Leaf Color Diagnosis and Control Methods for Red and Yellow Seedlings in the Rapeseed Seedling Stage
Rapeseed stem rot, commonly known as "white stalk", "hemp stalk", "moldy root crown" and so on, is one of the main diseases affecting rapeseed growth. The control of rapeseed stem rot should focus on prevention, and the main technical control measures are as follows. 1. Prevent seed-borne infection: eliminate sclerotia and kill pathogens on seeds through screening, air separation, chemical seed dressing and other methods...
Red leaves or yellow leaves, two types of abnormal seedlings, often appear in the rapeseed seedling stage. For red and yellow seedlings, one must observe the color to identify the "symptom" and treat accordingly, so as to transform them in time.Drought-induced red leaves: In the rapeseed seedling stage, if there is a long drought without rain, or if soil moisture is insufficient, rapeseed grows slowly due to lack of water, the plants are short and small, and the leaf color turns light red. For this, furrow irrigation for drought relief should be carried out in time, combined with topdressing with fertilizer before winter, to promote the transformation of rapeseed to normal growth.
Waterlogging-induced red leaves: Too much rain before winter and poor drainage cause waterlogging in the soil, poor absorption capacity leads to stunted seedlings, and the leaf color turns dark red. For waterlogging-induced red leaves, the three ditches should be opened to a high standard, and the ditches should be cleared in time to remove the waterlogging, lower the groundwater level, and eliminate the harm of waterlogging. At the same time, intertillage and loosening of the soil should be carried out in time to raise the soil temperature, strengthen the roots and promote growth.
Pest-induced red leaves: When aphid damage is severe in the seedling stage, rapeseed leaves turn red and become shriveled and stunted. For leaf reddening caused by aphid damage, pesticides such as Dagongchen, Pushi Ya, Yibianjing and others should be selected in time for spraying to promote the recovery of rapeseed growth.
Freeze injury-induced red leaves: If the weather changes suddenly in the seedling stage, and the temperature drops sharply, the leaves turn red due to freezing. For this, combine intertillage and earthing up around the roots, topdress with 50-75 kg of plant ash per mu, or spray a 0.3% potassium dihydrogen phosphate solution on the leaves, which can reduce freeze injury.
Nutrient deficiency-induced red leaves: Rapeseed with nutrient deficiency will show different red leaf symptoms. For example, phosphorus deficiency appears purplish red, potassium deficiency appears brownish red, and boron deficiency appears purplish red with leaf margins curling backward. For red-leaf seedlings caused by phosphorus or potassium deficiency, an appropriate amount of phosphorus and potassium fertilizer can be topdressed, or a 0.2%-0.3% potassium dihydrogen phosphate solution can be sprayed on the leaves. For red-leaf seedlings caused by boron deficiency, a 0.2% borax solution can be sprayed 2 times, or 500-750 g of borax per mu can be used together with water to drench the roots.
Nutrient deficiency-induced yellow leaves: Nitrogen deficiency in the seedling stage results in short and small plants, obviously chlorotic and yellow leaves, and old leaves appearing yellow-red. Zinc deficiency in the seedling stage results in short and small plants, and new leaves losing green and appearing yellow-white. Sulfur deficiency in the rapeseed seedling stage makes the plants light green, with chlorotic and yellowing leaves that are few and small. For yellow seedlings due to nitrogen deficiency, an appropriate amount of quick-acting nitrogen fertilizer can be topdressed. For yellow-leaf seedlings caused by zinc deficiency, a 0.1%-0.2% zinc sulfate solution can be sprayed 2 times in time. For yellow-leaf seedlings caused by sulfur deficiency, 10 kg of gypsum powder per mu can be topdressed together with intertillage.
Disease-induced yellow leaves: When rapeseed is infected with viral disease in the seedling stage, the leaves curl, shrink, and become unevenly green and yellow. After infection, pak choi-type rapeseed forms yellow-green mottled patterns. After infection, cabbage-type rapeseed develops yellow-brown necrotic spots on the leaves. If yellow leaves occur due to viral disease infection, the central diseased plants should be pulled out in time to reduce the source of disease. At the same time, use pesticides to kill aphids and control the disease. A mixed solution of virus A, Yibianjing (or Dagongchen, Sijihong, etc.) plus 500 times edible vinegar can be sprayed for treatment.
Acid-induced yellow leaves: Planting rapeseed in strongly acidic soil will cause acid damage and make the leaves yellow. This kind of yellow leaf generally does not wither, but it easily falls off. For this, 100 kg of plant ash or 50 kg of lime per mu can be topdressed to lower the soil acidity and alkalinity and eliminate acid damage.