From Permaculture in New Zealand website (permaculture.org.nz). Long list of prevention methods.
RECIPES FOR ORGANIC SPRAYS
Washing machine water Water from the washing machine can be collected and used directly on plants in the garden. This soapy water can be collected during the spin cycle and seems to work very well on tomatoes. Simply splash water over the plants to water and protect from a variety of pests.
Soapspray, Use for aphids, red spider mites, thrips 225g Plain soap 9 litres hot water Grate soap and dissolve in water, stirring well. Cool before use. After spraying infected plants gently hose down with clean water. Repeat as often as necessary.
Pyrethrum, Use for general insecticide for white fly, scale, thrips, leaf hoppers. leaf miners, borers, caterpillars, beetles Dried feverfew or Pyrethrum flowers Boiling water Pour boiling water over flowers and cover. Leave to seep until cool. Make small amounts at a time and use regularly after the sun has gone down, as this spray can harm bees. This spray should be pale in colour.
Garlic, Use for ants, spiders, white fly, Beetles, leaf hoppers, scale, citrus bugs (stink bugs), caterpillars, aphids, cabbage and tomato worms 4 cloves of crushed garlic 1 litre water Leave garlic to seep in water for several days before use.
Elderleaf, Use for fungal infections Leaves are boiled in water for 20 minutes. However, I recommend seeping in boiled water and leaving for a few days as the steam could be hazardous. Dilute solution to a pale yellow before use. Nettle tea, Use for white fly, aphids, leaf hoppers Cut tops of plants, leaving roots to re-grow Put leaves and stems in a pot with sufficient water to cover and bring to the boil. Boil for about 10 minutes. Cool, strain. Dilute to the colour of weak tea before use.
Seaweed tea, Use for mildew, fruit rot, rust and general feed Leave seaweed to soak in water for 2 weeks before use. Dilute to a pale sherry colour.
Comfrey tea, Use for rust Make as for Seaweed tea.
Chamomile tea, Use for rust Use fresh or dried flowers. Boil in water. Dilute until very pale in colour. Cool before use.
Horsetail, Use for mildew 1 Tablespoon dried or fresh horsetail 1 litre of water Boil for 20 minutes, then stand overnight or longer. High in Silica and vitamins so pour remains into the soil.
Bracken, Use for aphids Chopped fern covered in water left to steep for 2-3 days. Dilute to pale liquid.
Wormwood, Use for aphids, leaf hoppers, Use leaves over soil to deter slugs or make a strong tea. Seep in water for a fortnight. Dilute and spray to deter aphids, white fly, citrus bugs (stink bugs), caterpillars, flies and mosquitoes.
Onion spray, For spider mites, caterpillars, thrips Place onions in blender or chop. Cover in boiling water. Cool and dilute before use.
Chive tea, Use for mildew Dried or fresh chives finely cut steeped in boiling water until cool. Dilute and spray infected plants
Lettuce spray, Use for white cabbage moth Boil up leaves. Cool and dilute before spraying.
My own spray That worked miraculously well against white fly was made simply to give my plants a pick me up. But some how it cured the terrible infestation of white fly almost over night. It was probably the smell.
1 shopping bag full of seaweed 3 cow patties (fresh'ish) A few vegetable scraps Approximately half a bag of weeds Steeped in a large rubbish bin with lid. Fill to the top with water. Leave for approximately 3 weeks. Dilute to a pale tea colour and spray onto plants
BIOLOGICAL CONTROLS Biological controls can be artificially introduced however, plants that attract these insects should be planned for instead, as this ensures on going breeding sites and safe havens for the predator insects. The reason for no artificial introduction is a pure personal belief in leaving things to good planning and mother nature.
* Purchase disease free plants and seeds. Know your supplier. Do not be afraid of fungicidal coatings on seeds which will be direct sown out doors in cold soils, such as corn and peas. Seed borne disease can also be avoided by soaking the seeds for 15 minutes in a bleach soak (one teaspoon per quart of water) prior to sowing. * Use sterile well drained soil mediums. See article on soil mixes. Try to maintain a soil mix pH at the low end of the average scale, i.e. 6.4 pH is less susceptible to root rot than a pH of 7.5. Commercially prepared germination mixes usually have a pH around 5.5. As you water the seed pots and your seedlings with tap water (which in many municipalities is quite alkaline), the pH in your pots gradually increases as does the susceptibility to damping-off diseases. Know the pH of your tap water, and condition it if necessary to maintain a lower pH while the plants are still in the germination room. I prefer the use of vinegar at the rate of one tablespoon per gallon of water. * Plants must not have their crowns below the soil line. Seeds must not be covered more than 4 times the thickness of the seed. * Use plant containers with drainage holes, water from the bottom only, and avoid excess watering. Do not allow pots to stand in water as excess water cannot drain and the roots will be starved for oxygen bringing all growth to a halt. * Avoid overcrowding and overfeeding of plants. It is important to maintain constant levels of growth through proper lighting and complete control of the growing environment. * Avoid working with plants (taking cuttings or transplanting) when the soil is wet. Do not use water from ditches or drainage ponds or rain barrels in the germination room. * Avoid spreading soil from infested areas or tools which have been used out of doors. Disinfect tools and containers with one part bleach in four parts water or with 70 percent rubbing alcohol (isopropyl). * In the germination room, sow all your seeds on the surface of the media, then cover the seeds to necessary depth with a material which is less likely to harbor fungi than the media itself. Use one or more of the following seed toppings instead of soil mix: o milled sphagnum moss o chick grit o course sand or fine aquarium gravel o composted hardwood bark (steamed) * In the germination room, mist seedlings in communal pots or flats once or twice per day with water containing a known anti-fungal agent such as: o Captan (or other approved fungicide) especially if walls or floors are damp, or o Cheshunt compound, a copper/aluminum formulation, or o chamomile tea, or o clove tea, or o a one-time light dusting of powdered cinnamon on the soil surface, or o a one-time light dusting of powdered charcoal on the soil surface, or o if stinging nettle is endemic in your area, make a fermented infusion to use like clove tea. These last five actions are suggested by sufficient anecdotal evidence to prove the existence of a low level of fungicidal activity. I would not hesitate to use them in germination environments which have no history of damping-off diseases. * Rotate plantings on a 2 to 3 year schedule using plants from different families in order to starve out existing pathogens. * Provide constant air movement not tied in with the light timer. Air should move freely 24 hours per day, but not directly aimed at the plants. This helps the seedlings to aspirate, and excess soil moisture to wick. If you do everything else right but do not provide plenty of air movement, you will still get damping-off.
Joel Salatin has signs on his property that say "Trespassers will be Impressed!" Impressive tiny ad:
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