Strawberry Common Diseases

Strawberry cultivation is especially popular around the world. Although, strawberry diseases can affect fruit, flowers, leaves, roots, and crowns of strawberry plants, and sometimes cause the collapse of the whole plant. While many of the problems caused by bacteria, fungi and viruses can be treated when symptoms are observed, some of the most serious strawberry plant diseases cannot be treated after the plants are in the ground.

1. Botrytis

It is one of the most serious diseases of strawberry and is caused by the fungus Botrytis cinerea. It mainly affects the wrist and causes deformities and the appearance of dark color in it. The disease develops especially in conditions of high humidity. The infection usually starts at the point of contact of the fruit with the ground. The infection initially manifests itself on the wrist as a soft light brown spot. To prevent this disease, preventive measures are applied, such as thinner planting, covering the bed with plastic wrap to avoid contact of the fruit with the ground, the use of resistant varieties and to avoid excessive moisture in the field. In cases where spraying is necessary, the active substances Cyprodinil, Fludioxonil, Pyraclostrobin and boscalid bring good results.

2. Powdery mildew

The infestation is caused by the fungus Spnaerotneca maculiris. Infects leaves, flowers, fruits and shoots. Infected leaves turn red on the lower surface and in severe infestations cut edges appear. Severe powdery mildew infection reduces the vitality, productivity of the plant as well as the quality of the fruit. It affects the fruits resulting in the reduction of the commercial value of the production or the total destruction of the strawberry crop. To fight the disease, spray with suitable fungicides, such as pyrazopnow, triadimetor, bupirimate, bemomyl. Even for susceptible varieties wettable sulfur can be used, Dinocap 0.1% before flowering and Afucan 0.1% and Methoxytniopnanate can be used after harvest. Recent studies have shown that sulphur is sufficient to fight disease.

3. Rhizoctonia

The fungus Rhizoctonia fragariae causes severe losses to the plant. The plants suddenly collapse before or during the first fruiting period and during the summer in the nurseries. The lower surface of the leaves becomes violet and the leaf blade tends to twist upwards. The original plant dies and many young shoots are formed. It grows well at temperatures between 15C and 25C. Low temperatures of 2 - 14C favour the infestation of roots by the fungus, while higher temperatures above 18oC favour the infestation of shoots and leaf stems. To treat this disease in strawberry, the only solution is to uproot and burn the infected plants. Preventive measures are sparse planting, light digging for plant aeration and reduction of soil moisture.

4. Phytophthora

This disease is caused by the fungus Phytophthora cactorum which infects the fruits and all other parts of the plant. Infected fruits soften externally, show discoloration internally and externally and have a characteristic bitter taste. The disease usually occurs in conditions of high humidity and temperature of night 10-15oC and day 15-25oC. Pre-chilling of the fruits immediately after harvest significantly reduces the occurrence of the disease. To treat the disease, it is necessary to cover the soil with plastic wrap, so that the fruits do not come into contact with the soil.

5. Anthracnose

The most serious disease is caused by the fungus Colletotrichum acutatum, which causes rot of the plant head, infects the stolons and stems of the leaves, causes black spots on the leaves and rot on the fruit. In addition, it causes a spot 1-2 cm in diameter, chocolate-colored in the middle, while white mycelia appear peripherally. Favorable conditions are high relative humidity, high temperature and dense planting. To control the disease, sprays with suitable fungicides are required, such as C captafol, Hetniram-zinc, Dichlofluanid, Chlotnalonil. In addition, copper preparations help in its treatment.

6. Verticillium wilt 

It is caused by the soil fungus Verticillium albo-atrum. It is a fungal soil disease and affects the vascular system of plants. In new plantations the symptoms appear when the stolons begin to form. In established plantations the symptoms appear when the fruit begins to ripen. The leaves wither, the margins as well as areas between the nerves dry out. The affected surface becomes dark brown. The plant forms few or no leaves. The new roots formed from the base of the plant are short and have blackened tops. Plants with severe infestation collapse and die. Plants with less infestation are vulnerable to cold and not at all productive. The disease can occur in mother plants, but not in subsidiaries. To combat and prevent this disease in the strawberry it is recommended not to plant strawberries after solano (tomato, pepper, potato, eggplant), to prefer resistant varieties or to apply soil disinfection with chloropicrin, methyl bromide or methyl bromide.

7. Fusarium Wilt

The pathogen Fusarium oxysporum f. sp. fragariae infects germinating seeds found in the soil, seedlings and older plants. In seedlings it causes yellowing of the cotyledons and the first leaves, resulting in a delay in the growth of the plant. The disease can be manifested by abrupt wilting without previous chlorination. A characteristic symptom of the disease is a unilateral streak from the neck of the plant up to the top of the stem which is initially watery and light green in colour, while later it turns yellow-black and under high humidity conditions is covered by a white rash. In older plants the first symptoms appear shortly before flowering. They are manifested by gradual yellowing of the leaves or by abrupt wilting of the whole plant (stroke) or part (hemiplegia). Sometimes the wilting is so fast that the leaves retain their green colour for days. During the gradual yellowing of the leaves, a yellow tinge of the nerves is observed on one side. These leaves then become thick and brittle. The stems widen and are covered by rod-shaped necrosis from which dark gum is secreted. In the dead parts the fungus bears fruit forming rosy spores. In plants that show progressive wilting, brown discoloration appears in the vessels, also the intestinal blackens and acquires a spongy texture. Under favourable conditions, the fruits that are manifested by rot at the point of attachment of the stem and the stem are also affected.

8. Phomopsis Leaf Blight

On the leaves, the infestation appears in the form of small spots of light green color that later turn brownish-black. The presence of numerous spots can lead to necrosis of the leaf surface or their deformation. Symptoms of infection of the stems and legs are manifested by the formation of elongated necrotic spots with slits, which then dry out. To prevent the transmission of the disease, it is recommended to disinfect the cultivation tools and the propagating material to be completely healthy. In addition, all necessary cultivation measures should be taken to promote good air circulation in the field. In addition, the bacterium Pseudomonas fluorescent helps control the treatment of the disease in an environmentally friendly way, as it acts against the fungus that causes this disease.

In conclusion, essential is the usage of certified propagating material from approved nurseries. That movement can reduce the incidence of diseases. Even farmers should always be in consultation with agronomists and follow the spray plan.

Sources: Organic vegetable growing technique - Strawberry, by Charalambos Thanopoulos Msc Agronomist, Agricultural University of Athens, Athens 2008.

Organic strawberry cultivation, graduate study of students Manousaridis Themistoklis - Thymi Nikolaou, Thessaloniki 2012.

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https://strawberryplants.org/diseases-fungi-molds/#:~:text=%20Strawberry%20Plant%20Diseases%3A%20Problems%20Caused%20by%20Bacteria%2C,a%20problem%20for%20strawberry%20growers%20all...%20More%20

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https://www.wikihow.com/Identify-and-Treat-Strawberry-Diseases

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https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11113

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