Kale Disease That Causes Yellowing & Thinning of Leaves

Downy Mildew

• Downy mildew is causes by the fungus peronospora parasitica, according to Alabama Cooperative Extension. Fungal spores germinate when nighttime temperatures are between 46 to 61 degrees Fahrenheit and daytime temperatures persist below 75 degrees Fahrenheit, according to the Alabama Cooperative Extension. In addition, fungal spores spread through the wind or diseased transplants infect healthy plants. There are almost always downy mildew fungal spores in gardens. Spores are able to overwinter in debris and spread when temperatures favor their germination.

Symptoms

• Kale infected with downy mildew produces yellowish spots on the tops of leaves, according to the Alabama Cooperative Extension. As the disease progresses, yellow spots enlarge, leaves become thin or take on the consistency of paper, defoliation occurs and the plant dies. Furthermore, young kale plants may turn completely black when the disease enters their vascular system. Gardeners must monitor their kale crops when temperatures cool down or during times of excessive rainfall. Chemical control is used to prevent kale plants from dying.

Chemical Control

• Gardeners may spray their kale crops with fungicides to control downy mildew. Fungicides that contain active ingredients such as fenamidone, acibenzolar-s-methyl, copper sulfate, pyraclostrobin, dimethomorph, fosetyl-Al, mandpropamid, mefenoxam and potassium phosphite are used against downy mildew, according to Texas A&M University. When spraying your kale crops with fungicides, keep up your watering program. Fungicides harm water-stressed plants. Also, spray your kale with an even coverage of fungicides to obtain optimal results.

Prevention

• Clean up all plant debris at the end of the growing season. Eliminate nearby weeds to prevent the fungal spores that cause downy mildew from infecting kale crops. Also, avoid overhead watering; instead, apply water at the base of plants. Reduce the duration of time that leaves remain wet by watering in the morning. Also, make sure that your garden area has adequate drainage. Remedy poorly draining soils with amendments like compost before planting.