Scientists, come on, protect our Xinjiang cotton!

Author: Bug Squad

The article comes from the Science Academy official account (ID: kexuedayuan)

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Cotton is an important cash crop and strategic material. It is the second largest crop in my country after grain and plays an important role in the national economy. Xinjiang is the largest high-quality cotton production base in my country and has unique conditions. However, there are many restrictive factors in the planting process, such as pests and diseases.

It is reported that the cumulative area of ​​pests and diseases in Xinjiang in 2020 was 1.4599 million hectares. If cotton pests and diseases are not effectively prevented and controlled, not only will the area of ​​occurrence continue to expand and spread, causing a sharp decline in the yield and quality of local cotton fields, or even a total loss of production, but it will also become an obstacle to a bumper cotton harvest next year.

Scientists played a very crucial role in this battle to protect cotton.

In 2020, Xinjiang's cotton planting area was 2,501,900 hectares (37.529 million mu), a decrease of 1.5% from last year. However, thanks to good management, the yield per unit area increased by 93.8 kg/hectare (6.3 kg/mu) compared with last year (Photo source: CCTV.com)

The demons coveting Xinjiang cotton

"Know yourself and know your enemy, and you will never be defeated in a hundred battles." If you want to win this battle, you must first know which insects and "plague gods" are causing trouble. There are many pests that covet Xinjiang cotton. Let's first identify four insects: cotton aphids, cotton blind bugs, cotton spider mites, and whiteflies, and see what tricks they use.

1. Cotton Aphid

The cotton aphids that occur in Xinjiang are mainly black cotton aphids, long-tube cotton aphids and cotton aphids. They are a type of small pests. The wingless viviparous female aphids are less than 2 mm long and are one of the important pests in the cotton seedling stage. Cotton aphids mainly use piercing-sucking mouthparts to pierce the growth points and tender leaves of cotton. Small yellowish chlorotic spots or leaf curling will appear on the affected parts, affecting the photosynthesis of the leaves. In severe cases, the leaves will deform, curl, dry or fall. In addition, cotton aphids can also produce honeydew and sooty mold disease (click here to review useful knowledge about sooty mold disease). As vector insects, they can also help spread some plant viruses.

From left to right: wingless cotton aphid; damaged cotton leaves (Photo credit: Tianshan Plant Protection)

Cotton aphids have strong adaptability and can survive in different ways according to different regions and hosts. Under suitable temperatures, cotton aphids generally reproduce a generation in less than 10 days. If the conditions are right, one aphid can have more than one million offspring (including offspring produced by offspring). In recent years, cotton aphids have shown an increasing trend in pesticide resistance, which deserves our attention.

2. Cotton blind bug

Cotton blind bugs are also a pest that damages cotton with their piercing-sucking mouthparts. The most serious cotton blind bugs in Xinjiang are mainly pasture blind bugs, alfalfa blind bugs and green blind bugs. Cotton blind bugs have only three insect stages: eggs, nymphs (larvae) and adults. Both adults and nymphs can damage cotton. They mainly use their mouthparts to pierce and suck the apical buds, side cores, flower buds and young bolls, sucking the juice of cotton plants.

For the terminal buds, young leaves, and young buds, the cotton blind bug mainly attacks by "blackening" - when the terminal buds of cotton are attacked, they will wither and turn black, becoming headless seedlings or broken heads; when young leaves are attacked, they will form broken leaves; when young buds are attacked, they will turn from yellow to black and fall off after a few days. If the mature buds of cotton are attacked, they will form open buds, which will fall off soon; when young bolls are attacked, the wounds will appear as water-stained spots, and in severe cases, they will become rigid and fall off; when the top or side of the center is attacked, it will form broom cotton.

From left to right: Green stink bug; Damaged cotton leaves (Photo credit: Tianshan Plant Protection)

3. Cotton spider mite

Also known as cotton red spider, it is a type of pest that is common and causes serious harm in all cotton-growing areas of my country. In the Xinjiang cotton-growing areas, the dominant species are the truncate spider mite and the Turkestan spider mite. Spider mites are small in size, generally around 1 mm, and are difficult to see with the naked eye without careful observation.

Cotton spider mites mainly suck nutrients from the back of cotton leaves. When they first start to infest, many yellow and white spots appear on the front of the leaves. After a few days, the petioles turn red. In severe cases, the leaves fall off and the stalks become bare, as if they were burned, causing large-scale yield reduction or even total crop failure. Even if the stalks do not become bare, it will seriously affect the photosynthesis of cotton, preventing the cotton plants from growing normally and causing the plants to be short, resulting in reduced yields. The spider mites are not only interested in cotton, but also in other food crops and cash crops.

From left to right: cotton spider mites; cotton leaf damage (Photo credit: Tianshan Plant Protection)

4. Bemisia tabaci

Bemisia whitefly is also a type of pest with piercing-sucking mouthparts. Farmers call it "little white bug". It is also relatively small, about 1 mm in size. It has the characteristics of fast spread, strong reproductive capacity, serious harm, strong pesticide resistance, and great difficulty in prevention and control.

When harming cotton, whiteflies pierce and suck plants as adults and nymphs, causing the leaves to turn green, yellow, and wilt, or even the entire plant to die. They can also spread yellow spot virus disease, causing crop yield reduction. It is particularly noteworthy that the adults and nymphs secrete a large amount of honeydew, which contaminates plants and easily leads to sooty mold disease. They also contaminate cotton wool, increasing the sugar content of the fiber and affecting the progress of the textile process.

Bemisia whitefly is an extremely harmful invasive pest. This pest from the United States can be said to have traveled all over the world. According to reports, Bemisia whitefly was first discovered in Arizona, the United States in 1962. After that, it spread to many countries and regions in South America, Europe, Africa, Asia, and Oceania. Among them, cotton in Sudan, Turkey, Egypt, Israel and other countries and the Central Asian countries of the former Soviet Union after the 1980s was the most seriously affected. In 1998, Chinese scientific and technological workers first discovered Bemisia whitefly on poinsettias sold at the Bonsai Flower Wholesale Market on Nanchang Road in Urumqi; in 1999, this insect was also found in the cotton experimental field of the Turpan Long-staple Cotton Research Institute. In recent years, the occurrence of Bemisia whitefly in Turpan City, Hami City, Kezhou, and Kashgar has been relatively severe.

From left to right: Bemisia whitefly nymph; Bemisia whitefly adult (Photo source: Tianshan Plant Protection)

In addition to these leading insects, other pests that harm Xinjiang cotton include cotton bollworm, cotton thrips, two-spotted firefly leaf beetle, etc. Some "plague gods" are also unwilling to be lonely. They spread quickly and will bring "catastrophe" to cotton, such as cotton wilt and Verticillium wilt.

Both Fusarium wilt and Verticillium wilt are fungal diseases. The pathogens of Fusarium wilt and Verticillium wilt mainly overwinter in diseased residues, soil, and manure. Cultivation, harrowing, tillage, watering, and agricultural operations in diseased cotton fields are the main ways of close transmission. The disease mainly harms the vascular bundles and other parts of cotton. Once it occurs, it is difficult to eradicate and is called "cotton cancer." At present, the area of ​​Verticillium wilt in Xinjiang exceeds 50% of the sown area, of which the area of ​​seriously diseased fields exceeds 1 million mu.

It can be said that the pests and "plague gods" that covet Xinjiang cotton know how to reproduce quickly and spread harmful substances. Coupled with their increasing drug resistance, they have indeed brought certain difficulties to prevention and control work.

Scientists! Stop the bugs' conspiracy

Cotton is so valuable that insects and pests are naturally not allowed to run rampant. In response to cotton diseases and insect pests, people have adopted a variety of prevention and control measures, including plant quarantine, physical control, chemical control, biological control, agricultural control, etc.

The first three methods are relatively easy to understand. For example, plant quarantine is to prevent the introduction or export of some quarantine pests and diseases; physical control is to use light to lure and kill some phototactic pests; and chemical control is to apply appropriate pesticides for prevention and control according to the types of pests and diseases in the field.

However, we must effectively prevent and control pests and diseases, and overcome the adverse effects of chemical pesticides to avoid damage to biological resources and the environment. In Xinjiang, scientists have followed the principles of sustainable development and the plant protection concept of "prevention first, comprehensive management", made these attempts, and achieved good results.

1. Biological control - biological pesticides, precise strike

There are many natural enemies of cotton pests in nature. We should make good use of these natural enemies. For example, during the period of seedling aphids, when the ratio of natural enemy units in cotton fields (one seven-spotted ladybug, two spiders, two aphid lions, four aphid flies, and 120 aphid wasps as one natural enemy unit) to aphid population is higher than 1:150, no pesticides should be applied for prevention and control, and natural enemies should be used to control aphids. In addition, we can breed and release natural enemies such as ladybugs, trichogrammatids, and aphid wasps to achieve the purpose of directly suppressing pest populations.

In addition, spraying insect viruses, Bt and other biological pesticides at the beginning of the hatching of cotton bollworm eggs not only has a good prevention and control effect, but also can effectively protect natural enemies; in order to prevent seedling diseases, wilt and verticillium wilt, Bacillus subtilis, amino oligosaccharides and ethopropene can be used to treat seeds, and the pesticides can be applied with drip irrigation or foliar spray during the seedling and bud stages.

Qin Qilian's research group at the Institute of Zoology, Chinese Academy of Sciences, has successfully developed a cotton bollworm nuclear polyhedrosis virus insecticide. This viral insecticide contains up to 500 billion virus particles per gram of original medicine, which is more than 20 times more than similar products and is the highest content of viral insecticide known in the world. Using this biological pesticide, only 2 to 3 grams per mu of cotton field is needed to control pests.

Since 2005, researchers have conducted field efficacy comparison tests of new ultra-high-content insect virus pesticides in some cotton fields of the Corps, and the control effect on cotton bollworm is better than conventional chemical pesticides. Especially when chemical pesticides almost completely kill the natural enemies of cotton bollworm in the field, this virus pesticide has almost no effect on the natural enemies of cotton bollworm. After use, it can be self-degraded in nature without causing pesticide residues. Its overall control effect is 80%, reducing the release of nearly 100 tons of chemical pesticides into the environment, with significant ecological benefits.

2. Agricultural control - not only to eliminate pests, but also to increase production

This is an advanced version of biological control. Plants play an important role in the preservation and proliferation of natural enemies in the ecosystem and the natural control of pests. Agricultural control can use plants to regulate the biological relationship in the farmland ecosystem. It is different from traditional biological control in that it indirectly uses natural enemies instead of directly artificially breeding and releasing natural enemies. Agricultural control is achieved through crop layout and intercropping. Intercropping in cotton fields can reduce the occurrence of diseases and pests, and can also promote each other to increase production.

Based on research on Xinjiang's cotton-planting history and the occurrence patterns of cotton pests, experts from the Institute of Zoology, Chinese Academy of Sciences and the Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, found that the reason why cotton aphids in Xinjiang have become a major pest is that the winter wheat planting area has been greatly reduced, resulting in a reduction in the source of natural enemies of cotton aphids in cotton fields. Abundant food and insufficient natural enemies have caused cotton aphids to become a disaster in Xinjiang.

High-yield Xinjiang cotton (Photo source: Great Transformation - A large-scale exhibition to celebrate the 40th anniversary of reform and opening up)

After years of exploration and in-depth research, they found that alfalfa and bitter beans have the largest food insect storage capacity and can serve as natural enemy breeding pools. This created a simple way to induce natural enemies in the cotton field edge plant belt to enter the cotton field to control cotton aphids: plant alfalfa belts under the shade of trees at the edge of the cotton field. When cotton aphids enter the cotton field and begin to harm cotton, cut the alfalfa belts and place the cut alfalfa at the edge of the cotton field, thus achieving the purpose of fully utilizing natural enemies to control cotton aphids with human assistance. In addition, alfalfa is a high-quality forage grass suitable for the development of animal husbandry in agricultural areas. As a leguminous plant, alfalfa is also beneficial to improving soil fertility.

3. Promotion of new varieties - genetically modified cotton, RNAi cotton

If we can get varieties that are resistant to diseases and pests, the problem of diseases and pests will be fundamentally solved.

In 2007, the first transgenic insect-resistant cotton variety in Xinjiang, Xinlu Cotton No. 1, bred by the Institute of Economic Crops of Xinjiang Academy of Agricultural Sciences and the Institute of Biotechnology of Chinese Academy of Agricultural Sciences, passed the national approval. In 2011, the transgenic insect-resistant cotton variety Santa No. 6, bred by the cooperation, passed the national approval. According to the survey, the planting area of ​​transgenic insect-resistant cotton in Xinjiang exceeded half in 2012. Since the large-scale planting of transgenic insect-resistant cotton, there has been no serious damage to cotton bollworm in Xinjiang, which is under control, fully demonstrating the technical effect of transgenic insect-resistant cotton. Relevant research and analysis show that farmers can obtain direct income from transgenic insect-resistant cotton technology. Research on the planting of transgenic cotton from 1999 to 2001 shows that transgenic cotton can increase income by more than 1,800 yuan per hectare.

In addition to genetically modified cotton, RNAi cotton is also showing its prowess. In order to cure cotton Verticillium wilt, known as "cancer of cotton", Guo Huishan's research group at the Institute of Microbiology, Chinese Academy of Sciences, based on 20 years of experience in plant antiviral RNAi research, has made a series of important progress in the infection biology of cotton Verticillium wilt, the theory and disease resistance application of plant-fungus cross-RNAi, and the establishment of a broad-spectrum and rapid cotton genetic transformation system after more than ten years of hard work. Through technology integration, a cross-border RNAi-mediated upland cotton germplasm innovation technology system has been established, and the germplasm innovation of resistance to Verticillium wilt has been successfully achieved in early-maturing upland cotton.

Guo Huishan's research team from the Institute of Microbiology, Chinese Academy of Sciences, established a cotton verticillium wilt and fusarium wilt field workstation in Xinjiang (University of Chinese Academy of Sciences website)

The results of multi-year, multi-point continuous resistance identification showed that RNAi cotton had a 55.7% higher resistance to Verticillium wilt than the recipient variety. In 2017, the research team successfully cultivated a new line of early-maturing upland cotton (Zhongke Cotton No. 1) with high resistance to Verticillium wilt and complete independent intellectual property rights using the antigen-binding hybrid breeding method they created. The results of disease resistance identification and production tests in the Northwest Inland Cotton Region of the country showed that the new line had a 22.25% higher resistance to Verticillium wilt than the control variety in the pilot area, and the yield in the severely diseased field was 41.7% higher than the control variety (the main local variety).

New technology helps in the fight to protect cotton

The situation of cotton diseases and pests is complex and is closely related to the region and human operations. At the same time, the climatic conditions may be different every year. Therefore, the prevention and control of cotton diseases and pests should be adapted to local conditions, scientific prediction and forecasting technology should be established, and scientific prevention and control should be carried out to achieve the goal of green prevention and control and high yields.

With the development of science and technology in my country, some new technologies may be more widely used in the prevention and control of cotton diseases and pests: such as the application of new high-quality cotton germplasm resources, including more insect-resistant, disease-resistant and high-yield genetically modified cotton; the application of 3S technology (3S is the general term for GIS, RS and GPS, namely geographic information system, remote sensing and global positioning system) in disease and pest prediction and forecasting; the application of digital identification and monitoring and early warning technology of pests and diseases in disease and pest monitoring and forecasting; the application of big data and 5G technology in the monitoring, forecasting and prevention of some important pests; and the wider promotion of plant drones, etc.

These technologies can make it impossible for cunning insects and plagues to hide. I believe we will eventually win the battle to protect cotton.