Neopestalotiopsis, or Neo-P, has been a devastating pathogen for field-grown strawberries, but it also threatens strawberries grown in controlled environment agriculture (CEA) structures.
And while the majority of Neo-P cases in Ohio have been in field-grown strawberries, Melanie Lewis Ivey, associate professor of fruit pathology in the Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES), is part of a research team looking into how Neo-P could affect CEA-grown strawberries.
Lewis Ivey says it’s been hard to estimate the true losses in the state, because not all growers report losses and some growers struggled to get clean transplants, which is a major challenge.
“For growers that lost 100% in some cases, it was because they couldn’t plant a crop because they could not get clean transplants,” she says. “In other instances, the disease spread so quickly they could not do anything about it.”
Symptoms
Lewis Ivey says the research team has discovered different variability in the aggressiveness of the fungus as well as cultivar susceptibilities. Some growers plant in the spring, while others plant in the fall, which she says can also impact disease severity and incidence.
“The first symptoms that growers will notice are brown lesions on the leaves that begin at the edge of the leaflets,” Lewis Ivey says. “The lesions are often V-shaped but not always. As the lesions get larger, black spots (the spores) can be seen in the lesion if a hand lens is used. They may also notice that their plants are stunted or wilting. Stunting and wilting are due to an infection in the crown of the plant.”
Lewis Ivey says that Neo-P symptoms on the fruit appear as brown sunken spots; sometimes growers may confuse the pathogen with that of anthracnose fruit rot, and proper pathogen identification is crucial for treatment. But strawberry growers have yet to see symptoms appear in fruit because strawberry plants die from the Neo-P pathogen before fruiting.
Growers also face the challenge of limited options of nurseries that offer transplants, she says, and many plants can be asymptomatic, which makes it harder for nurseries to detect infections.
Lewis Ivey says it’s critical that growers take a defensive approach and quarantine all plug transplants for about a week. She says she also recommends growers cut open the crown of a small percentage of plugs — about 5% — and scout for discoloration. Growers can also use fungicide dips for bare-root transplants or drenches for plugs, but the efficacy of such treatments is still unknown, she says. Once growers plant the transplants, she recommends scouting often.
“Since this disease develops and spreads rapidly, it is important to catch it early,” she says.
Lessons Learned
In Lewis Ivey’s preliminary studies, she says her team discovered Neo-P can survive in silt loam soil for about four months.
“We infected strawberry plants and buried them about 5 centimeters in the soil within a high tunnel in December and sampled once a month,” she says. “We were able to recover the fungus from the plant debris in January, February and March, and April.”
Lewis Ivey says her team plans a more comprehensive study this fall, with a look at high tunnels and open fields to learn more about the pathogen’s survival. She says the team also plans to research what part of a strawberry plant offers the highest probability for fungal detection.
Her team also seeks to determine variety susceptibility to Neo-P in CEA structures as well as the efficacy of fungicides and fungicide alternatives to prevent the pathogen’s spread, she says.
“There are limited fungicides that are registered for strawberries grown in CEA, so finding alternatives, such as biological control or nanoparticles, is extremely important,” she says. “We are also in the early stages of developing an early detection assay for transplants. If we can detect the fungus in asymptomatic transplants, then we can develop best practices for handling infected transplants.”
Lewis Ivey says resistance management is also a big challenge for growers.
“Because there are so few fungicides registered for CEA growers, it is very challenging to develop a spray program that doesn’t overuse one specific mode of action,” she says. “Fungi can become resistant to a fungicide if the same mode of action is used repeatedly, so it is critical that different modes of action are used throughout the season.”
And growers often face more pathogens than just Neo-P, which can also complicate resistance management practices. Lewis Ivey says she sees an opportunity for control strategies that involve biological controls for CEA strawberry growers.
”Developing spray programs that integrate biologicals, focusing on application timing and disease risk level, is the future of strawberry disease management in CEA,” she says.
Lewis Ivey says her research team also wanted to look at how the pathogen moves through the greenhouse — through water and plants — but unfortunately, her research project faced funding cuts, so that portion of the research is on hold.
“As we learn more about the epidemiology of Neo-P in CEA, we will be able to make recommendations on system design, water management and best sanitation practices,” she says. “When considering system design and disease management, we must also consider plant growth and fruit quality, which makes the situation even more complex.”
