Time to test pulse seed for Ascochyta

Researchers at Montana State University are seeing an increase in the number of samples of pulse crops containing actionable amounts of Ascochyta in 2011 as compared to 2010. This is probably due to delayed harvesting this fall. With pulse crops going into the ground soon, there is some confusion about the acceptable level of Ascochyta in the crop.

Ascochyta is a potentially serious fungal disease of pulse crops including lentils, peas and chickpea. The disease can defoliate plants and spread rapidly. One way to prevent Ascochyta blight is to plant fungus-free seed. To test seed lots for Ascochyta, send a sample to the MSU Seed Lab. The test takes ten days after the seed is plated, as the fungus needs to grow out of the seeds before it can be identified. Send seed to the MSU Seed Lab now to leave plenty of time to receive the results and make management decisions before planting.

While there are no definitive acceptable levels of the fungus, there are guidelines. There is a zero percent tolerance for chickpea because it is very susceptible to Ascochyta blight. Pea and lentil are more resistant, so MSU plant pathologist Mary Burrows recommends less than two to five percent Ascochyta in the seed for these crops. There are no definitive thresholds for disease development: a higher number may indicate a greater risk for disease development because more fungus goes into the field, but it does not necessarily mean the disease will manifest. Conversely, a low/zero number does not mean the disease will not occur. The disease requires a susceptible crop, the pathogen and a conducive environment.

If the level of Ascochyta is above the threshold, Burrows recommends using LSP/Mertect at planting. This is the only seed treatment fungicide with good efficacy against Ascochyta blight according to university trials. This is applied in addition to seed treatment to control damping off and root rots. Dynasty (azoxystrobin) can also be effective for lentils, but is not registered for peas and not recommended for chickpea since it's a strobilurin. The species of Ascochyta causing blight in chickpea in Montana and North Dakota is resistant to strobilurin fungicides. There are a number of fungicide options if disease develops in the field, but application soon after disease onset is critical for the control of this rapidly spreading disease.