Lit review

The world’s population is growing rapidly. It reached 6 billion people in 1999 and is anticipated to reach 8.1 billion in 2025 and 9.6 billion in 2050 (Alexandratos et al., 2012). Our long-term ability to meet growing needs for food seems uncertain. Thus, one of the greatest challenges is increasing food production in a sustainable way so that everyone can have adequate food and proper nutrition without over-exploiting the Earth’s ecosystems.

Rice is predominantly produced in Asia, so much so that thirty–one percent of the rice harvested globally comes from Southeast Asia alone (OECD/FAO, 2012). The highest levels of productivity are found in irrigated areas, the most intensified rice production systems. Farmers can grow more than one rice crop per year here. Approximately 45 percent of the rice growing country in Southeast Asia is irrigated, with the largest irrigated areas been found in Indonesia, Vietnam, Philippines and Thailand (Mutert 2002). In South Asia, the two major rice-growing countries are India and Bangladesh. India has the largest rice growing area globally, about 43 million hectares, and contributes 25 percent of global rice production. Combined, rice production in South and Southeast Asia contributes around half of global rice production. If rice production in South and Southeast Asia is threatened, it will significantly affect global rice production.

Pests in rice production are significant yield reducing factors globally. (Oerke 2005) estimated that weeds, animal pests, and disease caused losses around 10.2, 15.1 and 12.2 percent of global rice production, respectively. In most Asian countries, rice yields average 3-5 t/ha. One recent survey estimated that between 120 and 200 million tons of grain are lost yearly to insects, diseases, and weeds in rice fields in tropical Asia (Willocquet 2004). The mean region-wide rice yield loss due to pests was estimated at 37 percent (Savary et al., 2000).

In crop fields, pests or so-called biotic constraints can be defined as organisms that cause plant injuries and lead potentially to economic losses. Among the pests that attack rice are microorganisms (viruses, mycoplasmas, phytoplasmas, bacteria, oomycetes, and fungi) that can cause diseases, parasitic plants, weeds, invertebrates (insects, mollusks), and even vertebrates such as rats and birds can cause serious damages.

Rice Pests

Rice fields are human-managed ecosystems, which harbor diverse communities of plant, animal, and microbial species. Many of them indeed benefit with rice plants, such as predators, parasitoids, flowering plants, and soil bacteria (Norton 2010). However, there are some species threatening the rice plant’s health and can cause the quantity and quality losses. I briefly review some pests including weeds, animal pests, and diseases that are concerned the major rice production.

Weeds are plants considered as unwanted plants in the crop growing area and compete for nutrition, water, or light with cultivated crops. Weeds are the cause of severe yield reduction problems. In Asia, they are estimated to cause yield losses up to 80 percent, depending on rice field conditions (crop establishment, water management, field management). Weeds also reduce grain quality, and increase the production costs such as labor cost and input costs (Litsinger, 1991).

Rat causes serious yield reduction problems in many countries in Asia such as Bangladesh, Cambodia, People’s Republic of China, India, Indonesia, Lao People’s Democratic Republic, Malaysia, Myanmar, Philippines, Thailand, and Vietnam. Rattus argentiventer is the major rat pest species in Southeast Asia. Crop losses due to this species are typically about 10 to 20 percent. Rat damage in the rice fields is easily observed when a large number of the tillers are cut. They damage to rice plants at all stages from sowing to storage. At the seedling stage, they chop down the young seedlings and also feed on the endosperm (Singleton, 2003).

Golden apple snail (Pomacea canaliculata (Lamarck)) is an exotic species in Asia. Its origin is South America. They were introduced to farmers in countries in Asia to increase their income and as a source of protein in their diet, and also as an aquarium pet (citation not found: joshi2007problems). Now they are spreading around Asia and have become a major rice pest in the areas where they have founded. Snails attack younger seedlings at deep water levels. (citation not found: basilio1991problems) estimated that snail density at 8 snails/square meter could damage the rice seedlings up to 93 percent. However, seedlings become tolerant to snail attacks at the age of 40 days old (citation not found: sin2003damage).

Insect pests

are serious threats to rice production in nearly all regions, where rice is grown. Yield losses due to insect pests based on surveys from 11 countries were estimated at 18.5 percent (citation not found: pathak1994insect). The introduction of high yielding technology in the 1960s involving rice varieties with high tillering ability, denser plant spacing, high fertilizer application and irrigation where farmers planted two or three crops per year provided abundant habitat and food sources where the insect pests can reproduce continuously throughout the year. Moreover, the use of nitrogen fertilizers increased the insects’ reproductive potential (citation not found: bottrell2012resurrecting). In South and South East Asia, rice is grown in warm, humid environments conducive to the survival and proliferation of key insect pests: stem borers, rice loaders, brown planthoppers, whitebacked planthoppers and green leafhoppers.

Stem borers are ubiquitous throughout rice fields in Asia and cause some damage in every rice field every year. There are six species, but rice yellow stem borer, Scirpophaga incertulas (Walker), is the most destructive species in Asia, which may cause 20 percent yield loss in early planted rice crops, and 80 percent in late-planted crops (Catling et al., 1987). The larvae bore into the stems and eat their way down to the base of the plant hollowing out the stem. If the damage happened during the vegetative stage the central leaves do not unfold, turn browns and die off, this is called deadhead”. If this damage occurs during the reproductive stage it results in the drying of the panicles, which may not emerge or do not produce grain. This is called “ whitehead”. Yield losses from stem borer damage can reach up to 95 percent in severe infestations.