Apple Scab

Apple scab can weaken the tree making it more susceptible to other insect or disease problems,

Apple scab is a foliar fungal disease caused by Venturia inaequalis. It is not considered a serious threat to crabapple or apple trees; however, repeated annual apple scab infections can weaken the tree making it more susceptible to other insect or disease problems. Apple scab can seriously reduce the aesthetic quality of apple trees; heavy infections can reduce growth, vigor, flowering and apple yields. Apple scab is dependent on cool, wet weather to develop.

Download Apple Scab Fact Sheet

Treatment Strategy

Minor apple scab is not injurious to the tree. However, severe apple scab infections will weaken the tree and make it unsightly.

Purchase Apple Scab Treatments Now!

Apple Scab Treatment Option 1

One method of apple scab treatment is to apply a fungicide, such as Myclotect 2 – 4 times in the spring as the leaves emerge. It is important to know that fungicide applications are preventive only and need to be applied as leaves emerge and then again 14 days later. Fungicides properly applied will be 95% effective for treating apple scab. Midsummer treatments after symptoms begin to appear will be unsuccessful.

Application Type – Foliar spray

DIY Product/Equipment Needed:

• Myclotect

• Hand pump sprayer with wand

• Gloves

• Safety glasses

Apple Scab Treatment Option 2

The use of a growth hormone regulator such as Cambistat® to minimize the effects of foliar diseases has been proven an effective apple scab treatment. Cambistat® reduces vegetative growth and increases the thickness of the leaf cuticle, making it more difficult for the disease to grow into the leaf. Unlike fungicides which set up a barrier on the leaf to fungal infection, Cambistat® works by physically changing the leaf structure. If you are looking for complete apple scab control, you will also need to spray with fungicides-  especially during wet springs. One treatment of Cambistat® is effective for 3 years.

Application Type – Soil drench

DIY Product/Equipment Needed:

• Cambistat®

• Measuring or diameter tape

Graduated cylinder measuring in mL

• Shovel

• Bucket or watering can

• Cambistat Soil Drench Kit

Apple Scab Treatment Option 3

Cultural practices can be an effective apple scab preventive treatment because they reduce the apple scab disease source. Raking and removing fallen leaves from your yard in autumn helps reduce spores. Each winter, prune suckers and branches throughout the crown to improve air circulation. Divert sprinkler heads away from the foliage of the tree. Constant moisture helps the apple scab fungus grow.

Apple Scab DIY Kit

For Apple Scab Treatment Option 1

Application Type – Foliar spray

DIY Product/Equipment Needed:

Myclotect

• Hand pump sprayer with wand

• Gloves

• Safety glasses


For Apple Scab Treatment Option 2

Application Type – Soil drench

DIY Product/Equipment Needed:

Cambistat®

• Measuring or diameter tape

Graduated cylinder measuring in mL

• Shovel

• Bucket or watering can

• Cambistat Soil Drench Kit

How Is It Spread?

• The apple scab pathogen overwinters in infected leaves on the ground from the previous year.

• In spring, overwintered spores (ascospores) mature and are discharged over a period of 5 to 9 weeks.

• Wind and splashing rain carries apple scab spores from infected leaves to new growth on nearby trees where new infections begin.

• In late summer or early fall,  primary apple scab infections produce secondary spores and create new infections, which can continue through the growing season during wet periods.

Susceptible Trees

All Malus species, including apple, fruit trees and flowering crabapples, and mountain ash.

Symptoms

• Brown to olive, irregular-shaped spots on the leaves in late spring.

• Spots become dark and velvety in appearance.

• Heavily infected leaves may become yellow and fall off the tree from late spring through late summer.

• Fruit may also be infected by apple scab and display similar symptoms to those on leaves.

Lookalikes

None

Related/Similar Problems

Girdling root syndrome; stem decay; insect damage

Timing

Leaf emergence (spring)

Urgency

Low

Risk of Spreading

Moderate

Back to Top