Field Evaluation of a New Sequential Sampling Technique for Determining Apple Scab "Risk"

Area of Science:

• Plant Pathology
• Agricultural Science
• Entomology

Background:

• Apple scab (Venturia inaequalis) is a major disease in New England apple orchards, necessitating fungicide applications.
• Current management relies on action thresholds, but a simplified autumn sampling technique for predicting spring scab risk has been proposed but not field-tested.

Purpose of the Study:

• To evaluate the field efficacy of a simplified, sequential autumn sampling technique for determining apple scab risk.
• To compare the new technique's risk ratings with a traditional nonsequential procedure.
• To assess the impact of a delayed-spray strategy in low-risk orchards.

Main Methods:

• Orchards were assessed using the sequential sampling technique over three autumns (1999-2001).
• Risk ratings were compared to a nonsequential procedure and analyzed via simulation.
• Delayed-spray (post-third infection period or pink stage) vs. full-spray (green-tip) experiments were conducted in two orchards.

Main Results:

• The sequential sampling technique yielded scab-risk ratings consistent with the nonsequential method, offering potential time savings.
• Simulation analysis indicated risk ratings remained stable with variations in sampled trees or shoots.
• Delayed-spraying in low-risk orchards did not significantly increase fruit scab at harvest compared to early spraying.

Conclusions:

• The sequential autumn sampling technique is a reliable and potentially time-saving tool for apple scab risk assessment.
• Delayed-fungicide application strategies are viable for low-risk apple orchards, reducing unnecessary treatments.