Cabbage Integrated Pest Management : An Ecological Guide.

Major Diseases of CabbageNitrogen (N) deficiencyIn cabbage plants, symptoms are usually a purple glow on the leaves. Symptoms are located throughoutthe plant, although the older leaves usually show symptoms most clearly. When nitrogen deficiencyoccurs early in the growing season, the plants may stay small in size and head formation may bedistorted. In light, sandy soils, nitrogen deficiency can easily occur after heavy rainfall. The rain will washthe nitrogen out to deeper layer of the soil where it is inaccessible for the crop.Adding nitrogen (chemical fertilizer) is usually sufficient to overcome nitrogen deficiency for the shortterm. Adding organic material to the soil improves nutrient holding capacity of the soil and it therefore amore permanent solution.Nitrogen (N) excessToo much nitrogen leads to tall, weak plants. Plants basically grow “too fast” and become weak andtherefore more susceptible to diseases. Sometimes, no cabbage heads develop. In addition, too muchnitrogen may result in a high concentration of nitrate in the leaves which is detrimental for humanhealth L.Phosphorous (P) deficiencySymptoms of phosphorous deficiency are plants that stay small in size. Leaves are dark green to bluishgreen in color. Sometimes, a purple color at the undersides of the leaves can be seen. Symptoms arelocated throughout the plant. It is difficult to correct deficiency symptoms with additional fertilizer applicationonce the symptoms are there. Proper fertilization before the crop is transplanted and use of lots of (welldecomposed)organic material is the best prevention.Potassium (K) deficiencySymptoms of potassium deficiency are a bluish-green coloration followed by yellowing and scorching ofthe leaf margins, accompanied by poor heading. The symptoms are located mainly at the older leaves.Potassium deficiency symptoms are liable to occur on land recently broken up from grass, on light soils,on heavy soil with deficient drainage and in land heavily manured with nitrogenous materials.Boron deficiencyCabbage heads may be small and yellow. The stems of cabbage may be cracked and corky. Leaves maybecome dry and papery. Light soils are more susceptible to boron deficiency, especially in very dryperiods. Also, soils with high pH are more susceptible to boron deficiency.Boron can be added to soils separately but a soil test is advisable to ensure that boron levels are not toohigh.Magnesium (Mg) deficiencyThe symptoms of magnesium deficiency are pale marbled areas between the veins (chlorosis), sometimesaccompanied by a purple color of the leaves. The pale areas finally dry out into brown dead patches. Thesymptoms are located mainly at the older leaves.Growth and maturity may be greatly checked and the plants may become badly affected with diseaseslike downy mildew.171 Cabbage Ecological Guide - 2000