Visual assessment
Scab monitoring and forecasting is an essential part of integrated disease management to rationalise fungicide use.
- However, it is not possible in the early part of the season to base decisions on fungicide use on assessment of visible scab because of the long time (up to three weeks at low temperatures) between infection and visible scab.
- Decisions on fungicide use are usually based on weather-related risks.
- Searches for and assessment of scab is still important, to check on inoculum levels at the start of the season and during the season; and to gauge the success of control measures such that any modification to spray decisions can be timely.
- Information on inoculum levels, classified as low, moderate, high is also an essential input for using ADEM.
- Visual monitoring of scab to meet the above criteria therefore should take place throughout the season.
Visual scab monitoring (20-50 trees/orchard)
| Time/growth stage (sampling unit) | Scab item | Threshold | Action |
|---|---|---|---|
| Dormant period whole tree | Wood scab | Presence | Remove during pruning |
| Whole orchard | Overwintering leaf litter | Easily found | Macertate to encourage breakdown prior to bud burst |
| Green cluster - pink bud whole tree | Scab on rossette leaves % infected trees | Presence ≤5 = low | Intensify programme |
| Early blossom – petal fall
whole tree
Mid May 10 rosettes on 4 branches per tree |
scab on rosette leaves, flowers, fruitlets % infected trees
scab on leaves, flowers, fruitlets % infected rosettes |
}5-20 = moderate
} >20 = high presence )
≤ 2.5 = low 2.5-9 = moderate >9 = high |
intensify programme
modify programme |
| Petal fall – harvest(every 2 weeks)extension shoots 4 per tree | scab on leaves/shoots% infected shoots | ≤ 2.5 = low2.5-9 = moderate >9 = high |
modify programme |
| Autumn – post harvest – before leaf fall10-20 leaves/tree | late scab on leaves% scabbed leaves | ≤ 3 = low
>3 = high |
macerate leaves, 5% urea before leaf fall |