The influence of additives on efficacy of fungicide used at low dosages and residual effect of fungicides evaluated in field trials and pot trials

A nonionic water, a mineral oil and a vegetable oil have been tested in mixtures with reduced dosages (1/1, 1/2, 1/4 and 1/8) of Tilt top (propiconazole + fenpropimorph) in order to see if adjuvants could increase the efficacy on mildew. The mixtures were tested in 2 winter wheat and one spring barley field trials. Adjuvants effect on rainfastness was tested for both Tilt top and Tilt 250ec (propiconazole) in semi-field trials with artificial inoculalion of Septoria nodorum. None of the additives tested gave significant increases in mildew control or significant better rainfastness. Only a significant dose-response was measured when reducing from full to 1/8 ot the normal dose. This was seen in both field trials and semi-field trials. In the rainfastness trial 1/8 of the normal dose gave a relatively big reduction in effect if treated with rain (5 mm) 1 hour after application compared to the other dosages. Trials were carried out in both greenhouse semi-field set up and fields to investigate the residual effect of various fungicides. Bayfidan (triadimenol) and Corbel (fenpropimorph) used at full and reduced dosages (1/1, 1/2 ,1/4, 1/8, 1/16) in a greenhouse trial with artificial inoculation of yellow rust gave a significant difference between the residual effect of the two products. Full and 1/2 dose of triadimenol gave full preventive effect when infecting plants up to 17 days after spraying. Even 1/16 of the normal rate gave more than 50% control at that date. Corbel at full and half rate gave after 15 days only about 50% control. After 7 days the effect of 1/8 and 1/16 was less than 25%. In a semi-field trial using artiticial inoculation of Septoria nodorum (1, 6, 12, 18 and 24 days after spraying) the residual effect of Tilt top was tested for 1/1, 1/2, 1/4 and 1/8 of the normal rate. Full rate gave a preventive effect of 85% when measured 24 days after application. 1/8 of the normal rate gave a very reduced effect (48%) already one day after spraying while the other dosages gave a gradual reduction in efficacy. Field trials with reduced rates of broad spectrum fungicides (propiconazole + fenpropimorph, flusilazol + fenpropimorph) have shown that the level of attack at the time of application has a considerable influence on the residual eftect. Full dose has generally lasted for approximately 40-45 days. If the disease is developing very epidemically the effect will however not last for more than 25-30 days. Half rate lasts for approximately 30-40 days and only 20-25 days for severe attack. One quarter last for approximately 25-30 days and only 0-15 days for severe attack