Neopestalotiopsis Crown, Leaf and Fruit Disease on Strawberry

Bill Cline and Swarnalatha Moparthi, Entomology and Plant Pathology Department, NCSU

Neopestalotiopsis crown, leaf and fruit disease (caused by Neopestalotiopsis sp. fungi) is an important emerging disease of strawberry that can affect every part of the plant (crown, roots, leaves, fruit). The symptoms were first widely known in the US on strawberry in 2018, following an outbreak in Florida in annual plasticulture fields. The pathogen is most frequently introduced via infected planting stock and has impacted production across the eastern US, the Gulf Coast and Mexico.

Symptoms and Signs

Leaf spots (Fig. 1) are often the earliest visible symptom of Neopestalotiopsis infections in newly planted strawberry fields and can occur in the fall and winter as plants are getting established. Leaf symptoms can resemble those caused by other pathogens such as Gnomonia leaf spot, Phomopsis leaf spot, or secondary organisms like Alternaria sp. Culturing or moist-chamber incubation followed by microscopic examination of spores is required for accurate diagnosis.

Crown infections cause wilting, stunting, and death of infected plants. Wilting can occur at any time in the growing cycle but is most severe when plants are producing fruit. Above-ground symptoms of crown rot include characteristic reddening of older leaves, while new emerging leaves may be stunted and mottled, followed by overall wilting and plant death (Fig. 2).

Fruit infection results in sunken, tan lesions with black sporulation (Fig. 3). Early symptoms resemble other fruit rots (Gnomonia, leather rot, Botrytis, anthracnose) but can be distinguished by the distinctive black spore masses on lesions (Fig.4), and further by microscopic identification of the distinctive spore morphology (Fig 5.)

Overview of the Disease

While infected planting stock is the most likely source of disease, the fungus can also persist in the soil on old, infected crowns and strawberry plant debris, so it is possible for the pathogen to carry over from one year to the next in fields with a history of Neopestalotiopsis. It is not clear to what extent this “oversummering” contributes to disease in North Carolina – infested fields have been observed to have little or no disease the following year when clean plants were used in the second year. The risk of carryover may be greater after severe outbreaks, or after multiple years without rotation.  In-field spread during the fruiting season is likely through rain-splashing and wind, and on contaminated hands, clothing and equipment, with infection occurring during periods of extended leaf wetness.

Best Management Practices

The use of disease-free plants is the primary means of avoiding this disease. There are no known resistant cultivars. The efficacy of dip treatments is not known. For fields with a prior history of strawberry production and especially where Neopestalotiopsis occurred in the previous year, bed fumigation is strongly encouraged. For fields that are fallow over the summer between strawberry crops (June to September), repeated passes with a disc harrow can be used to break up crop debris. Bottom plowing (turn-plowing) can be used to further bury crop debris.

Once strawberries are planted, avoid handling plants when wet, and practice sanitation of workers’ hands, clothing, boots and tools. To prevent the spread of disease, avoid moving from infected fields to clean fields during hand labor operations, such as when removing dead leaves or harvesting fruit. Work in problem fields last to minimize the risk of spreading spores to non-infested areas. Sanitize equipment and avoid sharing equipment between fields or between farms. It is not practical to remove infected leaves during the fruiting season, but there may be some benefit to removal and destruction of symptomatic plants with crown wilt symptoms, both to reduce spore production and to limit the spread of disease. Removing infected plants, including their crowns and roots, from the field helps reduce the amount of infected plant debris that could otherwise persist and serve as a potential source of infection in the following year. Fungicides known to have efficacy against Neopestalotiopsis (Thiram, Switch, Tilt, Inspire, Rhyme) should be used in the fall if plants are known to be infected, and can be incorporated into a weekly spray program during bloom and harvest. Apply fungicides in an alternating schedule to avoid relying on a single fungicide mode of action. It is currently not known whether any fungicide-resistant strains exist.

Where Neopestalotiopsis is Known or Suspected to be Present

• Pre-plant – Bottom plow and disc harrow to bury old strawberry crowns and debris.
• Pre-plant – Rotate fields for two years when possible.
• Pre-plant – Fumigate beds prior to planting.
• At planting – Bring in disease-free transplants.
• At planting – Cull plants – do not plant unhealthy plants and destroy those not planted.
• Fall – Apply efficacious fungicides after planting every 7-14 days until cold weather.
• Year-round – Limit field operations, such as harvesting and spraying, when plants are wet.
• Year-round – Sanitize hands, shoes, and clothing when moving out of infected fields.
• Year-round – Clean and disinfect equipment when moving out of infected fields.
• Year-round – Remove and destroy symptomatic plants to reduce the spread of disease.
• Spring – Apply efficacious fungicides in rotation with routine sprays for other diseases.
• Spring – Use good sanitation practices — avoid overhead watering, cull & destroy infected fruit.

Suggested Spray Program (Fall)

When applied as directed for control of labeled diseases, these fungicides have shown efficacy against Neopestalotiopsis and can be used in rotation as shown below.  Apply immediately after planting and continue as new leaves emerge, on a 7-to-14-day schedule.  Use longer intervals between sprays under dry conditions and shorter intervals in wet conditions when disease pressure is high.  Good coverage is critical. Use adequate pressure (>80 PSI) and 80-100 gallons of spray solution per acre. A good article on building a sprayer is linked below.

• Spray # 1 – Thiram SC at 2 to 2.5 qt per acre
• Spray # 2 – Tilt, Rhyme or Inspire at labeled rates
• Spray # 3 – Thiram SC at 2 to 2.5 qt per acre
• Spray # 4 – Tilt, Rhyme or Inspire at labeled rates
• Spray # 5 – Thiram SC at 2 to 2.5 qt per acre

Sources

• Neopestalotiopsis Leaf, Fruit, and Crown Rot of Strawberry
• UPDATE: Neopestalotiopsis (Neo-P)
• Dramatic Neopestalotiopsis Disease in Strawberry Tips and Plug Plant Production Nurseries
• Constructing a Cheap and Effective Strawberry Sprayer (PDF)