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Ascochyta blight research in field peas

Field pea, as with many other pulse crops, is susceptible to various foliar diseases. One of the most problematic diseases is ascochyta blight, caused by a complex of ascochyta pathogens. Although there are fungicide options available for control, research so far shows the results of control can vary considerably from year to year, making recommendations a challenge.

Ascochyta pisi is one of three main species, and seems to be on the rise. Photo courtesy of Randy Kutcher, University of Saskatchewan.

The Black Soil Zone Region in northeastern and north-central Saskatchewan has been particularly impacted by ascochyta blight in field pea in recent years. To try to find some answers, a three-year study was initiated in 2009 at three sites: Rosthern, Meath Park and Melfort. Led by Dr. Sabine Banniza, of the U of S Crop Development Centre (CDC), researchers wanted to evaluate the effectiveness of various fungicides on ascochyta blight in field pea. Researchers now have three years of data from three sites, with the final information from the 2011 sites still to be reviewed and analyzed.

“Although it’s a bit preliminary until we review all of the data, we are seeing similar results to studies conducted previously that show a variable response to fungicides from year to year,” says
Dr. Randy Kutcher, associate professor, Cereal and Flax Pathology, CDC. Kutcher is a collaborator on the project, managing the research at the Melfort site while at Agriculture and Agri-Food Canada (AAFC). “In some years, you can get quite a good response to fungicide in peas and then no response in the next year. We have seen responses with up to a 30 percent yield increase sometimes, but often no response, or in dry years even a yield decrease. This makes it almost impossible to make a recommendation on when growers will get a good response from fungicides.”

In the study, growers compared the fungicide Headline, with Serenade, a biological control product based on Bacillus subtilis. “The preliminary results of using Headline were variable, with good results in some years but not others,” explains Kutcher. “Serenade also produced variable results and overall didn’t seem to be as effective as Headline in control of ascochyta blight. Once all of the data is analyzed, we will be able to provide a final report on the results.”

In talking with growers, Kutcher understands that many regularly use a Headline fungicide application on their field peas for disease control, but also for improved crop standability. “I often hear from growers that when they spray peas with Headline, the crop stands up better. The concern is we don’t want to lose a good product like Headline because the fungus becomes insensitive to it, but on the other hand we understand that peas often are a challenge to harvest due to lodging and growers need to manage that aspect as well.”

Kutcher notes the results of this study so far are similar to earlier research conducted by AAFC in the late 1990s to 2001. Researchers looked at plant diseases of wheat, barley, pea, canola and flax in a four-year rotation cycle from 1994 to 1997 and a second cycle from 1998 to 2001. Dr. Karen Bailey, Agriculture and Agri-Food Canada, Saskatoon Research Centre, previously published results of the first four years, and Kutcher recently published the results of the second cycle.

“Although the data is from 1994 to 2001, the results clearly show the variability of yield response to fungicide application,” explains Kutcher. The study showed that the yield benefit from fungicide was variable, ranging from no effect on yield in 1999, to a substantial benefit (0–32 percent), depending on tillage system and rotation in 2000, to a yield decrease of 11 percent in the dry year of 2001. “In one year we got a fantastic yield response to fungicides in peas, in one year a moderate response, no response the next year and in a dry year there was actually a yield decrease, so not only have you spent money on the fungicide application, but you have also lost yield because of it.”

 This new CDC study confirms the results of the earlier eight-year AAFC study, and shows that trying to provide fungicide recommendations for field pea is very challenging due to the variability in responses from year to year. “Although researchers have been able to provide checklists to growers for diseases such as sclerotinia in canola, or for fungicide control in lentils, we just have not been able to do that with field pea because of the variability in results,” says Kutcher. “It is disappointing that we are unable to provide a lot of guidance to growers on the use of fungicides on field peas to date.”

Researchers are also looking more closely at the ascochyta blight complex and the three main species to try to find out more about the disease. Mycosphaerella pinodes is the main pathogen that causes mycosphaerella blight or ascochyta blight. Phoma medicaginis causes ascochyta foot rot and tends to cause the blackening at the base of the stem.

“The third species is Ascochyta pisi, which used to be more prevalent many years ago, but seemed to disappear with improved varieties. However, we are finding more of it across the province, and Robin Morrall has found higher levels of A. pisi in the southern part of the province compared to the north, which is surprising. We are not sure why and are curious to know if this pathogen is coming back.” Researchers will be finalizing the overall results of this three-year study and expect to report on their findings in the coming months.

For now, Kutcher recommends that growers rely on crop rotations, ensuring at least two years between field pea crops. Growers should also rely on past experiences when fungicide use paid off in field peas. Leaving a check strip is also a good idea to help assess fungicide response. Researchers hope to continue solving the puzzle of when to expect a response from fungicides in the control of ascochyta blight on field peas in Saskatchewan.

Root diseases or waterlogged soils?
In a second part of the study, researchers looked at root diseases and the use of various seed treatments, including Maxim 480FS, for control of Fusarium spp., Rhizoctonia spp. and other soilborne diseases, and Apron FL for control of root rots like Pythium sp., and a combination of Maxim 480 FS and Apron FL.

“Growers have been complaining the last few years that field pea crops are not yielding what they expect, and suspect that root diseases may be the problem,” explains Kutcher. “However, our research so far has not identified any significant root disease problems in any of our field surveys and no difference between plots with seed treatments and those no seed treatments. In some cases both treated and untreated plots were completely decimated.”

The problem may be related more to waterlogged soils than to root diseases directly. “Although we recognize growers are losing whole fields, and we have lost one foliar trial in Melfort because the soil was so wet, we don’t think it is because of root diseases,” says Kutcher. “The Melfort plot looked well until early July, then went downhill rapidly and within 10 days the crop was completely yellowed off.

So although there are pathogens in the soil, our preliminary findings suggest the problem is likely more a function of environment and waterlogged soils than root diseases.”