Strawberry diseases

Strawberry diseases are the leading cause of economic losses in professional strawberry production. Botrytis, powdery mildew, Verticillium wilt, anthracnose, Phytophthora — the list is well known. What is less understood is the real difficulty of diagnosis in production conditions: a wilting episode can stem from Verticillium dahliae, Phytophthora cactorum, water stress, or a combination of all three. Massive downgrading at flowering can result from poor ventilation management just as much as from established fungicide resistance. Each cause demands a different response — and an incorrect response costs as much as no response at all.

The challenge is not knowing that botrytis develops in wet conditions. The challenge is knowing which programme to implement on a given plot, at which growth stage, based on variety, cropping system and the season's fungicide history. This is where standardised advice structurally reaches its limits.

This article provides a comprehensive overview of strawberry diseases — aerial diseases, soil-borne diseases, viral diseases — structured around mechanisms, risk factors by cropping system, and integrated protection strategies. The objective is not to replace field diagnosis, but to give strawberry growers and market gardeners the foundation to ask the right questions — and get the right answers.

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Aerial diseases: leaves, fruits and stems

Aerial diseases are the most visible and most frequent in strawberry production. They act directly on commercial fruit quality and the downgrading rate — two indicators that determine the profitability of a season.

Botrytis (Botrytis cinerea): the permanent threat to fruit

Botrytis cinerea is the leading cause of downgrading in strawberry production, across all cropping systems. Its management directly determines end-of-season margins.

The fungus manifests as a dense grey mycelium covering fruit and flowers, progressive soft rot, and brown necrosis of petals. In humid conditions with insufficient ventilation, contamination spreads from fruit to fruit by direct contact — a single infected cluster is enough to contaminate an entire row within 48 hours.

Triggering conditions are precise: relative humidity above 75% combined with temperatures between 15 and 20°C is sufficient to initiate an epidemic. Rain, fog and the absence of ventilation under shelter all amplify risk. Mechanical wounds — hailstone damage, harvest cuts, tears — provide additional entry points; after a hail event, secondary botrytis outbreaks typically multiply within 5 to 7 days.

The most sensitive growth stages are flowering (BBCH 60 to 65) and fruit set (BBCH 69 to 71). The flowering period is critical: residual petals that have not fallen provide an ideal sporulation substrate. Overhead irrigation on open flowers directly increases risk — this practice should be strictly avoided during flowering. Fruit set warrants specific monitoring of attached petals and newly formed fruits.

The difference between cropping systems is significant. In open field, risk is concentrated during rainy periods at flowering and harvest. Under tunnel or under plastic cover, risk becomes structural as soon as ventilation is insufficient — overnight condensation creates conditions for permanent contamination regardless of outdoor weather.

Regular leaf removal is the primary prophylactic measure, often underestimated. A well-conducted leaf removal programme — removing senescent lower leaves, opening the canopy — can reduce by up to 40% the rate of botrytis-related fruit downgrading over a season. This is a directly measurable gain in farm accounting.

On the chemical protection side, rotation of fungicide families is imperative. B. cinerea develops resistance to SDHIs and benzimidazoles — families commonly used in conventional strawberry production. Two consecutive applications from the same family without alternation accelerate the establishment of resistant strains. The principle: never repeat the same mode of action twice in a row, integrate biocontrol solutions (Bacillus subtilis, Bacillus amyloliquefaciens, products such as Serenade or Amylo-X) in alternation or preventive position, particularly around flowering. In organic farming, these biological agents form the core of the anti-botrytis programme, supplemented by potassium bicarbonate.

Powdery mildew (Podosphaera aphanis): the dominant constraint under cover

Powdery mildew is today considered the most concerning disease of strawberries grown under cover. Its progression can be spectacular — from a weekend inspection to a generalised white coating by the start of the following week under favourable conditions.

Symptoms are characteristic: a powdery white coating on the upper surface of leaflets, reddening of the lower epidermis, upward cupping of leaves, and on heavily affected fruit an icing-sugar appearance with deformation and loss of sheen. Flower stalks can also be affected, compromising pollination.

The epidemiological mechanism differs from botrytis. Powdery mildew does not require prolonged free moisture — it is instead favoured by warm days followed by cool nights with morning dew formation. These thermal alternations and short wetting periods — condensation, dew — trigger spore germination and tissue penetration. This is why tunnel crops concentrate risk: day/night temperature swings are amplified, and morning dew persists longer than in open field.

In open field, temperature variations are less extreme and natural air circulation limits prolonged wetting conditions. Powdery mildew pressure is structurally lower than under cover, except in fog-prone areas or hollows.

The fruit swelling stage (BBCH 71 to 75) represents a peak vulnerability window. Monitoring must be at its most intensive at this stage — the first fruit symptoms at this point indicate an already-established epidemic, and treatment windows are short.

Variety choice plays a major role. Varieties tolerant to P. aphanis — Cléry, Verdi, Manon des Fraises among others — allow a reduction in fungicide pressure of 30 to 50% according to CIREF trials. In organic farming, this varietal tolerance criterion becomes near-essential, as the available arsenal is limited to micronised sulphur, potassium bicarbonate and Bacillus subtilis. In conventional production, triazoles, strobilurins and IBCs form the core of protection — with the same imperative to alternate modes of action to prevent resistance, documented in certain P. aphanis populations across Europe.

Ventilation management under cover is the primary operational lever: opening tunnels early in the morning as soon as temperatures allow to disperse dew, avoiding prolonged closure during risk periods.

Anthracnose (Colletotrichum acutatum): insidious and under-diagnosed

Anthracnose is probably the most frequently misdiagnosed strawberry disease in professional production — its fruit symptoms are easily confused with sunscald, early-stage botrytis or a pollination disorder.

The characteristic fruit symptoms are hard, round, slightly sunken necrotic lesions, turning from bronze to brown then salmon pink. The central depression — a characteristic "thumb-press" indentation — is a distinguishing sign. On petioles and runners, elongated dark brown lesions with sunken centres indicate systemic contamination. In severe cases, sudden collapse of entire plants — sometimes across an area of just a few square metres — can occur within days.

The fungus spreads primarily via water droplets: rain splash, overhead irrigation, handling during harvest. Germination is optimal between 20 and 25°C in the presence of free water — conditions frequently met in open field during harvest periods under warm weather with overnight rain.

The primary route of introduction on a farm is the use of contaminated plants — even asymptomatic at planting. Plant health certification is the first line of defence. Once inoculum is present in a plot, anthracnose can persist in the soil for several years as sclerotia.

Control in conventional farming relies on copper-based fungicides and captan; in organic production, Bordeaux mixture provides the main protection. Harvest equipment hygiene — disinfecting scissors between rows when outbreaks are present — actively limits mechanical spread.

Common leaf spot (Mycosphaerella fragariae): chronic foliar pressure

Common leaf spot is a fungal disease with essentially indirect impact: it does not attack fruit, but the foliar weakening it causes reduces the plant's photosynthetic capacity and, over several seasons, diminishes vigour and crop productivity.

Symptoms are characteristic: small round spots with a white or grey centre and a red-violet halo on the upper surface of leaflets. Under favourable conditions — high humidity, moderate warmth — spots coalesce and can necrotise large portions of the leaf blade.

The disease is frequent in rainy conditions on perennial strawberry crops, where inoculum accumulates from season to season. Sanitary leaf removal — removing affected leaves from the plot — is the primary management measure. Copper (organic and conventional) and sulphur in organic production provide effective preventive protection.

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Soil-borne and vascular diseases: the silent decline

Soil-borne strawberry diseases are the most difficult to diagnose reliably in the field, the slowest to establish, and the most damaging over the long term. Their management is almost exclusively preventive — late diagnosis generally leaves no room for curative intervention.

Verticillium wilt (Verticillium dahliae): inoculum that does not disappear on its own

Verticillium dahliae is a soil-borne fungus whose microsclerotia can survive in the soil for 10 to 15 years without a host. A contaminated plot remains problematic through an entire rotation cycle — and well beyond if no action is taken.

Symptoms begin with asymmetric wilting of the lower leaves: one side of the crown wilts while the other stays green. This asymmetric sign is an important diagnostic indicator. Progressively, leaves yellow from the margin inward, petioles collapse, and plants become stunted. A longitudinal section of the petiole or crown reveals a characteristic dark vascular discolouration — this is the signature of systemic infection of the conducting tissue. Wilting of 50% of a plant's leaves is a late warning sign: by this stage, the fungus is established throughout the vascular system.

There is no curative treatment. Management is 100% preventive and relies on several levers:

Long rotation is the primary pillar: a minimum of 5 to 7 years without strawberries, Solanaceae or Cucurbitaceae — these families also being hosts of V. dahliae. Alfalfa as a preceding crop should also be avoided. Maize, cereals and grasses are good preceding crops.

Soil solarisation — covering the soil with clear polyethylene film in summer for 6 to 8 weeks — achieves 50 to 55°C in the top 20 centimetres of soil. These temperatures destroy a significant fraction of microsclerotia present in the surface horizon. Efficacy is greater in regions with strong summer sunshine (Mediterranean basin, south-west France) than in cooler northern regions, where temperatures under the film may remain insufficient.

Biofumigation through the green incorporation of brown mustard (Brassica juncea) or sorghum-Sudan before planting releases glucosinolates and isothiocyanates with fungicidal and nematicidal properties. In organic farming, this technique is the primary alternative to chemical soil disinfection. The two approaches — solarisation and biofumigation — are complementary, and their combination gives the best results.

In conventional farming, chemical soil disinfection (Vapam, Telopic) is used but its application is increasingly restricted by regulation and its efficacy is partial against deep inoculum.

Variety choice is an underused lever: certain varieties such as Malwina display recognised tolerance to V. dahliae, making it possible to maintain a viable crop on moderate-risk plots.

Crown and root rot: P. cactorum and P. fragariae

The two Phytophthora species affecting strawberries attack different organs and develop at different rates — two essential points for differential diagnosis.

Phytophthora cactorum attacks the crown and its surrounding tissue. Its development is rapid: an apparently healthy plant can collapse within 48 to 72 hours. A longitudinal section of the crown reveals a characteristic reddish-brown necrosis descending from the crown base. Wilting is general and fast, without the asymmetric character of Verticillium wilt. Favourable conditions include waterlogged soils and root asphyxiation following heavy rain or excessive irrigation.

Phytophthora fragariae primarily affects the root system. Symptoms are more gradual: fine roots turn black and necrotise, main roots take on a thread-like "rat tail" appearance (brown central cylinder visible when cut). Plants progressively weaken, lose vigour and produce poorly, without sudden wilting. This disease often goes unnoticed or is attributed to poor plant establishment.

The risk factor common to both species is excess soil moisture. Insufficient drainage, compaction, water retention zones, poorly managed irrigation — anything that maintains soil in saturated conditions for several consecutive hours is a major aggravating factor. Drainage is the primary preventive lever, and often the most cost-effective.

One important figure: on a plot demonstrably contaminated by P. fragariae, the rotation required to return to an acceptable inoculum level can exceed 20 years. The decision to grow strawberries on such a plot must incorporate this parameter in the economic reasoning.

The preventive strategy combines: certified disease-free plants (the absolute first barrier), managed drainage, applications of Trichoderma harzianum at planting as preventive biocontrol, and registered root-treatment fungicides (mefenoxam, ametoctradin, mandipropamid) in conventional production.

Differential diagnosis summary:

Sign	Verticillium wilt	P. cactorum	P. fragariae
Speed of development	Progressive (weeks)	Rapid (48–72 h)	Progressive (weeks)
Wilting pattern	Asymmetric	General	General (weakening)
Organ affected	Vascular system	Crown	Roots
Cut symptom	Dark vascular discolouration	Reddish-brown necrosis	"Rat tail" roots
Soil	Contaminated host (persistent)	Waterlogged soil	Waterlogged / contaminated

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Viral diseases: delayed impact, often invisible

The strawberry virus complex primarily includes four viruses: SMoV (Strawberry mottle virus), SCV (Strawberry crinkle virus), SMYEV (Strawberry mild yellow edge virus) and SVBV (Strawberry vein banding virus). In the vast majority of cases, these viruses are present as co-infections — a single plant can carry two, three or four viruses simultaneously, which considerably worsens symptom expression.

Signs of viral infestation are often subtle and easily attributed to other causes: stunted plants, slowed growth, progressive dwarfing, unexplained loss of productivity, slight leaf distortion or mosaic patterns. In the absence of characteristic foliar symptoms, only serological (ELISA) or molecular (PCR) testing provides a definitive diagnosis — tests not feasible in the field.

The primary vector is the aphid Chaetosiphon fragaefolii, specific to strawberry, but also Myzus persicae with a broad host range. A viruliferous aphid can inoculate a healthy plant within minutes of feeding. Spread accelerates when aphid populations are large and uncontrolled.

The only genuinely effective strategy is preventive: use CAC-certified plants or, preferably, plants produced from in vitro multiplication of elite virus-tested material. This certification guarantees a virus-free sanitary status at planting — it does not protect against subsequent infections, but delays the risk of accumulation by a few seasons. In addition, managing vector aphid populations through beneficials (Aphidius colemani, A. ervi, lacewings) or targeted aphicide treatments outside flowering actively limits spread. Rapid removal of severely affected plants from the plot reduces the viral inoculum source.

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Fungal diseases and cropping systems: the same pathogen, different risks

Understanding strawberry diseases without integrating the cropping system in which they develop means working with an incomplete picture. The same variety, in the same growing region, does not carry the same risks depending on whether it is grown in open field, under cold tunnel, or in soilless cultivation.

In open field, botrytis is the primary constraint during flowering and harvest — rainfall is the dominant triggering factor. Anthracnose warrants particular monitoring in warm weather with overnight rain. Soil-borne diseases (Verticillium wilt, Phytophthora) depend on plot history and drainage quality. Powdery mildew pressure is structurally lower than under cover, except in fog-prone areas or hollows.

Under cold tunnel or plastic cover, powdery mildew becomes the number-one constraint from the start of vegetative growth. Overnight condensation and day/night temperature swings create near-permanent infection conditions in the absence of active ventilation. Botrytis remains present, but its management relies primarily on ventilation control rather than treatments alone. Managing tunnel closure at night during high-risk periods is an agronomic decision in its own right — it determines internal humidity levels as much as harvest management does.

In soilless cultivation on substrate, the absence of contact with natural soil mechanically eliminates Verticillium wilt risk and significantly reduces soil-borne Phytophthora risk — provided irrigation water is clean and substrate is disinfected between cycles. Powdery mildew remains the absolute priority. However, recirculation of the nutrient solution can become a Phytophthora contamination vector if an outbreak establishes itself in the circuit.

In organic farming, whatever the system, the available arsenal is reduced. Variety choice (powdery mildew tolerance, Verticillium tolerance) becomes the primary lever in the protection strategy — a lever decided at plant ordering time, not mid-season. Cultural prophylaxis (rotation, hygiene, leaf removal, water management) carries a greater share of the outcome than in conventional production.

Digital decision-support tools are now accessible to professional strawberry growers: botrytis (MS-BOT, BoMa) and powdery mildew (SPAW) epidemiological models integrated into connected weather stations (Sencrop, Promété, Meteus), and weekly regional Plant Health Bulletins (BSV). These tools allow growers to calibrate intervention windows based on real local weather data rather than a fixed calendar — and to reduce pesticide application frequency without increasing risk.

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Integrated pest management (IPM): prioritising the levers

Integrated pest management is not a philosophical option — it is the mandatory regulatory framework since EU Directive 2009/128/CE on the sustainable use of pesticides. In practice, IPM means prioritising interventions: agronomic prevention first, monitoring and thresholds next, biocontrol third, chemical control as a last resort when damage thresholds are reached.

Prophylaxis: the first and least costly lever

Prophylaxis encompasses all decisions made before symptoms appear. This is where a large part of a season's disease pressure is won or lost.

Variety choice is the most upstream lever of all. A powdery-mildew-tolerant variety in covered production, a variety with recognised Verticillium tolerance on a historically contaminated plot — these decisions made at plant ordering time determine the fungicide pressure level for the entire season. This choice cannot be recovered mid-crop.

Certified plants constitute the first barrier against anthracnose, viral diseases and Phytophthora. In professional strawberry growing, using plants without health certification is a poorly calibrated economic risk: the cost differential for certification is far outweighed by the potential losses from an anthracnose introduction or a viral complex.

Inter-plot hygiene — disinfecting tools (secateurs, harvest knives) and footwear between plots, particularly on farms with blocks across multiple sites — actively limits the spread of Phytophthora, anthracnose and nematodes. Disinfection with alcohol or diluted bleach is simple and effective.

Irrigation management is an often underestimated lever. Drip irrigation eliminates soil splash — the primary dispersal mechanism for anthracnose and botrytis in open field. It avoids leaf wetting that favours powdery mildew and botrytis. Overhead irrigation must never be triggered on open flowers or late in the day — in the latter case, foliage wet all night creates optimal infection conditions for botrytis and anthracnose.

Long crop rotation (5 to 7 years minimum without strawberries, Solanaceae or Cucurbitaceae) is the most effective measure against Verticillium wilt and nematodes. It is planned at farm level over multiple years — not at the individual season level.

Biocontrol: effective agents that require precise positioning

Biocontrol agents available in strawberry production have been the subject of serious trials in recent years. Data from CTIFL, ITAB and FiBL converge on partial but real efficacy, provided positioning is preventive rather than reactive to established symptoms.

Bacillus subtilis and Bacillus amyloliquefaciens (products such as Serenade, Amylo-X) form the core of anti-botrytis biocontrol. Their mode of action combining antibiosis and trophic competition makes them complementary to conventional fungicides in alternation. Applied preventively before flowering and at the start of fruit set, they reduce disease pressure without the risk of resistance selection.

Trichoderma harzianum protects the root system against Phytophthora. Its application at planting — as a root dip or localised substrate application — constitutes a relevant prophylactic investment on at-risk plots or in soilless cultivation.

Micronised sulphur is the reference fungicide for powdery mildew control in organic production and as a preventive in conventional farming. Its efficacy is preventive — it does not act on an established infection. Potassium bicarbonate provides a mild complementary curative action.

Rational chemical control: alternation and current registrations

Chemical control in conventional strawberry production is exercised within a context of continuous reduction in the available arsenal. Over the past decade, numerous key active substances have left the European market: chlorpyrifos, methomyl, certain neonicotinoids, ortho-phenylphenol. The list of registered products shrinks each year.

Before any application, verifying current registration status is both a regulatory obligation and an economic precaution. Official references are E-Phy (ANSES) for France, Fytoweb for Belgium, and the FOAG database for Switzerland.

For botrytis: SDHIs + benzimidazoles in strict alternation, 2 to 3 applications per flowering phase. Never two identical families consecutively. Products based on fenhexamide and fludioxonil are classically used — check current registration status.

For powdery mildew: triazoles, strobilurins, IBCs in conventional production. Wettable sulphur in a preventive position for both organic and conventional. Given that triazole resistance is documented in certain P. aphanis populations, alternation of modes of action is equally recommended.

For soil-borne diseases: mefenoxam or mandipropamid against Phytophthora as preventive or early curative root treatment. Soil disinfection (Vapam, Telopic) against Verticillium wilt — partial efficacy, regulated use.

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When the same symptom does not receive the same response

Everything presented above documents mechanisms, risk factors and available levers. What standard guides do not do — and cannot do — is take into account the specific situation of a farm to formulate an operationally adapted response.

Four concrete situations illustrate this point.

Recurring botrytis despite an alternating programme. The question is not "which fungicide to use" — it is "why alternation is no longer sufficient". Possible causes are multiple: resistance established against a specific family linked to the application history over the past two or three seasons; high varietal susceptibility not compensated by prophylaxis (certain varieties such as Gariguette are structurally more susceptible than Cléry or Darselect); applications timed too late relative to critical BBCH stages; tunnel microclimate driving permanent contamination not resolved by treatments alone. Without knowing these parameters, reformulating the programme is little more than guesswork.

Wilting on 15 to 20% of plants mid-season. The speed of onset (sudden or progressive), the symmetric or asymmetric character, the appearance of the crown and roots when cut, the nature and history of the soil — all elements that orientate the diagnosis towards Phytophthora cactorum, Verticillium wilt or water stress. Three diagnoses, three responses: emergency drainage and root treatment for P. cactorum; anticipation of soil contamination and adaptation of rotation for Verticillium; adjustment of irrigation management for water stress. An ill-adapted intervention resolves nothing and delays the right decision.

Explosive powdery mildew in year N, controlled the two previous seasons. Several causes can explain this change: introduction of a triazole-resistant strain via contaminated plants; modification of tunnel ventilation management (prolonged night closure); varietal change towards a more susceptible profile; mild winter favouring mycelium survival. Identifying which cause is at play determines whether the response is a programme adjustment, a change in shelter management, or a varietal decision for the following season.

Anthracnose or a physiological disorder? The round sunken lesions of anthracnose on fruit are distinguished from sunscald by their texture (firm and necrotic vs soft and discoloured), their distribution on the row (focal vs uniform exposure) and the presence of salmon-pink sporulation under humid conditions. An incorrect diagnosis leads to a futile fungicide intervention — or worse, no fungicide intervention while anthracnose is actively spreading through splash.

These four cases share a common thread: the variability of field contexts makes all standardised advice insufficient. The technical guide delivers protocols; it cannot integrate the climatic vintage, the plot's phytosanitary history, specific varietal behaviour, or the farm's cultural practices. It is precisely in this space — between the general protocol and the field decision — that adapted advice makes the difference between a programme that holds and one that drifts.

Securing crop management decisions against unexpected disease events is exactly why Agronomia developed its crop-specialised AI agronomy advisors. Fraisibot takes into account your variety, your cropping system, your local climatic conditions and your practices to formulate a response adapted to your real situation — not a generic protocol.

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Strawberry diseases: documenting is not enough — making the right decision is what matters

Strawberry diseases have been known and documented for decades. The mechanisms of Botrytis cinerea, the infection conditions of Podosphaera aphanis, the persistence of Verticillium dahliae in soils — all of this is in the technical literature, available in regional crop health bulletins, taught in agricultural training.

What the professional in the field lacks is not general information. It is the response adapted to their specific situation, at the exact moment the decision must be made: at flowering in wet conditions, facing an unexplained wilting in high summer, confronted with a tunnel full of powdery mildew three weeks before harvest. These moments do not wait for a scheduled advisory visit.

The strawberry growers who secure their yields are not necessarily those who run the heaviest programme. They are the ones who make the right diagnosis at the right moment, who adjust their strategy to the reality of their plot, and who do not let a disease gain ground for lack of a response available at the critical moment.

For further reading on the two most complex soil-borne diseases to manage in terms of rotation and alternative methods, see our dedicated article Verticillium wilt and Phytophthora in strawberries. For soil-borne diseases in strawberry production more broadly, the article Soil-borne diseases in strawberry crops provides a useful complement. On the pests that interact with disease dynamics — D. suzukii, spider mites, weevils — see our article Strawberry pests. And to understand how rotation and mulching fit into an overall disease management strategy, see Strawberry agroecology: rotation and mulching.

Fraisibot, Agronomia's AI agronomy advisor specialised in strawberries, is available 24/7 to answer your crop protection, diagnosis and crop management questions. Access personalised advice on your strawberry crop — tailored to your variety, your system and your context.

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