Synergism of hydrogen fluoride and leaf necrosis on freesias

Continuous fumigation with HF at a concentration of 0.5 µg/m³ and intermittent fumigation with 0.3 µg/m³ aggravated leaf necrosis in freesia. In the cultivars Rose Marie and Royal Blue, symptoms of leaf necrosis develop earlier and increase in severety with these concentrations of HF. The agent of this disease has not yet been identified nor isolated. The normal symptoms are initially chlorosis and later necrosis but HF causes necrotic spots and stripes as the first foliar symptoms in the places where under uncontaminated conditions chlorotic spots would appear.