To take preventative action (for example, fungicide application), crops need to be monitored early in the growing season so that diseases are identified early in their development and controlled before they reduce crop growth and yield. Some leaf diseases, (for example, downy mildew in peas, ascochyta on beans and yellow leaf spot in wheat), occur on seedlings and are often less apparent in spring. Hence an assessment at 4-8 weeks after sowing is necessary for these diseases.
Identifying disease on your farm may also point to the need to alter other agronomic management practices, such as:
- selecting resistant varieties
- widening the rotation gap between crop types
- avoiding planting susceptible crops next to the previous seasons infecting stubble
- the need to seek clean, disease free seed for sowing next year
- using seed dressings.
How to monitor leaf disease
- At 10 random sites along your monitoring path, place a 50cm ruler at random between two rows of crop
- Examine crop plants on both sides of the ruler carefully, examining all parts of the crop plants
- Identify diseases that are on the plants (see diagnostic tool links below)
- Rate the severity of disease on individual plants using appropriate rating scales, and estimate the per cent leaf area of the crop affected by each disease. In most cases the severity of leaf disease is given as the percentage of leaf area covered by the disease (% LAD).