THE POTENTIAL OF CULTIVAR MIXTURES IN ORGANIC LETTUCE PRODUCTION

H.J. Schärer
One major disease affecting yield of lettuce (Lactuca sativa) is downy mildew (Bremia lactucae), which may cause 100% crop loss. No plant protection product is registered in Switzerland against downy mildew in organic production. Most of the organically acceptable plant protection products tested did not show satisfactory disease control. However, there are other possibilities for at least partial prevention, e.g., complete elimination of crop debris, planting density, no overhead watering, fast drying after watering, early harvesting or using cultivar mixtures. Experiments with lettuce cultivar mixtures in the UK showed that mixtures might yield 10-15% more than the mean of components and significant reductions in downy mildew severity at harvest were observed on a susceptible cultivar. In two experiments, lettuce mixtures composed of six cultivars were grown in single cultivar plots and as systematically arranged alternating cultivars within each mixture plot. It was observed that, depending on the disease pressure and time of first infections, the reduction of disease in the mixtures was higher either early in the growing cycle or later in the season. At harvest, the mean disease level of pure stands was either higher or similar to the disease level in the cultivar mixtures. Highly susceptible cultivars were better protected in mixtures than cultivars with median susceptibility. A slightly higher trimmed head weight was observed in mixtures compared with the mean of the pure stands. Investigations with local dealers showed that the commercial quality of mixture harvest was accepted by the market. Cultivar mixtures have an influence on the development of downy mildew in a field and they might improve yield of a susceptible cultivar grown in a mixture. Therefore, cultivar mixtures can be one piece of the strategy against disease.
Schärer, H.J. (2008). THE POTENTIAL OF CULTIVAR MIXTURES IN ORGANIC LETTUCE PRODUCTION. Acta Hortic. 767, 159-168
DOI: 10.17660/ActaHortic.2008.767.15
https://doi.org/10.17660/ActaHortic.2008.767.15
Lactuca sativa, Bremia lactucae, epidemiology, yield, disease
English

Acta Horticulturae