Fish as a component of integrated pest management (ipm) in rice production

INTEGRATED PEST MANAGEMENT (IPM)

IPM is a pest control concept that uses the best available mix of technologies for a particular pest problem. It promotes practices available to the farmer and permits pest control with the least use of chemicals to get high yields and maximum profits. Reducing pesticide application is an important factor because this control method is often uneconomical and unsafe to humans. Moreover, many pesticides kill both pests and their natural enemies at the same time, leaving the crop open to an uncontested invasion of pests.

IPM includes a variety of technologies such as choosing pest and disease-resistant varieties, using crop rotation, fallows and simultaneous planting over wide areas. It also encourages the establishment of natural enemies of rice pests.

Economic threshold levels are used to help farmers decide when the application of pesticides is economically justified. The presence of parasites and predators, including fish, minimizes the need for the farmer to take action.

FISH AS PREDATORS IN RICE FIELDS

The most widely spread fish species in paddies are common carp (Cyprlnus carplo), Nile tilapia (Oreochromis niloticus) and silver barb (Puntius gonlonotus). However, there is a large additional number of both stocked and wild fish species in ricefields.

Among those, there are larva-feeding and mollusc-feeding fish which are of considerable importance in the control of human vector-borne diseases, like malaria and schistosomiasis. Plant-eating fish species directly feed on weeds and are reported to be efficient in keeping irrigation canals free from vegetation. Turbidity and high water level add to the effects of fish-controlling weeds.

Different fish species will affect difenent pests in different ways. Common carp, for instance, appear very effective at controlling the golden apple snail. In Malaysia, tilapia was not able to control this pest but the giant walking catfish performed well.

The effectiveness of fish in fields where rice is broadcast is doubtful, since the rice will be too crowded to give fish good access to the field. There is no evidence for an optimal fish stocking density for pest control, but higher densities are presumed to be more effective. Fish eat older, outer rice leaves which are more likely to be infested with pathogens. This will make the rice plants healthier.

There are several reports documenting either reduced number of pests or less damage caused by pests and diseases with the presence of fish (Table 1). Most of this work has been done in concurrent rice-fish systems. In some cases, the underlying mechanisms have been described (Fig. 1-7). However, this list is far from complete. It is likely that more direct and indirect effects will be revealed with continuing research.

Problematic organisms in rice production, predation of fish and susceptible life stage of prey.

? - no information available
+- based on documented observation

OUTLOOK

To date feeding habits of fish in the ricefield habitat are not well-established.

· Feeds can be given daily at 5% of the shrimps' body weight (If no manure loading) or 2-3% (with manure loading). Mix ingredients thoroughly, form them into balls and put them in feeding trays. The use of feeding trays controls consumption of feeds and prevents wastage.

Feeds can be given daily

· Feed twice a day: one third of the quantity in the morning and the rest in the aftermoon.

· Check feed consumption daily to adjust the feeding regime as necessary. Below is a recommended formula for shrimps in rice paddies.

50% - rice bran, broken rice or rice grain
20-30% - cassava root or broken maize
20-30% - trash fish, shrimp head wastes or oil cake

PREDATOR PREVENTION

Predators include sea bass, tilapia, snake head and other wild fish that compete with the shrimps for feeds. Predation can result in very low shrimp yields.

Before stocking shrimp, use any of the following measures:

· Drain rice fields and apply lime at the rate of 10 kg/100 sq m (15-20 kgs for sulphate acid soils)
· Apply Derris root (Derrls elilptica), 1-1.5 kg soaked in 10l water/1000 sq.m
· Release ducks into the rice fields for several days.

Within the culture time: Put gill nets in the trenches to catch the predators going to the rice fields.

CARE AND MAINTENANCE

· Water exchange is essential to supply oxygen to the shrimps and to remove detrimental substances in the water. This should be done at least twice a month. The more frequent the water is changed, the more suitable it is for the shrimps' growth and development.

· Water exchange also improves the pH value in the fields especially in sulphate acid soils.
· Dikes should be repaired yearly.
· Cover crab holes along the dikes to prevent leakage.
· Daily-check the screen mesh on the outlet and inlet pipes.

HARVESTING

· Harvest shrimps 5-6 months after rice harvest.
· Open the outlet pipe at low tide and drain the field and trench.
· Hand-collect shrimps in the rice field and use a net to harvest in the trench.

Harvesting

· Harvest only the trig shrimps (bigger than 15 9). The small ones are reserved for the next culture.

Note: Transfer small shrimps immediately to a hapa (cage net) to keep them alive for the next culture.

Bring harvested shrimps as soon as possible to the dealer or keep them in ice so that they stay fresh.

LAND PREPARATION AND TRANSPLANTING FOR RICE

· Local varieties are recommended. Transplanting should be done when the salinity is lower than 5 ppt.

· Plough and harrow thoroughly before transplanting.

· Transplant 30-40 days after seeding.

FERTILIZING

· Apply 50 kg diammonium phosphate and 5 t manure/ha before ploughing.
· Use 50 kg urea/ha for top-dressing

PEST CONTROL

· No pesticide or herbicide is applied in integrated shrimp-rice culture.
· Use brown planthoppe -resistant varieties of rice.
· Release one-month old ducks into ricefield to feed on insects, especially hoppers.

Note: In case the above measures cannot control pests, pesticide application can be an alternative. Before applying the pesticide, drain water in the field to let shrimps take refuge in the trench for 35 days.

MONOCULTURE OF SHRIMP IN THE FIELDS IN DRY SEASON

· Nipa and coconut trees are indicators of salinity lower than 10 ppt. Rhizophora is an indicator of salinity higher than 10 ppt.

· During the dry season when salinity level is not suitable for rice growing, the fields can be used for shrimp monoculture.

· Freshwater prawn (M Rosenbergll) can be grown if the salinity is not higher than 10 opt. The procedure is similar to those applied in the rainy season. When the salinity is higher than 10 ppt, freshwater prawns become stunted.

Monoculture of shrimp

· Tiger prawn (Penaeus monoden) and banana shrimp (Penaeus mergulensis) can be cultured in rice fields when the salinity is higher than 10 ppt in the dry season.

Other procedures are similar to freshwater prawn culture.

Estimated cost and return of rice-shrimp culture In coastal areas in south vietnam (for one hectare).

1 US $ = 7000 VND

Prepared by: LE THANH HUNG

FARMER-PROVEN INTEGRATED D AGRICULTURE-AQUACULTURE:
TECHNOLOGY INFORMATION KIT (IIRR-ICLARM)