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Feed the soil organically to ensure healthy plants that are resistant to attack. Do not place diseased plants on the compost heap. Burn fruit tree prunings and use the ash as a fertiliser – the shoots are likely to carry mildew infections. Do not compost potato tops – they may carry potato blight. Always use clean plant pots and trays. Encourage beneficial predators. Other bacterial, fungal and virus diseases Plant Disorders And Their Treatment. Where physical pest control is not practical, you may have to use chemical control. Several organic pesticides will not harm your garden ’friends’ if used with care. Such pesticides are non persistent (active for only one day). Organic fungicides, such as Bordeaux Mixture, though not really organically derived but they are non persistent and still a useful tool in the wildlife friendly garden. The organic chemicals listed below are usually available under a number of manufacturers trade names.
Spray in the evening when many beneficial insects are asleep. Do not spray on open flowers because of possible harm to bees. Avoid spraying beneficial insects with non selective chemicals. Always read instructions & follow carefully. Antko and Flyko are pesticide free insect killers supplied in handy aerosol form. Brassica Collars will prevent attack from Cabbage Root Fly. Buzzline Bird Scarer will protect seedlings against troublesome birds. Bordeaux Mixture controls a wide variety of fruit & leaf diseases. Cat Stoppa Granules deter cats from delicate plants. Citrox is a good organic garden and greenhouse disinfectant. Environmentally Friendly Animal Scarers deter birds, mammals & pets. Growing Success Rat & Mouse is a natural vegetable food effective for rat & mouse control. Alternatively use a “live” trap or buy a cat! Enviromesh is a fine mesh netting that protects plants and vegetables without insecticides. Horticultural fleece will prevent attack from caterpillars. A Fleece ‘fence’ around crop controls low flying carrot fly. Garlic Barrier tricks insects in to believing they have come across a garlic crop. Humane Mole Traps are available to permit release of troublesome moles away from your garden. Ultrasonic mole repellers are also available. 1” Mesh netting 1.2 metres high and 30cm buried outwards will keep rabbits out of the garden. Natures Answer range of fungicides and insecticides are made from natural pyrethrins, fatty acids & sulphur. Pheromone traps can be used for Apple Maggot and Plum Moth. Safer Ant Killer contains natural plant oils suitable for organic gardening. Slug traps or Slug Stoppa granules provide effective slug control. Squirrel Stop contains natural plant extracts that are extremely distasteful and irritant to squirrels. Winter Moth Barrier Spray & Insect barrier glue protects against winter moth caterpillar, adult vine weevil, etc. Yellow Sulphur is effective against mildew and is used for bulbs, corms & tubers in storage. Ants are attracted by the honeydew excreted by aphids that causes sooty mould. They move the aphids to better feeding sites and overwinter adults & eggs in their nests. They effectively protect aphids, scale insects, whitefly & mealy bugs from predators. Ants uproot seedlings and even larger plants with their burrows. Strewing spearmint & pennyroyal will repel them. Growing mint or tansy by their entry point is also effective. Non-drying sticky bands & organic pyrethrin based ant killers are also effective. Aphids allow the plant sap to be pumped through them onto the leaves, resulting in sooty mould forming on the foliage. They also transmit viruses from plant to plant. Chives discourage aphids and nasturtiums, while being attacked themselves, usually keep broccoli clear. Ladybirds & hoverflies are the best control, so plant attractants such as Limnathes douglasii, buckwheat, and Convolvulus tricolor. Erecting insect hibernation boxes can boost overwinter survival. The pungent foliage of Tagetes & Calendula attracts hover-flies & minimises aphids. Various pyrethrin & horticultural soap based insecticides are available. (Never ever use detergent!). Use horticultural fleece to prevent attack. Use sticky traps to control whitefly. Whitefly infested plants can be sprayed with Derris (3x at 5 day intervals). Natural predators such as Lacewing larvae, Ladybird larvae, Aphidius and Aphidoletes can help provide good natural control. Apple Aphids. Spray with horticultural soap or pyrethrin based insecticide or derris at leaf. Spray thoroughly in pre blossom period & the ‘green cluster’ stage. Use a winter wash to kill over wintering eggs. Apple Sawfly larvae burrow into fruit causing a ribbon like scar. Remove & destroy affected fruits. Asparagus Beetle. Adults & grubs feed on shoots & foliage. Dust with derris as soon as seen. Usually in summer. Big Bud Mite. Gall mite attacks blackcurrant buds causing swelling and causes reversion virus. Remove & burn big buds in late winter & early spring. Always purchase certified stock. Birds. Use a humming line to deter birds from seeds & seedlings. Use environmentally friendly bird scarers. Use a fruit cage or netting cloche. Cover newly seeded lawns with perforated polythene. Cabbage Root Fly. Adult fly lays eggs around stem. Larvae burrow into roots. Use brassica collars. Carrot Fly. Plant onions, leeks & garlic nearby. The smell deters attack. A fleece ‘fence’ around crop controls low flying carrot fly. Caterpillars. Use horticultural fleece to prevent attack. Pick off by hand and destroy. Rub off eggs. Spray with derris. Bacillus thuringiensis is a naturally occurring bacterium, can be very effective if sprayed when caterpillars are feeding. Worst offender is Cabbage white butterfly – Plant Tagetes between the rows. The pungent foliage will deter them. Celery Fly. Leaves turn pale, then brown & shrivelled. Burn affected leaves. Chafer Grubs are the larvae of Scarab Beetle and feed on the roots of turf and pasture grasses, damaging roots and spreading disease. Symptoms are akin to drought or sress, infected turf wilting and browning. The grubs are soft bodied, white in colour with tan heads. Heterorhabditis, a natural predator, can give effective control. Citrus Gall Wasps lays eggs in new growth. Larvae cause swellings/galls on leaves. Cut out visible galls as soon as seen & burn. No effective control. Cutworms. Living just below soil feeding on plants at base. Hoe to 1 metre around affected plants to expose grubs & destroy. Encourage Ground beetles with groundcover plants. Earwigs crawl in the flower buds to nibble embryo flower. Although they damage flowers, they do feed on caterpillars, aphids, insects and moth eggs. They can be found resting during the day in narrow crevices. Put a flowerpot, with dried grass or leaves, upside down on a cane. Earwigs will crawl in and contents can be removed & burned once a week. Eelworms or Nematodes. Nematodes that are pests are too tiny to be visible but can cause considerable damage. Plant Tagetes between the rows. A secretion from the roots will deter them. Castor Oil plants & Calendula may also discourage them. Flea Beetles are tiny beetles that make hundreds of shotholes in leaves of seedlings & other plants. They dislike moist conditions so frequent watering is an effective deterrent. Interplanting with lettuce, spinach, mint or wormwood can deter them. Sticky flypaper waved overhead is very effective as they jump when disturbed. Leatherjackets. Fat, white ugly larvae that nibble the roots. Remove & destroy when digging & hoeing. Encourage Ground beetles with groundcover plants Leaf Miner. Pest burrows into leaves leaving characteristic ‘tunnels’ clearly visible. Remove affected leaves. Squash grubs by squeezing leaves. Mice. Use a humane mouse trap or buy a cat! New Zealand Flatworm is a relatively new pest which destroys all true worms & damages soil fertility. It can be attracted to worms as bait & trapped in buried jam jars & in piles of flat tiles, under bricks, etc. Mealy Bugs are similar to scale insect but more mobile. Bought in cryptolaemus predators are effective under glass. They are also attracted to potato shoots, where they can be sprayed with derris or horticultural soap. Millipedes. Cultivate soil regularly to expose to birds, hedgehogs & Ground Beetles. Moles. Various sonic mole repellers and humane traps are available. Or just appreciate the excellent pest control they provide & fine soil they leave behind! Onion Eelworm. 1 – 2mm adults move through soil & enter bulbs causing swelling & distortion. Grow brassica & lettuce for 2 - 3 years to remove host for eelworm. Effective weed control & good crop rotation essential. Burn suspect plants. Collect up leaves & debris to prevent spread by wind or shoes, implements, containers etc. Onion Fly. Plants yellow & die in summer. White maggots around roots. Hoe regularly to deter grubs. Female fly attracted to onion scent. Grow from sets. Plant carrots & parsnips nearby. The smell deters attack. Pea & Bean Weevil. Beetle make U shaped notches in leaves. Not usually a great problem. Lightly dust with derris if necessary. Pea Moth. Moth lays eggs in peas. Use horticultural fleece to prevent attack. Use derris if attack is severe. Pear Sucker. Pest damages buds & creates honeydew that forms sooty mould. Spray with insecticidal soap or derris 3 weeks after petal fall, repeating 3 weeks later & again after harvest if required Plum Sawfly. Caterpillars make holes in fruits. Pupae live in soil. Hoe regularly around tree to expose larvae for birds. Spray with derris. Rabbits. Use 1” mesh netting 1.2 metres high and 30cm buried outwards. Raspberry Beetle. Beetle feed on fruit causing malformation. They pupate in soil. Hoe around plants to bring pupae to surface for birds. Spray raspberries with derris when fruits turn pink, hybrid berries immediately after flowering. Spray blackberries with pyrethrum based insecticide when flowers first open (in evening to avoid bees) Sawfly. Small brown spotted caterpillars defoliate plants. Encourage birds, especially robins, for effective but not total control. Spray with pyrethrum based insecticide when required. Scale Insects are small disc like insects cling to leaves, which turn yellow and drop and are most troublesome under cover & on walls. Encourage beetles, lacewings & ladybirds that feed on the pest. Spray with soft soap or derris. Hand pick minor infestations. Metaphycus, a natural predator, are effective under glass. Sciarid Fly damages seedlings, rootstock and cuttings. The flies are often found in damp environments, the larvae feeding on rooting or young plant material. Steinernema, a natural predator, can control large infestations. Hypoaspis is suitable for small infestations. Slugs and Snails. Use a bird & animal friendly slug repellent. Slug tape is useful to protect container plants. Slug traps are also successful. Going out each evening with a torch is very effective! Attract hedgehogs. They eat hundreds of slugs. Use a Hedgehog house. Encourage birds, toads & frogs. Nemaslug, a natural predator, can provide effective control. Spider Mites attack plants under cover & in sheltered locations. They cover shoots with fine webbing and turn leaves a mottled yellow. They hate humidity so spraying water discourages them. Attract them on to sweet tobacco plants that can be removed & composted. Spray with horticultural soap & derris with derris 3 times at 6 day intervals (not with biological control). Bought in phytoseulis predators are effective under glass. Lacewings, ladybirds & hoverflies are the best control outside, so plant attractants such as Limnathes douglasii, buckwheat, and Convolvulus tricolor. Vine Weevils. Small white larvae with brown heads. Make up a solution of derris & immerse pots completely in it. Heterorhabditis, a natural predator, can be effective. Wasps are very beneficial in early summer, hunting insects in great numbers but become pests at fruiting time. Wasp traps are available but care is sometimes needed with siting to avoid luring bees. Puffing derris dust in the entrance can destroy nests. Whitefly can be a serious problem. Thin out flying adults with a vacuum cleaner. Sticky traps are also useful. Bought in encarsia predators are effective under glass but remove sticky taps before use. Outdoors, try growing hops, as they breed up stethosorus ladybirds that feed on whitefly. Large infestations can be treated with pyrethrin & horticultural soap based insecticides. Winter Moth. Wingless female moths crawl up tree to lay eggs between autumn & spring. Caterpillars feed on leaves in summer & over winter in soil. Use greasebands, fruit tree grease or glue during egg laying period. Wireworms. Thin, shiny, yellowish worms eating potatoes, carrots, etc. Grow a row of wheat in the rows to attract the pest, then dig up & burn. Old potatoes & carrots can be spitted on a stick to mark location & buried. Dig up & burn. Split old cabbage stalks. Push 6cm into ground near affected plants. Remove periodically & burn. Woodlice. Cultivate soil regularly to expose to birds, hedgehogs & Ground Beetles. Woolly Aphids. Living in colonies covered in a white waxy coating. Spray large areas with derris. Brush small areas with methylated spirits. Remove severely infested shoots before spraying & burn. Biological control can be applied. Botrytis (grey mould) Brown spotting followed by furry grey mould. Improve hygiene, ventilation. Avoid wetting foliage. Fertilise sparingly. Apply fungicide. Burn affected shoots. Cankers. Sunken, discoloured patches of bark form white pustules in summer & red fruiting bodies in winter. Remove & burn affected parts. New trees can be treated with an organic insecticide at time of leaf fall to reduce infection but otherwise not worthwhile. Be aware that new trees will develop canker if planted near other cankered trees. Do not over apply high nitrogen fertilisers. CLICK HERE FOR OUR NATURAL PREDATORS.
Leaf moulds. Leaves with yellow patches above, brown below. Grow resistant varieties. Spray once with copper fungicide to control. Sooty mould - Black fungus on foliage caused by sticky secretions from aphids. Control aphids & the mould will disappear. Leaf Spots. Brown spots appear in spring causing early leaf fall & reduced yield. Burn affected leaves. Spray with copper fungicide every 10 days.
Mildews. Pale grey coating on buds, leaves & shoots commonly caused by dryness at the roots and stagnant air. Good growing conditions & careful pruning to aid air circulation will reduce problems. Avoid watering onto the foliage. Many Alliums growing nearby may offer some protection, but this can take time to work. Remove & burn all diseased material. Seaweed based foliar feeds can make plants tougher & more resistant. Apply copper or sulphur based fungicide. Yellow Sulphur is effective against mildew and is used for bulbs, corms & tubers in storage. Rusts. Yellow, red, brown or black pustules on leaves & stems. Some rusts have alternate hosts, moving from one plant type to another. Burn infected foliage. Spray with sulphur based fungicide. Improve hygiene, ventilation. Avoid wetting foliage. Avoid poultry manure. Top dress with rock potash.
Wilts & Rots. Usually caused by soils based organisms which attack unhealthy plants, especially seedlings. Sow thinly, reduce watering, increase temperature, Water with copper fungicide. Yellow Sulphur is effective against mildew and is used for bulbs, corms & tubers in storage.
Other bacterial, fungal and virus diseases. Good hygiene, healthy plants & control of vectors spreading the disease. For example, removing the mite swollen buds from blackcurrants will help prevent reversion virus.
Plant Disorders And Their Treatment.
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