Entomology

A Virtual Presentation on Paddy Bug and Paddy Bug Management by GRDB’s Entomologist, Dr. Viviane Baharally – October 21st, 2020. Click to View.

Entomology is the study of insects. At GRDB, entomology includes the study of the major pests of rice.

Areas of focus include:

• Species identification and distribution
• Rice ecosystem biodiversity
• Arthropod population dynamics and forecasting
• Economic impact of invertebrate pests (insects, snails, slugs)
• Varietal evaluation
• Chemical evaluation
• Biological control
• Post-harvest and storage pest studies
• Training and demonstrations for staff and farmers

 Major pests of rice include:

1. Water weevil (Helodytes foveolatus)

larvae

Adult

Damage caused

Larvae feed on the roots, resulting in stunted growth, yellowing of leaves (chlorosis) and thus, easy uprooting of plants. The adults feed on leaves and produce narrow, longitudinal scars that are parallel to the veins, or slit-like leaf scars often referred to as “windowing”. Leaf scarring by adults rarely causes economic losses, but large numbers of adults feeding on very young rice can remove enough leaf tissue to kill the plants.

Damage caused by adult (left) and damage caused by larvae (right)

Control measures:

1. Sampling activity should be done one week after permanent flooding. Inspect 100 randomly selected leaves and if 50 and above have feeding scars apply insecticide

(Fastac, Pestac, Karate or Pronto).

2. Control is most effective 7-14 days after a permanent flood when weevil numbers are at or above economic threshold level.
3. Control of larvae can be done by draining field and allowing it to dry until it cracks.
4. Good field sanitation will get rid of alternative weed hosts (also refer to the Integrated Pest Management (IPM) strategies).

2.     Leaf miner (Hydrellia sp.)

Adult (left) larva (right)

Damage caused:

Larvae tunnel into the leaves and feed between the two leaf surfaces, feeding on cell sap. Often the entire leaf tip will wilt and die. Reduced tillering and stunted growth may result, and in badly affected crops, delayed panicle initiation may occur.

Damage caused my leafminer

Control measures:

1. Plant early and use high tillering varieties
2. Drain fields after sowing (not in excess of 3 days) to provide a poor habitat for leaf miner reproduction,
3. If infestation is high, employ chemical control with a systemic insecticide such as Pronto,

Actara, Regent (also refer to the Integrated Pest Management (IPM) strategies).

1. Caterpillar (Spodoptera frugiperda)

Damage Caused:

Complete cutting of leaf tips and margins by larvae; however, the greatest damage occurs on seedling rice, where plants are too young to flood.

Control measures:

1. Plough deeply to expose pupae to predators.
2. Flood infested fields for 24-48 hrs in order to drown caterpillars.
3. Spray contact insecticides such as Fastac or Pestac during high infestation, that is, a threshold of 30 damaged leaves/square metre (also refer to the Integrated Pest

Management (IPM) strategies).

4. Snails (Pomacea sp.)

Damage Caused:

Snails feed on young and emerging rice plants and can completely destroy a crop during crop establishment. Feeding results in missing seedlings, with cut leaves sometimes seen floating.

 Control measures:

1. Place a wire or woven bamboo screen on the main irrigation water inlet and outlet to prevent initial entry.
2. Snails are active in standing water and thus there is need to ensure good land levelling and field drainage to help reduce infestation and damage to the crop.
3. After the final land preparation, construct small canals, which will serve as focal nesting points for snails, making manual collection or killing easier.
4. Place bamboo stakes to attract adults for egg laying. Handpick snails and crush egg masses. This is best done in the morning and afternoon when snails are most active.

5. Paddy Bug (Oebalus )

Damage caused

Nymphs and adults feed on the endosperm at milk and dough stages. Adults inject an enzyme to predigest sugars (C₆H₁₂0₆) and in the process contaminate the grain with fungus that causes grain discolouration. Panicles attacked by the paddy bugs result in wind grains, malformation and discoloration of grains. Consequently there are lower yields, reduced quality and brittleness, which result in increased breakage on milling.

Control measures

Use the Integrated Pest Management (IPM) approach, which is discussed in detail below.

 INTEGRATED PEST MANAGEMENT (IPM)

There is no one way to manage these pests effectively, since pests can never be completely eliminated. That is why Integrated Pest Management (IPM) is the recommended approach, which should begin with the decision to cultivate rice. IPM is the use of multiple control measures, which are compatible, economical, environmentally sound, and culturally feasible strategies for managing pest populations at an acceptable level. Chemicals will continue to play a vital role but only after systematic monitoring of pest populations, which will guide in the effective application of the appropriate chemical, or combination of chemicals.

The package of suitable control measures includes:

1. Cultural Practices

• Block planting is recommended for areas where there is a large section of rice land. It prevents staggered growth stages of the crop and makes pests, water and application of other resources easy to manage.
• • Good land preparation or soil tillage is necessary, because it is known that plugging not only improves soil condition but helps to disrupt the life cycle of insects that are found in the soil, through exposure to sun (extreme temperature), predators and/or mechanical injury.
  • Field sanitation is an important and highly effective farm practice to reduce the incidence of pest infestation. It involves keeping weeds under control at all times from in and around the field, because these often serve as alternate hosts for pests. Always clean irrigation canals and remove crop residues after harvest.
  • Water management, since proper monitoring of the amount of water in the field or timely intervals of drainage and irrigation, not only suppresses weed infestation, but also reduces the early season pest complex (water weevil, leaf miner and caterpillar).
  2. Physical Practices
  • Hand picking or rouging, where plants that are heavily infested, especially with egg masses of paddy bug or snails, are pulled out and properly disposed of.
  • Rouging of volunteer plants and red rice, which also serve as alternative hosts to the paddy bug within the rice fields.
  3. Monitoring

  This is vital for decision making at any stage of crop development and to determine whether or not, or when to apply insecticides. It should be done systematically for a guide in determining the insect pest population, as spraying should be based on economic threshold levels. Monitoring by the sweep net method should be done in the fields for paddy bug incidence during the cool periods (early morning and late afternoon), from late tillering to harvesting. Should the number of bugs exceed 1 bug/2 sweeps, then chemical control is needed.

  4. Biological Control

  This refers to the conservation of the natural enemies that are already prevalent in rice fields.  Known natural enemies of the paddy bugs are:

  

Note: These insecticides should be applied during early morning or late afternoon when the rice is flowering. Failure to do so will cause interference with pollination and hence “wind

paddy will result”.  For practical knowledge of IPM, as well as understanding the systems of rice cultivation, farmers can attend the Farmer’s Field Schools held periodically in their district or region.

Effective use and application of insecticides for managing paddy bugs

STEPS ARE AS FOLLOWS:

1. Determine the need to spray by monitoring with a sweep-net.
2. Spray if the number of bugs caught is 25 or more in a total of 50 sweeps.
3. Mix the insecticide properly:
   1. Fill the motor blower halfway with water
   2. If insecticide is a power or granule, then dissolve the recommended rate in a bucket before adding it to the half-filled blower.
   3. If the insecticide is a liquid, then add the recommended rate directly into the half-filled blower.
   4. Shake the half-filled blower containing water and insecticide.
   5. Add water to the blower up to the 13-liter mark, then shake again.
4. The spray-man is now ready to spray.
5. Determine the swath (spray) width based on the wind direction and speed.
6. Ensure overlap of the spray mixture for best results.