The Best of the Rest

Articles from print or electronic sources that deserve every exposure that they can be given.

Nature's Way

Noel Kingsbury, writing in June/July 2001 issue of 'The English Garden,' takes up the idea of self-sown plants (see "Last Year's Garden this Year" elsewhere), but deals with biennials and short-lived perennials that thrive in the temperate climate of his garden. He remembers the charms and the frustration of seedling appearances in unpredictable places, and has had the experience, that we must all have shared, of the irresistible attraction that gravel and a crack between paving stones seems to exercise for these wanderers.

While the main attraction for him lies in the semi-wild or cottage garden look that self-sown plants can give, he also values the changes in populations that develop season by season as some of the highly bred garden plants self-pollinate and cross to give a kaleidoscope of forms. A planting of a few colours of aquilegia will, season by season, give new colours, and the same is true of hellebores and astrantia. As they flower, the least desirable forms should be discarded so that only the best are thrown back into the crossing game. Some very interesting plants have been developed and selected in this way.

Some of the most reliable self-seeders for Mr. Kingsbury are : Alchemilla mollis, Dipsacus fullonum (teasel), Digitaria (foxglove), Eryngium giganteum, Foeniculum vulgare (fennel), Helleborus foetidus, Linaria spp. (toadflax), Lychnis coronaria, Oenothera spp. (evening primrose), Onopordon acanthium (Scotch thistle), Salvia pratensis, Silybum marianum, Stipa arundinacea, Stipa tenuissima, Verbascum spp., Verbena bonariensis.

Compatibility of pesticides with Biological Control Agents

The efficiency and ease of use of chemical controls makes them the first choice of most nurseries and greenhouses, but the advantages of biological pest controls is winning a place for them as well. Dr. Kevin Heinz of Texas A.& M. University, writing in the July 2001 Greenhouse Business, discusses the difficulties in combining the two systems of control, and suggests some guidelines.

The problem, of course, is that chemical pesticides are not often specific enough in their targeting to distinguish between friend and foe. With careful planning, the natural control organisms may be kept away from the chemicals in time or space. Releasing the natural control at an interval after the final application of a short residual pesticide may be effective, as may the use of such a pesticide when the control organism is in a resistant stage of its life cycle.

Spatial separation is possible if pesticide use can be made only to very restricted areas in the nursery so that the bulk of a control organism population is not exposed to the chemical.

There is some hope for the future development of pesticide-resistant natural controls, and extensive testing is under way to discover compatible chemicals for specific controls or for whole control programs He cites examples for particular crop problems and their controls, and is encouraging about the possibilities of incorporating both chemical and biological control into an integrated pest management program.

The final report on the grant from American Floral Endowment that was the partial funding for this work, is on-line at http://www.endowment.org/pr/heinz_finalreport.htm

Fungus Gnats

The small dark flies that alarm homeowners when they appear around their plants are more than just a nuisance to greenhouse operators.Greenhouse Product News, June 2001 issue has an article by Drs. Raymond Cloyd and Edmond Zaborski (of the University of Illinois and the Illinois Natural History Survey Center for Economic Entomology respectively) that reports work just beginning on controls for this insect.

Adults are found on the surface of the soil or resting under leaves. They live 7-10 days, and the females lay 100-200 eggs into crevices in the potting medium. Moist conditions that favor fungal growth on organic materials in the soil provide food for the developing larvae, but in the absence of fungal strands they will attack plant roots. The larvae are about 1/4" long, white with a shiny black head cap, and are most common in the upper 2'' of the medium.

Control is usually done with common greenhouse insecticides, but since some of these may be lost to the industry, biological controls have been tried with some success. A nematode, Steinernema feltiae, and a predatory mite, Hypoaspes miles appear promising. For the homeowwner, some control is possible with insecticieds, and the flies are also discouraged if the top layers of the soil can remain dry most of the time, to discourage fungal growth.

The authors are planning work that includes new techniques of assessing populations in order to evaluate the new combinations of control methods which they will test.

Greenhouse Product News has a web-site with a searchable archive of articles from back issues at http://www.onhort.com/onhort/

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