Frequently asked questions
about plant diseases and treatment
Our current disease knowledge focuses primarily on strawberry production, where Moleda has extensive practical experience and scientific evidence. This knowledge centre will continue to grow as further research and application data become available.
Botrytis (grey mould)
Botrytis cinerea
Botrytis, also known as grey mold, is a widespread fungal disease of strawberries caused by Botrytis cinerea. It primarily affects flowers and fruit, causing soft brown decay and characteristic grey fungal growth, and can lead to significant fruit losses and reduced crop quality.
Can you steam-treat strawberry plants to stop Botrytis (grey mould)?
Yes. Botrytis cinerea travels as latent inoculum on the transplant leaf. In the Florida heat study on Florida Radiance, leaf colonisation fell to 0–3% and grey-mould leaf incidence dropped 95.3–100% — a near-complete clean before planting, with no yield penalty from the standard cycle.
Source: Zuniga, Wang & Peres (2023) — Heat Treatment to Reduce Botrytis Inoculum on Strawberry Transplants, Plant Health Progress 24
Does treating strawberries for grey mould cost yield?
No measurable cost under the standard cycle. In the NMBU tray-cultivar study, cv Soprano showed cumulative fruit yield statistically unchanged — numerically a touch higher — with days-to-first-flower and runner number unaffected. Survival and yield held across Soprano, Murano, Falco, Favori and Sonsation.
Source: Gahatraj (2021/2023) — Aerated steam treatment against grey mould in strawberry transplants, M.Sc. thesis, NMBU
Does steam protect against Botrytis in the field later in the season?
No — and we say so plainly. Aerated steam clears the latent grey-mould inoculum the plant carries in before planting. It is not a spray and does not protect against reinfection from field or air later in the crop. It gives a clean start, not season-long field cover.
Source: Zuniga, Wang & Peres (2023) — Heat Treatment to Reduce Botrytis Inoculum on Strawberry Transplants, Plant Health Progress 24
Which strawberry variety is the Botrytis reference in the research?
Florida Radiance is the grey-mould test cultivar — the source of the headline figures, leaf colonisation to 0–3% and grey-mould leaf incidence down 95.3–100%. Five tray cultivars (Soprano, Murano, Falco, Favori, Sonsation) then confirmed survival and yield hold under the standard cycle.
Source: Zuniga, Wang & Peres (2023) — Heat Treatment to Reduce Botrytis Inoculum on Strawberry Transplants, Plant Health Progress 24
How is steam different from a Botrytis fungicide?
A spray acts in the field, on the growing crop. Aerated steam acts once, on the transplant, before planting — clearing the latent Botrytis cinerea the plant would otherwise carry in. It is a clean-start tool, not a field treatment, and does not protect against later reinfection.
Source: Zuniga, Wang & Peres (2023) — Heat Treatment to Reduce Botrytis Inoculum on Strawberry Transplants, Plant Health Progress 24
Powdery mildew
Podosphaera aphanis
Powdery mildew is a common fungal disease of strawberries caused by Podosphaera aphanis. Typical symptoms include white, powdery fungal growth and upward curling of the leaves, while flowers and fruit can also become infected, affecting plant health, fruit quality and marketability.
Can steam treatment control powdery mildew on strawberry transplants?
Yes. Aerated steam is documented to eradicate strawberry powdery mildew (Podosphaera aphanis) from transplants, including multiresistant strains. In the European practice trials, Korona plug plants came through with mildew killed and aphids dried, then recovered well after planting — the basis for a clean, chemical-free start.
Source: Stensvand et al. (2023) — Aerated steam eradicates powdery mildew from strawberry transplants, Eur. J. Plant Pathol.
Does steam work on fungicide-resistant powdery mildew?
This is where it matters most. Powdery mildew is exactly the pathogen where chemistry is failing. A Norwegian grower lost 60,000 plants in a single multiresistant-mildew event — the kind of collapse a clean steam start prevents, because heat does not depend on a chemical mode of action.
Moleda record — Ekeberg Myhrene, Norway (~6-season Florice/Favori powdery-mildew record)
How many fungicide sprays can a clean start save?
In the Norwegian record, sprays fell from 5–6 to 0–2 a season across roughly six years running 720,000 Florice and Favori plants through Plantsauna. Over that period two collapse events alone represent about 3.3% of crop safeguarded — a conservative floor, before any silent season-long gain.
Source: Moleda record — Ekeberg Myhrene, Norway (~6-season Florice/Favori powdery-mildew record)
Will the heat damage the plant?
Dormancy protects it. The more dormant or cold-stored the plant, the better it tolerates the cycle — two weeks near 0 °C raised tolerance in trials, and a pre-heat step induces heat-shock proteins that raise it further. Korona plug plants recovered well after treatment.
Stensvand et al. (2023) — Aerated steam eradicates powdery mildew from strawberry transplants, Eur. J. Plant Pathol.
Which varieties is the powdery-mildew evidence based on?
Korona plug plants in the European practice trials (mildew killed, aphids dried, good recovery), and Florice and Favori in the six-season Norwegian commercial record — the operation where the multiresistant-mildew collapse event a clean start prevents was documented.
Source: Lieten & Gallace (2020–21) — Aardbeien: ervaringen met de plantsauna (Fruit) / Recenti sviluppi in vivaio (Frutticoltura)
Angular leaf spot
Xanthomonas fragariae
Angular leaf spot is a bacterial disease of strawberries caused by Xanthomonas fragariae. It typically appears as small, angular, water-soaked lesions on the leaves and can spread through infected plant material, posing a particular risk in strawberry propagation and production. In severe cases, the disease can reduce plant quality and affect overall crop health.
Does steam treatment clear angular leaf spot from strawberry plants?
Yes, when the cycle is matched to the variety. Angular leaf spot (Xanthomonas fragariae) is carried on the transplant; in the field it appeared only on untreated plants. Heat took ALS on Oso Grande to zero, and on tolerant Strawberry Festival a harder cycle cleared it with minimal survival loss.
Source: Turechek & Peres (2009) — Heat Treatment Effects on Plant Survival & Angular Leaf Spot, Plant Disease 93
Why must the treatment be matched to the variety for angular leaf spot?
Because the hard cycles that clear the bacterium can stunt sensitive cultivars. Festival tolerated a harder cycle; Camarosa and Ventana need a gentler cycle with the pre-heat. Matching the cycle to the cultivar is the whole craft — clear the pathogen without costing the plant.
Source: Turechek & Peres (2009) — Heat Treatment Effects on Plant Survival & Angular Leaf Spot, Plant Disease 93
Which varieties carried angular leaf spot in the trials?
In the Florida field study, ALS appeared untreated on Strawberry Festival, Camarosa and Oso Grande. Festival was heat-tolerant, Oso Grande intermediate (heat took its ALS to zero), and Camarosa heat-sensitive — the reason it needs the gentle cycle and the pre-heat.
Source: Turechek & Peres (2009) — Heat Treatment Effects on Plant Survival & Angular Leaf Spot, Plant Disease 93
Is angular leaf spot a variety weakness or a plant-hygiene problem?
Both — but it rides in on the transplant, which is why a pre-plant treatment is the logical intervention point. The bacterium showed only on untreated plots in the trial; a clean, matched-cycle start is what kept it out of the treated crop.
Source: Turechek & Peres (2009) — Heat Treatment Effects on Plant Survival & Angular Leaf Spot, Plant Disease 93
Insect Pests
Insect pests can cause significant damage to strawberry plants by feeding on leaves, flowers, roots or developing fruit. Common pests in strawberry production include tarsonemid mites, leatherjacket larvae, flower thrips and aphids, which can affect plant health, growth and crop quality at different stages of production.
Mites (strawberry & spider mite)
Phytonemus pallidus / Tetranychus urticae
Does steam treatment kill mites on strawberry transplants?
It clears strawberry mite, but not spider mite. In the NIBIO study, a full aerated-steam cycle killed every strawberry-mite (Phytonemus pallidus) egg, larva and adult; the shorter cycle killed all stages bar a single egg. The two-spotted spider mite (Tetranychus urticae) was barely affected — an honest limit.
Source: Johansen et al. — Aerated steam against mites (P. pallidus, T. urticae) in strawberry transplants, NIBIO
Does steam work on two-spotted spider mite?
No — and we say so. The two-spotted spider mite was barely affected by the same aerated steam that fully clears strawberry mite; it needs a different tool. Note: a 99.8% mite figure quoted elsewhere is the CATT method, a different treatment from aerated steam.
Source: Johansen et al. — Aerated steam against mites (P. pallidus, T. urticae) in strawberry transplants, NIBIO
Nematodes
Plant-parasitic nematodes are microscopic roundworms that can damage strawberry plants by feeding on roots and other plant tissues. Infestations can lead to poor root development, stunted growth and reduced plant vigor, potentially affecting crop establishment, yield and overall plant health.
Root-knot Nematode
Meloidogyne javanica
Which strawberry variety is most at risk from nematodes?
Susceptibility is a varietal trait. In the organic Florida trial, Winterstar FL 05-107 carried the highest root-knot nematode (Meloidogyne javanica) densities — with galling, canopy reduction and a gall index of 4.4. The pest, not the treatment, was what limited its fruit yield, making it the cultivar most worth starting clean.
Source: Oliveira et al. (2023) — Nematode dynamics & plant steaming on strawberry cultivars, organic Florida, Nematology
Do nematode levels vary between strawberry cultivars?
Yes, markedly. The organic Florida study tracked root-knot nematode (Meloidogyne javanica) dynamics across cultivars and found densities differed by variety, with Winterstar FL 05-107 the clear magnet. Because the burden travels with susceptible planting stock, a clean start matters most on the prone cultivars.
Source: Oliveira et al. (2023) — Nematode dynamics & plant steaming on strawberry cultivars, organic Florida, Nematology
Phytophthora crown rot
Phytophthora cactorum
Phytophthora crown rot is a serious soil-borne disease of strawberries caused by Phytophthora species, particularly Phytophthora cactorum. The pathogen attacks the crown and roots, causing wilting, stunted growth and characteristic reddish-brown discoloration inside the crown, and can ultimately lead to plant death.
Can steam treatment stop Phytophthora crown rot in strawberries?
Yes — this is steam’s strongest, most-repeated result. Phytophthora cactorum rides in on the transplant. Across seven Hoogstraten trials on cv Sonata, steam consistently lowered plant loss, often to near zero: at one grower loss fell from about 46% to 1% with a correct treatment.
Source: Moleda dossier — Proefcentrum Hoogstraten (Risicover VLAIO) Phytophthora trials, 2020–2022
How does steam compare to a chemical programme for Phytophthora?
It beat one, chemical-free. On deliberately inoculated stock the sauna limited dropout and gave a fuller, more uniform crop — below both untreated plants and a full six-spray chemical programme. In inoculated field trials, crown rot fell from 80% to 5%.
Source: Moleda dossier — Proefcentrum Hoogstraten (Risicover VLAIO) Phytophthora trials, 2020–2022
Does Phytophthora risk depend on the strawberry variety?
Less than growers assume — it is variety × stock quality × nursery. The same Sensation Florida127 stock ran 0% to 62.5% Phytophthora depending only on where it came from; Florida Radiance ran 0–20%. That spread within one cultivar is why a clean start matters regardless of variety.
Source: Baggio, Marin & Peres — Phytophthora Crown Rot of Florida Strawberry: Inoculum Sources & Thermotherapy of Transplants
For a winter or frigo crop, should plants be treated before or after frigo storage?
After frigo, never before. In the Hoogstraten trials, treating after frigo storage gave the lowest loss (~3%); untreated ran ~9%, chemical ~10.5%, and treating before frigo was worst at ~16.5%. For winter and frigo crops the timing rule is decisive: defrost, then treat.
Source: Moleda dossier — Proefcentrum Hoogstraten (Risicover VLAIO) Phytophthora trials, 2020–2022
Does steam work against mefenoxam-resistant Phytophthora?
Yes. Heat does not depend on a chemical mode of action, so thermotherapy worked even on mefenoxam-resistant isolates in the Florida trials — cutting crown rot from 80% to 5%, and to 2.5% versus 30% in a second run. It also lengthened the disease-incubation period across storage.
Source: Baggio, Marin & Peres — Phytophthora Crown Rot of Florida Strawberry: Inoculum Sources & Thermotherapy of Transplants
Pestalotia leaf spot
Neopestalotiopsis sp.
Pestalotia leaf spot is a fungal disease of strawberries associated with Neopestalotiopsis species. It can cause brown to dark leaf spots and lesions and may also affect crowns, roots and fruit, potentially leading to plant decline, reduced fruit quality and significant crop losses.
Can heat treatment control Neopestalotiopsis on strawberry transplants?
It reduces the inoculum sharply, though it does not fully eradicate it. Neopestalotiopsis sp. — cause of Pestalotia leaf spot — rides in on cryptically infected nursery transplants. In the Florida thermotherapy study, treatment cut disease incidence by 49.7–68.8% and severity by 82.2–94.6% on naturally infected plants.
Source: Zuniga, Baggio, Lopes, Duarte & Peres (2025) — Thermotherapy of Strawberry Transplants as a Possible Tool for Neopestalotiopsis sp. Management, PhytoFrontiers 5:402–410
Does the treatment eradicate Neopestalotiopsis, or only suppress it?
Suppress — and we say so plainly. It is a strong knock-down of the transplant inoculum, not a clean kill. Under heavy artificial inoculation the effect was smaller (incidence reduced about 52.5% on heat-treated inoculated plants), so it is best used as one tool within a management programme.
Source: Zuniga, Baggio, Lopes, Duarte & Peres (2025) — Thermotherapy of Strawberry Transplants as a Possible Tool for Neopestalotiopsis sp. Management, PhytoFrontiers 5:402–410
Where does Neopestalotiopsis come from, and why is it spreading?
It arrives on nursery transplants as a cryptic, hidden infection — first introduced to Florida in the 2017–2018 season through infected nursery material. Because it travels on the plant, a pre-plant treatment targets it at the point of entry, before it establishes in the crop.
Source: Zuniga, Baggio, Lopes, Duarte & Peres (2025) — Thermotherapy of Strawberry Transplants as a Possible Tool for Neopestalotiopsis sp. Management, PhytoFrontiers 5:402–410
Is Neopestalotiopsis a problem in Europe and Spain?
Yes — it is an emerging threat. A 2026 study confirmed three Neopestalotiopsis species behind strawberry outbreaks in Spain (N. rosae predominant, plus N. iranensis and a new isolate), causing leaf spot and crown rot. It is reported across several countries as a cause of fruit rot, leaf spot and root rot.
Source: López, Pastrana, Marín, Borrero, Peres & Avilés (2026) — Molecular characterization reveals three Neopestalotiopsis species causing strawberry disease outbreaks in Spain, Frontiers in Plant Science
Does treating for Neopestalotiopsis cost early yield?
No measurable cost. In the thermotherapy study, no significant differences were found among treatments for early-season yield. The reduction in transplant inoculum came without an early-yield penalty — consistent with steam’s record on other strawberry pathogens of clearing load without costing the crop.
Source: Zuniga, Baggio, Lopes, Duarte & Peres (2025) — Thermotherapy of Strawberry Transplants as a Possible Tool for Neopestalotiopsis sp. Management, PhytoFrontiers 5:402–410
Anthracnose
Anthracnose is a fungal disease of strawberries caused by several Colletotrichum species. It can affect leaves, runners, crowns, flowers and fruit, causing dark lesions, crown rot and fruit decay, and can lead to plant decline and significant crop losses.
