Ascochyta blight is a fungal disease that under favourable conditions can severely reduce field pea yields and cause crop lodging.
In 2005, field trials were conducted in north-central Alberta to evaluate pea yield response, thousand-kernel weight, standability and level of ascochyta infection of seeds when the fungicide Headline was applied.
Five sites were chosen in the Westlock and Barrhead regions based on beneficial management practices that made these sites suitable for experimentation.
The experimental design was a randomized complete block with four replicates for each of the sprayed and unsprayed treatments, with each plot approximately 60 by 25 by 30 metres depending on the size of the sprayer used.
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The selection of suitable sites was based on high plant populations with a minimum of 75 plants per sq. metre, good weed control, even crop emergence and high rhizobium nodulation. The Newbrook site had plant populations below the minimum requirement and was replaced by a site at Shoal Creek.
Starting at the end of June, an ascochyta prediction system was used to detect the level of ascochyta risk. It was based on canopy density, humidity, presence of disease symptoms and the short-term five-day weather forecast.
Four scores that were taken biweekly influenced when the plots should receive Headline fungicide. The decision to spray was made once the total prediction score reached or exceeded 65. Spraying occurred in the middle of July, depending on the scores at each site.
Following the Headline application, standability scores were recorded at the end of August for the treated and untreated plots to determine if the fungicide treatment was effective at reducing lodging.
The plots were harvested and yield was weighed in an electronic weigh wagon and compared between the sprayed and unsprayed plots.
In 2005, all locations reached the minimum 65 prediction score. The final yields revealed a significant yield increase from Headline application at all locations, ranging from 14 to 35 percent. The average yield increase from Headline application was 26 percent.
The thousand-kernel weights were compared between treated and untreated plots.
Three of the sites showed a statistically significant difference in terms of thousand-kernel weight between the treated and untreated plots, with the treated plots having larger seed.
Seed samples were sent to 20/20 Seed Labs to detect the level of ascochyta infection.
There was a slightly higher ascochyta infection level in the untreated seed samples of 10 percent versus five percent, but no statistically significant results were observed.
Due to the weather in 2005, no differences were observed in crop standability. The results showed that Headline was successful in reducing yield losses due to ascochyta blight and that the ascochyta prediction system proved to be helpful in predicting the onset of disease.
