Pest Management: How to control rice field rats

Rat

Rattus argentiventer Robinson and Kloss, R. exulans Peale, R. rattus spp., R. tanezumi

What it does

Rice field rats cut or pull up transplanted plants. They also chop young seedlings. At ripening stage, they feed on developing rice buds.

Why and where it occurs

Rats occur in lowland irrigated rice crops. Both the wet and dry seasons are favorable for rat reproduction and crop damage. In rainfed rice crops rodents have their greatest impact in the wet season. The availability of food, water, and shelter are factors, which provide optimum breeding conditions. The presence of grassy weeds also triggers their development.

Rice field rats feed at night with high activity at dusk and dawn. At daytime, they are found among vegetation, weeds, or maturing fields. During fallow period, they utilize major channels and village gardens as prime habitats. At tillering, 75% of time they are in burrows along the banks and after maximum tillering, 65% of time they are in rice paddies.

How to identify

Rat feeding can cause the following damages:

• missing germinating seeds
• missing hills
• chopped young seedlings
• missing plants
• irregular cuttings of stem
• chewed developing buds or ripening grains
• tillers cut near base at 45° angle
• retillering of stems
• delayed grain maturity
• missing grains
• missing panicles

The feeding damage on the stem caused by the rice field rats may resemble insect damage although rat damage is usually distinguished by the clean cut at 45° of the tiller. The damage on the grains is similar to bird damage.

• Check muddy areas for runways, active burrows, and footprints of rice field rats. These are usually near the damage they have created.
• Check for presence of rice field rats: cut tillers and active holes on the bunds that surround the fields.
• When possible, catch rats to identify the species. Place traps along runways, or dug the rats from their burrows.

Why is it important

Rattus argentiventer is the major agricultural rodent pest across much of island and mainland Southeast Asia. Crop losses in rice-growing areas due to this species are typically in the order of 10−20%. Losses are generally higher in the second crop in areas with double cropping.

For fields positioned close to refuge habitats such as canals or extensive upland areas, chronic losses of 30−50% are reported. Very high chronic losses are also reported in areas where triple cropping is practiced and rat densities are especially high.

In Malaysia, this species has caused yield losses of 6−11%. In Indonesia, an estimated 17% of the total planted area is estimated to be damaged annually.

How to manage

Effective community control

• Flooding, digging, or fumigating rat burrows
• Scare rats out of areas with high vegetation cover or around villages (using netting, dogs, clubs, and others to catch rats)
• Use dogs to locate active rat burrows, then do Step 1
• Hunt rats at night using flashlights, clubs, bow and arrows, and netting
• Set local kill-traps along runways of rats
• Use registered rat poisons that are placed in covered bait stations (but not where children, pets, or livestock have easy access).

Management actions

• Keep rice bunds (banks) in the crops less than 30 cm wide to prevent rats from burrowing.
• Keep the edges of the field, the bunds, and surrounding areas clean and free of tall weeds and hiding areas for rats.
• Plant at the same time as your neighbors—within 2 weeks of each other.
• Strategic use of Trap Barrier System (TBS)—during the rice season with the most rodent damage.
• Keep area around fields, homes, and villages clean — no piles of wood or brush, no garbage heaps, no weedy areas.
• Keep grain stores and surrounding area clean.

Reference Source: http://www.knowledgebank.irri.org/

Rice Disease: Bacterial blight

What it does

Bacterial blight is caused by Xanthomonas oryzae pv. oryzae. 

It causes wilting of seedlings and yellowing and drying of leaves.

Why and where it occurs

The disease is most likely to develop in areas that have weeds and stubbles of infected plants. It can occur in both tropical and temperate environments, particularly in irrigated and rainfed lowland areas. In general, the disease favors temperatures at 25−34°C, with relative humidity above 70%.

It is commonly observed when strong winds and continuous heavy rains occur, allowing the disease-causing bacteria to easily spread through ooze droplets on lesions of infected plants.

Bacterial blight can be severe in susceptible rice varieties under high nitrogen fertilization.

Hot to identify

Check for wilting and yellowing of leaves, or wilting of seedlings (also called kresek).

On seedlings, infected leaves turn grayish green and roll up. As the disease progresses, the leaves turn yellow to straw-colored and wilt, leading whole seedlings to dry up and die.

Kresek on seedlings may sometimes be confused with early rice stem borer damage. 

To distinguish kresek symptoms from stem borer damage, squeeze the lower end of infected seedlings between the fingers. Kresek symptoms should show yellowish bacterial ooze coming out of the cut ends. Unlike plants infested with stem borer, rice plants with kresek are not easily pulled out from soil.

 

Check for lesions.

On older plants, lesions usually develop as water-soaked to yellow-orange stripes on leaf blades or leaf tips or on mechanically injured parts of leaves. Lesions have a wavy margin and progress toward the leaf base.

On young lesions, bacterial ooze resembling a milky dew drop can be observed early in the morning. The bacterial ooze later on dries up and becomes small yellowish beads underneath the leaf.

Old lesions turn yellow to grayish white with black dots due to the growth of various saprophytic fungi. On severely infected leaves, lesions may extend to the leaf sheath.

To quickly diagnose bacterial blight on leaf:

• cut a young lesion across and place in a transparent glass container with clear water
• after a few minutes, hold the container against light and observe for thick or turbid liquid coming from the cut end of the leaf

Why it is important

Bacterial blight is one of the most serious diseases of rice. The earlier the disease occurs, the higher the yield loss.

Yield loss due to bacterial blight can be as much as 70% when susceptible varieties are grown, in environments favorable to the disease.

When plants are infected at booting stage, bacterial blight does not affect yield but results in poor quality grains and a high proportion of broken kernels.

How to manage

Planting resistant varieties has been proven to be the most efficient, most reliable, and cheapest way to control bacterial blight.

Other disease control options include:

• Use balanced amounts of plant nutrients, especially nitrogen.
• Ensure good drainage of fields (in conventionally flooded crops) and nurseries.
• Keep fields clean. Remove weed hosts and plow under rice stubble, straw, rice ratoons and volunteer seedlings, which can serve as hosts of bacteria.
• Allow fallow fields to dry to suppress disease agents in the soil and plant residues.

Reference Source: http://www.knowledgebank.irri.org/

Insect: Hoverfly

Hoverfly (Eupeodes corolae)

Hoverflies, sometimes called flower flies or syrphid flies, make up the insect family Syrphidae. As their common name suggests, they are often seen hovering or nectaring at flowers; the adults of many species feed mainly on nectar and pollen, while the larvae (maggots) eat a wide range of foods. In some species, the larvae are saprotrophs, eating decaying plant and animal matter in the soil or in ponds and streams. In other species, the larvae are insectivores and prey on aphids, thrips, and other plant-sucking insects.

Aphids alone cause tens of millions of dollars of damage to crops worldwide every year; because of this, aphidophagous hoverflies are being recognized as important natural enemies of pests, and potential agents for use in biological control. Some adult syrphid flies are important pollinators.

About 6,000 species in 200 genera have been described. Hoverflies are common throughout the world and can be found on all continents except Antarctica. Hoverflies are harmless to most other animals, despite their mimicry of more dangerous wasps and bees, which wards off predators.

Mimicking Hoverfly

Description

The size of hoverflies varies depending on the species. Some, like members of the genus Baccha, are small, elongate and slender, while others, like members of Criorhina are large, hairy, and yellow and black. As members of Diptera, all hoverflies have a single functional pair of wings (the hindwings are reduced to balancing organs). They are brightly colored, with spots, stripes, and bands of yellow or brown covering their bodies. Due to this coloring, they are often mistaken for wasps or bees; they exhibit Batesian mimicry. Despite this, hoverflies are harmless.

With a few exceptions, hoverflies are distinguished from other flies by a spurious vein, located parallel to the fourth longitudinal wing vein. Adults feed mainly on nectar and pollen. They also hover around flowers, lending to their common name.

Reproduction and life cycle

The Life Cycle of The Hover Fly

Unlike adults, the maggots of hoverflies feed on a variety of foods; some are saprotrophs, eating decaying plant or animal matter, while others are insectivores, eating aphids, thrips, and other plant-sucking insects. This is beneficial to gardens, as aphids destroy crops, and hoverfly maggots are often used in biological control. Certain species, such as Lampetia equestris or Eumerus tuberculatus, are responsible for pollination.

An example of a well-known hoverfly maggot is the rat-tailed maggot, of the drone fly, Eristalis tenax. It has a breathing siphon at its rear end, giving it its name. The species lives in stagnant water, such as sewage and lagoons. The maggots also have a commercial use, and are sometimes sold for ice fishing.

On occasion, Hoverfly larvae have been known to cause accidental myiasis in humans. This occurs when the larva are accidentally ingested on food or from other sources. Myiasis causes discomfort, pain, or itching, however, Hoverflies do not normally prey upon humans and cases of myiasis from Hoverflies is very rare.

Distribution and habitat

Hoverflies are a cosmopolitan family found in most biomes, except deserts, tundra at extremely high latitudes, and Antarctica. Certain species are more common in certain areas than others; for example, the American hoverfly, Eupeodes americanus, is common in the Nearctic ecozone, and the common hoverfly, Melangyna viridiceps, is common in the Australasia ecozone. About 6,000 species and 200 genera are in the family.

Larvae of hoverflies are often found in stagnant water. Adults are often found near plants, their principal food source being nectar and pollen. Some species are found in more unusual locations; for example, members of the genus Volucella can be found in bumblebee nests, while members of Microdon are myrmecophiles, found in ant or termite nests. Others can be found in decomposing vegetation.

Episyrphus balteatus on flower

Pollination

Hoverflies are important pollinators of flowering plants in a variety of ecosystems worldwide. Syrphid flies are frequent flower visitors to a wide range of wild plants as well as agricultural crops and are often considered the second most important group of pollinators after wild bees. However, there has been relatively little research into fly pollinators compared with bee species. It is thought that bees are able to carry a greater volume of pollen on their bodies, but flies may be able to compensate for this by making a greater number of flower visits.

Like many pollinator groups, syrphid flies range from species that take a generalist approach to foraging by visiting a wide range of plant species to those that specialize in a narrow range of plants. Although hoverflies are often considered mainly non-selective pollinators, some hoverflies species are highly selective and carry pollen from one plant species. It is thought that Cheilosia albitarsis will only visit Ranunculus repens.

Specific flower preferences differ between species but syrphid fly species have repeatedly been shown to prefer white and yellow coloured flowers. Non-visual flower cues such as olfactory cues also help the flies to find flowers, especially those that are not yellow. Many syrphid fly species have short, unspecialized mouth parts and tend to feed on flowers that are more open as the nectar and pollen can be easily accessed.

There are also a number of fascinating interactions between orchids and hoverflies. The orchid species Epipactis veratrifolia mimics alarm pheromones of aphids to attract hoverflies for pollination. Another plant, the slipper orchid in southwest China, also achieves pollination by deceit by exploiting the innate yellow color preference of syrphide.

Case study - New Zealand

There are more than 40 species of syrphid flies in New Zealand. These flies are found in a variety of habitats including agricultural fields and alpine zones. Two hoverfly species in Switzerland are being investigated as potential biological control agents of hawkweeds in New Zealand.

Native hoverfly species Melanostoma fasciatum and Melangyna novaezelandiae, are common on agricultural fields in New Zealand. Coriander and tansy leaf are particularly attractive to many species of adult hoverflies, which feed on their pollen. In organic paddocks hoverflies were found to feed on an average of three and a maximum of six different pollens. M. fasciatum has a short proboscis, which restricts it to obtaining nectar from disk flowers.

Syrphid flies are also common visitors to flowers in alpine zones in New Zealand. Native flies (Allograpta and Platycheirus) in alpine zones show preferences for flower species based on their colour in alpine zones; syrphid flies consistently choose yellow flowers over white regardless of species. However, syrphid flies are not as effective pollinators of alpine herb species as native solitary bees.

Two Simossyrphus grandicorins mating in midair

Relationship with people

Many species of hoverfly larvae prey upon pest insects, including aphids and the leafhoppers, which spread some diseases such as curly top. Therefore, they are seen in biocontrol as a natural means of reducing the levels of pests.

Gardeners, therefore, will sometimes use companion plants to attract hoverflies. Those reputed to do so include alyssum, Iberis umbellata, statice, buckwheat, chamomile, parsley, and yarrow.

Source: wikipedia.org/wiki/Hoverfly