No abstract

Leek (Allium porrum L.) is an Important field vegetable in most of western and central Europe. Infestations of onion thrips (Thrips tabaci Lindeman) cannot be controlled with the range of insecticides now available in The Netherlands. Leek rust (Puccinia allii Rudolph) is now also difficult to control. Experiments in which no insecticides or fungicides were applied, were carried out to assess the effects on thrips populations and infection by leek rust when leek crops were undersown with subterranean clover (Trifolium subterraneum L.). To evaluate the economic aspects of this approach, both the quality and quantity of the leeks produced in the two systems were compared. Undersowing leeks with clover drastically reduced thrips infestations which was reflected in improved quality of leeks at harvest. Leek rust incidence was also reduced slightly by undersowing with clover and the quality of the leeks at harvest was also better. Although the quality of the leeks was improved when the crop was undersown with clover, the quantity of crop produced was reduced considerably as a result of plant competition.

The assessment of air quality standards for forest ecosystems requires proper knowledge about concentration‐effect relations of air pollutants for tree species. In this study, 2‐yr‐old Douglas fir seedlings [Pseudotsuga menziesii (Mirb.) Franco] were exposed to 23, 81, and 169 µg O3/m3 during 8 h/d, 5 d/wk for a period of 4 wk. After exposure, the trees were placed in an atmosphere containing 14CO2. Release of 14CO2 in the root/soil compartment was analyzed once a day and was regarded as an index of transport and utilization of 14C photosynthates. Respiratory release of 14C was temporarily inhibited by O3 during the first days following exposure to the air pollutant. Within 2 wk after the O3 treatment, 14CO2 in the root/soil respiration was the same in all treatments, indicating that trees were recovering from O3 injury.

No abstract

No abstract