The effect of fungicides on seed yield and disease control in Italian ryegrass.

Under Belgian climatic conditions, the incidence of fungal diseases like mildew, crown rust and stem rust is much lower in seed crops of Italian ryegrass than crops of perennial ryegrass, because of the cleaning effect of the preceding forage cut and the much quicker growing rate of Italian ryegrass. However, in some mild and warm seasons, above diseases can give detrimental effects on seed yield, so a preventive fungicide programme would be very recommended in order to obtain consistently high seed yields over the years. Six different fungicides and an untreated control were tested on two tetraploid varieties of Italian ryegrass, namely cv. Meroa and cv. Salomé (more tolerant to crown rust); one fungicide application took place at early ear emergence for all three trials (2006-07-08). Only in the 2007-trial with very severe rust pressure, the most efficient fungicides increased seed yield by 22-25 % against the control (100%) and the tebuconazol-treatment (106.6%). Yield differences could be attributed to a healthier seed crop, i.e., less withered flag leaf and to a higher thousand seed weight. As both years 2006 and 2008 had very little disease pressure throughout the season, the best treatments (Allegro and Opera) resulted in a moderate seed yield increase of 6-7% in 2006, while 2008 did not give any yield response at all between the fungicide treatments and the untreated check. Seed yield, yield components and disease development are discussed and explained in relation to the seasonal meteorological conditions.