Plant disease is becoming a common issue because of short crop rotations and high yielding crops. Plants just like animals can get bacterial, viral and fungal diseases. Disease can happen in the leaf, stem, or even the root. Disease starts in the weakest or the most exposed part of the plant.
When plants are infected, they are robbed of nutrients and energy. With cereal leaf disease, the plants ability to produce food and energy is disrupted because photosynthetic area is reduced by leaf spots. The production capacity of your plants energy factory, the “healthy green leaf”, is diminished. Types of leaf diseases include blotch (septoria leaf, net, spot), leaf rust, powdery mildew, stripe rust and tan spot.
When disease infects the stem it blocks nutrient and water flow, which deprives the plant of nutrients and translates into smaller yields. Sclerotinia in Canola is a good example of a stem disease that cuts off nutrients to the pods and does not allow proper seed fill thus reducing yield.
The fundamental requirements for disease impact are the; host (crop), pathogen (disease), and environment. The disease triangle (Figure 1) illustrates that the crop, disease and environment must be present and conducive in order for disease to have a major impact on your crop.
High moisture levels, tight rotations and heavy stubble from previous crops are generally much more conducive to disease and correlate very strongly with the amount and severity of disease in a crop. For example rain in cereal wills often move the leaf disease from the bottom of the leaves up to the flag leaf. In cereals your flag leaf and 2nd last leaf are the main contributors to yield. This is why it’s very important to “protect the flag leaf” from getting leaf disease. Fungicides are protective, therefore you need to be proactive and prevent disease. With cereals you can start to see some of the leaf disease symptoms early. When scouting your fields look on the lower leafs for spots or striping. If you see disease developing you should consider spraying soon to stop the disease from moving up the plant.
Sclerotinia disease is much harder to predict because once you see the visual symptoms the damage is done and you are too late to spray. If you have a good canola crop and the environment is conducive to Sclerotinia you must spray proactively while the plant is still flowering. Sclerotinia fungicides are sprayed to protect the flower petals so that once they drop into the plant they are protected from disease. During harvest if you do have Sclerotinia the plants will appear white and often not produce any seed.
When you have a root disease like club root, it will inhibit the plants ability to uptake water and nutrients that are required for the plant to mature. This could lead to decrease in yield or even a completely dead plant. Currently there are no fungicides that control clubroot however you can purchase clubroot resistant seed varieties. It is important to have a clubroot management plant and a longer canola crop rotation can go a long way in reducing your clubroot risk.
It is important to scout for all of these diseases throughout the growing season and also note if you have any disease during harvest. Recent research done by SVF has shown strong yield responses with a fungicide application. We would be happy to go through this data with you and see if fungicide is a good fit on your farm. Fungicide application timing is different with every crop and the ideal timing will change depending on the disease pressure. With some crops, depending on disease pressure, you may even want to consider two applications of fungicide. Disease control is very important and it is something that needs to be monitored every year. Spraying fungicide can be the crucial last step to insure your crop’s yield potential is achieved! Talk to your local SVF agronomist for all of your fungicide and disease scouting needs.