6 November 1998

Dampness suits weed treatment by friendly fungi

WET weather this year has caused big weed control problems for organic growers. In future, however, damp conditions could help rather than hinder control.

Researchers at Aberdeen Universitys Centre for Organic Agriculture have already identified strains of fungi that could be used to attack important weeds.

Fat hen can be controlled with an Ascochyta fungus, for example, and one type of Alternaria is a specific pathogen of redroot pigweed (Amaranthus). Wendy Seel and Carlo Leifert have started trials across Europe to test their efficacy in the field.

The diseases spread very quickly, covering a weed plant within two to three days. "The younger the weed, the quicker the kill," says Dr Seel.

Treatments are best applied in the early evening or after irrigation. "It is essential to have high humidity, otherwise the fungal spores wont germinate," says Dr Seel. "Once germinated, they are quite resistant to dry conditions as they get all the moisture they require from the plant."

The fungi are highly specific so do not affect crop plants, but they also fail to control a wide range of weeds. That means they are likely to be best suited to large stands of a single weed, such as fat hen. &#42