As temperatures climb and buds break across Wisconsin, apple scab management is top of mind. Warmer weather trends are occurring across the state, and the next few days bring multiple predicted rain events, setting the stage for high-risk disease periods. Growers should stay alert and make regular use of the NEWA Apple Scab Model to time fungicide applications and avoid early infections that can impact fruit quality later in the season.

Ideal conditions for a scab infection event are occurring especially in the southern and central parts of the state of this week. Temperatures are expected to reach the 60s and low 70s with several rain events – these are ideal conditions for the apple scab pathogen to spread and infect. Looking at the NEWA models for several locations in the state, I’m also seeing several days with 6 or more hours of leaf wetness which is ideal for the apple scab pathogen to infect.

If your trees have already reached ¼” green tip or further, protective fungicide coverage is critical now.

Start with protectant fungicides to protect emerging tissue from early-season spores (i.e., ascospores).

• Mancozeb 3 to 6 lb/A – consult the label for pre-bloom/bloom and extended application schedule directions (choose a rain fast formulation!)
• Mancozeb + Syllit (1.5 pt/A)
• Mancozeb + Captan (2.5 lb/A)
• Organic options:
  • Sulfur
  • Potassium bicarbonate

Management During Tight Cluster:

As trees continue to develop, utilize protectants with systemic or locally systemic fungicides. Always rotate FRAC groups to avoid resistance.

Tank Mix with Mancozeb:

• Some FRAC 3 options: Cevya (5 fl oz), Indar (8 fl oz), Procure (16 fl oz)
• FRAC 9 options: Scala (5–10 fl oz), Vangard (5 oz)
• Inspire Super (FRAC 3 + 9; 12 fl oz)
• Organic Options:
  • Sulfur
  • Potassium bicarbonate
  • EcoSwing

The timing of your sprays is just as critical as the products you choose. Targeting sprays just before infection periods and making sure trees are covered ahead of rain will help reduce the buildup of primary scab and limit future pressure. Even one missed application during a high-risk window can lead to infections that persist all season. With the season off to a warm and wet start, proactive management is key.

Resources:

• NEWA Apple Scab Model
• Midwest Fruit Pest Management Guide
• Apple Scab Management: Starting Strong After a High-Inoculum Year

This article was posted in Apples, Disease and tagged Apple Scab, Apples, disease, Green Tip, Leslie Holland, Tight Cluster.