MSc Huynh Kim Ngoc

In the past, panicle rice spiders appeared and caused damage in crops in some provinces in the Mekong Delta River… However, recently, panicle rice spiders have also been reported to appear and cause damage in some northern provinces, yield loss can be up to 50%.

Symptom:

Panicle rice spiders can appear at almost every stage of rice growth from seedling stage to blooming, ripening and damage parts of rice such as leaf sheath, leaf veins, stem, spike peduncles and even the rice grain . In the seedling stage, spiders mainly harm the outside of the sheath, the junction between the sheath and stem. The tillering- earing stage,spiders bore inward, live and damage in the sheath and veins of the leaves. In the stage of blooming-ripening, spiders cause damage mainly in sheaths, leaf veins, stems, peduncles and if the density is high, the spiders crawl up and burrow into the husk and cause damage on seeds. Common symptoms caused by spiders damage on the sheath, the stem is long dark brown stripes that farmers call wind scrubbing disease or a chewed betel quid. If spiders cause damage on spike, it will cause the spike to have an upright shape because most of the grains are unfilled. Infected grains are brown speckled, distorted. In addition to sucking sap, mechanical wounds caused by spiders also create conditions for some fungi to penetrate and cause harm, notably the fungus causing sheath rot: Sarocladium oryzae.

Agents and biological properties:

The spider has the scientific name: Steneotarsonemus spinki (Oligonicus oryzae), belongs to the spider order: Acarina. Spiders are very small, transparent, difficult to see with the naked eye, but can be seen with a magnifying glass. The life cycle of spider is short from 10 to 12 days. Female spiders lay about 50 eggs, white eggs, scattered in the sheath, unfertilized eggs will hatch into male spiders. Eggs after 1-2 days will hatch into young spiders, pointed body, long, with 3 pairs of legs.Young spiders last about 4-5 days, then adults last about 5-6 days, with 4 pairs of legs. Spiders live mainly in rice sheaths, leaf veins above water level and cause damage by sucking sap causing long dark brown stripes on sheaths, stems or speckled spots on grains.

Environmental conditions:

Panicle spiders develop favorably in hot, dry weather and lack of water in the fields, so spiders cause damage mainly in May-June Summer-Autumn crop in the Mekong Delta River and August-September monsoon in the North. It has been shown that mid- and late-season outbreaks of panicle spider are associated with heavy use of insecticides early in the season, thereby reducing the population of spiders natural enemies such as carnivorous spiders and parasitic wasps. The fields are sown thickly, over-fertilized with nitrogen, the fields are dry, in zero tillage, sown continuously, the field hygiene is poor, The field is left with rice that grows from the stubble, weedy rice of the previous crop was infected with spider siders, susceptible varieties (IR.50404, Khang Dan 18, Cai sticky rice with yellow flowers…) are favorable for panicle spiders to develop and cause harm.

Management measures

- Rotate: (if possible) to cut off the host source.

- After harvest, burn the field if the field is often damaged by panicle spider .

- Plowing and drying the soil, making the soil carefully, especially the fields of previous crops are often damaged by spiders.

- Sanitize the fields, kill the stubble-grown rice and weedy rice of the previous crop that were damaged by the spider siders.

- Not sowing thickly

- Fertilize balance, reasonable, do not over-fertilize nitrogen.

- Keep the appropriate water level for each growth stage of rice, do not let the field dry out.

- Protect natural enemies (bees, parasitic spiders), use pesticides when necessary.

- Visit the field regularly, pay attention to the tillering-blooming stage (35 - 60 DAS), especially the period from : 35 -50 DAS, use a magnifying glass to observe in the sheath if there are spiders or on the sheath, vein, stem, If peduncles have symptoms as described above (long dark brown stripes), it is necessary to spray insecticides to prevent spider immediately, do not let spiders cause harm on spike peduncles or grains because it is too late.

- Regarding spider killer, the following special products can be used to treat spiders:

+ Sulox 80WP: Mix 60 - 80 g / 20 liters.

+ Sarosider 57EC: Mix 15 – 20 ml / 20 liters

+ SK Enspray 99EC Mineral oil : Mix 60 ml / 20 liters.

- When spraying product, pay attention to:

(1) Before spraying, if possible, put water into the field, so that the spiders move upwards, when spraying, it is easy to hit the product.

(2) It is recommended to adjust finely sprayed nozzle and spray on places where spiders live and cause damage (sheath, leaf, stem).

(3) Because spiders are very small, hiding in rice sheaths, and covered in thin silk cocoons, they need to spray a lot of water (400 - 500 liters of water/ha). Can spray early morning or cool afternoon. If the rice is blooming, spray in the afternoon (if it does not rain). Follow the instructions on the label carefully.