory et al. 2009).

CGIAR’s work on climate change
What are IITA and the other centers of the Consultative Group on International Agricultural Research (CGIAR) doing to mitigate the impacts and adapt to the effects of CC on pests? Historically, CGIAR centers have a broad R4D focus; centers have been developing knowledge (e.g., pest profiles), products (e.g., new crop varieties, biocontrol agents against invasive pests), and technologies (e.g., predictive models, diagnostic tools) that are suitable for diverse agroecologies including the tropics, wet, humid, semiarid, and dry, and to some extent the temperate zones as well. The broad knowledge and experience of centers provide an unprecedented advantage to assess the products and technologies in different agroecologies and weather settings and to determine their resilience and ability to cope in altered climatic situations.

Several programs directly focus on managing pests. For instance, the breeding of crop varieties for resistance to pests and pathogens has always been a focus of the CGIAR. With the uncertainties of CC, this work has become more relevant. Breeding for resistance to drought and waterlogging, although not the primary objectives, also aim at making varieties better able to tolerate biotic threats, since drought and excess water in the soil both increase the plants’ vulnerability to these factors.

A good example is the effort to develop drought-resistant maize cultivars by CIMMYT and IITA. These will not only allow the expansion of maize production into areas with less reliable rainfalls but also ensure the continued production in regions that are prone to future water scarcity. Drought- tolerant cultivars also reduce the risk of aflatoxin contamination in the field. Additional characters are incorporated into the drought-tolerant maize, such as resistance to maize streak disease which is endemic in Africa. Similar programs are ongoing to develop drought-resilient cassava and cowpea, and yam with tolerance for major pests.

The CGIAR centers are also working towards the development of cropping systems with greater intra- and interspecific diversity to increase resilience to CC-induced threats from biotic factors. For example, IITA is promoting maize–cowpea intercropping to reduce the pest pressure on cowpea.

Bioversity International is exploring how intra-specific crop genetic diversity on-farm not only reduces current crop losses to pests and pathogens, but also decreases the risk of genetic vulnerability and the potential of future crop damage, thus enhancing the impact of other IPM strategies and providing farmers with increased adaptive capacity to buffer against climatic changes.

CIP developed a temperature-driven phenology model for the potato tuber moth, Phthorimaea operculella that provides good predictions for the population in areas where the pest exists at present (Kroschel et al. 2010). Linked with geographic information systems (GIS) and atmospheric temperature, the model allows the simulation of risk indices on a worldwide scale to predict future changes in the distribution of the species due to increasing temperatures. The approach can also be used for other insect species. Hence, CIP created the Insect Life Cycle Modeling software (ILCYM) to facilitate the development of other insect phenology models. With its support, the phenology model can be implemented and allows for spatial simulation of insect activities.

Many centers support the collection and conservation of plant genetic diversity that can be built into new cultivars to enhance their resistance to biotic stresses. Diagnostics capacity is continuously augmented for the accurate and timely recognition of endemic pests, new variants, and invasive pests. Crop biodiversity—landraces and wild relatives that are the reservoirs of genes for abiotic and biotic factors—is conserved ex situ to protect the species from erosion by CC-induced changes.

In a collaborative effort, CIP, IITA, icipe, and partners in Germany and Africa are implementing a project to understand the effects of rising temperatures on the distribution and severity of major insect pests on main food crops. ILCYM will be further improved and adapted to cover a wide range of insect species. The results will contribute to filling the knowledge gap about CC effects on economically important insect herbivores and their natural enemies.

IITA is planning to research the effect of changes in temperature on the invasion potential of major biotic threats in the Great Lakes region of East Africa and elsewhere: Banana bunchy top virus (BBTV), Banana Xanthomonas Wilt (BXW), and Panama Disease–Tropical Race 4, cassava brown streak virus disease, cassava mosaic disease, maize streak, soybean rust, and pod borer pests, among others.

As whiteflies and aphids are considered to become more problematic with increased temperatures, IITA is also preparing research on the biocontrol of different whitefly and aphid species in vegetables and staple crops.

A project has been proposed on the bio-enhancement of seeds and seedlings of cereals and vegetables for East Africa to stimulate the plants’ defense mechanisms against pests and pathogens expected to increase in number, frequency, and severity. This project also addresses the registration of biopesticides and the availability of endophytes to the tissue culture industry.

CGIAR research programs
Under the new CGIAR Research Programs (CRPs), centers are addressing CC-induced crop health issues in various ways. Breeding for resistance to predicted biotic stresses continues to be a major focus in CRP3 (roots, tubers, banana) and its subcomponents. This component, coordinated by CIP, specifically recognizes CC and agricultural intensification as drivers for higher pressure from pests. Hence, this program aims at developing management strategies for priority biotic threats to these crops. These include the development of improved detection and monitoring tools, and surveillance methods for detecting and mapping existing, emerging, and resurgent molecular pests and pathogens. It will look into increasing general plant and root health through the enhancement of the natural disease suppressing potential of soils, and the antagonistic pest and disease potential of the aboveground agroecosystems.

The CRP on Integrated Systems for the Humid Tropics, led by IITA, will have a substantial focus on CC, its impact on pests, and plans for mitigation. For example, research will establish the relationship between CC and key cassava pests to develop integrated pest management (IPM) strategies including those for whitefly, African root and tuber scale, termite, green mite, aphid, and mealybug.

Phenology models for insect and mite pests and their antagonists on several crops will be developed and validated and their potential for changes in warming will be determined.

In collaboration with CABI, community surveillance for pests and diseases will take place through the expansion of the mobile plant clinic network.

Larva of the noctuid moth feeding on the pistil of cowpea. Photo by S. Muranaka, IITA.
Larva of the noctuid moth feeding on the pistil of cowpea. Photo by S. Muranaka, IITA.

Knowledge and decision support tools for the management of potato and sweetpotato pests (diseases and insects) will be developed and assessed in relation to the expected intensification of the agroecosystems in the humid and subhumid tropics.

Sustainable management of cassava virus disease in the cassava-based system will also be studied, and the vulnerabilities of these systems to CC- induced pest and disease problems will be determined.

The CIAT-coordinated CRP on CC, Agriculture, and Food Security began operations this year. It will continue the activities initiated by the CGIAR Challenge Program on CC. This CRP aims at mainstreaming strategies that address the management of CC- induced pest and disease threats among international and national agencies. It will identify and test innovations that enable communities to better manage and adapt to climate-related risks from biotic factors.

Recommendations
A lot of surprise shifts in ecosystems could come. It is therefore important that research capacity and knowledge bases are maintained to understand and rapidly react to mitigate any debilitating impacts (Shaw and Osborne 2011).

To accomplish this, it is necessary to establish good baseline data on current pest status in agroecosystems. This knowledge base will serve as a reference point to measure the fluctuations and the effectiveness of interventions.

It is important to determine the key weather variables that could change as a consequence of CC and their influence on agroecosystems and pests, and establish preemptive coping strategies. Available CC models could be handy for predicting CC factors.

A diverse scientific base including specialists in pathology, entomology, ecology, taxonomy, and epidemiology is required. They should work together to ensure that the outcomes of their research are linked to existing knowledge, economic forces, and common understanding (Shaw and Osborne 2011).

As it generally takes more than 10 years to breed a new resistant cultivar of a crop, breeding programs must start well in advance of the serious risk of a biotic threat Breeders need to be informed on the problems which might become important in the future (Chakraborty et al. 1998 in Juroszek and Tiedemann 2011).

Crops being bred for abiotic threats such as drought, waterlogging, and salinity should be prepared for the pests that could flourish under these conditions and select varieties that can tolerate pests as well.

Changes in occurrence, prevalence, and severity of infections and infestations will also affect crop health management (CHM) practices. There is a need to effectively disseminate and use those techniques that are currently underused (Juroszek and Tiedemann 2011).

Significant contributions could be made in improved field monitoring of pests and diseases, and better delivery systems for pest control products (Strand 2000 in Juroszek and Tiedemann 2011). Preventive crop protection measures may become more relevant under CC to reduce the risks (Juroszek and Tiedemann 2011).

CC is a global problem that affects all countries. Hence, global cooperation is required. However, given the nature of plant pests and pathogens, more local or regional strategies need to be put in place that define potential risks and measures to tackle expected threats. Investments in early detection systems, including border controls to monitor the migration of pests through plants, plant products, and other goods, will be the key to avoid the spread of invasive pests and reduce high management and eradication costs (FAO).

New farming practices, different crops, and IPM technologies must be developed to control the established pests and prevent the spread of new ones (FAO).
Governments should consider developing country-specific strategies to cope with CC-induced changes and put in place favorable policies for the introduction and promotion of new technologies for CHM.

It is also crucial to create and augment awareness about the effects of CC among policymakers and other officials involved in developing agricultural strategies.

References
Chakraborty S and Newton AC. 2011. Plant Pathology 60: 2-14.

FAO. unknown. ftp://ftp.fao.org/docrep/fao/010/i0142e/i0142e06.pdf

Govindasamy B et al. 2003. Climate Dynamics 21: 391-404.

Gregory PJ et al. 2009. Journal of Experimental Botany 60: 2827-2838.

Juroszek P and von Tiedemann A. 2011. Plant Pathology 60: 100-112.

Kroschel J et al. 2010. http://www.spipm.cgiar.org/ipm-research-briefs

Shaw MW and Osborne TM. 2011. Plant Pathology 60: 31-43.

Biological Control 101

Chemical pesticides have become a mainstay in pest management because of their “quick-fix” effects and their ease and convenience of use. Their use over time, however, has some negative effects on human health and the environment.

Farmer in Parakou, Benin, participates in the release of Fopius arisanus, a parasitoid of Bactrocera invadens
Farmer in Parakou, Benin, participates in the release of Fopius arisanus, a parasitoid of Bactrocera invadens

Biological control or biocontrol is an alternative to the use of chemical pesticides. It uses natural “enemies” to reduce pest populations and their damage to crops and food products. These enemies include predators, parasitoids, or pathogens.

Biocontrol approaches build on the natural control already existing within an ecosystem by strengthening a naturally occurring enemy or by importing and introducing a natural enemy into that ecosystem.

Predator and pest mites
Predator and pest mites

IPM toolbox
Biocontrol is just one of the many components in the integrated pest management (IPM) toolbox that includes, among others, the use of cultural practices, planting of resistant or tolerant crop varieties, and the application of inorganic (or chemical) pesticides.

Biological alternatives involve the use of biological control, biological pesticides, botanicals, semiochemicals, and transgenic organisms.

Biocontrol
Biocontrol is the use of natural enemies, also called biological control agents, such as predators or parasitoids that attack the pest to reduce pest damage. In an undisturbed ecosystem, insects, mites, or microorganisms, and other species that prey on or parasitize different species are part of the natural control or balancing mechanisms.

Biocontrol approaches include conservation biocontrol, augmentation biocontrol, and classical biocontrol.

10Maize cob being co-inoculated with toxigenic and atoxigenic strains to identify competitive atoxigenic strains in the field
10Maize cob being co-inoculated with toxigenic and atoxigenic strains to identify competitive atoxigenic strains in the field

Conservation biocontrol enhances the effectiveness of natural enemies already present in the ecosystem through, for example, the application of cultural practices. Examples include planting food sources for natural enemy pests or reducing the amount of chemicals in the system to allow natural enemy numbers to increase.

Augmentation biocontrol means the addition of a predator or parasitoid to an ecosystem to increase numbers or begin a new population when the natural enemy has disappeared. Inoculation is adding small numbers of the species, which increase naturally over time, whereas inundation means adding large numbers of the natural enemy for a rapid effect on the pests.

Classical biological control involves importing natural enemies to a location where they have not been present before, especially, when a pest has been accidentally introduced. Classical biocontrol has been applied successfully to control hundreds of pests in horticultural and field crops and in forestry. Despite the initial high investment, it is the most economical form of pest control.

Biopesticides

Diseased cassava leaf
Diseased cassava leaf

Biopesticides involve the use of pathogens—microorganisms that cause disease—to kill pests. Also called microbial pesticides, they contain pathogenic microorganisms as their active ingredient, e.g., bacterium, virus, fungus, nematode, or protozoa. They are applied in a manner similar to chemical pesticides, but their “live” ingredient gives them a potentially greater advantage over chemicals since this is able to reproduce and provide continuing pest control.

Some popular examples include the use of Bacillus thuringiensis (Bt), which naturally occurs in the soil and in plants, or mycopesticides (insect-killing fungi) such as Beauveria bassiana and Metarhizium anisopliae, which attack a relatively wide range of insects. IITA has been using these fungi for its biocontrol work.

Botanicals

<em/>Bactrocera invadens ovipositing on a mango fruit” title=”11Bactrocera invadens” width=”250″ height=”188″ class=”size-full wp-image-1149″ /><figcaption class=Bactrocera invadens ovipositing on a mango fruit

Also called botanical pesticides, these contain plant extracts that have biocidal properties. The best example is the use of the extracts from the popular neem tree (Azadiracta indica) (active ingredient: azadirachtin), which can be used to disrupt molting in a wide range of insect pests. Such botanicals can be grown alongside agricultural crops.

Semiochemicals
These are chemicals produced by insects and other species that stimulate behavior or interactions, and are used to manipulate behavior to control pests. Well-known examples are pheromones, which stimulate behavior between individuals of the same species, and allelochemicals, which mediate interaction between different species.

Transgenic crops
Transgenics contain protectants produced by the plants themselves, following the introduction of genetic material coding for that substance, as in Bt transgenic plants, e.g., Bt maize, potato, and cotton. The gene coding for the Bt toxin is inserted into the chromosome of the crop plant so that the plants themselves become toxic to the pest.

Source: SP-IPM. 2006. Biological alternatives to harmful chemical pesticides. IPM Research Brief no. 4. SP-IPM Secretariat, IITA.