Apple scab protection strategies for early spring

By Blake Jackson

Apple growers are navigating a tricky weather situation as spring approaches. While temperatures remain cool, apple scab spores are developing and spreading just as green tissue emerges on trees. This creates a potential risk of infection even though the number of spores is currently low.

Fortunately, recent dormant copper applications should offer some protection for the trees. However, growers should be vigilant from March 30th to April 3rd, as the forecast predicts rain events that could trigger significant apple scab infection.

Here's a breakdown of disease management strategies for different stages of apple tree development:

Green Tip (half-inch):

• Recent dormant copper applications provide protection during this period.
• Mancozeb fungicide can be used alone or tank-mixed with other options like Syllit, sulfur, or potassium bicarbonate.
• It's highly recommended to use a rainfast form of mancozeb (Manzate Pro-Stick, Roper Rainshield) throughout this stage and the first cover spray. Rainfast formulations offer better disease control in wet weather. Non-rainfast mancozeb can be enhanced with a spreader sticker for increased resistance.
• Captan fungicide is another option, but it doesn't require a spreader sticker as it's already rainfast. However, captan mixed with mancozeb (captozeb) doesn't need an additional spreader.
• If using ziram instead of mancozeb or captan, a spreader sticker is necessary for rain resistance.

Tight Cluster:

• This stage marks the beginning of powdery mildew control.
• For dry conditions, focus on powdery mildew with fungicides like Cevya, Rally, Topguard/Rhyme, Procure, Torino, Gatten, or sulfur. Organic options include sulfur, potassium bicarbonate, and EcoSwing. Remember, dry weather favors powdery mildew, so even if rain isn't a concern, monitor the number of dry days above 53°F.
• Some strong powdery mildew products may not be as effective against scab. However, tank-mixing them with a broad-spectrum fungicide like mancozeb provides scab control during wet periods within dry stretches.
• Low-risk programs can utilize sulfur and potassium bicarbonate for combined powdery mildew and scab control.
• If wet and warm weather favors scab development, consider fungicides from FRAC Groups 3 or 9. Examples include Cevya, Indar, Inspire Super, Procure, Scala, and others.
• It's crucial to avoid FRAC Group 7 fungicides during this time. These are best reserved for peak apple scab and Marssonina blotch pressure later in the season.

By following these guidelines and staying alert to weather forecasts, apple growers can effectively manage diseases and protect their crops during this critical transition period.

Photo Credit: istock-rixipix