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Plant and Pest Advisory – Andy Wyenandt – August 23, 2024
Neopestalotiopsis, a new disease on strawberry is back in the news. Please see the excellent article
by Dr. Phil Brannen from the University of Georgia August 21, 2024.
Neopestalotiopsis fruit rot and leaf spot, caused by Neopestalotiopsis species, was first reported
to cause damage in strawberry fields in Florida in 2019 and 2020. This disease has since been
observed in most southeastern states, and it is already making headlines for this coming 2024-2025
season. As many strawberry producers are aware, some nurseries are already “ringing the alarm
bells” for Neopestalotiopsis. There is a major pass through to strawberry nurseries and producers
through use of tips from Prince Edward Island. One of the major nurseries that provides tips sent
out a letter on August 19, 2024 associated with the problem, and other nurseries are following suit.
They are basically canceling orders (and in many cases refunding the deposit) or telling plug plant
producers and farmers to take plants at their own risk – no reimbursements for bad or infected plants
delivered this year. The disease levels currently observed in nurseries, as well as these limitations
on accepted liability, will likely impact the supply of tips and therefore plug plants for many strawberry
producers. As far as we are aware, this is the first year that there has appeared to be a direct and
immediate link to Prince Edward Island, and that is a major concern for the industry as we move
forward. With that said, we have to do the best we can with the hand we have been dealt.
In the nursery phase, some plug plant producers will still attempt to produce plants from infested
tips. Indeed, some may produce plants that appear healthy or relatively healthy. If a producer opts to
receive plug plants from suspect nurseries, those with known Neopestalotiopsis-infected plants, they will need to cull any plants that appear unhealthy when they arrive. Though this may seem
wasteful, the inoculum levels of Neopestalotiopsis are directly related to the levels of disease that
will be observed as the season progresses. Therefore, culling unhealthy plants prior to planting will
be instrumental to producing a crop. Also, unless a producer receives plants from a region that does
not have Neopestalotiopsis issues yet (e.g. California), all producers should assume that the plants
are coming in with the pathogen – even if the plants look clean and healthy. Therefore, an aggressive
spray program that incorporates management for Neopestalotiopsis, as well as all other strawberry
diseases, will be necessary from the time of transplanting.
There has been a strong association with this disease and long periods of rainfall, so a dry season
may limit the disease levels observed. However, rainfall is generally prevalent at some point during
strawberry production, and this will trigger a field epidemic if the Neopestalotiopsis pathogen is
present. The following are the current best management options: (1) bring in disease-free transplants;
(2) avoid planting varieties that are highly susceptible (no true resistant varieties available yet); (3)
do not plant unhealthy plants and destroy the ones not planted; (4) limit field operations, such as
harvesting and spraying, when plants are wet; (5) sanitize hands, shoes, and clothing when moving
out of infected fields; (6) clean and disinfect equipment when moving out of infected fields; (7) remove
and destroy symptomatic plants (including crowns and roots) during production to reduce inoculum
and disease spread; and (8) incorporate “efficacious” fungicides into an ‘aggressive’ spray program.
After harvest is complete, make sure that fields are thoroughly harrowed to break up the remaining
strawberry crowns. Following harvest, rotation for two years with other crops would be ideal, allowing
survival structures to break down and die. Pre-plant fumigation is recommended and helpful in order
to reduce inoculum levels, but it will not control the disease fully from year to year. Use of both Vapam
and PicClor 60 may broaden the efficacy of fumigation against fungal pathogens.
Of the options above, we are now limited due to timing. Producers should bring in the best plants that
are available. Since finding clean plants may be difficult at this late date, producers will simply need
to think about their level of risk tolerance, with some opting to skip production this year altogether.
For those who move forward, Thiram will provide the backbone of a spray program this year. It is
a contact fungicide, but it has pretty good efficacy against Neopestalotiopsis, as well as Botrytis.
However, EPA will likely remove Thiram from the market soon, so make sure to keep abreast of
potential regulation changes. For now, some Thiram labels allow up to 12 applications if a farm is
east of the Mississippi River, but the same labels limit applications to five if west of the Mississippi
River. Keep that in mind. Without regard, consider spraying the maximum number of applications
of Thiram allowed by label (every 10-14 days and optimally ahead of rain events) – starting soon
after transplanting but ceasing with extreme cold during the winter and continuing in the spring. In
addition, tank mix and/or alternate the following fungicides with Thiram for the maximum number of
applications allowable – Switch (five applications at 11 oz/acre) and four applications of Rhyme or Tilt
or Inspire (all of these are DMI fungicides); note that Tilt and other generics containing propiconazole
should be limited to three or fewer applications, as stunting and yield reduction has been reported
in Florida with this fungicide. If east of the Mississippi, that will give you a total of 12 applications of
Thiram, and nine of these applications can include a mixture of a contact material (Thiram) and a
systemic material (Switch or DMI fungicides), and the combinations should provide the best control of
Neopestalotiopsis available, while also providing control of Botrytis and powdery mildew.
Despite these challenges, we hope that we can still have a successful strawberry production year.
For additional information on strawberry diseases and their management, please go to the IPM Guide
located at www.smallfruits.org or download the MyIPM app. Your local county agent is also your first
point of contact for any questions or issues you might have, so please contact them directly if you
have additional questions relative this disease or any other strawberry production issues.