In 1991, 1992, and 1994, 2,936 accessions of Pisum sativum from the USDA Plant Introduction collection were screened under field conditions for resistance to Mycosphaerella pinodes without replication due to seed supply. These trials were conducted at the Oak Park Research Station at Carlow, Ireland, where conditions are highly favorable for disease expression. In 1995, the 157 most resistant accessions were again screened at Carlow and at the Food and Crops Research Station at Gore, New Zealand, in replicated trials. At both locations, disease was severe and ranged from 20 to 100% foliar blight. Five accessions were as resistant as the commercial cultivar Radley at both locations: PI 142441, PI 142442, PI 381132, PI 404221, and PI 413691. No accessions were more resistant than the cultivar Radley.
The effect of the quinone outside inhibitors (QoI) azoxystrobin and pyraclostrobin on yields of winter wheat where QoI resistant Mycosphaerella graminicola isolates were dominant was investigated in field trials in 2006 and 2007. Pyraclostrobin significantly increased yields by 1AE57 t ha )1 in 2006 and 0AE89 t ha )1 in 2007 when compared to the untreated controls, while azoxystrobin only provided a significant increase of 1AE28 t ha )1 in 2006. These yield increases were associated with reduction in septoria tritici blotch (STB) development as determined by weekly disease assessments over a 7 week interval. The effect of pyraclostrobin on STB was studied in controlled environment experiments using wheat seedlings inoculated with individual M. graminicola isolates. Pyraclostrobin significantly reduced STB symptoms by up to 62%, whether applied 48 h pre-or post-inoculation with resistant M. graminicola isolates containing the cytochrome b mutation G143A. Extremely limited disease (<1%) was observed on similarly treated seedlings inoculated with an intermediately resistant isolate containing the cytochrome b mutation F129L, while no disease was observed on seedlings inoculated with a wild-type isolate. Germination studies of pycnidiospores of M. graminicola on water agar amended with azoxystrobin or pyraclostrobin showed that neither fungicide inhibited germination of spores of resistant isolates containing the mutation G143A. However, pyraclostrobin significantly reduced germ tube length by up to 46% when compared with the untreated controls. Although the QoIs can no longer be relied upon to provide effective M. graminicola control, this study provides an insight into why QoIs still provide limited STB disease control and yield increases even in situations of high QoI resistance.
SU MMARYField experiments were conducted between 2003 and 2005 to compare the efficacy of five interactive decision support systems (DSSs) (DESSAC, PLANT-Plus, proPLANT Expert, CerDis and Crop Protection Online (CPO)) and an in-crop system (Septoria Timer) to schedule fungicide applications to winter wheat cultivars (Madrigal and Claire) for the control of Mycosphaerella graminicola. The effectiveness of the crop management programmes proposed by the DSSs was compared with that of standard 2-spray programmes applied at GS 37 and 65 and 3-spray programmes applied at GS 32, 39 and 65. Compared with the 3-spray programme, the programme scheduled by CPO advised application of the least active ingredient to the six trials over three seasons, while together with the Septoria Timer it also advised the least number of applications (average 2 . 3 per crop). The PLANTPlus system advised the highest input of active ingredient and the highest number of applications (average of 4 . 0 per crop). The interactive DSSs responded to cultivar susceptibility to M. graminicola by scheduling more applications to the susceptible cv. Madrigal compared with the moderately resistant cv. Claire. Whether control of M. graminicola is expressed as reduction in the proportion of necrosis per leaf or a reduction of the area under the disease progress curve, the 3-spray programme provided the most effective control. The Septoria Timer provided a similar level of control. For the remaining programmes, the effectiveness of control varied with observation date, leaf and cultivar. The 2-spray programme provided the least successful control. Fungicide application significantly increased grain yield each season. The fungicide scheduling programme that provided the highest grain yield varied by cultivar and season. Grain specific weight was enhanced by fungicide application compared with the untreated control, except for cv. Claire in 2004. The fungicide scheduling programme that provided the highest specific weight varied with cultivar and season. The highest average margin over fungicide cost was provided by the Septoria Timer.
SUMMARYThe effects of varying the timing of nitrogen application and the frequency of fungicide sprays on the incidence of foliar disease and on the grain yield of winter barley (cv. Panda) were investigated at two sites in Ireland over three years, 1986–88. Nitrogen application timing had little effect on the amount of foliar necrosis due to disease but delaying application of all the nitrogen until April significantly reduced grain yields in two of the three years when compared with standard split dressings in March and April. The reductions in yield reflected small differences in 1000-grain weight.The number of fungicide sprays applied had significant effects on the amount of foliar necrosis and on grain yields. One-spray and two-spray programmes increased average yield by 16 and 32%, respectively. The yield increases were attributable to more ears/m2 and larger grains (greater 1000-grain weight). Fungicides also delayed the onset and significantly reduced the amount of brackling. Delaying nitrogen application in the spring did not decrease the number of fungicide sprays required to achieve maximum yield.
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