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Fungal, bacterial and viral disease can cause leaf discoloration and sometimes death. Certain diseases are better treated environmentally. Read your insecticide- and fungicide packaging details for warnings, the best method of application, safety for edible crops, frequency of spraying and so on.
Bacterial Canker affects tomatoes and deciduous fruit trees. Tomato plants wilt and the fruit is centred brown and covered outside with white spots. The leaves curl and brown. Deciduous fruit trees' leaves have brown spots, encircled with yellow and cankers appear on stems, discharging a sticky matter.
Control: Apply a product with the active ingredient of Copper oxychloride.
Bacterial spot affects beans, cabbage, green peppers, lettuce, tomatoes and many deciduous fruit trees. Water-soaked spots appear on the fruit and leaves. Tree stems may develop cankers and die back. Leaves' grey, water-soaked spots turn brown or black, dry and eventually leave holes in the foliage. Control: Spray every two weeks with an active ingredient of Copper oxychloride.
Black speckle affects mainly pawpaws which rot fast under sunken black patches on the fruit and foliage.
Control: Spray with Mancozeb.
Black spot affects citrus trees and roses, dark brown to black spots appear, followed by a yellow radiance and ends with foliage dropping off.
Control: Triforine or 20g Bicarbonate of soda diluted in 10 litres of water (roses); Mancozeb or Oxychloride (citrus trees).
Blossom Blight and Brown Rot affects plum-, apricot- and peach trees' individual parts. Blossom blight causes browning and wilting of blossoms, even cankers and dieback in the following season. Brown rot causes fruit to rot, after the brown spots. These two diseases cause fruit to dry out, packed with fungal spores they remain on the tree. Pick these and burn them.
Control: Weekly spray with Benomyl (Brown rot) or weekly spray with copper oxychloride (Blossom blight).
Botrytis Rot affects strawberries, guavas, grapes, tomatoes and gladioli when fungal threads of fuzzy grey follow brown or wet-looking patches.
Damping off affects any seedling, especially when planted too densely, stems flop over just above the ground.
Control: Drench the soil with Copper oxychloride.
Downy mildew affects lettuce, cauliflower, roses and other plants when fungal growth appears on leaves' undersides, foliage dies and plants defoliate.
Control: Mancozeb or Copper oxychloride.
Early blight affects tomatoes and potatoes especially in hot, humid weather. Black spots surrounded by yellow appear on leaves and defoliation occurs.
Control: Mancozeb and prevent with flood irrigation instead of spraying with water.
Fusarium wilt affects many flower species, beans, cabbage, tomatoes, onions and potatoes mainly during hot, dry periods. Plants start wilting and beans' roots are streaked red and die back. Cabbage leaves start yellowing from the outer lower leaves inwards. Potatoes and tomatoes have yellowing on the lower foliage, spreading up. Most of the foliage wilts and the plants finally die. Onions rot after the browning and wilting of foliage.
Control: Dust potato seed with Mancozeb, otherwise difficult.
Late blight affects potatoes and tomatoes mainly during hot, humid weather. White, furry layers appear on the leaves' undersides and brown blotches on the upper sides. A fast spreading disease. Control: Prevention sprays of Dithane or Virikop, two weekly, alternatively try a spray of 20g Bicarbonate of soda diluted in 10 litres water.
Leaf curl affects nectarines and peaches and causes discolouring and thickening on the foliage. The infestation starts with pink colouring, turning yellow and also thickens and distorts the leaf.
Control: Apply Virikop before the opening of buds.
Mosaic affects roses, many flowering species, beans, Cucurbits, Cruciferae, tomatoes and potatoes, distorting and discolouring their foliage. A "mosaic" of light- and dark greens appears on the foliage. Control: Keep aphids and weeds in control.
Powdery mildew affects many plants and fruit trees, Cucurbits, peas, tomatoes and lettuce, causing defoliation. The infestation starts with a white powder-like substance covering the leaves.
Control: Apply Triforine or alternatively try 20g Bicarbonate of soda diluted in 10 litres of water.
Rust affects geraniums, beans and many other plants. The leaves have a pale spot usually on the upper side of the leaf, with a corresponding patch on the underside with colours reminiscent of rust.
Control: Apply Copper oxychloride or Triforine.
Tomato-spotted wilt affects tomatoes, chrysanthemums and dahlias. Tomato plants' fruit are pale in colour and don't thoroughly ripen. The foliage is spotted orange between the veins and small brown spots on older leaves. Stems may be streaked brown.
Control: Keep thrips and weeds in control.
Treatments through Chemical Fungicides
Powdery mildew, brown rot, botrytis, white mould, rose black spot, azalea petal blight and dollar spot: Benomyl (withholding period of 3 - 21 days), sold as Benlate.
Fungal leaf spots and damping off in lawns and seedlings: Captab (withholding period of 1 day), sold as Kaptan, Orthicide or Merpan.
Lawn diseases and downy mildew: Chlorothalonil (withholding period of 3 days), sold as Daconil or Bravo.
Lawn diseases and leaf spotting: Propineb/triadimefon (withholding period of 3 days), sold as Bayleton A.
Treating potting soil and root rot: Quintozene (withholding period not available), sold as PCNB, Brassical or Terrachlor.
Citrus scab and melanose, leaf spot, downy mildew, peach leaf curl, damping off and rusts: Copper oxychloride (withholding period of 1 day), sold as Kopperspray, Blitox, Koprox, Cupravit etc.
Powder mildew on ornamental plants: Dinocap (withholding period of 21 days), sold as Crotothane, Karathane or Krotaan.
Botrytis, powdery mildew and rose black spot: Imazalil (withholding period of 1 day), sold as Fungazil or Fungaflor.
Brown rot (peaches), botrytis (grapes), purple blotch (onions) and other target spot diseases: Iprodione (withholding period of 7 days), sold as Rovral.
Late blight on tomatoes and potatoes: Mancozeb/metalaxyl (withholding period of 14 days), sold as Ridomil.
Trunk rot, root rot, collar rot (in citrus and avocados) and blight (potatoes): Metalaxyl (withholding period of 30 days), sold as Ridomil.
Late blight and downy mildew: Mancozeb/sulphur (withholding period of 7 - 14 days), sold as Fungikill, Protecta or Milrust.
Rusts on ornamental plants: Oxycarboxin (withholding period not available), sold as Plantvex.
Soil borne fungus such as fusarium root rot: Thiabendazole (withholding period not available), sold as Mertect, Tecto or Tecto flowable.
Damping off diseases: Thiram (withholding period of 14 days), sold as Thiram or Pomarsol.
Rusts, powdery mildew and black spot on roses: Triforine (withholding period of 3 days), sold as Denarin, Funginex or Saprol.
Dealing with Downy Mildew / Winter Garden Care: To Spray or Not to Spray? / Using Winter Annuals Effectively / Guidelines to Planting Seedlings / Februaury in the Kitchen Garden / Start a Kitchen Garden / Container Recipes / Garden Plants Perfect for Attracting Beneficial Insect Parasites and Predators / The Living World of Conifers / Preparing Roses for Spring / Pruning is Rewarding / Spring Seed Sowing / Spiders and Pesticides / Cold Blooded Wildlife: The Gift of Nature / Predatory Ladybirds: Nature's Solution to Aphid Control / Organic Plant Nutrition / Organics and Chemicals / Irrigation Practice in Landscaping - An Alternative View / Drip Irrigation in Landscaping