Rice Flashcards
How much rice is produced worldwide and who are the biggest producers?
600,000 metric tonnes
China - 200,000 (30m/ha) India Indonesia Bangladesh Vietnam Thailand
Facts on Rice
Produced in tropical and sub-tropical countries
Unique crop plant in that it can grow with roots partially submerged
Cultivation dates back 3,500 years
>1,500 cultivars have been developed
2 most common cultivars Oryza sativa & O. glaberrina
Cereal - Graminae
Planting to harvest takes 90-150days
Cultivated as an annual crop (like cotton)
What parts of the plant are damaged by which pests?
All plant parts damaged by pest species e.g.
Roots - termites & rice water weevil
Stems - Various lepidopterous stem borers
Leaves - various hemipterous, coleopterous and lepidopterous pests
Grain - Hemipterous pests
Why is insecticide use considered harmful in rice cropping systems?
Rice crops support extremely high numbers of predators and parasitoids
What are rice crops extremely good at?
Compensating for pest feeding - crops with over 50% of visible damage to leaves have shown zero yield loss
What are the average crop losses of rice?
Range from ~ 30% in Asia to 2% in Europe
Can however suffer complete crop failure
What is the paradox of pesticide use?
Crop losses increase following the use of high-yielding varieties and intensification of production
Increased pesticide use has paradoxically lead to crop losses as a result of higher yielding crop varieties
Describe intensive rice cultivation
Continuous cropping (2-3 per year) Increasing agrochemical inputs Use of higher yielding varieties Expansion of areas for rice cultivation Increasing plant density More fertiliser application Use of short-season varieties
What are the major rice pests worldiwde
Rice water weevil (Lissorthoptrus oryzophilus)
Brown Plant Hopper (Nilaparvatus lugens)
Green Plant Hopper (Nephotettix virescens)
Rice Stem Borer (Chilo suppressalis)
Armyworm (Spodoptera)
Describe the Rice Water Weevil
Lissorthoptrus oryzophilus Coleopterous pest of rice crops Larvae are major root pests, adults feed on foliage Developmental time is ~70-80 days Parthenogenetic populations exist
Describe the Brown Plant Hopper and Green Plant Hopper
Nilaparvata lugens & Nephotettix viresvens
Hemipterous pests that cause direct and indirect damage to crops
Leaves turn brown hence “hopper burn”
Only emerged as pests in the 60s with the intensification of rice farming
Normally controlled by predators (thus secondary pests)
Farm field schools have helped to reduce pesticide use (and thus problems with plant hoppers) whenever they have been implemented
Describe the Rice Stem Borer
Chilo suppressalis
Major lepidopterous pest of rice crops
Larvae bore in stems and kill plants and/or severley reduce grain yields
Describe armyworms
Spodoptera spp.
Generalised pests of Graminae
So called because the larvae march from grasses to crops to feed
Larvae feed externally on leaves
Life cycle in the region of 4-5 weeks
Females can lay up to 1,000 eggs thus highly fecund
What pest management techniques are incorporated in pest management today?
Host plant resistance (including GM crops)
Biological control
Cultural techniques
Selective pesticide use and farmer field schools
Describe Host plant resistance in rice
Initiated in 1960s at IRRI to develop HPR
Major focus of this work is/was resistance to planthoppers
Exact resistance mechanisms include antixenosis (waxiness) and antibiosis (toxic extracts)
Use of Bt rice (2005, China mostly)
Bt plants target Lepidopterous pests (cause 10% of yield loss)
Describe biological control in rice
Unsprayed rice supports large populations of predators/parasitoids
Spiders are especially important predators in rice crops
Avoiding chemical use supports build up of predators
Most pest of rice in Asia are indigenous and have evolved with a complex of predators/parasitoids
Led to devlopment of continuous cropping systems that are staggered so these beneficial species survive and move from crop to crop
Describe cultural techniques in rice PM
Trap crops for stem borer management
Adjacent habitats comprised on grasses support the build up of parasitoids
Sequential cropping also sustains predators
Hand Weeding reduced herbicide applications
China case study
30 million ha devoted to rice (1/3 of crop land)
200bn kg produced per year (50% of China’s food output)
Lissoroptrus oryzophilus
- Native to N.America feeds on grasses
- Now worldwide pest (especially important due to parthenogenesis)
- arrived in China 1988
- initial control efforts at detection, quarantine and isolation/control by fumigation were ineffective at stopping spread
- Now over 400,000 ha affected
- attempts to manage now involve use of thresholds for spray applications and the fungi Metarhizium and Beauvaria
India Case Study
Neem extracts used instead on synthetic insecticides
Fungal pathogens (especially after rainfall for control on Hemipterous pest species)
Trchogramma for Lepidoptera control when crops 45 days old
Light traps for monitoring Lepidoptera
Hand collection of pest spp.
