My Blackberries Are Rotting: Reasons For Fruit Rot Of Blackberry Plants

My Blackberries Are Rotting: Reasons For Fruit Rot Of Blackberry Plants

By: Mary H. Dyer, Credentialed Garden Writer

What are my blackberries rotting? Blackberries are vigorous and easy to grow, but the plants may be afflicted by fruit rot, a common fungal disease that affects various fruits and ornamental plants in moist, humid environments. Fruit rot of blackberry is difficult to control once the disease is established. Read on to learn about blackberry fruit rot causes and steps you can take to prevent this pervasive disease from occurring in your garden.

Reasons for Rotten Blackberries

Blackberry fruit rot is caused by Botrytis cinerea, a fungus that can affect nearly every part of the plant. Fruit rot favors humid environments. It is especially prevalent when weather is wet before and during blooming, and again when berries ripen.

The fungus overwinters on plant debris and weeds. In spring, the spores spread via wind and water, including moisture from dew, fog, rain, or irrigation water, or by direct contact with plants. Once fruit rot of blackberry finds its way into your garden, it can be treated and reduced but not eradicated.

Recognizing Blackberry Fruit Rot

If your blackberries are rotting from botrytis, the blackberry fruit rot displays as a watery rot followed by a hairy, gray, or brown fungal growth. Flowers will appear brown and shriveled.

Blackberry canes may look bleached with whitish-brown lesions. Small, black patches may appear on any part of the plant. Unharvested berries left on the vine become mummified.

Preventing and Treating Fruit Rot of Blackberry

Site blackberries where the plants are exposed to direct sunlight. Ensure the soil is well drained. Never plant blackberries in low areas where water pools.

Spread a layer of straw or other organic mulch around blackberry plants to prevent fruit from direct contact with the soil. Space plants far enough apart to provide ample air circulation.

Avoid high-nitrogen fertilizers, especially in spring. The fertilizer produces dense foliage and shade, thus preventing rapid drying. Adjust your irrigation schedule, if needed. Water blackberries with a soaker hose or drip system and avoid overhead watering. Keep the plants as dry as possible.

Practice good weed control; weeds limit air movement and slow drying time of blooms and fruit. Keep the area clean.

Pick blackberries frequently and don’t allow fruit to over ripen. Harvest in the morning as soon as the plant is dry. Refrigerate berries as soon as possible. Discard rotten blackberries carefully. Never leave them in the garden and don’t place them on the compost pile.

Chemical fungicides may be effective when used in conjunction with the above techniques. Check with your local cooperative extension office to determine which product is suitable for your area. Don’t overuse fungicides. Strains are already resistant to certain fungicides in several regions, including the Pacific Northwest.

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Fresh blackberries picked straight from the vines in your garden are a delicious summertime treat. Blackberry (Rubus fruticosus) vines may have stiff arching canes or long, limber canes that need a trellis for support. Hardy in U.S. Department of Agriculture plant hardiness zones 5 to 10, blackberry canes grow one year, bear fruit the second year and then die. This is the normal growth pattern for blackberries, but several fungal diseases can cause the unexpected death of blackberry plants.

2 Answers 2

You may have a problem with raspberry beetle, which does affect blackberries too - it causes parts of the berries to dry up, as yours have done, although I've never seen whole berries so badly affected. Sunscald in the UK doesn't seem likely, but actually, the recent heatwave may have had some effect, though as its so recent, I suspect not. Its worth cutting open a few of the affected fruits, both those which are completely dry and those which are partially dry to see if there's a grub inside, which would confirm the presence of this pest. Information below

There is some possible evidence of red berry mite too, which causes uneven ripening of fruits, but that's difficult to identify for sure because its still relatively early and the fruits may not yet have fully ripened anyway. Information regarding this pest here

As for the presence of ants, they might be after damaged fruits for the their juice, or they may be present because of aphid infestation on the plant, so a close inspection to determine whether there are aphids anywhere is a good idea.

This Is What Eating Moldy Fruit Does To Your Body

Summer is here, and that means we’re all probably going to be eating a lot more fresh fruit as so many beloved options come into season. We’re talking strawberries, raspberries and blueberries, as well as peaches, plums and blackberries. But all this fresh produce also means that we’re going to be coming across a lot more moldy fruit.

As fruit starts to go bad, mold is almost inevitable. But before you start throwing everything out at the first sign of a little mold, hold tight.

We talked to Marianne H. Gravely, senior technical information specialist on the food safety education staff at the USDA, and asked about the dangers of eating moldy produce (and how to handle mold when we see it).

What happens if we eat moldy fruit?

Most of us don’t intentionally eat moldy produce, but it can happen without realizing.

“If you accidentally eat a piece of fruit with mold, [chances are] nothing is going to happen,” Gravely told HuffPost. “Don’t worry about it. Most people won’t get sick from eating moldy foods. Of course, some people are more sensitive than others. If you develop symptoms or if you became ill, for most people, any illness at all would be temporary. But if you develop nausea that lasts more than a day, see a doctor. But for most, any gastrointestinal upset would be transient.”

What’s the best way to handle moldy produce?

Sometimes the answer to this question is easy. If a peach is completely soft and covered in mold, don’t eat it. But what about a piece of fruit that only has one spot that’s gone bad? Or what about the rest of the strawberries in a box that were sitting next to a moldy berry?

“It’s fine. What I tell people is just to look at all the other berries. Sometimes it’s just dust that’s touching it ― that’s fine, wash it off ― but sometimes there are berries that are kind of clumped or stuck together by the mold ― toss those,” Gravely said.

“It is true that mold has branches and roots that will penetrate the food, so you have to use judgements on how soft it is. The softer the food, the easier it is for roots to penetrate,” Gravely elaborated. “Big strawberries, for example, you can cut off the moldy part ― a healthy margin. But if it’s all soft, don’t eat it.”

The best practice for eating fresh produce is to wash it with water first (stay tuned for a caveat!). This way you’ll get a good look at the fruit or vegetable you’re about to eat and will be able to identify soft or moldy spots easily. If you are washing produce with a tougher skin on it, rub it with a brush.

And here’s the aforementioned caveat: If you bought berries, don’t wash them until ready to use. Water will actually cause them to grow spoiled.

Botrytis Fruit Rot “Gray Mold” of Strawberry, Raspberry, and Blackberry

Many fungi are capable of rotting mature or near-mature fruits of strawberry, raspberry, and blackberry. Under favorable environmental conditions for disease development, serious losses can occur. One of the most serious and common fruit rot diseases is gray mold. The gray mold fungus can affect petals, flower stalks (pedicels), fruit caps, and fruit. In wet, warm seasons, probably no other disease causes a greater loss of flowers and fruit. The disease is most severe during years with prolonged rainy and cloudy periods during bloom or during harvest.


Figure 1. Early stages of gray mold fruit rot on strawberry.

Young blossoms are usually very susceptible to infection. One or several blossoms in a cluster may show blasting (browning and drying) that may extend down the pedicel. Fruit infections usually appear as soft, light brown, rapidly enlarging areas on the fruit. If infected fruits remain on the plant, the berry usually dries up, “mummifies,” and becomes covered with a gray, dusty powder which gives the disease its name, “gray mold.” Fruit infection is most severe in well-protected areas of the plant, where the humidity is high and air movement is poor. On strawberry, berries resting on soil or touching another decayed berry or a dead leaf in dense foliage are most commonly affected. The disease may develop on young green fruits, but fruits become more susceptible as they mature. Usually, the disease is not detected until fruits are mature at harvest time. After picking, mature fruits are extremely susceptible to gray mold, especially if bruised. During picking, the handling of infected fruit will spread the fungus to healthy ones. Under favorable conditions for disease development, healthy berries may become a rotted mass within 48 hours after picking.

Causal Organism

Gray mold is caused by the fungus Botrytis cinerea. The fungus is capable of infecting a great number of different plants. The disease cycle is very similar for both strawberries and brambles. The fungus overwinters as minute, black, fungus bodies (sclerotia) or as mycelium in plant debris, such as dead strawberry or raspberry leaves. Recent research has shown that nearly all of the overwintering inoculum in strawberry plantings comes from mycelium in dead strawberry leaves within the row or planting. In early spring, the mycelium becomes active and produces large numbers of microscopic spores (conidia) on the surface of old plant (leaf) debris in the row. Spores are spread by wind throughout the planting where they are deposited on blossoms and fruits. They germinate when a film of moisture is present and infection can occur within a few hours. Temperatures between 70 and 80 degrees F (20 to 27 degrees C) and free moisture on the foliage from rain, dew, fog, or irrigation water are ideal conditions for disease development. The disease can develop at lower temperatures if foliage remains wet for long periods. Strawberries and raspberries are susceptible to Botrytis during bloom and again as fruits ripen. Recent research indicates that most fruit infection actually occurs during bloom however, symptoms usually do not develop until close to harvest. During bloom, the fungus colonizes healthy or senescing flower parts, often turning the blossoms brown. These blossom infections establish the fungus within the receptacle of the young fruit as a “latent” or “quiescent” infection. The fungus generally remains latent in developing (green) fruit until the fruit starts to mature, at which time the fungus becomes active and symptoms (rot) appear. Thus, the most critical period for applying fungicides to control gray mold is during bloom. This is an important point to remember when considering fungicide applications for controlling this disease.


Figure 2. Later stages of gray mold fruit rot on strawberry. Note that the fruit is covered by a “gray” mass of fungus growth. Figure 3. Gray mold fruit rot on raspberry.

Select a planting site with good soil drainage and air circulation. Plants should be exposed to direct sunlight. Plant rows with the direction of the prevailing wind to promote faster drying of foliage and fruit.

A good layer of straw mulch (or other material) between the rows or around the plants aids greatly in controlling fruit rots. The mulch acts as a barrier that reduces fruit contact with the soil.

Proper spacing of plants and timing of fertilizer applications are also important. Excessive applications of nitrogen fertilizer, especially in the spring before harvest, can produce excessive amounts of dense foliage. Shading of berries by thick foliage prevents rapid drying of the fruit during wet periods and creates ideal conditions for disease development.

Good weed control is very important. Weeds prevent air movement in the plant canopy. This slows drying time of flowers and fruits and increases the chances for infection. Pick fruit frequently and early in the day as soon as plants are dry. Cull out all diseased berries but do not leave them in the field. Handle berries with care to avoid bruising. Refrigerate fruit promptly at 32 to 50 degrees F (0 to 10 degrees C) to check gray mold.

Fungicides are an important disease management tool in commercial plantings, but are generally not effective unless they are timed properly and used in conjunction with the above mentioned cultural practices. Homeowners are encouraged to emphasize the use of cultural practices in order to avoid the use of fungicides. For the most current fungicide recommendations and spray schedules, commercial growers are referred to Bulletin 506, Midwest Fruit Pest Management Guide, and backyard growers are referred to Bulletin 780, Controlling Diseases and Insects in Home Fruit Plantings. These publications can be obtained from your county Extension office or the CFAES Publications online bookstore at

Figure 4. Disease cycle of gray mold on strawberry. We wish to thank the New York State Agricultural Experiment Station for use of this figure. It was taken from the Small Fruit IPM Disease Identification Sheet No. 1.

This fact sheet was originally published in 2008.

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