Mosaic,Yellow Leaves Of Legumes 23/08/2021

Ph.D. Nguyen Minh Tuyen

Mosaic, yellow leaf disease (mosaic) is very common on legume species, especially the disease is often severe in areas with hot, arid climates and specialized cultivation in legume. The disease has significantly reduced the yield and quality of beans. Fields infected early when the plants are young will not yield. However, until now, many people still do not know the cause and how to cure this disease. The dry season of 2020 is forecasted to be very hot and dry, so there is a very high risk of disease.

Symptoms and harms:

Depending on the virus species, the weather and the stage of infection, the time of disease onset and symptoms will vary. Normally, when infected with a virus, the plant will be dwarfed, the tops will droop, the leaves are not uniform in color (mosaic), or get yellowed, sometimes small and wrinkled etc.. Small plant stage, if the plant is If infected with the virus soon after growing, the plant will develop disease very soon. When grown plants are infected, the disease occurs later (due to resistance), or no disease when the plant is old. The sooner the plant develops the disease, the greater the damage will be, even if it is not harvested.

 

Pathogens:

Mosaic disease, yellowing of bean leaves caused by some viruses. For example, on mungbeans caused by MYMV virus (Mungbean Yellow Mosaic Virus), on soybeans caused by SMV virus (Soybean mosaic virus) etc... The disease is caused by viruses, so there must be insects as vectors such as aphids , whitefly (Bemisia tabaci),... In the newly-grown stage, when the weather is hot and dry, the density of suckers will increase rapidly, which is the ideal condition for the disease to develop. In nature, the virus exists in many host plants such as weeds, wild plants, so the source of the disease is very abundant etc...

Management measures:

The disease is caused by a virus, so there is currently no cure. However, we can effectively manage the disease by managing the way it is spread. To manage the disease, we must apply many measures simultaneously:

- Sanitize the remnants of the previous crop, especially those that are host to viruses such as legumes... Avoid planting near fields and gardens where beans are grown at the stage of growing to near-harvesting Clean up weeds and wild plants around the border.

- Should be planted early and concentrated to avoid spreading diseases to each other.

- Use varieties resistant to sucking pests, and resistant to viruses.

- Uproot and destroy diseased plants, do not throw diseased plants indiscriminately.

- Avoid over-fertilizing nitrogen fertilizers, enhance micronutrients by using TANO-601 foliar fertilizer to increase the resistance of plants.

- Closely monitor the density of sucking pests to prevent timely from the time the plants just grow until 20-25 days after growing (because this is the stage that determines the rate of diseased plants and the severity or mildness of the disease). ). Currently, the most popular and effective product for suckers is SK Enspray 99EC mineral oil. This is a completely non-toxic product. To increase the effectiveness of killing suckers, chewing worms and harmful spiders, farmers often combine with some biological products such as Comda Gold 5WG to prevent.

 

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 Miner has the scientific name Phyllocnistis citrella Staint., family Phyllocnistidae, order Lepidoptera. The  miner occurs in many countries in the tropics and subtropics. The main host of the miner is the citrus family - Rutaceae. In addition, the miner also attacks mangosteen and some other plants.

 

Adult is a small planthopper, with a body 2-3 mm long, the whole body is ash gray, slightly greenish, the wings are opaque with many small brown spots.Eggs are oval, 0.3 mm long, have a pointed end and are attached directly to the leaf surface, leaf axils.Larvae are very small, oval in shape, newly hatched are bright yellow. Age 2 and age 3 are in green. Age 4 and age 5 are golden brown and 2 small wing sprouts.

 

Green bugs specialize in the fruit of citrus groups (oranges, tangerines, lemons, grapefruits, kumquats...), some people call them orange bugs, or orange suckers. Their scientific name is Rhynchocoris poseidon or Rhynchocoris humeralis.

 In Vietnam, yellow leaf curl disease is very common on papaya trees, especially the disease is often severe in areas of high and continuous planting, areas with hot and arid climates. The disease has significantly reduced the yield and quality of papaya. Gardens that are infected early when the plants are young may not yield. However, up to now, many gardeners still do not know the cause and how to fix it.

 

 Spider mites are common pests on citrus trees, especially in hot and dry climates that are suitable for spiders to grow and cause severe damage.The group of harmful spiders is usually very small in size, unlike the natural enemy spiders.Spiders have a very short life cycle, high reproductive ability, create many generations in a year, so it is easy to break out into epidemics in a short time.

 

 This group includes species that are generally very small in size, causing damage by sucking plant sap (on leaves, fruits, branches, stems).

There are many species of mealybugs present on the group of Oranges,Tangerines,Grapefruits and Lemons (Citrus), which can be divided into 2 groups:

+ Group of sticky mealybugs with common varieties such as Lepidosaphes, Aonidiella, Coccus and Saissetia.

+ Group of flower mealybugs with common genera and species such as Pseudococcus, Planococcus and Icerya purchasi.

Dry branches and berries disease often appear to be common damage on coffee gardens during the rainy season. The disease causes death of branchs, dry fruit, severely affects the canopy structure and coffee yield if not paid attention to prevention.

  

 Pink disease commonly causes diseases on rubber plantations in the rainy season, especially on garden from 4-8 years old. This year, rubber has to go through a period of severe drought, weakening the tree, so now in tnshe rainy season it is easy to get infected. Therefore, it is necessary to pay attention to good management to avoid affecting the garden.

In recent years, the area of citrus has been expanded because it is a fruit tree with high economic efficiency. However, in order to sell at a high price, not only in quality but consumers also require the external beauty of the fruit, so pest management on citrus is a matter of great concern to farmers. The hot season is a favorable condition for thrips to develop and cause damage, affecting the commercial value of fruit.

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