make ideal houseplants. The hot dry atmosphere produced bycentral heating is very similar to environmental conditions in the desert! The plants generally have ...
Undergraduate projects in organic agriculture and horticulture This article, the third in a series, summarises the resuUs of some of the research projects carried out in conjunction with the HDRA, and published in Undergraduate Projects in Organic Agriculture and Horticulture (Volume 1, 1989), available from the HDRA
at£3.95, post free. A fundamental principle of organic growing is the rejection of modem synthetic pesticides. Bychoosing resistant varieties, growing healthy plants, and encouraging natural biological control, we aim to avoid the need to reach for the sprayer, so often the first resort of conventional growers. However, when all else fails, there is a range of safer chemicals such as soft soap or sodium bicarbonate, and natural products such as derris or pyrethrum, permitted by the organic standards controlling commercial growers and well known to organic gardeners. Many traditional herbal preparations have also been used for pest and disease control, although the latest Government regulations prevent us from recommending them. Over the years, the HDRA Newsletter has carried reports of the traditional use of plant extracts such as that of nettles or rhubarb against insects and elder against fungi. There is sound scientific proof to confirm the natural pesticidal properties of some of these plants while others remain entrenched in folklore with only anecdotal evidence to support the claims of their devotees. Two of our undergraduate projects last year involved the search for scientific evidence for the effectiveness of plant extracts as fungicides, while a third examined the natural herbicidal properties ofTagetes minuta (Mexican marigold). Mike Wing, at Coventry Polytechnic, used the highly concentrated oils of mint and garlic to try to control barley powdery mildew in a standard greenhouse test which shows up formulations likely to be useful as
38
general fungicides. Being oils, these extracts must be mixed with a wetting agent before they can be diluted with water. Savona soft soap, a liquid seaweed extract marketed by Asco Products of Holland, and Nuftlm-P, a pine resin extract, were all used as wetters. As we have observed in other similar experiments, each of the wetting compounds alone caused a significant reduction in disease levels. Mint oil mixed with NuFilm- P gave excellent mildew control, being appreciably better than the NuFilm-P alone, but high concentrations of mint oil damaged the young barley plants. Reasonable disease control without plant damage was obtained with 2 parts ofNuFilm-P and 1 part of mint oil to 200 parts water. Whilst definitely antifungal, garlic was less effective than mint and may well taint edible food crops with which it comes into contact. Jacqueline Bond, also at Coventry Polytechnic, employed a different approach, testing the effects of plant extracts directly on the growth and spore germination of three fungi. Two of these were species of the troublesome Botrytis group, Botrytis fabae, which causes chocolate spot on broad beans, and Botrytis dnerea (grey mould) which attacks a wide range of fruit, vegetables and ornamentals. The third fungus was AspergiUus niger. Oils extracted from garlic, mint, nutmeg and Mexican marigold all had significant effects on at least one of the fungi, as did the pine extract NuFilm-P. Extracts offresh leaves of elder, New Zealand spinach or walnut, and of dock roots and onion bulbs, all failed to reduce fungal growth or spore germination. Tagetes minuta is well known for use in weed control. T agetes is generally thought to act by releasing inhibitory substances from its roots into the soil and great success has been claimed in controlling ground
elder. Other reports suggest promising activity against nematodes, insect pests and fungal diseases. In laboratory experiments at Durham University, Tim McGarraghy confirmed the observations of HDRA members over many years, that the survival and growth of ground elder is reduced by Tagetes growing nearby. Tagetes was also grown in liquid culture to collect any inhibitory chemicals released by the roots. A very sensitive assay was used to test for these compounds, in which pollen grains of
plants were germinated in the presence of the test liquid. A failure of the pollen to germinate indicates the presence of natural inhibitory substances, and the Tagetes liquid prevented the germination of pollen from three test plants, confirming the weed control properties of this remarkable plant. No doubt many further uses ofTagetes remain to be discovered by gardeners and the seed is available through the HDRA 1990 Organic Gardening Catalogue.
Phil Harris
Brighten your lounge and the world's deserts! The Drought Defeaters Project is actively involved in supplying tree and shrub seeds to drought susceptible areas of the world. We are providing seeds to twenty-two different countries. To date we have handled over 200 woody species, with our collection of seeds expanding rapidly. Many of the seeds we send overseas are purchased from commercial seed merchants with the unusual and rare species being procurred from members, botanical gardens and any other contacts we can find. A small sample of each is grown up in the laboratory to check the seed and then to carry out tests on the plant. Usually, after the bulk of the seed has been used to grow our trees, we are left with a few grammes of each species. Many of these drought tolerant species make ideal houseplants. The hot dry atmosphere produced by central heating is very similar to environmental conditions in the desert! The plants generally have very interesting and delicate foliage and could provide unusual and attractive houseplants. A few are hardy enough to be grown on the patio and several have proved to be excellent bonsai trees.
In exchange for a donation to the Drought Defeaters Project we will supply a small sample of five different species from our collection for you to try. The package will include growing instructions. The plants will need minimal watering and feeding but maximum sunlight. We cannot fully guarantee the survival rate of the plants. However, all the species have been through our tests conducted at Coventry Polytechnic. Please send donations to 'Houseplants' Drought Defeaters Project, HDRA, Rvton-on-Dunsmore, Coventry CV8 3LG. The money collected will go back into purchasing more tree seed for planting in the true deserts of the world, so please be generous.
Jackie Gear 39
