11 Strawberry Diseases: How to Identify, Prevent, and Treat Them

Botrytis is most commonly found on strawberries as they ripen. The key identification factors include:

• Small brown lesions near top of berries (early on)
• Powdery dead young leaves
• Velvety gray or brownish mold on fruit
• Soft and mushy rotten holes or areas on fruit
• Weird, misshapen fruit
• “Mummy berries” covered in moldy white to gray cotton-like mass

When the rotten areas start to appear soft and mushy, they’ll continue to expand until they take over the whole fruit. Unfortunately, this creates perfect conditions for the slightest breeze or touch to spread the moldy spores all around the garden. Once you notice botrytis, you have to act fast!

Preventing botrytis is all about maintaining clean garden beds with excellent air flow and removing any diseased or dead plant material.

Follow these preventative sanitation practices every season:

• Remove and destroy any infected or dead plant material (throw it away- don’t put it in your compost pile!)
• Never leave dead strawberry plants, fruits, or leaves to overwinter in the garden
• Rake up and remove any surrounding debris
• Remove any fruit with signs of decay or rot (be careful not to spread spores in the wind)
• Use straw mulch or landscape fabric to prevent rain splash up onto the berries
• Grow in plastic low tunnels or greenhouses (especially if you live in a rainy climate)
• Maintain adequate air flow between plants

Research also shows that there is a significant correlation between denser plantings and more disease. Give strawberry plants at least 1 square foot of space and keep up with thinning and pruning to ensure that the bed does not get overcrowded.

To end on a good note, you can prevent gray mold growth in post-harvest strawberries simply by chilling them immediately after you harvest. Keep the berries between 32 and 37°F and if you notice a moldy berry in a clamshell, remove it immediately. The rest should be fine!

Once botrytis takes hold, it’s hard to get rid of. Sure, you have removed all the infected berries and dead foliage, but the disease may keep spreading via its tiny windborne spores. Luckily, there are plenty of organic control strategies.

Our go-to boytrits control methods include:

• Natural Fungicide: Neem oil is one of the bet natural fungicides that can be used preemptively as well as after an infection. Dilute the neem solution per the bottle specifications and spray directly on plants to reduce the chances of a botrytis breakout. Neem is a safe compound from a tropical tree, however it can taste pretty gross, so don’t forget to thoroughly wash your berries!
• Biocontrol: Fight fungi with bacteria! Bacillus subtilis QST 713 (sold under the brand names Serenade or Cease) can be used as a preventative and treatment for botrytis. Streptomyces lydicus WYEC 1078 (brand name Actinovate AG) can also be helpful to apply once all diseased material has been removed.

Powdery mildew starts out looking, well… powdery. The key identification characteristics are:

• White powdery splotches on the top of leaves or stems
• Leaves look like they’re dusted with white powder (especially the underside)
• Curling and twisted leaves
• Purple or brownish blotches on leaves
• Deformed fruit or no fruit
• Seedy fruits with white powdery mycelium on the surface

The fluffy, white patches start to appear on leaves in late spring when daytime temperatures start to reach over 60°F. The mildew will cause younger leaves to curl and cup upwards.

As it spreads and ages, the leaves may turn purplish-red and brown underneath and eventually on their top surface as well. The mildew favors young, tender tissue and isn’t often found on older leaves.

Powdery mildew often overwinters on remnants of last year’s strawberries, which is why maintaining a clean garden is so important. It can also come into your garden via contaminated crowns or transplants, or the spores can blow in from nearby gardens, fields, or greenhouses.

If you want to avoid a nasty powdery mildew outbreak, try these preventative measures:

• Remove all old crop debris and dead leaves
• Use only certified disease-free strawberry plants or crowns from a reputable source
• Buy varieties that are more resistant (none are completely immune), including ‘Albion’, ‘Seascape’, ‘Chandler’, or ‘Hood’
• Apply a compost tea or horsetail (Equisetum spp.) preparation as a foliar spray to help boost the fungal resistance on leaf surfaces
• Apply sulfur or neem sprays as a preventative
• Avoid excessive use of nitrogen fertilizer
• Prevent overcrowding and maintain air flow between plants

Powdery mildew loves dry leaves, high humidity, and warm air temperatures. Unlike botrytis, overhead irrigation and raindrops on the leaves can actually inhibit the mildew from forming spores. But we still think it’s best to avoid sprinklers in the strawberry patch.

Thankfully, there are more options for treating powdery mildew than other strawberry diseases. First, carefully remove all dead or infected leaves, stems, or fruit from the area. If a plant is totally overtaken by powdery mildew, just pull it out and throw it away. Don’t forget to wash your hands before going back to the garden! Next, prepare a simple non-toxic spray

The best organic powdery mildew treatments include:

• Homemade Baking Soda Spray: This old time granny remedy is highly effective as long as it includes a secret viscous ingredient (oil or soap) to hold the sodium bicarbonate on the leaf surface. Mix 1 tablespoon baking soda with 1 teaspoon horticultural oil or liquid soap (I like Dr. Bronners) and 1 gallon of water. Spray on the plants every 1-2 weeks.
• Vinegar Spray: Mix 2-3 tablespoons of apple cider vinegar (about 5% acetic acid) in a gallon of water and spray all over plant surfaces. The acidity kills powdery mildew spores.
• Milk: I know it sounds weird, but there have actually been reputable scientific studies showing that high concentrations of milk sprayed on plant leaves can be more effective than fungicides at controlling powdery mildew! Put milk in a spray bottle and cover plant surfaces once or twice per week until you notice a reduction in powdery mildew.

Once again, scientists named this disease with a fair amount of logic. The key identifying factor of leaf spot is dead spots on strawberry leaves. But symptoms can also show up on fruits, berry caps, and runners. It’s important to distinguish leaf spot symptoms from blights or pest damage.

Key signs of leaf spot include:

• Small, round, dead spots speckling the leaf surface
• ⅛ to ¼ inch spots are purplish to deep red colored
• Spots may later turn into tan or white centers with rusty-brown margins
• Spots may merge together and kill whole leaves
• Shallow black spots (up to ¼ inch) on fruits
• Black or brown leathery texture on fruits near spots

The main difference between leaf spot and blight is that leaf spot has separated small “bullet hole” dots whereas blights form larger masses that are often “v-shaped” or follow the major veins of the leaf.

Preventing leaf spot is fairly easy to do and typically goes along with all your other standard strawberry sanitation practices.

Key preventative measures include:

• Remove all old plant material at the end of the season
• Mow plants down after they finish fruiting to encourage new growth
• Avoid overhead irrigation
• Maintain adequate airflow between plants
• Plan resistant varieties such as ‘Earliglow’, ‘Ogallala’, ‘Ozark Beauty’, and ‘Glooscap’

Leaf spot is technically “incurable”. Once it’s on your plants, your only goal is to slow the spread. Because this is mostly an aesthetic issue, researchers say that fungicide use isn’t usually warranted.

Leaf spot isn’t a huge issue unless you are noticing spots joining together and killing off significant numbers of leaves. At this point, you may want to remove plants and renovate the beds.

Identifying leaf blotch is really straightforward:

• Gray and tan lesions that begin at leaf margins
• Blotches spread to cover first new leaves of spring plants
• Tiny brown or black fruiting bodies on undersides of leaves
• Brownish decay of the fruit calyx (green leaves on top of berries) that is purely cosmetic

Preventing leaf blotch is also relatively simple:

• Always remove old plant residues where the fungus could overwinter
• Plant in plastic mulch or landscape fabric if you live in a very rainy climate
• Keep plants thinned out
• Avoid overhead irrigation
• Plant in low tunnels to protect from rains

Leaf blotch can only be prevented using the above methods. Plant scientists emphasize that this is only a minor disease that typically disappears once winter and spring rains stop. There are no fungicides or treatments recommended for this pathogen.

The first signs of verticillium wilt usually show in new strawberry plantings right when the first runners begin to grow. In mature patches, symptoms may appear right before harvest.

The main signs you may have verticillium wilt include:

• Rapid wilting and death of lots of plants
• Older leaves wilt and droop no matter how much irrigation they get
• Leaves turn dry, yellow, reddish, or brown at the margins and in the veins
• New leaves stop developing
• If new leaves grow, they are stunted and curled
• Overall stunted plants
• Bluish or brownish-black blotches on runners
• Dwarfed roots growing from the crown

Sometimes verticillium wilt symptoms look very similar to red stele, black root rot, and winter injury. If this disease is extreme, you may have to consult your local extension agent to test for the pathogen or avoid growing strawberries altogether.

Verticillium wilt overwinters in the soil and attacks plants from the roots. Research shows that it often waits for overcast, cooler spring weather that alternates with bright, sunny days. It thrives on weak or stressed strawberry plants, which is why maintaining a healthy strawberry patch is so important.

Prevent wilt with these measures:

• Always plant in well-drained, fertile soil
• Always remove old strawberry debris from the garden
• Avoid growing strawberries in soggy or wet, compacted areas
• Avoid high nitrogen fertilizer
• Maintain a robust soil microbiome with healthy additions of quality compost or vermicast
• Rotate strawberries around the garden and avoiding ever replanting in infected areas
• Use more resistant cultivars like ‘Albion’ or ‘Camino Real’
• Source only certified disease-free planting stock

Because verticillium wilt can lie dormant in the soil for many years, it isn’t really a treatable disease. There are no fungicides or fumigants that will eliminate the pathogens. Instead, try to optimize your soil health with plenty of microbially-rich compost, or establish new strawberry raised beds or containers.

The first signs of red stele include:

• Leaves lose shiny luster
• Runner production slows
• Younger leaves appear metallic or blush-green
• Older leaves turn red or yellow

As the disease progresses into the hotter and dryer parts summer, red stele shows these definite symptoms:

• Rapidly wilting and dying plants, starting with lower leaves
• When pulled up, you will notice very few roots
• Little to no lateral roots
• Central root has a naked “rat tail” appearance
• Strawberry crowns have a dark rotten appaerance

The soil-dwelling fungus Phytopthora fragariae that causes red stele root rot can persist in your garden for up to 10 years or longer.

But even if the fungus is present, it may not take out your strawberry plants if you take proper preventative measures, including:

• Only plant strawberries in well-drained soils
• Amend soil with generous amounts of compost and peat moss to improve drainage
• Use a broadfork or raised beds to improve drainage before planting
• Rotate strawberries around the garden every other year
• Choose highly resistant varieties such as ‘Earliglow’, ‘Midway’, ‘Allstar’, and ‘Surecrop’
• Only buy certified disease-free planting stock from a reputable source

The key “treatments” for red stele are centered around proper soil water management. While commercial growers may opt to use fungicides, university extension services recommend that gardeners simply pull out sick plants and prioritize replanting in an area with better drained soil.

Like many crown rots, charcoal rot causes strawberry plants to become reddish-brown and rotten in the center. They may suddenly wilt and collapse with very little notice.

Key symptoms of charcoal rot include:

• Wilting foliage in spite of ample water
• Stunted growth
• Older leaves drying and dying off while younger leaves remain green
• Collapsed or dead plants
• Orange or reddish-brown coloration in center of crowns when cut open[2]

Charcoal rot can look fairly similar to other crown rot diseases, so you may need to cut open the crown to confirm.

LIke most strawberry diseases, charcoal rot becomes the most severe when plants are under extreme stress.

Preventing Macrophomina crown rot is all about cultural control:

• Manage plant stress (provide consistent irrigation, drainage, weed and pest management, and moderate fertility)
• If you’ve had a problem with this disease, try planting tolerant cultivars like ‘Florida Festival’, ‘Amiga’, ‘Naiad’
• Some research has shown that crop rotation with broccoli may help reduce fungal populations

M. phaseolina survives in garden soil within hard black encasements called sclerotia. They are virtually impossible to get rid of unless you fumigate the soil, which is extremely toxic and not recommended for home gardeners. Your best bet is planting strawberries in a different bed or container and using the preventative methods outlined above.

Leaf scorch makes strawberry leaves look like they’ve been burnt by something.

Beginning signs of leaf scorch include:

• Irregular dark purple or brown spots scattered over leaf surface
• Appearance of “tar drops” on leaves
• Spots with purple centers and no defined border (the leaf spot disease has a clear margin)

As the disease progresses, the symptoms intensify and look more unsightly:

• Large sunken lesions where spots have merged together
• Purplish to brown colored areas that can girdle leaves from the base
• Brown, curled up leaves
• Scorched dying leaves
• Weakened vigor
• Dead leaves, flowers, or fruit (in severe infections)

The preventative measures for leaf scorch are very similar to other fungal strawberry diseases. It all comes down to reducing plant stress and preventing excess moisture:

• Grow strawberries as annuals (replace plants every years)
• Increase airflow with adequate spacing (10-12” between each plant)
• Avoid overhead irrigation
• Keep weeds under control
• Avoid excess nitrogen in the spring
• Remove all foliage at the end of the season (the fungus overwinters on crop debris)
• Use mulch or landscape fabric
• Avoid waterlogged or poorly drained soil

When the leaf scorch fungus takes hold of your leaves, there’s not much you can do. It may look unsightly but it probably won’t harm your fruit yields. The only treatment options are removing infected leaves and practicing the preventative measures outlined above.

Finally, a disease that is super obvious the second you see it! Alternaria causes strawberry fruits to be ruined by a large black moldy spot with a gross greenish-hue. As opposed to the multiple lesions of Anthracnose, Alternaria black spot is usually a single black mass on the ripe red berry.

Technically caused by the same pathogen as the fruit spot, there is also a form of alternaria that attacks the leaves.  Alternaria leaf spot looks a lot like other leaf spot diseases except it has a signature yellow halo. If you notice the spots with a slightly fuzzy texture or yellow halo, chances are it’s alternaria.

Alternaria is technically a secondary infection. It can only take hold when the berries have been damaged. To prevent physical wounding of your strawberries while they ripen, take these preventative measures:

• Keep slugs, mites, and other pests away with biological and cultural controls
• Use floating row cover
• Spray diluted neem oil before fruiting to repel mites (their bites are points of entry for the fungus)
• Protect plants from hail (when possible)
• Use low plastic tunnels
• Mulch around plants to prevent fruit from resting on soil surface
• Avoid cracking, stabbing, or otherwise damaging developing fruits

Once alternaria starts attacking your strawberries, they won’t be edible anyways. Remove infected berries and throw them away. Organic copper fungicides are available as a last resort.

Leaf blight is technically a summertime disease that attacks northern strawberries only during hot, warm months but can be a problem in southern plantings year round.

You know you have leaf blight if:

• Young leaflets have reddish purple blotches ⅜” to ½” in diameter
• Signature “V-shaped” lesions
• Blotches are delineated by leaf veins
• Central dark brown to purple zone with reddish or lighter brown outer areas
• Excessive defoliation of plants

Preventing leaf blight is fairly straightforward:

• Avoid overhead irrigation
• Use landscape fabric or straw mulch to keep soil surface covered and prevent splashing
• Remove all old strawberry debris
• Prune off infected leaves

There aren’t any known varieties with resistance to leaf blight nor are there specific fungicides for dealing with the issue. Some organic gardeners have had success with horsetail (Equisetum spp.) compost tea, copper sprays, or neem sprays.

Anthracnose can be caused by three different fungal species, but they all cause similar symptoms:

• Brown or black colored spots on green and ripe berries
• Spots appear water-soaked
• There are several spots on each berry (rather than just one large spot as in Alternaria black spot)
• When dry, the fruit may appear mummified
• Dying or sunken black flower petals
• Large brown or blackened leaf regions

The main source of anthracnose infections in gardens is through strawberry transplants. This is why it’s so important to source quality planting stock from a reputable nursery or seed company.

Other preventive measures include:

• Stay on top of weed control
• Maintain adequate thinning and spacing to keep air flowing through
• Straw mulches reduce spore dispersal
• Avoid plastic mulches (they act like a springboard for spore droplets)
• Avoid overhead irrigation
• Don’t work in the garden when plants are wet
• Remove infected plants and berries as soon as you spot them
• Rotate strawberries around your garden

The main control options for anthracnose are copper-based fungicides, however copper can build up to toxic levels in the soil and harm earthworms or soil microbes. The best treatment for anthracnose is removing diseased plants and following the sanitation measures described above.