By: Kristi Waterworth
Growing apples is supposed to be easy, especially with the many new cultivars that require very little care. You just need to water, feed and watch the tree grow — there are no tricks to apple growing, and yet some years it seems like nothing goes right. So what do you do if your entire crop turns black for no apparent reason? Keep reading to find out.
Sooty blotch fungus is a common problem in apple trees with poor air circulation or where humidity is high during the cool season. The fungus Gloeodes pomigena is responsible for the dark, smutty discoloration that makes affected apples look impossibly damaged. Fortunately for growers, sooty blotch on apples is a surface disease only; it may make your apples hard to sell at market, but if you’re eating them at home or canning them for later, a thorough wash or peel will remove all of the fungus.
Sooty blotch fungus requires temperatures between 65 and 80 degrees Fahrenheit (18-26 C.) and relative humidity of at least 90 percent to initiate germination. Under ideal conditions, infection can take place in under five days, but typically requires 20 to 60 days in an orchard setting. Repeated chemical sprays are often used to keep this disease at bay, but both sooty blotch and flyspeck, fungal diseases that tend to appear together, can be controlled in the home orchard with careful environmental modifications.
Once your apples are covered in black, sooty fungal bodies, there’s not a lot you can do but clean each fruit carefully before using them. Prevention is a lot simpler than you probably imagine. Sooty blotch appears when temperatures are warming and humidity is high, so removing one of those factors can stop this disease in its tracks. Of course, you can’t control the weather, but you can control the humidity in the canopy of your tree. Sooty blotch on apples is primarily a problem of under pruned trees, so get in there and prune that apple tree like mad.
Apples are generally trained to two or three main trunks, with a middle that’s open. It may feel counter-intuitive to prune a fruit tree, but at the end of the day, it can only support so many fruits, no matter how many branches it has. Removing excess branches not only increases air circulation, preventing the build-up of humidity, but it allows the fruits that remain to grow larger.
Thinning fruits soon after they begin to swell is another way to help keep sooty blotch down. Remove every second fruit to prevent fruits from touching and creating microclimates where sooty blotch can thrive.
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This fall we had numerous calls and emails about the unsightly look of apple fruit in the home orchard. This disease is known as sooty blotch and flyspeck, a fungal disease that only affects the appearance of the apples.
These apples have sooty blotch and flyspeck. A ruler is shown to convey size of fungus.
Sooty blotch and flyspeck is considered a complex of several fungi that usually occur on the same fruit. Sooty blotch appears as superficial, dull black spots or blotches that may merge to cover most of an apple. Flyspeck appears as clusters of 6 to 50 or more slightly raised, black shiny round dots that resemble fly excreta (frass).
Because the fungi that cause sooty blotch and flyspeck grow superficially on the surface of the fruit, losses are primarily through lowered quality. (The black discoloration can be removed by vigorous rubbing.)
Several cultural practices aid in the control of sooty blotch and flyspeck. Pruning, which facilitates drying, has been shown to reduce disease incidence and severity. The value of pruning, however, is somewhat dependent on the season. It appears to help more in dry seasons than wet seasons. Proper thinning of fruit is also helpful. These tactics combined with the use of protectant fungicide sprays can help reduce the cosmetic damage on the fruit.
Can the fruit be eaten? See the article Can Sick Plants Make People Sick?
Originally prepared by Paula Flynn, updated by Lina Rodriguez Salamanca
Sooty Blotch and Flyspeck are superficial diseases of apples found on the waxy apple cuticle. Sooty blotch appears as discolored gray blotches or smudges on the apple and in severe cases can cover a large portion of the apple as seen in the picture below.
Flyspeck consists of several black dots grouped together in circular areas on the fruit.
These diseases are caused by several different fungal species. The disease thrives in moderate temperatures (65-80°F) and extended periods of wetness making North Carolina summers conducive for disease development.
Over the years a lot of research has been done to determine ideal spray times using weather models. It has been determined that once a spore lands on the fruit surface approximately 273 hours of leaf wetness are needed before seeing noticeable symptoms. Ascospores, the primary inoculum are typically released during petal fall each year. Accumulated hours of leaf wetness are tracked beginning at petal fall to identify when to start spraying for sooty blotch and flyspeck during the summer months. The NEWA forecasting system has a model for sooty blotch and flyspeck and tracks hours of leaf wetness from the petal fall date entered by a grower. An example of the fly speck sooty blotch (fssb) model interface with NEWA is pasted below. There are only two inputs that need to be entered: Petal Fall date and Last Fungicide Application Date which have been circled in blue below. We don’t grow many McIntosh down here, so I’d suggest entering your petal fall date for an early cultivar such as Gala. You will see that the risk is LOW right now for fssb. That is because the ascopores are being released and for the most part are infecting hosts other than apple. After the initiation of fungicide sprays for the season for fssb, it’s really a residue game for keeping the disease under control. In Glomerella susceptible varieties, this shouldn’t be an issue, however, in cultivars where you may not be spraying as frequently, you may want to consider using the model.
Summer sprays will need to be continued as additional spores can land on fruit surfaces from nearby hosts throughout the season. Each spore or infection event will still require 273 hours of leaf wetness before seeing symptoms which is important to remember for planning out spray programs especially as harvest approaches. As an example, say a late season spray has been applied and the residues were rinsed off due to a heavy rain event, the fruit then has to accumulate 273 hours of leaf wetness from the date the fungicide residue was rinsed off until seeing symptoms on the fruit. This is important fact to think about as final sprays are made during the season. Topsin or other products containing T-Methyl have been standards for years for controlling FSSB. For the past two years in our fungicide trials here at MHCREC, our level of control with t-methyl has been marginal and not any better than Captan + ProPhyt. We’ve seen most success for fssb control with Aprovia, Inspire Super, and strobilurins tank mixed with a protectant
More information regarding products and amounts can be found in the 2018 Integrated Orchard Management Guide for Commercial Orchards in the Southeast. In addition to spraying, it is important to allow for better air movement in the orchard to help trees dry out faster. This can be achieved through pruning practices along with mowing and keeping the weed pressure down.
By Mark Gleason
Plant Pathology Extension
Iowa State University
One of the most common problems of apples in Iowa begins to show up just about this time of year. The sooty blotch and flyspeck fungi have been showing up since late August, as they often do after moist growing seasons like 2009.
These tiny creatures live above the skin of apple fruit, in the protective layer of wax. The wax layer is what makes an apple shiny after you rub it on your shirtsleeve. The fungi hunker down in the wax, sipping dribbles of apple juice that seep through the skin.
Sooty blotch and flyspeck (SBFS) seems harmless enough – unless you are a commercial grower who wants to sell your apples as fresh fruit. Then SBFS becomes a disease problem, since it can prevent you from selling your apples.
Sooty blotch and flyspeck may be as old as apples themselves. Drawings of apple varieties from the 1820s clearly show sooty blotch on every fruit. It wasn’t until sprayed-on pesticides, such as lime sulfur and lead arsenate, became popular around 1900 that consumers began to expect to buy apples without a heavy coating of sooty blotch and flyspeck. The cosmetically perfect apples found in today’s supermarkets weren’t common until the middle of the 20th century, when more effective organic fungicides appeared.
The names “sooty blotch” and “flyspeck” describe what these fungi look like on apples. Sooty blotch, as the name implies, shows up as dark brown to black smudges. The blotches range in size from half-inch-diameter circles to smears that can cover half the apple surface. Some blotches are so faint they are barely visible.
Flyspeck also resembles its name. Groups of several to 50 or more, shiny black dots cover more or less circular areas, from less than 1/8 inch to more than an inch in diameter.
An interesting twist to the SBFS story is that at least 60 species of fungi can cause these spots and blotches in the U.S. alone. Over the last five years, our research group at Iowa State keeps finding more and more new fungi in these smudges and spots.
Since many of these species look alike, nobody could tell them apart in the past. Even a microscope was not help.
Then, a few years ago, along came molecular genetics. By going down even deeper than a microscope could manage, down into their genetic building blocks, a whole new, diverse world of fungi came into view. Even though the SBFS species looked alike, many behaved quite differently. Like a book, you can’t judge a SBFS fungus by its cover.
As a result of our research, we are re-thinking everything we thought we knew about these humble fungi.
Back to your backyard orchard. How can an apple grower cope with SBFS in a less chemical-dependent way? We know enough about the biology of SBFS to point out some simple tricks to reduce disease risk.
One good principle is to keep the air moving. Give apple trees plenty of clearance, in full sun, and cut down any trees whose branches touch the apples’ canopies. Every year, sometime between January and the end of March, prune your apple trees.
Pruning is as much an art as a science, but it’s vital to allowing wind and sun to penetrate the foliage. Air currents dry the apples and leaves after a rain or dew, and dryness discourages the sooty blotch/flyspeck fungi. Mowing the grass and controlling weeds under apple trees also helps the apples to stay dry.
Another key to good air movement is to thin the fruit load early in the season. Within a few weeks after bloom, when the apples are still smaller than grapes, remove excess apples so that only one remains per six inches of branch. Apples on a properly thinned tree not only dry faster, but also get the right amount of sunlight to develop large size and good flavor.
The presence of raspberries or blackberries adds risk of sooty blotch and flyspeck. The sooty blotch/flyspeck fungi use the brambles to multiply. During a rainstorm, spores from the brambles float through the air and infect nearby apples. Since growing raspberries or blackberries near apple trees increases the risk of sooty blotch and flyspeck, try to keep apples and brambles as far apart as possible.
One of the apple tree diseases is Apple Scab, and this disease can infect the McIntosh, Cortland, and Macoun species.
The symptoms that appear are olive green dots or brown spots on apple leaves. Then the leaves will curl and eventually fall off. Likewise apples, dark green spots appear, dark and turn into scaly, some even cracked. Infection with this disease can cause fruit to fall and can inhibit the formation of new flowers.
What causes this disease? The cause is spores that escape from apple leaves, fall to the ground during winter, then these spores infect other apple plants that are close to it. This condition will get worse if there is continuous rain.
Take the infected apple leaves and remove or move them to another place in May. If you must uproot an apple tree, then remove it from your garden or burn the trunk for firewood. The University of Maine Cooperative Extension provided a solution to this, they mentioned using preventive sprays such as sulfur, fungicides and captan.
Infection can occur as early as Mai or when green tissue appears at the top. Throughout the rainy season, this disease will continue to spread.
Apple scab disease rarely kills apple trees. In severe cases, apple scab disease can cause defoliation in early summer. If this infection occurs continuously it can weaken the apple tree, and this makes your apple tree susceptible to various diseases.
Apart from apple scab, there is also an apple tree diseases called Sooty Blotch and Flyspeck. This includes dangerous diseases. To date, no apple tree is known to be immune to this disease.
Among the symptoms of Sooty Blotch and Flyspeck is a fungus that grows on the surface of the apple. This disease causes stains on the surface of the apples but does not damage the apples. These diseases often appear together in late summer.
Flyspeck is a fungus that appears coiled up on apples and is formed with small, distinct black dots. Sooty blotch forms irregularly shaped, olive green spots also appear on the surface of the apples.
After infection, this disease does not appear immediately, it takes a month to appear and appear clearly on the surface of the apple. Sooty blotch and flyspeck usually appears on dewy apple plants or apple trees that are not protected from high humidity. Apple trees with lots of morning dew are also the target of this disease.
The fungus that causes apple tree diseases is overwintering in the twigs of apple, pear, and woody plants. These spot spores spread to apples during the rainy season, they also spread into the air and it affects the surrounding apples.
One of the apple tree treatments for this disease is as recommended by UMaine Cooperative Extension. They apply fungicides from mid to late July. This implementation will be carried out again in August. At this point prune the apple plant and remove a few branches to allow air to enter.
The development of this disease will occur from August to September. The humid weather in this season will encourage the appearance of the sooty blotch and flyspeck.
This disease does not cause the apples to rot. Apples that have an impact are still safe to eat. It’s just that, the shape and color of the fruit no longer look fresh.
Cedar Apple Rust is an apple tree diseases that is prone to attack the Golden Delicious. However, there are several varieties of apples that are resistant to this disease such as Enterprise, Black Oxford, and William’s Pride.
The symptom of this disease is the appearance of yellow or orange spots on the leaves that are 1/4 inch in size. Over time, these spots then spread to the center of the leaf.
This is a disease that occurs when apple trees are planted near eastern red cedar and other types of juniper. These apple, juniper and eastern red cedar trees can spread disease between one another. So make sure you plant apple trees away from these types of plants to avoid possible cedar apple rust.
Throughout the winter, the fungus infects apple branches and galls on juniper trees. While in the spring, galls produce gummy, orange and gummy and this causes spores to be wet. These spores are then carried by the wind to a distance of 1 mile and hit the apple tree, this then causes your apple to become infected with disease. Then, in the summer, these spores then develop even more viciously and develop red spots on the upper scaly. These infected apple trees will then release these spores to hit your juniper and red cedar trees. That is what is called by infecting one another.
For the treatment and prevention of cedar apple rust, UMaine Cooperative Extension recommends using a fungicide that contains phenarimol or myclobutanil. So, the most important step is not to plant the host tree close to the apple tree. Check to see if your juniper and red cedar are infected with spores, pruning off the branches in early spring and removing the galls.
This apple tree diseases spreads during certain seasons, usually from April to mid-June.
This type of disease does not cause severe damage, but is very disturbing to your apple tree.
Another apple tree diseases is Powdery Mildew. This type of disease infects several types of apples such as: Jonathan, Jonagold, Bonza, Elstar, Lady William, Pink Lady, and Gala apples.
The symptom of this disease is a fungus that causes a white color on the leaves, this grayish white color can cause resistance to apple plants. This can cause the apple tree to grow kerdir, and the flowers that do not bear fruit, as well as the leaves and shoots sometimes turn brown in the summer.
The cause is the fungus present in the infected shoots over the winter. When spring comes, these buds open and they are covered with powdery spores. These spores are carried by wind and can infect the fruit, leaves and shoots of apples.
Infected branches and twigs are pruned at the start of the season. However, if the disease looks severe, you can use a gungicide.
This apple tree diseases likes hot as well as dry conditions. It spreads when buds open in the spring. This fungus does not kill the apple plant, but it inhibits fertilization which results in decreased apple production.
Some types of apples infected with black root disease are Empire and Cortland.
Symptoms of black rot are the appearance of frogeye leaf spots, rot on the fruit, and canker appearing on the branches. Apple leaves that are exposed to black rot will form spots like frog eyes. The edges are reddish and the center is brown. These brown, rotting spots are very common at the tips of the flowers. This disease causes the apples to shrink and dry out but still stick to the tree.
The cause of black rot is fungus. The fungus attacks the trunk, fruit and branches. Spore-producing structures called Pycnidia develop on exposed (infected) fruit. it appears as small black spots, when wet and cold conditions and winds carry the spores to other areas. This fungus can infect leaves, wood and fruit, through existing wounds. Apple trees are particularly susceptible to black rot when they are infected with fire blights.
Burn any infected branches or twigs, as well as any dried fruit. Everything is buried or burned to get rid of the diseases that exist in the branch. If you are destroying an apple tree, pluck the roots to make sure no spores are left. To overcome this blak rot do not use fungicides. However, you can use captan and sulfur products specifically produced to fight black rot. Prevent the formation of blight as it is a very susceptible cause.
The University of Minnesota Extension says that these leaf spots are not very harmful to apple plants. It doesn’t affect the health of the apples, but it can be a problem with apples if the leaves turn yellow and fall off. Take precautions and treatments for impacting apple trees as soon as possible.
White rot is a type of apple tree diseases that infects Golden Delicious, Jersey Mac and Empire apples. This type is susceptible to being compared with other types.
White rot or also known as “bot rot”, is a disease that infects apples caused by a severe fungal pathogen. It infects the twigs and legs, this is especially evident in the summer where the spots are small blisters. White rot infects the apples and stems, but it does not infect the leaves. If infected, the wood will be soft and the red fruit will fade.
Causes of white rot are dryness, winter injury or stress. Black pycnidia, or spore-producing structures develop on the surface of the cankers. From the fruit structure, spores come out and infect the injured stem, causing rot.
The treatment of apples from this disease is to remove any wood that is wilted and soggy. Trim dead wood and make sure the trees don’t stress. Remove blighted wood and water trees during times of dryness. This will keep the apple plant from stressing out.
This is an apple tree diseases that is common at the end of the season.
Be careful with this disease, if it attacks the apple tree, you may experience a 50% decrease in apple production. So, if you see symptoms of “white rot” on an apple tree, take precautions and treatment right away.
Prevent apple sooty blotch spoiling the appearance of your apples, using organic or chemical means described in our guide.
Published: Saturday, 23 March, 2019 at 3:00 pm
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Apple sooty blotch is caused by an overwintering fungus, which is typically found on trees or branches growing in shade and damp. It creates a splatter of dark, sooty spots all over the skin of the fruit, although the flesh isn’t affected at all and the taste doesn’t suffer. The spots can be easily scraped off.