Are the seedlings dying and the stems are girdled or rotted at the soil line?
Do the leaves have spots or blotches?
Do the leaves and stems have white, cottony clusters on them?
Are the roots dark brown, the plant is wilting, yellowing, and dying?
Are the leaves yellow, branches, and leaves are covered with small bumps?
If your seedlings are falling over and the stems are girdled or rotted at the soil line, the most likely cause is a damping-off disease. Remove and destroy all infected plants. To prevent damping-off let the soil surface dry between waterings, thin seedlings to avoid overcrowding, and do not add nitrogen fertilizers until plants have developed leaves.
Your plant is suffering from a fungal leaf spot. These can come from several fungus diseases, causing spots to occur on foliage. Spots may enlarge rapidly, especially in wet weather. Destroy infected leaves or plants. Spray plants with sulfur to prevent the disease from spreading, especially if the weather is wet. Spray between rains. Prevent problems by thinning plants to provide good air circulation.
White, cottony clusters on leaves and stems are caused by mealybugs. These tiny insects are covered with a fluffy white coating. They feed by sucking plants sap. They produce the sticky substance honeydew which makes leaves sticky. You can control them by washing them off the plant with water spray. Insecticidal soap should be used with severe infestations.
These symptoms indicate a fungal disease - Pythium Root Rot. Do not overwater plants. Remove affected plants and their roots, and discard surrounding soil. Plant only in the pasteurized soil. Hold back on fertilizing too. Keep hose ends off the ground. Apply a copper-based fungicide to protect plants.
Soft scales often attack Natal plums. Scrape off minor infestations with your fingernail. Prune out badly infested growth, or use a soft brush and soapy water to gently scrub the scales off the stems. Control scales by spraying insecticidal oil during the growing season.
Mineral deficiencies can cause tip chlorosis or necrosis or cause foliage to discolor, fade, distort, or become spotted, sometimes in a characteristic pattern that can be recognized to identify the cause. Nutrient deficiencies rarely occur in most woody landscape plants. When they do occur, nitrogen and iron are the most commonly seen deficiencies. Apply only the mineral found to be deficient.
http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/natalplum.html
Wilen, C., Dimson, M., Plant and Pest Guide - Los Angeles State Historic Park, The University of California, Division of Agriculture and Natural Resources
Ellis, B. W., Bradley, F. M., & Atthowe, H. (1996). The Organic gardener's handbook of natural insect and disease control: a complete problem-solving guide to keeping your garden & yard healthy without chemicals. Emmaus, Pa.: Rodale Press.
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Sreten null
Hi! I’m Sreten Filipović. I graduated from the Faculty of Agriculture at the University of Belgrade, with a master's degree in Environmental Protection in Agricultural Systems. I’ve worked as a researcher at Finland's Natural Resources Institute (LUKE) on a project aimed at adapting south-western Finland to drought episodes. I founded a consulting agency in the field of environment and agriculture to help farmers who want to implement the principles of sustainability on their farms. I’m also a founding member of the nonprofit organization Ecogenesis from Belgrade whose main goal is non-formal education on the environment and ecology. In my spare time, I like to write blog posts about sustainability, the environment, animal farming, horticulture, and plant protection. I’ve also published several science-fiction short stories.
You can find me on LinkedIn at https://www.linkedin.com/in/sreten-filipovi%C4%87-515aa5158/