As bloom wraps up across much of Wisconsin, many growers are beginning to shift their attention from blossom blight to shoot blight management. Reports of fire blight symptoms are already beginning to emerge in some orchards, and the warm temperatures forecast for the coming weeks may accelerate symptom development.

It is important to remember that blossom blight symptoms appearing now are generally the result of infections that occurred during bloom. While we cannot change those infection events, there are still several important management steps you can take to reduce disease spread and suppress shoot blight development throughout the remainder of the season.

Scout Apple Orchards Early and Often

The first step is regular scouting. Growers should begin walking orchards weekly, paying particular attention to highly susceptible cultivars, vigorous young plantings, and blocks with a history of fire blight. Look for:

• Brown or black flower clusters that remain attached to the tree.
• Wilted shoot tips that form a characteristic “shepherd’s crook.”
• Darkened leaves.
• Water-soaked or blackened shoot tissue.
• Bacterial ooze during warm, humid conditions.

Early detection often allows growers to intervene before infections move into larger scaffold limbs or the central leader.

Pruning Considerations

When infections are limited, removing strikes can reduce inoculum and prevent pathogen movement deeper into the tree. When pruning:

• Remove infected tissue well below visible symptoms (8-12 inches into the healthy tissue).
• Avoid leaving blighted shoots in the canopy.
• Remove or destroy prunings when feasible.
• Delay extensive pruning during periods of hot, wet or humid weather when bacterial spread is highly likely.

For larger outbreaks, aggressive pruning may not always be practical. In these situations, focusing on suppressing new shoot infections may provide the greatest benefit.

Managing Shoot Blight 

Apogee/Kudos (prohexadione-calcium) for Wisconsin Apples

One of the most effective tools available for reducing shoot blight susceptibility is prohexadione-calcium, sold as Apogee or Kudos.

These products function as plant growth regulators that suppress shoot elongation by inhibiting gibberellic acid production. The result is shorter, thicker shoots with more lignified tissue that is less susceptible to invasion by Erwinia amylovora.

Unlike antibiotics, Apogee and Kudos do not kill the fire blight bacterium. Instead, they make the host tissue less favorable for infection.

Applications are most effective when made early, typically between pink and petal fall when shoots are approximately 1–3 inches long. Because growth regulation takes approximately 10–14 days to occur, these products should be applied preventatively rather than after significant shoot blight is already present.

In moderate-risk orchards, a single application may provide adequate suppression. However, vigorous trees, highly susceptible cultivars, and orchards with a history of fire blight may benefit from repeat applications every 2–4 weeks.

Actigard (acibenzolar-S-methyl) for Wisconsin Apples

Another tool for shoot blight management is Actigard (acibenzolar-S-methyl).

Actigard functions differently from Apogee. Rather than affecting shoot growth, it activates the tree’s natural defense mechanisms through systemic acquired resistance. In essence, Actigard acts like a vaccine by priming the plant’s immune system before infection occurs.

Because Actigard requires time to activate host defenses, preventative applications provide the greatest benefit. Protection can persist for several weeks following application.

Benefits of Combining Apogee/Kudos and Actigard

Research has consistently demonstrated that combining Apogee (or Kudos) with Actigard provides greater suppression of shoot blight than either product alone.

This combination works because the products target different aspects of disease development:

For orchards with a history of severe fire blight, highly susceptible cultivars, or vigorous growth, tank-mixing Apogee and Actigard can provide a valuable integrated management strategy. Field studies have reported substantial reductions in shoot blight incidence when both products are used together.

Cost may be a consideration for some operations. In lower-risk orchards, Apogee alone often remains a cost-effective option.

Considerations for Organic Orchards

Organic growers have fewer options for managing shoot blight after bloom, making preventative management especially important.

Cueva and other soluble copper formulations may provide suppression when applied during bloom and early shoot development. However, these products can cause fruit russeting, particularly on sensitive cultivars, and should be applied cautiously.

Products such as OxiDate provide rapid surface sanitation but have little to no residual activity. Their greatest value is typically as a preventative tool prior to bloom or when inoculum levels are expected to be high.

Products such as LifeGard and Regalia stimulate host defense responses and may provide additional protection when incorporated into an integrated disease management program. These materials generally perform best when applied preventatively and combined with bloom-targeted biological products.

Wisconsin Apple Management In the Coming Weeks

The next several weeks will be critical for determining the overall severity of fire blight this season. As temperatures increase and shoot growth accelerates, conditions become increasingly favorable for shoot blight development.

While blossom infections that occurred during bloom cannot be reversed, growers still have opportunities to limit disease spread. Regular scouting, strategic pruning, and the use of tools such as Apogee, Kudos, and Actigard can substantially reduce shoot blight severity and help protect orchard productivity throughout the growing season.