Rice

Question 1

How much rice is produced worldwide and who are the biggest producers?

Answer 1

600,000 metric tonnes

China - 200,000 (30m/ha)
India
Indonesia
Bangladesh
Vietnam
Thailand

Question 2

Facts on Rice

Answer 2

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)

Question 3

What parts of the plant are damaged by which pests?

Answer 3

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

Question 4

Why is insecticide use considered harmful in rice cropping systems?

Answer 4

Rice crops support extremely high numbers of predators and parasitoids

Question 5

What are rice crops extremely good at?

Answer 5

Compensating for pest feeding - crops with over 50% of visible damage to leaves have shown zero yield loss

Question 6

What are the average crop losses of rice?

Answer 6

Range from ~ 30% in Asia to 2% in Europe

Can however suffer complete crop failure

Question 7

What is the paradox of pesticide use?

Answer 7

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

Question 8

Describe intensive rice cultivation

Answer 8

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

Question 9

What are the major rice pests worldiwde

Answer 9

Rice water weevil (Lissorthoptrus oryzophilus)
Brown Plant Hopper (Nilaparvatus lugens)
Green Plant Hopper (Nephotettix virescens)
Rice Stem Borer (Chilo suppressalis)
Armyworm (Spodoptera)

Question 10

Describe the Rice Water Weevil

Answer 10

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

Question 11

Describe the Brown Plant Hopper and Green Plant Hopper

Answer 11

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

Question 12

Describe the Rice Stem Borer

Answer 12

Chilo suppressalis
Major lepidopterous pest of rice crops
Larvae bore in stems and kill plants and/or severley reduce grain yields

Question 13

Describe armyworms

Answer 13

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

Question 14

What pest management techniques are incorporated in pest management today?

Answer 14

Host plant resistance (including GM crops)
Biological control
Cultural techniques
Selective pesticide use and farmer field schools

Question 15

Describe Host plant resistance in rice

Answer 15

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)

Question 16

Describe biological control in rice

Answer 16

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

Question 17

Describe cultural techniques in rice PM

Answer 17

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

Question 18

China case study

Answer 18

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

Question 19

India Case Study

Answer 19

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.