In August 2024, nurseries sounded the alarm that Neopestalotiopsis-infected strawberry tips were likely to emerge from Prince Edward Island, Canada and be shipped to plug producers and growers in the United States. They also cautioned that producers and farmers should accept plants at their own risk, as no reimbursements would be given for bad or infected plants that were delivered in the fall. Unfortunately, those warnings have come true, and the situation is as bad as anticipated.

There was an understanding that unless producers sourced plants from other regions of the country that do not have issues with the disease (e.g., California), then they should assume that plants are coming in infected with Neopestalotiopsis, even if they look clean and healthy. Growers in the Southeast responded by either looking elsewhere for disease-free planting material, taking the year off from growing strawberries, or accepting infected plants, knowing an aggressive fungicide spray program would likely be necessary in order to have a chance at a productive crop.

Impact in Alabama

There have been a handful of growers in Alabama that were able to order Neopestalotiopsis-free plant material from California. However, other producers in the state accepted plants from infested nurseries and are now fighting the battle to keep the disease at bay. The disease has been detected at multiple commercial farms this fall. Reports from Alabama Cooperative Extension System regional agents and producers suggest that most farms dealing with the disease are ones that accepted plants originating from Canada.

Neopestalotiopsis leaf spot and fruit rot is a relatively new disease to Alabama, first reported in the state in 2022. Damage from the disease in Alabama has been uncommon, but severe outbreaks have occurred in Florida and Georgia over the last 5 years. The common link among past outbreaks was the nursery sources from which the transplants originated.

Dispersal

The pathogen can spread quickly across a planting and to other fields by wind, rain, irrigation, farm equipment, and field workers during harvest and cleaning operations. Disease development is favored by frequent or extended rain events and temperatures above 50 degrees F. The disease has been associated with long periods of rainfall, and this can stimulate a field epidemic if the Neopestalotiopsis pathogen is present. Dry conditions seem to inhibit or reduce spread of the pathogen.

Symptoms

Neopestalotiopsis can produce leaf and petiole lesions and a dark black fruit rot. Leaf spots can be tan to dark brown, of various sizes, and irregularly distributed on infected leaves (figure 1).  Black fruiting bodies, similar to grains of pepper, become visible within the lesion under moist, humid conditions and are visible with a hand lens (figure 2). Petiole lesions appear as brown-to-black lesions that cause the petiole to die back when girdled (figure 3). Fruit rot begins as dry, light tan, slightly sunken, and irregularly shaped lesions. The lesions expand and may take over the entire fruit. These large lesions are eventually covered by dark fungal fruiting bodies (figure 4).

Because the disease can be confused with other diseases of strawberry, Extension plant pathologists recommend weekly scouting for the disease and, when necessary, submitting samples to the Auburn University Plant Diagnostic Lab for proper identification.

Best Management Options

• Do not use unhealthy plants or plants with obvious symptoms of the disease. Destroy plants that are not used in your operation to limit inoculum levels laying around the farm.
• Limit field operations when plants are wet to avoid spreading the pathogen.
• Always work fields that are known to be infected with Neopestalotiopsis last.
• Sanitize your hands, shoes, and clothing when moving out of infected fields.
• Clean and disinfect equipment after moving out of infected fields.
• Remove and destroy symptomatic plants, including crowns and roots, during production to reduce inoculum and disease spread.
• Follow an aggressive fungicide spray program to reduce damage from the disease.

Considerations for a Fungicide Spray Program

A fungicide program will rely on the fungicide, Thiram, as its anchor. Thiram is a contact fungicide but has been found to be moderately effective against Neopestalotiopsis. The Thiram label allows twelve applications east of the Mississippi River. Consider spraying Thiram every 10 to 14 days and optimally ahead of rain events.

Start the fungicide program soon after transplanting but stop the program when temperatures drop below 50 degrees F, as fungal sporulation is inhibited below this temperature. Also, tank mix and/or alternate Thiram with the following fungicides: five applications of Switch and four applications of Rhyme or Tilt or Inspire (these are all DMI-type fungicides). Tilt and other generic products containing the active ingredient, propiconazole, have been reported to cause stunting and yield reduction in other states, so use these products judiciously.