How to accurately monitor and identify cereal foliar diseases 

It’s that time of the season where if you’re not on the ball and checking crops regularly then disease can take off and ruin your potential crop yields. We don’t want that to happen. Here are our top 5 tips on how to accurately monitor and identify foliar diseases.

1. Know what to look for.

Firstly, know what damaging diseases may be present and what they look like. For example, you should be looking for:

In wheat: Septoria tritici blotch, yellow leaf spot & rusts 

In barley: Spot form net blotch, net form net blotch, powdery mildew, rusts and scald.

Secondly, be aware of what other factors can cause leaf disorders such as herbicides, nutritional disorders, insects, and environmental stresses.  

Thirdly, look for telltale patterns in crops. These will appear as patches, uneven distribution in the canopy height, alignment with sowing, spraying, waterlogging areas, headlands, fence lines, etc.  

2. What you need.

We highly recommend having an identification guide nearby in the ute, which is particularly helpful for minor diseases. 

The best: We recommend Cereal leaf and stem diseases by GRDC. This guide also includes necessary information on biology and control. 

Other alternatives: Cereal diseases – The Ute Guide (GRDC). A quick but limited visual guide. 

Wheat and barley leaf diseases – The Back Pocket Guide (GRDC). A quick guide that helps key out problems based on symptoms.  

3. When to survey crops.

Early (seedling to tillering) surveys required for yellow leaf spot and insect damage. 

For leaf diseases (except the rusts) to be severe in spring, they need to establish in the crop by late tillering or by the first node stage. Therefore, conduct surveys at this time for scald and the net blotches in barley, and Septoria tritici blotch in wheat. These diseases will generally occur throughout the crop. If the disease is well established in the crop, a decision about spraying to protect the upper canopy during grain filling can start to be considered. 

Weekly inspections should occur when rust is known to be around and where susceptible crops are grown. Rust diseases can go through one generation every eight days in ideal conditions, and severe damage can occur soon after rust is first seen in very susceptible (VS) varieties. Before rust is reported in the district, inspect susceptible varieties every 2-3 weeks during winter and then more frequently in early spring. 

Other disease problems can become apparent at any time throughout the season. Monitoring should be done on a regular basis, depending on seasonal conditions and risks. In wet, humid conditions, monitoring should be done fortnightly. Under dry conditions where yield potential is low, less frequent monitoring should suffice. 

4. How to survey a paddock. 

There are two types of surveys that could be required depending on the diseases present. 

A. Damaging diseases with long-distance dispersal – i.e. Rusts 

These require frequent inspections. During winter and early spring, stripe rust first appears in “hot spots”. There may only be a couple of these in a crop, but they can spread very rapidly. Until about two weeks after flag leaf emergence, stripe rust will be on the lower leaves and hard to see under the healthy younger leaves. Therefore, it is best to monitor throughout the crop if stripe rust hotspots are known to be in the region. Other rusts tend to occur generally through the crop, so less area needs inspecting. It is best to monitor areas of high yield potential and where crop humidity is highest. 

B. Splash dispersal and less damaging diseases – i.e. Scald, YLS, Septoria, SFNB, etc 

Only requires localised monitoring. Areas to sample are along the edges of paddocks where infected stubbles remain in nearby crops and in areas of high yield potential where humidity is the highest. 

If you check ten random locations, each with two plants, and it reveals no symptoms, then the level of disease incidence is likely to be below 5% and therefore of no immediate concern. An exception is if rust is known to be nearby and conditions are favourable, then 20 random locations should be sampled. Where levels greater than 5% are recorded, then weekly monitoring should be used, and spraying could be considered if seasonal conditions and varietal susceptibility are likely to favour the development of the disease. 

6. Know the importance and understand the biology and dispersal of pathogens 

When looking for damaging diseases, you should be aware of the origins and dispersal mechanisms of the pathogens. Check out the table below for details on each disease and what you should be looking for.

Why are these important? Well, if you know the survival mechanism, it will help you to plan how to avoid disease risk situations. If you know the dispersal mechanism of a pathogen, it will help inform you of the likelihood of a disease appearing in your crop at different times of the season. 

And knowing what sort of environmental factors will increase diseases will help inform you whether a fungicide spray is likely to be economical and when to apply one. 

Table source: GRDC GrowNotes