Ascochyta Blight can be a dangerous disease for lentil crops. And this season, SARDI is warning that the varieties PBA Hurricane XT, PBA Hallmark XT and PBA Highland XT need to be monitored particularly closely for disease outbreaks. Their testing reveals an increase in infectious isolates, so ensure you’re out there early and keeping an eye on things.

What’s so bad about it?

As you know, Ascochyta Blight is a common disease wherever lentils are grown and favoured by cool, wet conditions. The disease is driven by rainfall, which will spread and become more severe with each rain event.

The disease can reduce crop yields in wet seasons and will affect seed quality and marketability. When lentils are infected with ascochyta blight, the leaves, stems, and pods develop circular or oblong shapes, and tan spots with scattered small black dots appear. Severely infected seeds are shrivelled and have purple-brown stains on the seed coat. 

Seed photos below.

What’s new this year?

Currently, disease isolates that can overcome the resistance in PBA Hurricane XT, PBA Hallmark XT and PBA Highland XT are present. This is particularly important to Yorke Peninsula growers, where lentils make up a significant portion of crop plantings. If we don’t control the disease and keep growing the same varieties over and over, the resistance in these varieties will be overwhelmed. These isolates that can overcome the plant resistance genes will build up and become the dominate isolate of Ascochyta present in the area, posing a large threat to current varieties.

SARDI has advised that their testing of isolates in controlled environments in SA in 2021 showed that all isolates tested were able to infect PBA Hurricane XT’s. Not only that, but 79% of these isolates were able to infect at a moderate to high level.

Testing also revealed that 45% of the isolates infecting PBA Hurricane XT were able to infect PBA Highland XT at low (MR) to moderately high (MS) level.

Testing also confirmed that a new reaction group – a dual virulence between Nipper and Hurricane isolates – has emerged in the pathogen population.

In SA, 58% of isolates collected in 2021 and tested in 2022 have dual virulence. This is up from 51% last year, suggesting that the new reaction group may be being selected for in our growing regions.

Note, the takeaway here is that the resistance rating of MRMS may need to be downgraded, and previously resistant varieties are under pressure. It would be best if you treated your lentils with a high degree of caution regarding Ascochyta Blight risk.

What can you do:

Thorough monitoring of PBA Hallmark, Hurricane, and Highland XT’s is necessary this growing season to avoid yield loss.

It is important to be on the front foot and act quickly with fungicide applications. Ensure you apply one as a preventative spray before the disease takes hold, usually ahead of rain fronts that will splash the pathogens around.

Any rain event of 5-10mm or more can spread disease. And keep in mind that with a fungicide spray, you are only protecting the present growth – no new growth will be protected.

In saying that, the disease will not spread during dry periods, and you can hold off on fungicides while there is no rain.

However, if the disease is present and rainfall is coming, you need to apply a fungicide at podding to protect the developing grain.

There are multiple fungicide options to control Ascochyta blight in lentils, including: chlorothalonil, mancozeb, Veratis Opti and the newly released Miravis Star, which combines fludioxonil with pydiflumetofen. Please speak to one of our agronomists about which fungicide strategy is best for you.

Looking forwards to subsequent years it is beneficially not to have all your egg in 1 basket and grower a couple of different lentil varieties which have differing resistance genes/groups.

Read more on SARDI’s release here.