Monday , December 5 2022

How to identify and control soot stains and flyspeck in apples

Imagine this scenario with me: you examine your fruit trees, some that you have been growing for years. Much to your horror, most of your apples have nasty-looking sooty spots that can band together to cover all of the fruit, or spots that look like fly waste.

Extension agents often get panicked questions about these symptoms.

Top photo by Flyspeck courtesy of Katie Hargrave under CC 2.0. Below photo of soot stain courtesy of Wurzele under CC 4.0.

But there is good news! You can be sure that your fruits are in order, and these blemishes are only cosmetic. In fact, you can actually rub off many of them like a scratch on your car’s shiny new paint job.

This is fine if you only make apple sauce or apple butter with them, but what if you want to sell your apples? At Gardener & # 39; s Path we give you tips on how to prevent these diseases from affecting your trees and what to do if they occur.

What are soot stain and flyspeck?

First of all, it is important to understand that these symptoms are due to the activities of two different diseases. Sooty stain is caused by different types of fungi, while fly stain is caused by the fungus Zygophiala jamaicensis.

These two diseases are usually grouped together because they often occur together on fruit and are controlled in the same way.

Flyspeck manifests itself as a cluster of 6-50 black, shiny, slightly raised round dots. Sooty stain is what it sounds like – dark stains that can cover most of your apples.

A close-up of an apple showing signs of fly stain.
Usually Flyspeck is not that noticeable and most people who appreciate organically grown products don’t mind. Photo courtesy of Jerzy Opioła under CC 4.0.

One thing to remember if your tree is prone to this problem is that the symptoms will look a lot worse with light fruits. Especially when selling your apples, you should consider growing red-skinned varieties.

The process of the insidious disease

Sooty and fly stains are the most serious in cool, wet weather. In fact, one of the things that make your tree much more vulnerable to attack is when it’s dark and shady inside.

Top view of a stack of apples with signs of sooty stain.
As in this case, a sooty spot breakout can range from barely noticeable to extremely. Regardless of the severity, the apples are still edible. Photo courtesy of Jerzy Opioła about CC 4.0.

The worst infections occur when spring is cool and rainy. It rains in summer and the autumn temperatures are cool.

Your fruits can become infected at any time after the petals fall. However, this usually happens in the middle or late summer.

Sooty stain often begins to populate apple branches. However, the hyphae – long, branched structures that are the main growth method of fungi – can fragment. These fragments can fall anywhere on your apples, leading to this nasty infection.

Rub your fruit like a ghost

These infections are superficial, so rubbing your fruits can really bring you luck. You can often rub it off immediately!

While they don’t look like new, your harvest is definitely good enough to eat.

And if the grating doesn’t work, you can bleach your apples at any time.

Cultural control methods

There are steps you can take to limit these infections:

1. Manage blackberries

The fungi that cause these diseases can live on a variety of hosts – more than 50! However, They particularly like berries. One way to limit this disease is to control your blackberry spots.

A close-up of an intricate, messy blackberry bush.
Keep blackberries away from your apple trees like these wild blackberries. They can share fungal diseases and also help keep moisture. Photo via Shutterstock.

If you have wild spots, you should remove them in spring and summer. If you intentionally grow berries, plant them on the other side of a hedge.

2. Pruning

The fruits on trees that are pruned each year dry faster. If you want to use fungicides, they also penetrate the canopy more effectively.

A man on a ladder prunes apples in an orchard.
A strong cut not only promotes fruit formation and lets the sunlight reach the apples, but also lets the trees dry out quickly and inhibits fungal growth. Photo via Shutterstock.

3. Mow

This may seem strange, but low-hanging fruit often doesn’t dry well when grown in tall grass. Removing grass that grows near the base of your trees increases the likelihood of them drying, making them less susceptible to fungi.

Two rows of apple trees with a freshly cut strip of grass in between.
Keep your grass cut short to allow better blood flow and evaporation of water from across the area and to prevent fungal outbreaks. Photo via Shutterstock.

4. Thin

Apples that are large and grow in clusters can provide the mushrooms with a moist environment to thrive in and also prevent fungicides.

An apple tree with lots of fruits of different sizes.
Although it can be difficult for some beginners to start practicing, removing the smaller, undeveloped fruits can result in the higher quality fruits reaching their full potential. It also enables better air circulation to fight fungal diseases. Photo via Shutterstock.

Fungicides that let you control this ugly duo

There is a number of commercial fungicides that you can use to control these diseases. If you are concerned about side effects, some are “reduced risk fungicides”.

Two strobilurin class fungicides are promising for combating soot and fly stains. These include Kresoxim-Methyl and Trifloxystrobin. They are safer for the environment and human health, but still highly effective.

You should start the applications shortly after the petals fall and continue in autumn when the weather is cooler. Typically, growers apply the fungicides at 10 to 14 day intervals.

Now you know how to get rid of these diseases

The symptoms of soot and fly stains are extremely alarming. Fortunately, these diseases are superficial, and you may even be able to rub the evidence off your crop.

Although your fruits are good to eat, they can be difficult to sell. If your trees are prone to these diseases, consider red-skinned apples because the blemishes are less noticeable.

Fortunately, there are a number of cultural control methods you can use to prevent these diseases, and two relatively safe fungicides that you can use when needed.


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