How to prevent and control weeds in rapeseed? Master the occurrence characteristics and control methods
The amount of nitrogen, phosphorus and potassium absorbed by rapeseed is nitrogen greater than potassium, and potassium greater than phosphorus. For every 1000 kg of rapeseed produced, it needs to absorb 2.76 kg of nitrogen, 0.33 kg of phosphorus and 2.06 kg of potassium. The absorption ratio of nitrogen, phosphorus and potassium is 8.38:1:6.24. A deficiency of the trace element boron will produce boron deficiency symptoms. Rapeseed plants...
I. Main weed speciesRapeseed in Jiangsu Province is mainly winter-sown rapeseed, with very little spring-sown rapeseed. The weed species occurring in winter-sown rapeseed fields are basically the same as those in wheat fields, and the preceding crops include both dryland stubble and rice stubble. The main weeds in dry-stubble rapeseed are: Galium aparine, Galium tricorne, Veronica persica, Chenopodium serotinum, Descurainia sophia, Capsella bursa-pastoris, Thlaspi arvense, Cardamine hirsuta, Poa annua, Avena fatua, Polygonum aviculare, Silene conoidea, Cirsium setosum, Convolvulus arvensis, etc.; in some areas Avena fatua causes serious damage. The main weeds in rice-stubble rapeseed are Alopecurus aequalis, Alopecurus japonicus, Sclerochloa kengiana and Poa annua, with others including Polypogon fugax, Galium aparine, Stellaria aquatica, Stellaria uliginosa, Vicia sativa, Cardamine hirsuta, Capsella bursa-pastoris, Veronica persica, Lapsanastrum apogonoides, etc., among which Alopecurus aequalis causes the most serious damage, and in some areas Sclerochloa kengiana and Poa annua also cause relatively serious damage. In spring-sown rapeseed fields, the main weeds include Avena fatua, Chenopodium album, Polygonum aviculare, Sonchus brachyotus, Cirsium setosum, Polygonum convolvulus, Galium aparine, Chorispora tenella, Elsholtzia ciliata, Galeopsis bifida, Amaranthus, Echinochloa crus-galli, Comastoma, Equisetum arvense, etc., among which Avena fatua causes the most serious damage. The number of weeds in rice-stubble fields is greater than in dry-stubble fields.
II. Occurrence characteristics
Rapeseed cultivation methods include direct-seeded rapeseed and transplanted rapeseed, and in terms of tillage methods there are also no-till sowing/transplanting and plowed sowing/transplanting, and the weed occurrence in the fields also differs markedly.
During the seedbed stage of transplanted rapeseed, the main species are Alopecurus aequalis, Polypogon fugax, Veronica persica and Stellaria media. The peak of weed emergence is 7-10 days after sowing, the symbiotic period with rapeseed is relatively short, and because the rapeseed seedlings are dense and grow quickly, weed damage is relatively light.
The weed occurrence characteristics of winter-sown, plowed and sown/transplanted rapeseed fields are basically similar to those of wheat fields sown at the same time. A weed emergence peak appears 10-30 days after sowing/transplanting; the amount of weeds emerging in this period is large and forms the main weed population causing weed damage in rapeseed fields. Weeds emerging in dryland stubble are mainly broadleaf weeds, and the amount emerging is relatively small; while weeds emerging in rice stubble are mainly grass weeds, and the amount emerging is relatively large.
In winter-sown no-till sown/transplanted rapeseed fields, because the soil surface outside the sowing/transplanting holes (rows) has not been disturbed, the weed seeds on the soil surface have already germinated before sowing/transplanting, forming an early weed community in the field; when sowing/transplanting, the surface soil of the sowing/transplanting holes (rows) is disturbed, and the peak emergence of weeds germinating in the sowing/transplanting holes (rows) and the turned-up soil layer appears 10-30 days after sowing/transplanting.
Because rapeseed fields grow vigorously after spring and grow quickly, only a few weeds such as Vicia sativa, Galium aparine and Avena fatua can have a relatively large impact on rapeseed production, and most naturally die out due to shading by the rapeseed plants. Except for a very small number of late-sown and late-transplanted fields where rapeseed growth is poor, weeds emerging in the field in spring have very little impact on rapeseed and can all be left untreated.
III. Control techniques
The control of weeds in rapeseed fields should, on the basis of applying various agricultural measures, select suitable herbicide varieties and formulations according to the rapeseed planting method and the characteristics of the main weed communities in rapeseed fields, with the focus on carrying out control in autumn and winter.
1. Chemical control in seedbeds or direct-seeded fields after sowing and before seedling emergence. Because the period of weed damage is short and the dominance of the rapeseed seedling population is easily established, it is only necessary to ensure the safe early growth of the rapeseed seedlings. Therefore, 75-120 ml of 60% butachlor emulsifiable concentrate, 200-250 ml of 50% benthiocarb emulsifiable concentrate, or 200-250 ml of 48% alachlor emulsifiable concentrate can be selected, mixed with 40-45 kg of water for manual spraying, and applied after sowing and before seedling emergence of rapeseed for control.
2. Chemical stubble killing before sowing/transplanting. For no-till rapeseed, before sowing/transplanting, the weeds already germinated in the field after harvesting the preceding crop, or the regrown plants of the preceding crop, should be controlled with a non-selective herbicide. 100-150 ml of 41% glyphosate aqueous solution or 200-250 ml of 20% gramoxone (paraquat) emulsifiable concentrate, or similar agents, can be selected and mixed with 30 kg of water for manual spraying for control.
3. Soil treatment at sowing/transplanting. For rapeseed fields dominated by grass weeds such as Alopecurus japonicus, 100-150 ml of 48% trifluralin emulsifiable concentrate can be selected and applied 3-5 days before sowing/transplanting of rapeseed, and mixed into the soil; or 45-60 ml of 65% S-metolachlor, 50 ml of 48% clomazone emulsifiable concentrate, or 75-100 ml of 50% acetochlor emulsifiable concentrate can be selected and applied after sowing and before seedling emergence of direct-seeded rapeseed, or before transplanting or the next day after transplanting of transplanted rapeseed. For rapeseed fields where grass weeds are mixed with broadleaf weeds such as Stellaria aquatica, Capsella bursa-pastoris and Cerastium, metolachlor or clomazone, or a mixture of pretilachlor and clomazone, can be selected and applied before sowing or before transplanting of rapeseed.
4. Post-emergence stem and leaf spraying. For rapeseed fields dominated by grass weeds, 20-30 ml of 10.8% haloxyfop-R-methyl, 35-50 ml of 10% quizalofop emulsifiable concentrate, 40-50 ml of 6.9% fenoxaprop-P-ethyl emulsifiable concentrate, etc. can be selected for control before the weeds reach the 4-leaf stage. For fields dominated by Vicia sativa, Descurainia sophia, Lapsanastrum apogonoides, Cardamine flexuosa, Geranium carolinianum, etc., 30-40 ml of 50% benazolin suspension concentrate or 50 ml of 33% pendimethalin emulsifiable concentrate can be used per mu, mixed with 40 kg of water for spraying, for control in autumn and winter. For fields dominated by Sclerochloa kengiana and Poa annua, 20-30 ml of 24% clethodim emulsifiable concentrate can be used per mu, for control at the 3-4 leaf stage of the weeds.