As tar spot continues to spread northeast across Ontario's corn region, growers are looking to build a better defence against the yield-robbing leaf disease.

Crop genetics and fungicide will likely be the one-two punch growers use to control the disease, which is characterized by tar-like speckling on the upper surface of corn leaves. The fungal pathogen has been delivering yield hits ranging from 20 to 60 bushels per acre (in highly infected fields) since it was first identified in Indiana and Illinois in 2015.

Fungicide chemistry has been key to controlling the disease with a range of efficacious products delivering yield protection when applied at the VT/RI stage. Plant genetics also offer a defence but it typically takes longer to develop hybrids tolerant to a disease like tar spot that it does to formulate and test a fungicide. Seed companies have done a good job of testing current hybrids to identify products in their seed lineup that provide strong tolerance to tar spot as well those that are susceptible.

On this episode of RealAgriculture Corn School, host Bernard Tobin catches up with PRIDE Seeds product development manager Matt Chapple to look at seed company efforts to develop genetics and new hybrids that will give growers stronger protection against the disease. In PRIDE's product development nursery at Chatham, Ont., and throughout its nursery network, Chapple and the PRIDE team are working to ground truth the performance of inbreds with higher tolerance identified with help from molecular markers.

He notes that developing hybrids takes time because genetic findings have to move from the lab to the field where their effectiveness is tested in real-world conditions. He stresses that new genetics must be tested in field environments with known disease presence to accurately assess tolerance.

When new hybrids do emerge from the product pipeline, the goal is to deliver improved stalk integrity, better harvestability and the ability to mitigate huge yield losses that can be associated with tar spot infection. What's the timeline for commercial arrival of those hybrids?

Chapple says it will likely take at least five years before seed companies can really pump out commercial hybrids that are above and beyond the level of tolerance currently available in commercial seed lineups.