Monitoring establishing crops for leaf diseases

Crops should be monitored for leaf diseases in order to undertake appropriate control measures when first detected and to alter management strategies in subsequent crops that will minimise the impact of disease. An ability to identify the incidence and severity of disease is important if yield loss is to be minimised. Leaf disease can occur at any time in the crop growing season. Most leaf diseases reach their highest levels during the warmer moist conditions that occur in spring.

Cotyledon infection
Yellow-tan oval spots or lesions on leaves that become tan-brown in their centre with a yellow edge as lesions grow.
The blotches expand eventually covering the entire leaf.

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

  1. At 10 random sites along your monitoring path, place a 50cm ruler at random between two rows of crop
  2. Examine crop plants on both sides of the ruler carefully, examining all parts of the crop plants
  3. Identify diseases that are on the plants  (see diagnostic tool links below)
  4. 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).

Percentage of leaf area covered by Powdery Mildew

<p>Percentage of leaf area covered by Powdery Mildew</p>

Percentage of leaf area covered by leaf rust

<p>Percentage of leaf area covered by leaf rust</p>

Percentage of leaf area covered by scald of barley

<p>Percentage of leaf area covered by scald of barley</p>

Percentage of leaf area covered by Septoria Nodorum Blotch and Yellow Spot of wheat

<p>Percentage of leaf area covered by Septoria Nodorum Blotch and Yellow Spot of wheat</p>

Page last updated: Tuesday, 26 July 2016 - 1:22pm