Disease Update: The latest about apple scab and more info for fire blight management

Posted: June 17, 2014

The primary infection period for apple scab is over. If growers are experiencing apple scab at this time, control measures will be needed throughout the remainder of the growing season to keep the disease in check. An option for fire blight management is also discussed.
Apple scab primary lesions producing spores

Apple scab primary lesions producing spores

Well, there is a little bit of good news this week… Primary scab infection is defined as the ascospores released from the overwintered leaves from the previous year’s infected leaves. Over the last two weeks, our spore counts from overwintering leaves have drastically dropped off, which indicates we are finished with the primary infection period for scab. If you made it through the primary infection period with no scab to be seen: Congratulations! This has been a tough spring, and if you are experiencing some level of infection, you will want to read on…. Whatever spores established on leaves and/or fruit during the primary infection period will produce additional spores called conidia in vast quantities. These summer spores can cause infection throughout the summer and we call this stage the “secondary infection period.” It is important to monitor your orchard for any scab infection that became established during the “primary” period because scab control will be needed throughout summer in order to prevent the disease from causing significant damage to fruit, especially since we continue to experience weather conditions ideal for infection.

A possible option to control shoot blight: Serenade Optimum

After the fire blight update went out, I received information about using Serenade Optimum to control shoot blight.  The product has been evaluated in New York with favorable results seen using the product on small trees, pears, and susceptible varieties. The recommendation is 1 pound/acre and can be applied on a 7-day interval when environmental conditions favor disease development.

What is Serenade Optimum and how does it work?

Serenade is a broad spectrum biological control agent, which is made from a unique strain of the bacteria Bacillus subtilis. B. subtilis occurs naturally in the soil, air, water, and decomposing plant material. The bacteria produce fungicidal and bactericidal molecules that can provide contact control or suppression of harmful fungal and bacterial diseases. The Serenade product brands have been popular products used to control diseases and many may be familiar with Serenade MAX or Serenade ASO.  All Serenade products are the same B. subtilis strain; however the concentration of the bacterial active ingredient is different. The amount of active ingredient for Serenade ASO is 1.34%; for Serenade MAX is 14.6%; whereas Serenade Optimum is more concentrated at 26.2%. When used as a foliar spray, the disease control activity of Serenade comes from the fungicidal and bactericidal molecules of B. subtilis. In other words: you are spraying the products the bacteria produce and not the bacteria itself onto your trees. Consequently, the Serenade products can be safely tank mixed with copper since copper has no effect on the bacterial ingredients. In addition, sunlight does not breakdown the activity of the product.

Additional info added to the Fire Blight Update

Over the last couple of days, I’ve received questions and comments about fire blight management. As a result, I am updating the article (as we speak) to include these few details I believe will be helpful.

When controlling for disease, weather and tree growth conditions need to be monitored at a local level within one’s own orchard. Before chemical products are applied, be sure to be in compliance by obtaining the current usage regulations and examining the product label. Product information can be easily obtained from CDMS. Specific chemical recommendations are in:

Contact Information

Kari A. Peter
  • Assistant Professor
Phone: 717-677-6116