This summer, the North American strawberry sector was shaken by outbreaks of Neopestalotiopsis, a fungal disease that affected nurseries in Nova Scotia. Alarm bells were raised there, as nurseries could no longer guarantee clean plant material, and it has been confirmed strawberry pot plants were sent to growers that were infected with the disease Neopestalotiopsis. Petra van der Goes, an expert on strawberries and plant diseases from Plant Quality Solutions, is familiar with the disease from Europe. "Neopestalotiopsis is manageable if we take the right measures, both above and below ground."
The emergence of Neopestalotiopsis in Europe
Neopestalotiopsis is not a newcomer to plant diseases. It has been a known threat in Europe for years, particularly in strawberry cultivation. "In the Netherlands, we started noticing the disease around 2010 when several systemic fungicides were banned," Petra explains. "These chemicals had unknowingly played a significant role in preventing Neopestalotiopsis. Once they were removed, plants suddenly began to fail without an immediate understanding of the cause."
"Initially, we suspected Phytophthora," she continues. "The symptoms, such as wilting and brown spots on the leaves, seemed to match. However, when we sliced through the rhizomes, the plant's root structures revealed different patterns caused by the fungus Pestalotiopsis, which was later reclassified as Neopestalotiopsis."
Through research, the origins and spread of Neopestalotiopsis have become increasingly clear. Since 2015, it has been recognized as a disease in Dutch cultivation, causing issues similar to Fusarium and other soil pathogens. "It's troublesome, but not cause for major alarm."
Symptoms
Petra emphasizes that the symptoms of Neopestalotiopsis are not always immediately visible on the surface of the plant, which makes the disease particularly insidious. Growers often focus on above-ground symptoms, while the real damage usually occurs underground. "You might only notice small spots on the leaves or a plant that appears slightly limp. But if you look deeper, at the rhizome, you may find that the fungus has already made significant progress," she explains.
The fungus blocks the plant's vascular bundles, disrupting the flow of water and nutrients. "It's like trying to push water through a flattened straw: the plant can no longer absorb water, it wilts, and ultimately dies." She advises growers to slice through the plants and conduct a thorough inspection, especially if they suspect something is wrong. "Only by checking the rhizome can you be certain if it's Neopestalotiopsis. Cut it open and, if necessary, replant."
The spread of Neopestalotiopsis
One of the challenges posed by Neopestalotiopsis is the rapid speed at which the fungus can spread, particularly through root contact. "If a plant in a field becomes infected, the fungus can quickly transfer from one plant to another via the roots, spreading like wildfire," she explains. This makes it especially dangerous in fields with soil cultivation, where plants are closely spaced and root contact is inevitable. "In outdoor field production, rain can also facilitate the spread from leaf to leaf as droplets splash onto the ground." Additionally, the fungus can be carried by wind. "Neopestalotiopsis is not just a pathogen of strawberries; it can also cause dieback in various shrubs."
In greenhouse or other controlled environments, the spread is more limited. Here, irrigation water can act as a carrier for the fungal spores, particularly in regions using drip irrigation or where rain is a factor. "In the greenhouse, you can keep the crop drier to limit the spread, but outdoor cultivation is a very different story," Petra warns.
Rain plays a significant role in this context. Since plants are often grown in tray fields, infections can easily occur with the tray plants. In greenhouses, the further spread is primarily through root contact. "This is easy to manage in containers or bags, but the spread is less significant between bags."
Why now?
A logical question is why Neopestalotiopsis has suddenly appeared in North America. According to Petra, the disease has likely been present for years. The outbreak may be attributed to a combination of factors, including changes in pesticide use and weather conditions. "High temperatures, heavy rainfall, and elevated nighttime temperatures—all of these factors can cause stress," she explains. "This weakens the plants and makes them more susceptible to infections. One grower might face Colletotrichum, while another deals with Neopestalotiopsis. It's like playing Russian roulette."
What should you do if you've placed an order with a nursery that warns of Neopestalotiopsis? After the disease was identified in nurseries on Prince Edward Island in Canada, several plant growers informed their customers this year that orders could be canceled at no charge, or that plants would need to be accepted at the buyer's own risk.
However, for plant buyers, finding an alternative supplier can be challenging. "They either have no plants available or are unwilling to ship from a small nursery," explains a grower from Florida. "We might not have strawberries available in 2025." She refuses to accept infected plants. "The risk is too great," she says. "We can place an order, but if we lose everything, we lose everything."
Control and prevention
Growers are generally advised to assume that pathogens may be present in plant material, regardless of its origin. At the same time, having clean starting material is a key aspect of prevention, according to Petra. "If the mother plants are infected, there's a high chance that the cuttings will also be infected. This is especially true for tray plants grown outdoors, where the fungus can spread through the air, as well as for bare root plants in the field." Accepting infected material, therefore, depends on the severity and percentage of infection. "You shouldn't have to accept completely diseased material, but contamination can occur through various means. You can't prevent stress and airborne spores."
While North American growers are often advised to spray aggressively, the strawberry expert sees much more potential in biological prevention, such as inoculation with endophytes. "These are often fungi that protect the plant from both the outside and inside through the root system. This method acts as an endophyte, meaning it lives within the plant and helps combat the fungus," she explains. She emphasizes that if contamination occurs, it's crucial to take preventive measures. "Once you see symptoms, it's often too late to save the plant. At that point, it's essential to protect the rest of the crop." She isn't convinced about the effectiveness of spraying above ground. "Contact treatments don't reach where they need to. While you see the symptoms above ground, the cause lies underground. Focus on controlling the spread there. Use biological control agents and ensure they are well incorporated: spray and drench."
A silver lining is that Neopestalotiopsis is not extremely aggressive. Even with some infection, it's still possible to have a good season. However, Petra advises growers to carefully inspect plants before transplanting them. "If you see a plant that doesn't look healthy, you should remove it immediately to protect the rest of your crop," she says. "You might only have a few sick plants, but if you don't act quickly, the entire crop could become infected." She reiterates the importance of slicing through the plants and inspecting the rhizomes.
Impact on the market
Living with Neopestalotiopsis is manageable, but the available resources for disease control are increasingly limited. "In Europe, many treatments have already been banned. I have a harder time assessing the situation in North America, but there too, the focus will need to shift more towards prevention in cultivation," Petra observes. This, combined with market pressures and extreme climate conditions, certainly presents challenges for growers. "Many want to be on the market by Christmas, but not all varieties can handle that. With temperatures exceeding 35 degrees Celsius and nighttime temperatures above 20 degrees, it's tough for the plants. You need to choose varieties that can withstand these conditions or adjust your cultivation practices."
"We're already seeing countries like Italy and Spain increasingly adopt soil-less cultivation systems, such as greenhouses, troughs, and tunnels," she continues. "These methods help keep diseases like Neopestalotiopsis under better control and provide protection from the weather. In North America, the shift to soil-less systems is not yet fully realized. They do use tunnels for protection, but once the covering is removed for harvesting, the plants are still exposed to the outside environment." Petra anticipates that the focus in the coming years will increasingly be on reducing exposure to environmental factors and developing resistant varieties.
For more information:
Plant Quality Solutions
Petra van der Goes
Email: [email protected]
www.plantqualitysolutions.com