What causes herbicide damage in Schisandra chinensis
Chemical herbicides are widely used because they have the advantages of low investment, quick results and labor savings. The types of herbicides increase year by year, and the application rate keeps rising. Although the agricultural authorities have done a great deal of publicity and training work specifically for farmers on the use of herbicides, recent surveys by the Northern Medicine Office and the Yichun City Plant Protection Station show that, due to the drift of herbicide spray droplets, the problem of damage of varying degrees to nearby planted Schisandra chinensis is particularly prominent.
According to a survey by the Northern Medicine Office of Tieli City, Heilongjiang Province, and the Taoshan Forestry Bureau, as of June 16, the area of Schisandra chinensis in Tieli City affected by herbicide damage reached more than 95% of 2730 mu, with estimated economic losses of about 5 million yuan. Of the 2265 mu of Schisandra chinensis under full light at the Taoshan Forestry Bureau, the affected area reached 833.3 mu, accounting for 36% of the total area; of the 1031.5 mu of Schisandra chinensis cultivated under forest, the affected area reached 581.25 mu, accounting for 59% of the total area, with direct economic losses of 3.25 million yuan. Because herbicide damage has brought serious economic losses and social impact to Schisandra chinensis growers, to some extent it has become a major obstacle restricting the development of characteristic agriculture in Yichun City.
Schisandra chinensis cultivation gardens are mostly adjacent to soybean and corn fields. Acetochlor + 2,4-D butyl ester, Dadouhuan, clomazone and others are commonly used herbicides in soybean and corn fields, and their usage ranks first. The survey found that the main causes of herbicide damage to Schisandra chinensis are farmland herbicides such as 2,4-D butyl ester and clomazone.
1 Main characteristics of herbicides
1.1 2,4-D butyl ester
It is currently a widely used herbicide for pre-emergence soil treatment in soybeans, pre-emergence soil treatment in corn and post-emergence stem and leaf treatment, and it is also a chemical herbicide that causes relatively great damage to Schisandra chinensis. 2,4-D butyl ester is a phenoxyacetic acid hormone-type selective herbicide with strong systemic conductivity, affecting multiple physiological metabolic processes of plants by interfering with endogenous hormones. After the spray liquid is applied to the surface of weed stems and leaves, it passes through the cuticle and cytoplasmic membrane, and finally is conducted to all parts of the plant. At the top of the plant, it inhibits nucleic acid metabolism and protein synthesis, causing the growing point to stop growing and young leaves to fail to extend, and inhibiting the normal progress of photosynthesis; the agent conducted to the lower part of the plant increases the synthesis of nucleic acid and protein in stem tissues, promotes abnormal cell division, causes root tips to swell and lose absorption capacity, resulting in twisted and deformed stems, blocked sieve tubes, damaged phloem and obstructed transport of organic matter, thereby destroying the normal living ability of the plant and ultimately leading to plant death.
The drift of 2,4-D butyl ester spray liquid is the main reason it causes damage to surrounding sensitive crops. The drift of 2,4-D butyl ester is of 2 types: the first is spraying drift. When sprayed on the ground, it can drift 1000-2000 m. This agent has good spreading properties and strong permeability, easily enters plants, and is not easily washed away by rain, causing nearby contaminated sensitive crops such as watermelon, Schisandra chinensis, trees and other dicotyledonous plants to suffer damage. The other is volatilization drift. It has strong volatility. In high-temperature and dry weather above 15°C, that is, when the temperature is too high and sunlight is strong, the chemical activity of 2,4-D butyl ester can be enhanced, causing its active ingredients to evaporate from the soil surface and volatilize and drift with the wind. The agent droplets can drift very far in the air, increasing with rising temperature, making dicotyledonous medicinal plants weak in resistance to 2,4-D butyl ester and slow in degrading 2,4-D butyl ester, resulting in damage.
1.2 Clomazone
Clomazone is an organic nitrogen-containing heterocyclic herbicide (English common name Dimethazone), Chinese names isoxaflutole and clomazone, chemical name: 2-(2-chlorobenzyl)-4,4-dimethylisoxazolidin-3-one. It is a selective herbicide. The single agent can be used for pre-emergence and post-emergence weed control in soybean fields. Early post-emergence application in soybeans is safe for soybeans and has a very good contact-killing effect on weeds. Mixed formulations such as Dadouhuan, whose main ingredients are 2,4-D butyl ester + clomazone + propisochlor, can only be used for pre-emergence weed control in soybean fields. Clomazone is absorbed through plant roots and young buds, conducted upward, and diffuses to the leaves through the xylem, inhibiting the synthesis of chlorophyll and carotene in sensitive plants. Although these sensitive plants can sprout and emerge, they become white seedlings due to lack of pigments and die within a short time. Soybeans are selective; after absorption by the crop, through special metabolic action, the active ingredients of clomazone are converted into non-toxic degradation products. Clomazone has relatively high solubility in water, but has a moderate degree of binding to soil, which affects its mobility in soil. It will not flow below 30 cm of the soil surface and is one of the soil residual herbicides. In soil it is mainly degraded by microorganisms, with a half-life in soil of about 30-135 days, and its biological activity in soil can last more than 6 months. Clomazone is volatile, and droplet or vapor drift can cause the leaves of the sensitive plant Schisandra chinensis to turn white. Poplar and pine in forest belts are safe, while willow is sensitive, but can resume normal growth after 20-30 days.
2 Causes
2.1 Unreasonable crop layout. Dispersed land management leads to disorderly interplanting of multiple crops, and it often happens that one household's pesticide use causes crops of multiple households to suffer damage.
2.2 Concentrated application time and large area. Soybeans and corn are generally sprayed with herbicides in mid-to-late May. During this period the temperature is relatively low and rainfall is frequent; after application, high temperatures occur, and the sprayed area accounts for more than 90% of the sown area, causing the suspended concentration of herbicides in the air to be too high in a short period. Drifting with the wind or falling onto plant bodies with rain is the main reason sensitive crops such as Schisandra chinensis suffer damage.
2.3 Improper application methods. Most farmers use motorized mist blowers to spray herbicides to control weeds in soybean and corn fields, which aggravates the degree of spray drift.
3 Prevention
3.1 Do a good job in regional planting planning
When planting crops, district (bureau) forest farms (stations) should plan uniformly and lay out rationally. Schisandra chinensis should be planted in concentrated contiguous blocks, preferably far away from crops such as soybeans and corn. Within 2000 m of Schisandra chinensis, it is strictly forbidden to use herbicides with drifting damage for chemical weed control. Within the safe distance, this agent should also be used when there is no wind and the temperature is low. Avoid herbicide drift damage.
3.2 Application methods must be correct
When using herbicides in soybean and corn fields, choose windless or breezy weather, and use a knapsack manual sprayer for high-volume uniform spraying. When applying, the nozzle should be kept as low as possible, or directed spraying should be done, or a protective cover should be added to the nozzle. Generally, 40-50 kg of water is used per mu (667 square meters, the same below).
4 Remedial measures
4.1 Timely detoxification
Pay attention to the use of herbicides in neighboring fields. If the amount of drifting herbicide used is too large, detoxification measures should be taken as early as possible. The method is to rinse the plants with water as soon as possible to reduce the pesticide sticking to the plants.
4.2 Chemical regulation
Once mild herbicide damage is found in Schisandra chinensis, plant growth regulators should be sprayed in a targeted and timely manner for reverse regulation. Plant growth regulators have a very good stimulating effect on the growth and development of crops, and at the same time, micro-fertilizers such as zinc, iron and molybdenum and foliar fertilizers can also be used to promote crop growth and effectively reduce herbicide damage. Commonly used plant growth regulators mainly include gibberellin (920), Tianfengsu, brassinolide, etc. If crops are damaged at the seedling stage, a 30-50 mg/kg gibberellin solution can be sprayed on the leaves, which has an obvious effect of promoting plant growth. Specific method: spray 10-40 mg/kg gibberellin (920) or 1 mg/kg Tianfengsu 2-3 times consecutively, and timely topdress and water, which can effectively accelerate the recovery growth of damaged crops.
4.3 Fine management
After herbicide damage occurs, promptly remove chlorotic and abnormal branches and leaves, which can reduce the penetration and conduction of the agent in the plant; timely cultivate and loosen the soil, and appropriately increase the application of phosphorus and potassium fertilizers, which can promote root development and help enhance the plant's resistance; it is best to supplement foliar fertilizer, which can alleviate the damage and restore growth. The principles for selecting foliar fertilizer are: foliar fertilizers with high content of major elements, moderate trace elements, a concentration that does not cause damage, and resistance to rain washing, such as Xiaoyedi, Lulingbao and plant activators; a suitable amount of quick-acting nitrogen fertilizer can also be applied to crop seedlings to promote tillering and leaf growth, so that the plants can restore normal growth and development as soon as possible.