Not planting corn? What to plant instead? Investigate pesticide residues first
Original title: An important step that cannot be ignored in the "Sickle Bend" structural adjustment --
Long-residual herbicide phytotoxicity must be avoided
File photo
This year, for farmers in the "Sickle Bend" region, the most important thing is nothing other than the structural adjustment of corn. If not planting corn, what to plant? When farmers are making plans, there is one issue they may not have thought of. Recently, at the "Sickle Bend" region corn structural adjustment weed control technology training class held by the National Agricultural Technology Center in Keyouqian Banner, Inner Mongolia, several weed control experts highlighted that atrazine and nicosulfuron, commonly used in corn fields, are both long-residual herbicides that pose a phytotoxicity risk to subsequent crops. Some long-residual herbicides have a residual period of up to two to three years for sensitive crops, so before switching from corn, what to plant needs to be decided based on herbicide use, in order to avoid unnecessary losses. In response, experts also provided countermeasures and technical guidance recommendations for screening and promoting new high-efficiency, safe alternative herbicide varieties, vigorously integrating and applying herbicide reduction techniques, and scientifically guiding the arrangement and layout of subsequent crops. How should corn fields and subsequent crops be scientifically and safely weeded? Let's hear what the experts say.
★Li Xiangju, researcher at the Institute of Plant Protection, Chinese Academy of Agricultural Sciences --
Irrational herbicide use restricts corn structural adjustment
China's perennial weed occurrence area exceeds 1.4 billion mu, accounting for about 85% of the grain sown area. Weeds compete with crops for water, fertilizer, and light, spread diseases and pests, and release toxic substances, reducing crop yield and quality and causing crop yield reductions of 10%-15%. Chemical weed control is fast, efficient, and low-cost, and can recover more than 21 million tons of grain loss each year, but irrational herbicide use can also cause frequent phytotoxicity, poor efficacy, increased costs, and other problems.
Irrational herbicide use in the "Sickle Bend" region has become a limiting factor for corn structural adjustment. This is even more prominent in Northeast China (the three northeastern provinces and Inner Mongolia). Northeast China is a key corn production region in China and also a province-level region with large herbicide use in corn fields. In 2015, the corn sown area in the four northeastern provinces and regions was 254 million mu, with a cumulative herbicide application area of 308 million mu-times, an average of 1.2 treatments per growing season, a general application rate of 300-500 grams per mu, and a total use of 56,200 tons. In corn production in Northeast China, the long-term large-scale use of the long-residual herbicide atrazine and its compound formulations has led to accumulation of atrazine residues in the soil, affecting the growth of subsequent crops and becoming a bottleneck for crop rotation and planting structure adjustment.
So how should herbicides be used scientifically and safely? In our survey in Jilin, we found that farmers, large grain growers, and cooperatives all hold the notion of "eradicating all weeds." In fact, weeds have an economic weed control threshold, which refers to the weed population level at which the loss caused by weeds equals the control cost. For example, under different weed control effects and yield levels in Beijing corn fields, the ecological and economic threshold for crabgrass control is 4.62-7.11 plants/m2. When below or equal to this value, weed control may not be necessary.
Understanding the weed-killing spectrum of herbicides is crucial. For example, acetochlor targets grassy weeds, atrazine is used for broadleaf weeds, nicosulfuron is used for grassy weeds and broadleaf weeds, and mesotrione and topramezone are used for broadleaf weeds. Only by fully understanding these can good target effects be achieved. Herbicides should be used in rotation, which can delay weed resistance and slow community succession. Herbicides should be applied during the period when crops are not sensitive, and excessive application should not be used. Attention should be paid to avoiding effects on subsequent crops and drift phytotoxicity. Consecutive years of application, soil drought, little rain, tillage of the soil layer, and high organic matter content all increase the amount of herbicide residue in the surface soil layer, affecting the growth of subsequent crops.
Herbicides with low toxicity should be selected, used in reduced amounts, and high-quality application machinery should be chosen to reduce drift and volatilization and achieve targeted application. The effective utilization rate of pesticides with conventional spraying is 20%-30%. Motorized spraying, adding adjuvants, optimizing droplet diameter, reducing spray volume, and adding anti-drift devices can improve utilization. These measures can be supplemented by straw mulching + post-emergence application, increasing organic fertilizer, plastic film mulching + pre-emergence application, selecting optimal crop varieties, and rational close planting to reduce herbicide dosage.
★Wang Guangxiang, researcher at the Institute of Plant Protection, Jilin Academy of Agricultural Sciences --
Chemical control of crops following corn requires attention
For corn fields using atrazine + acetochlor (propisochlor, metolachlor) + 2,4-D isooctyl ester, when the annual atrazine use is less than 1710 grams (active ingredient), spring soybean can be planted with caution as a subsequent crop; when the annual atrazine use is 1710-2400 grams (active ingredient), spring soybean as a subsequent crop will suffer severe phytotoxicity and obvious yield reduction when rainfall occurs after sowing and there is sufficient sunlight after the rain, so spring soybean is not recommended, and silage corn, fresh-eating corn, sorghum, proso millet, etc. can be planted; when the annual atrazine use is higher than 2400 grams (active ingredient), only silage corn, fresh-eating corn, or popcorn, etc. can be planted as subsequent crops.
For plots where corn fields use metribuzin + acetochlor (propisochlor, metolachlor) + 2,4-D isooctyl ester, subsequent crops can include soybean, silage corn, fresh-eating corn, potato, peanut, etc.
For plots where corn fields use cloransulam-methyl (or cloransulam) + acetochlor, intercropping and rotation with soybean can be carried out.
For fields where corn fields use nicosulfuron (mesotrione, benzobicyclon) + atrazine + safener, or fields with reduced atrazine use (soil treatment changed to stem and leaf spray treatment - reduction of 20%-50%, addition of functional adjuvants - reduction of more than 20%, use of standard nozzles, etc.), after 2-3 years, crops such as silage corn, fresh-eating corn, potato, spring wheat, spring soybean, peanut, miscellaneous grains and beans, rapeseed, cucurbits, vegetables, fruit trees, or forage grass can be planted.
The overall principles of chemical weed control for subsequent crops are: on the premise of crop safety, effectively control weed damage; select appropriate herbicide varieties and application methods according to the crop; determine the correct herbicide dosage according to soil type (sandy loam, mildly alkaline soil, meadow soil, loam, black soil, etc.) and soil organic matter content; and determine the correct herbicide dosage according to climatic conditions (soil moisture or temperature levels).
Silage corn and fresh-eating corn
Thiencarbazone-methyl + isoxaflutole + safener: pre-emergence soil treatment in corn or early post-emergence stem and leaf spray treatment in corn; wheat should not be planted as a subsequent crop; it slightly inhibits potato but does not affect later growth and yield; other crops such as sorghum and legumes are safe.
Mesotrione + nicosulfuron + safener: used at the 3-5 leaf stage of corn after emergence.
Mesotrione-methyl + rimsulfuron: pre-emergence soil treatment in corn. S-metolachlor + atrazine + mesotrione: 47.2% suspension concentrate at 6 kg per hectare for pre-emergence soil treatment in corn.
Topramezone (+ S-dimethenamid or isoxadifen): stem and leaf spray treatment before the 8-leaf stage of corn.
Dicamba + safener: used before corn emergence and before the 7-leaf stage after emergence. Thiencarbazone-methyl + tembotrione + safener: used before the 7-leaf stage of corn after emergence.
3% foramsulfuron oil dispersion: stem and leaf spray treatment at 45-54 grams per hectare to control grassy weeds and some broadleaf weeds.
When using 20% fluroxypyr emulsifiable concentrate at 150-180 grams of active ingredient per hectare to control broadleaf weeds, especially the resistant weed velvetleaf, if more than 210 grams of active ingredient per hectare is used, corn stems and leaves bend to one side and leaves curl, and recovery takes 3-4 weeks.
Soybean
Soil closure treatment in soybean fields:
Cloransulam-methyl: content 80%, effective amount 30-48 grams per hectare, applied as soil spray treatment after soybean sowing and before emergence, mixed with 750 liters of water per hectare (+ amide herbicides or pendimethalin or flufenacet - replacing amide herbicides). This variety is suitable for rice-soybean mixed cropping, intercropping, and rotation.