Sixty commercial pea crops were surveyed in 1995 to determine the causes of declining yields. Blackspot (Mycosphaerella pinodes and Phoma medicaginis var. pinodella) and downy mildew (Peronospora viciae) were prevalent in most crops and were identified as probable major contributors to the syndrome. Short rotation intervals (<5 years) between pea crops in paddocks were correlated with increased levels of blackspot and lower grain yields. Early sowing dates were correlated with increased levels of blackspot. A detailed survey of blackspot development was conducted in 5 commercial paddocks in 1996. The relative importance of sowing time and rotation varied between regions and seasons. The impact of a range of herbicides and the micronutrients manganese and zinc on blackspot, caused by the M. pinodes component of the blackspot complex, was investigated in a field trial during 1996. The herbicides diuron, metribuzin, and fluazifop significantly increased blackspot crown lesions compared with the nil treatment. There was a significant interaction between blackspot severity, herbicides, and the micronutrients manganese and zinc. Manganese concentration in pea plants was negatively correlated with the severity of blackspot crown lesions and positively correlated with severity of downy mildew.

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Didymella rabiei, the causal agent of ascochyta blight, survives on infected seeds and seedlings. Diseased seedlings originating from infected seeds occasionally serve as the source for primary infection in chickpea crops. Experiments carried out independently in Australia and in Israel provided quantitative information on the temporal and spatial distribution of ascochyta blight from initial infections and on the relationship between the amount of initial infection and the intensity of subsequent epiphytotics for cultivars differing in susceptibility to the pathogen. Disease spread over short distances (<10 m) from individual primary infections, was governed by rain and wind, and was up to five times greater down-wind than up-wind. Cultivar response to D. rabiei significantly affected the distance and area over which disease spread and the intensity of the disease on infected plants. At onset of the epiphytotic, the relationship between disease spread and time was exponential (P < 0.05; R 2 > 0.95) and the area of the resulting foci was over 10 times greater in susceptible cultivars than in resistant cultivars. Regression equations showed the relationship between disease severity and the distance from the focus-plants was inverse-linear for all cultivars tested (P < 0.05). A simulation model based on the experimental data revealed that even if primary infection is infrequent (less than 1% of plants), the consequences are potentially devastating when susceptible cultivars are used. The epidemiological information and simulation model generated by this study provide an increased understanding of the development of an epiphytotic in which the primary foci of disease originate from infected chickpea seedlings.

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