Strawberry plant protection: sanitation practices and biocontrol in professional strawberry growing

Strawberry crop protection is one of the most demanding components of the technical itinerary in professional strawberry growing. Between the pressure of aerial pests — spider mites, thrips, aphids, Drosophila suzukii — and recurring fungal diseases such as Botrytis cinerea or powdery mildew, a poorly managed season can result in losses of 20 to 40% of marketable yield, not counting the downgrading that directly weighs on margins.

What distinguishes a strawberry operation that secures its yields from one that simply weathers each season is rarely the curative treatment product chosen. It is the coherence of the upstream strategy: rigorous cultural sanitation, population monitoring, timely introduction of beneficial insects, and positioning of biocontrol inputs within critical phenological windows. Strawberry protection is built — it is not improvised.

This article sets out the operational foundations of integrated biological protection (IBP) in strawberry growing: the sanitation levers to implement from planting, the commercially available beneficial insects by target pest, the approved biofungicides and bioinsecticides and their positioning within the crop cycle, and the specifics of HVE and organic certification. The goal is not to provide a turnkey programme — which would in any case be unsuited to your specific production system — but to give you the reference points to build your own strategy.

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Integrated biological protection in strawberry growing: rationale and principles

Integrated biological protection (IBP) is not an alternative to crop protection products — it is a pest management method that organises all available levers in a priority sequence: sanitation first, monitoring second, biological and biocontrol levers before any recourse to conventional inputs.

In strawberry growing, this approach is particularly relevant because the crop combines several pressure factors: extended cycle duration (6 to 9 months for tunnel systems with cold-stored plants), high planting density, confined tunnel microclimate favouring fungal pathogens, and marked susceptibility of many varieties to powdery mildew or Botrytis as soon as climatic conditions shift.

Damage thresholds and intervention logic

IBP is built on a threshold logic: intervention only occurs when pest pressure exceeds the level at which the economic impact justifies the cost of treatment. This concept is central — it avoids systematic preventive treatments that weaken the natural beneficial fauna and accelerate resistance development.

In practice, this requires regular monitoring: counts on coloured sticky traps — yellow and blue — (thrips, whiteflies, winged aphids), weekly observation of plant organs, and tracking of in-tunnel climate data. The most sensitive phenological stages — flowering (BBCH 51–65) and early fruit set (BBCH 71–89) — require an increased monitoring frequency.

Epidemiological decision-support tools exist for Botrytis: the MS-BOT and BoMa models estimate risk based on local climate data (temperature, relative humidity, leaf wetness duration). Platforms such as Movida, RIM Pro or Agrometeo.ch integrate these models with local weather data. Regional Plant Health Bulletins (BSV) serve as a complementary first-level resource.

TFI and regulatory constraints

The Treatment Frequency Indicator (TFI) is the reference management metric in France for evaluating the phytosanitary intensity of a production system. Its reduction is an explicit objective of agricultural policy (Écophyto, CAP conditionality), and is also an eligibility criterion for HVE level 3 certification.

HVE and organic positioning

High Environmental Value (HVE) level 3 includes a specific indicator on phytosanitary strategy. In strawberry growing, this translates concretely into the recognition of alternative practices: beneficial insect releases, biocontrol, documented sanitation, BSV monitoring. The audit focuses on quantitative results (TFI, share of biocontrol products in the programme).

For Organic Agriculture, the constraint is more structural: only organically approved inputs are authorised, excluding synthetic insecticides and fungicides and requiring the entire protection programme to be built on biological levers and biocontrol products. The conversion period is 24 months (particular cases for soilless strawberry growing to be clarified with the certification body). In practice, organic feasibility depends closely on the production system: pest pressure differs significantly between a climate-controlled tunnel and open-ground growing.

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Cultural sanitation: creating conditions unfavourable to pests and diseases

Sanitation is the most undervalued lever in strawberry protection — and yet the most cost-effective. It involves not treatments, but a set of cultural practices that reduce pest and disease pressure upstream of any need for intervention. A well-managed defoliation programme can reduce Botrytis fruit losses by up to 40%. Rigorous runner management generates a yield gain of 15 to 25% depending on the variety. These figures frequently exceed the impact of a well-targeted curative treatment.

Plant hygiene during the crop cycle

Runner removal: in fruit production, systematic runner suppression is the most important maintenance operation of the crop cycle. It must be carried out at a weekly to bi-weekly frequency depending on varietal vigour. Beyond the yield benefit, it reduces canopy congestion that promotes stagnant humidity.

Sanitation defoliation: removal of diseased, old or necrotic leaves reduces the fungal inoculum source (Botrytis, powdery mildew) and improves air circulation through the canopy. In tunnels, this foliage aeration is a direct lever on ambient humidity. For non-remontant varieties, a post-harvest defoliation is recommended 2 to 3 weeks after the end of harvest to stimulate autumn flower initiation.

Removal of affected fruit: daily removal of overripe, damaged or attacked fruit is essential, particularly for managing Drosophila suzukii and Botrytis. Culls must not remain on the ground or be added to open compost — they must be sealed in airtight containers and removed from the growing area. A single day of fruit left on the ground can initiate a suzukii infestation or a massive Botrytis sporulation event.

Tool disinfection: 70% alcohol or diluted bleach between rows or blocks limits the mechanical transmission of pathogens such as Colletotrichum (anthracnose) or Phytophthora.

Climate management in tunnels

Overnight humidity is the primary trigger for Botrytis cinerea in tunnels. Epidemic risk develops when relative humidity exceeds 75% for extended periods at temperatures of 15 to 25°C. Ventilation management — opening vents in late afternoon to evacuate humidity accumulated during the day, measured overnight ventilation to avoid excessive foliar wetness — is a sanitation measure in its own right.

Crop rotation and soil rest

For open-ground systems, maintaining a long rotation is non-negotiable: 5 to 7 years without strawberries or solanaceous crops significantly reduces pressure from soilborne pathogens — Verticillium dahliae, Phytophthora cactorum, Rhizoctonia fragariae, root-knot nematodes. Returning too quickly to the same plot accumulates residual pressure that cannot be compensated by treatments.

Summer solarisation is a complementary soil disinfestation lever: under clear plastic film, temperatures reach 50 to 55°C in the top 20 centimetres over 6 to 8 weeks, significantly reducing populations of heat-sensitive pathogens.

For further detail on soilborne diseases and their link to cultural practices, see our article on soilborne diseases in strawberry growing. Agroecological practices in strawberry growing — biofumigant cover crops, alternative mulches, functional biodiversity — extend this sanitation logic to the system level.

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Beneficial insects and bioinsecticides: what levers are available against aerial pests?

Commercially available beneficials by target pest

Building an IBP strategy in strawberry growing relies on selecting beneficials suited to each dominant pest. Below are the pest/beneficial pairings documented in professional French strawberry growing.

Two-spotted spider mite (Tetranychus urticae): the reference predator remains Phytoseiulus persimilis, a specialist predatory mite effective between 12 and 30°C. It is introduced preventively from the first signs of infestation. Neoseiulus californicus has a slightly wider thermal range and can persist in the absence of prey. Feltiella acarisuga, a predatory midge, is useful as a complement on dense infestations.

Thrips (Frankliniella occidentalis): the main lever is Neoseiulus cucumeris, a predatory mite that develops rapidly above 20°C (activity reduced above 30°C). Recommended for bulk introduction from early April as soon as temperatures allow. Amblyseius swirskii is better suited to warm spring-summer conditions (optimal window 20–35°C, introduction generally between mid-May and early June). Orius laevigatus, a predatory bug, establishes naturally between late May and June and remains active through September — larval releases can be made punctually during heavy attack.

Aphids (Chaetosiphon fragaefolii primarily): Aphidius colemani is the reference parasitoid for Myzus and Aphis spp. Mixed introduction from the start of the season. Aphidoletes aphidimyza (predatory midge) and lacewings complement the toolkit on dense colonies. Strawberry aphids are also vectors of viruses — sanitation and management of primary inoculum sources (certified plants, destruction of volunteers) remain a priority.

Whiteflies: Encarsia formosa (parasitoid) and Macrolophus pygmaeus (generalist predatory bug) are the baseline levers. Macrolophus is particularly valuable for its predatory capability across multiple pests simultaneously.

For a full presentation of pest biology and intervention thresholds by pest, see our dedicated article on strawberry pests.

Conditions for successful releases

Beneficial insects are living organisms: their effectiveness depends directly on the conditions in which they are introduced. A release made outside the thermal window is a wasted release.

Three critical rules to follow:

First, beneficials are preventive tools, not curative ones. They cannot recover a population explosion already underway. Introduction must precede the damage threshold, not follow it.

Second, incompatibility with conventional crop protection products is total for most beneficials. Pyrethroids, certain SDHIs and broad-spectrum insecticides can eliminate beneficial populations within hours. The rule is straightforward: no foliar treatment with conventional products for several days before and after a release. For precise intervals by active substance, the E-Phy database from Anses (the official French plant protection register) is the reference — any compatibility list published in a generic guide must be cross-checked against current official data.

Third, pollinators (bumblebees) must be introduced at the precise BBCH 60 stage (first open flowers). Introduction too early generates pointless foraging; too late, it misses the first flowers that carry the first fruit.

Drosophila suzukii: management without a commercial beneficial

Drosophila suzukii is the pest for which IBP offers the most limited levers: to date, no commercially available predator or parasitoid has demonstrated reliable efficacy under professional growing conditions. No strawberry variety has documented resistance.

The strategy relies on four cumulative levers. Physical exclusion using insect-proof netting (mesh ≤ 0.8 mm) is the most effective barrier, now near-essential for summer and autumn crops. Very frequent harvesting — daily to every two days — drastically reduces the window of infestation of ripe fruit. Hermetic disposal of unmarketable fruit in sealed containers prevents on-site multiplication. Mass trapping at plot borders (apple cider vinegar + water + syrup + soap bait) then within the crop at first damage signs (density of 1 trap per 30 to 100 m²) allows monitoring and reduction of adult pressure.

On the biocontrol front, trials have shown that Beauveria bassiana (Naturalis) and Bacillus thuringiensis (Solbac) deliver the best documented biological protection against the fly, with observed efficacy levels of 50 to 70% — insufficient as a standalone measure, but relevant when combined with sanitation levers.

Approved bioinsecticides and bioacaricides

Several bioinsecticides and bioacaricides present operational value in strawberry growing as a complement to beneficial insects:

Beauveria bassiana acts on a broad spectrum (thrips, whiteflies, aphids) by contact — its efficacy depends on a relative humidity ≥ 70% to allow spore germination. Applications should therefore be timed to humid conditions, preferably in the late afternoon.

Spinosad has documented efficacy against thrips, but its use must be restricted due to its toxicity to beneficials and pollinators. It should be reserved for high-pressure situations, in the absence of active beneficial populations.

Azadirachtin acts primarily as a repellent and development disruptor. Its compatibility with beneficial insects is better than spinosad, making it a useful tool in support of an IBP strategy.

Vegetable oils (rapeseed, etc.) and essential oils (sweet orange) have a contact acaricidal effect usable in organic production.

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Biofungicides: protecting strawberries against Botrytis, powdery mildew and anthracnose

The three priority fungal diseases

Fungal management in professional strawberry growing focuses on three pathologies that together largely determine the quality and marketable volume of the harvest. For a full description of symptoms and risk factors, see our article on strawberry fungal diseases.

Botrytis cinerea (grey mould) is the most feared pathogen in tunnels. Triggering conditions are precise: relative humidity > 75% over extended periods, temperatures between 15 and 25°C, and the presence of wounds or necrotic tissue (petals fallen on fruit, defoliation wounds). Losses can exceed 30% of harvested volume in a poorly managed humid season. Flowering is the primary contamination stage.

Powdery mildew (Podosphaera aphanis) develops under conditions opposite to Botrytis: warm and relatively dry weather, with large diurnal temperature ranges. Contrary to common belief, powdery mildew does not require leaf wetness to develop. Varietal susceptibility is highly variable: some varieties such as Gariguette are significantly more tolerant than others. Resistance to SDHIs and SBIs (triazoles) has been documented across several P. aphanis strains in Europe — mode-of-action management is a durability issue here.

Anthracnose (Colletotrichum spp.) is a risk primarily at planting. Contamination comes through the plants — sanitary quality of plants at purchase is the first lever. During the crop cycle, strict tool hygiene and particular care around handling wounds limit spread.

Approved biofungicides and programme positioning

Biofungicides available for use on strawberries cover primarily Botrytis and powdery mildew. Their shared characteristic is the requirement for preventive positioning — none has the curative efficacy of a conventional fungicide. Integrated into a protection programme from BBCH 60 (first open flowers), they contribute to pressure reduction without eliminating biological levers already in place.

Bacillus amyloliquefaciens (products Serenade, Amylo-X) and Bacillus subtilis cover a Botrytis and powdery mildew spectrum in preventive positioning. Their efficacy remains lower than that of reference conventional fungicides, but their integration in alternation within a multi-lever programme contributes to reducing TFI and preserving the durability of conventional actives.

Potassium bicarbonate is approved against powdery mildew in organic production — satisfactory preventive efficacy, to be reapplied at short intervals under favourable conditions.

Wettable sulphur is the reference organic tool against powdery mildew. Note: phytotoxicity is possible above 28°C — applications should be avoided during heat waves or scheduled for early morning.

Plant defence stimulants (PDS) — laminarin, chitosan — are a complementary lever: they induce defence responses in the plant, but with a latency period of 3 to 5 days before expression. Their value lies in systemic preventive positioning, not in response to an observed pressure event.

Resistance management: rotating modes of action

Resistance of Botrytis cinerea to SDHIs and benzimidazoles is increasingly documented in intensive production areas. That of Podosphaera aphanis to triazoles and strobilurines is also progressing. The rule of rotating modes of action across the 2 to 3 applications made during flowering — a critical window of 3 to 5 weeks — is an agronomic imperative, not an optional recommendation.

Integrating biofungicides into this rotation offers a dual benefit: reducing selection pressure on conventional actives, and maintaining an acceptable protection level in operations engaged in HVE or undergoing organic conversion.

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Why your protection programme cannot be a copy of your neighbour's

This is the point that published technical guides — however well constructed — cannot resolve: strawberry protection is a system, and systems are singular.

Variability by production region

Pest and disease pressure differs structurally from one region to another. A grower in Brittany under glass tunnels faces chronically high relative humidity favouring Botrytis and aphids, in a context where native beneficial insects struggle to establish due to the confined microclimate. A grower in the Rhône valley manages heat peaks that create conditions favourable to powdery mildew and spider mites, but allow greater natural beneficial activity. The same treatment calendar cannot work in both contexts.

Differentiated varietal susceptibility

Tolerance to fungal diseases varies significantly by variety. Gariguette has relatively greater tolerance to powdery mildew than Charlotte; Mara des Bois is more susceptible to Botrytis in humid conditions. A protection strategy calibrated to one variety may be under- or over-dimensioned for another grown in the same tunnel. This is especially true in operations growing several varieties simultaneously on separate blocks.

Impact of the production system

The distinction between soilless growing and mulched open-ground fundamentally changes pest and beneficial dynamics. In soilless substrate growing, the absence of living soil reduces reservoirs for certain soilborne pathogens, but gutter-based growing creates a plant density and air circulation profile that can favour aerial pests. Natural beneficials are virtually absent — everything depends on releases. In mulched open-ground production, the natural fauna can contribute, but soilborne pathogen pressure imposes a rotation and disinfection strategy that soilless growing does not require.

Plot history and established resistances

A strawberry planting established on a plot that has experienced heavy Verticillium pressure in recent years cannot ignore that context in its health strategy. Likewise, an operation that has applied SDHIs over several consecutive years on the same blocks must assess the actual resistance level of the local Botrytis population before constructing its programme — or risk paying for treatments that no longer have any effect on the strains present.

The questions a standard programme cannot answer

Here, concretely, are situations that a head grower regularly faces and that no guide can resolve on their behalf:

Should Amblyseius swirskii be introduced now, or wait until overnight temperatures sustainably exceed 20°C, given that thrips pressure is already visible on traps?

My programme includes an SDHI scheduled for next week against Botrytis: is this compatible with the Encarsia formosa release planned in 4 days, and if not, which of the two should be postponed as a priority?

Next week is forecast to bring nights at 14°C and humid conditions — is that sufficient to justify a Bacillus amyloliquefaciens application before the next flowering stage, or has the threshold not yet been reached in my type of tunnel?

These decisions simultaneously draw on the biology of the organisms involved, local climate data, the exact phenological stage of the crop, and the history of the current programme. This is precisely where generic advice reaches its limits — and where the value of contextualised advice available at the exact moment you need it becomes concrete.

The real cost of poor timing

In an IBP strategy, poor timing does not cost you immediately — it costs you a week later, when the thrips population has multiplied tenfold for lack of active beneficials, or when Botrytis has sporulated on fallen petals during the 3 days you hesitated to apply the biofungicide.

This time dynamic is one of the major practical difficulties of integrated protection for the professional managing an operation. Conventional advisory support — weekly bulletins, monthly technician visits — is structurally out of step with the actual decision window. A beneficial release missed at D+7 on an emerging thrips infestation cannot be recovered at D+14. A Bacillus applied after the Botrytis epidemic has no curative effect.

The reduction in conventional inputs, an objective of current agricultural policy and a condition of HVE and organic certification, requires in return greater precision in decision-making, not less. Fewer synthetic products available means each biological lever must be used at the right time and under the right conditions — which requires access to agronomic information at the exact moment the decision must be made, not several days later.

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Conclusion: building your protection strategy, one decision at a time

Professional strawberry protection is not a programme to apply mechanically — it is a sequence of decisions to be made at the right moment, in the right order, consistent with the production system, the season, and the pests and diseases actually present.

Cultural sanitation — defoliation, runner management, tunnel humidity, long rotation — is the first cost-effective investment. It creates the conditions in which beneficial insects can work and biofungicides can express their efficacy. Without this foundation, beneficial releases are under-dimensioned and biocontrol inputs insufficient.

Commercially available beneficial insects, introduced within the correct thermal and phenological windows, provide durable control of aerial pest pressure — provided they are not undermined by incompatible treatments applied without anticipating their impact on beneficial fauna.

Approved biofungicides and bioinsecticides complete the programme for fungal pathogens and pests for which beneficials are insufficient — provided they are positioned preventively, within rigorously chosen application windows, with rotation of modes of action to preserve their durability.

The variability of all these factors — climatic, varietal, plot-specific, phenological stage — means that the right decision this week on your operation will not be the same as the correct decision on your neighbour's operation, nor the same as the decision you would have made last week.

Fraisibot, your specialist AI agronomic advisor for strawberries, answers your questions in real time taking into account your specific context: your production system, your variety, your phenological stage, and the decisions already made in your programme. Get personalised advice on your strawberry crop with Agronomia — no appointment, no travel, 24/7.

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To explore other aspects of the strawberry growing technical itinerary, browse our articles in the strawberry technical guide.