GALL MIDGE( Orseolia orizae  HARM AND PREVENTION 25/05/2022

Gall midges cause damage in many rice-growing countries in Asia. Yield loss due to gall midges can reach 30-40%.

Agent: The gall midge has the scientific name Orselia (Pachydiphosis) oryzae, belongs to the order Diptera, family Cecidomyiidae.

Ways of harm and symptoms:

The gall midge larvae move to the middle of the sheath and the stem, then penetrate the growth apex, where the caterpillars bite and cause damage and release toxins contained in the saliva, making the base of the rice sheath swell, the inside is hollow. That is where the bud develops abnormally into a tube like an onion leaf, which is pale white, about 1 cm wide, 10 - 30 cm long, the tip of the onion tube is sealed by the leaf tissue. Onion tubes appear about a week after gall midge entry. Damaged rice stalk does not produce spikes  but the rice can grow new shoots to compensate. Symptoms of gall midge  are like drought, K deficiency, viral diseases (yellow dwarf disease, Tungro disease), stem borers, 2,4 D herbicide poisoning or thrips. Gall midges only cause damage from seedling stage to the end of tillering, before appearing ears. In the later stage, the  gall midge  is no longer harmful.

Biological properties:

Eggs: long and slender, white when newly laid, yellow before hatching. Eggs are laid scatteredly on the ligules, blades or sheaths, and are laid one by one or in groups of 3-4. Egg incubation time: 3-8 days.

Young caterpillars: maggot-like, flat body, milky white, 4-5 mm long. The larval stage has 3 - 4 age levels, 15 - 28 days long. Each bud has only one caterpillar and when the onion tube is stretched out, the caterpillar pupates at the same time.

Pupae: pale pink, before mating, red, 2 - 4 mm long, pupal stage 3 - 5 days long, both larvae and pupae live and cause damage in the onion tube. The pupa can move up and down in the onion tube. When about to pupate, the pupa moves to the top of the onion tube, use the abdominal spines to punch holes, get out half of  body, peels off the pupal shell to leave the top of the onion tube to become an adult gall midge that flies out.

Adults: like house mosquitoes, wingspan is 3-5 mm, female mosquitoes are light red, male mosquitoes, smaller than female mosquitoes, yellow-brown. Antenas have 10 segments. Mosquitoes are active (mating, laying eggs) strongly at night, with low flight power, so their range of harm is limited in a limited area, being lured by light. Females lay 100-200 eggs. Adult stage: 1-3 days.

Natural enemies: Gall midges have many natural enemies that parasitize eggs, larvae (Obtusiclava oryzae, Eurytoma setitibia…) and pupae. Usually when the larvae appear, the natural enemies of the parasites increase, so it is necessary to pay attention when spraying pesticides, which can reduce the number of parasitic natural enemies later.

Secondary hosts: Ratoon rice , Leersia , Echinochloa sp , Panicum Repens , Brachiar Mutica

Factors favorable for the growth of gall midges:

Flooded fields.

Rice: thick sowing.

Strong branching variety.

Rice from seedling to tillering stage.

Intensive farming, excess nitrogen fertilization.

There are secondary hosts: ratoon  rice , weeds.

The weather is murky , cloudy,  rainy and sunny alternately. Years of experience with a lot of rain, a lot of gall midges

The previous crop was infected, the next crop was severely affected.

Few natural enemies due to early spraying, pesticide abuse. It was noted that when the gall midges appeared, the parasitic wasp increased sharply.

Prevention:

Sanitize the field, kill weeds, bank weeds.

Light traps: monitor the gall midges to prevent it at the right time (spray as soon as the mosquitoes are in full bloom).

Do not sow thickly.

Fully fertilize, balance NPK, do not over-fertilize the tillering stage.

Protect natural enemies (parasite bees), do not spray pesticides early.

Regular field visits, if there are gall midges, you can drain the water to dry the fields to limit the spread.

If the gall midges density is high, the weather conditions are favorable, the rice is tilling, the field is often attacked by gall midges, etc., spray and spread the product immediately.

Pay attention to spraying and spreading products early. Do not spray, broadcast after effective tillering period (30-35 days after sowing).

Pesticides:

In case the field is often harmed by gall midges, the weather and farming conditions are favorable for gall midges to arise and cause harm. You can use a light trap to monitor, if there are many gall midges, you can immediately spray insecticide: Sapen alpha 5EC, Sec Saigon 5.10 EC, Diaphos 50EC.

In case the field has many gall midges, the onion tube appears scattered, it is necessary to spray insecticide immediately, combined with broadcasting granular products with systemic characteristics and deep penetration such as Ga Noi 4G, Diaphos 10H or Sargent 6G.

In case of severe damage to the field, the prevention and treatment will be less effective, but to avoid damage to the yield and limit the spread of the next crop, it is possible to combine spraying with deep penetrating, fumigant insecticides such as Diaphos 50EC, sairifos 585 EC, combined with granular product broadcasting (as above).

Note:

Early detection is essential for timely treatment. If the rice is past the maximum tillering stage (30-35 days after sowing ), product spraying or broadcasting will be costly in vain.

The field is broadcast with granular product, it is necessary to maintain the water level of 3-5 cm, for 3-5 days