Mary Helen Ferguson

Louisiana strawberry farmers regularly contend with a multitude of challenges, including labor costs, unfavorable weather conditions, insect and mite pests, and plant diseases. In February 2022, a new-to-Louisiana disease was identified when a Tangipahoa Parish strawberry grower asked me to look at a field where plants were dying. To some extent, the symptoms resembled those of other common strawberry diseases, but the combination of collapsing plants with distinctive leaf spots was unusual.

The fungal spores I observed under a microscope immediately caught my attention. They appeared to be those of a pathogen, Neopestalotiopsis sp., that had been recognized several years before in Florida as the cause of a consequential strawberry disease called Pestalotia leaf spot and fruit rot. Because closely related fungi have spores that look similar but do not cause the same disease, a plant sample was sent for DNA sequence-based confirmation of the pathogen.

Within a day of when the farmer called attention to the problem, information was sent to strawberry growers and LSU AgCenter colleagues about the disease, with information on symptoms and what was known about how to manage the disease.   

Since then, my fellow LSU AgCenter Extension agent Clark Robertson and I have worked to keep abreast of research findings about the disease and to educate growers about how to manage it. Besides working one-on-one with growers and providing updates by email, we held meetings for strawberry growers in July of 2023 and 2024 to provide education about managing this disease and other topics of relevance. Each time, the United States’ leading specialist on the disease, Natalia Peres of the University of Florida, joined the group via video conference to answer growers’ questions.

Robertson and I have participated in a project led by the University of Georgia to find out what strains of the Neopestalotiopsis fungus are involved in the disease in the southeastern U.S. Nine of 10 samples tested from Louisiana during the 2023–2024 season were the originally identified aggressive strain. Led by extension specialist and Plant Diagnostic Center director Raghuwinder Singh, the LSU AgCenter recently released a new fact sheet about the disease titled Neopestalotiopsis Leaf, Fruit and Crown Disease of Strawberry.

Besides leaf spots and eventual plant collapse, this aggressive strain of Neopestalotiopsis sp. causes spots on fruit, which make it unsellable. Some plants with infected crowns show leaf reddening before leaf spots or fruit rot are obvious. Like many plant pathogens, the Neopestalotiopsis sp. fungus can survive on diseased plant tissue left in the field. University of Florida research has shown that the pathogen can survive for at least 17 months in intact strawberry crowns. Because of this, growers should practice crop rotation if possible. Crop rotation — or moving where a given type of plant is planted from year to year — is a good practice for managing many diseases. However, because of space and logistical limitations, many growers plant in the same field in consecutive years. When this is done, practices to reduce the population of the pathogen are especially important.

Removing plants from the field is preferable but may not be practical. If plants are left in the field at the end of the season, implements such as disk harrows that chop up plant materials should be used so that they will break down faster. Fumigation with a combination of 1,3-dichloropropene and chloropicrin can substantially reduce Neopestalotiopsis sp. populations in the soil, and fumigation has an important role in managing this disease. However, because fumigants are typically only applied in the raised rows, the fungus can survive in row middles.

It is important that growers acquire clean plants from reputable nurseries, and plants diagnosed with Neopestalotiopsis sp. prior to planting should not be used. However, symptoms are not always apparent at this point. The LSU AgCenter Plant Diagnostic Center plans to offer rapid turnaround testing prior to planting in the upcoming season to identify infected plants before they go in the ground.

If Neopestalotiopsis is suspected, growers should contact their AgCenter Extension agent. Laboratory-based confirmation is needed because several other strawberry diseases have similar symptoms. If the pathogen is identified on the farm, good sanitation is critical. Areas with the disease should be worked in last, and equipment, clothing (including footwear) and hands should be cleaned before moving to other areas. People should avoid working in fields when plants are wet from rainfall or dew because the fungal spores spread in water.

Sampling of row covers that growers use to protect flowers and fruit from cold temperatures revealed that Neopestalotiopsis sp. can survive on soiled areas of the row covers. They may play a role in spreading the fungus and creating an environment more favorable for disease, though growers who use wire hoops to hold up row covers may have a lower risk of spreading the fungus because of reduced contact with plants. Exposure to temperatures of 104 F and hotter has been shown to reduce survival of Neopestalotiopsis sp. spores, so practices such as storing row covers in closed metal tractor trailers during the summer may be beneficial if row covers will be reused.

Fungicides do not provide complete control of Neopestalotiopsis, but Switch (cyprodinil and fludioxonil) and thiram are considered the most effective options. Each can only be used a certain number of times in a season, as indicated on their labels. Switch should be used when conditions are most favorable for disease. Rhyme (flutriafol) and propiconazole (Tilt and others) provide some suppression of Neopestalotiopsis, as well.  

Neopestalotiopsis continues to pose challenges to strawberry growers, but growers have learned to recognize symptoms of the disease and have learned much about how to manage it, including the importance of sanitation practices and what fungicides are effective.

Problematic diseases are not new to strawberries. Besides Neopestalotiopsis, farmers contend with disease issues like grey mold (Botrytis sp.), Phytophthora root and crown rot, and anthracnose fruit rot. The fungi that cause grey mold readily develop resistance to fungicides when products with the same modes of action are used repeatedly. Robertson and I have participated in projects to test for fungicide resistance so that we can let growers know what fungicides remain effective for this disease. 

Agriculture requires continual vigilance for the arrival of new diseases and arthropod (insect and mite) pests. The LSU AgCenter addresses emerging issues that threaten Louisiana crops so farmers can continue to produce them economically and so local fruits and vegetables remain available to Louisiana consumers.

Mary Helen Ferguson, an AgCenter Extension agent focusing on horticulture, is based in Tangipahoa Parish.

This article appears in the spring 2025 edition of Louisiana Agriculture.

These Florida Brilliance strawberry plants show symptoms of Neopestalotiopsis. Photo by Mary Helen Ferguson

A diseased strawberry fruit has a light brown sunken lesion caused by Neopestalotiopsis fruit disease. Photo by Raghuwinder Singh

Leaf spots are caused by the Neopestalotiopsis fruit disease. Photo by Mary Helen Ferguson