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A new article by Dr. Phil Brennan (University of Georgia) from the Strawberry News website (UGA)
has been published with information compiled by Dr. Guido Schnabel (Clemson University) and Dr.
Bill Cline (North Carolina State) on managing fall-planted strawberries with the known presence of
Neopestalotiopsis. New Jersey growers who may have purchased strawberry plants this fall from
sources with known Neopestalotiopsis issues need to be proactive in mitigating it as best they can
this fall and develop a plan for the upcoming spring.
The below information was compiled by Guido Schnabel (Clemson University), Bill Cline (North
Carolina State), and I to give a recipe of sorts for Neopestalotiopsis management with fungicides after
planting this fall. It does not address spring applications, but you will need to incorporate remaining
applications of fungicides at that time.
Whether or not Neopestalotiopsis will substantially harm your strawberries this season depends on
many things – including the cultivar, sanitation practices, initial inoculum levels, weather conditions,
the fungicides you apply, and application timing. This article focuses on chemical management
options after planting – including thiram, fludioxonil (a component of Switch, Alterity, Miravis Prime),
and the DMI fungicides propiconazole, difenoconazole, and flutriafol. There are a few issues that
need to be discussed, but let’s not get into the possible cancellation of thiram. That is another story.
Here are some key points to consider:
1. Spray fungicides every 10-14 days even when conditions are dry, and when conditions are
wet, your spray program should be tightened to include a fungicide application every 7-10 days.
2. We only have 4 applications of Switch (or any of the labeled generics such as Alterity) if
applied at the full rate of 15 fl oz. If you use the lower rate (11 fl oz) you may use it five times. We will
need most, if not all, of those applications in spring/early summer for fruit rot prevention. And no, you
cannot legally use four more applications of Miravis Prime after having exhausted the Switch label
restrictions.
3. Thiram solo applications should be the backbone of your spray program to keep inoculum
levels low. It is a good Neopestalotiopsis and Botrytis material.
4. Ahead of an infection event (12 hrs of rain at >70F), spray a mixture of Thiram with something
else. Use a DMI, but note that some (including propiconazole and difenoconazole) can act as
plant growth regulators (PGR), especially on young plants. That is why nurserymen know not to
use propiconazole when growing plugs or bare-root plants from tips. Also, repeated application of
propiconazole and difenoconazole on bigger plants have been shown to stunt plants and cause
reduced yields. We still need to investigate how much (if any) one or two applications of these DMIs
will stunt plants when applied in the fall or whether there are differences in cultivar susceptibility. We
do know that Rhyme (flutriafol) does not have this negative effect, but it is also the least effective of
the three DMIs.
For the first 4 weeks after planting, we do not recommend you use a DMI fungicide (especially
propiconazole and difenoconazole) for fear of PGR effects. Use Rhyme with Thiram if you must use a
DMI during this time. During late fall, be aggressive before high disease-pressure situations by using
Thiram PLUS Inspire OR Thiram PLUS Tilt tank mixtures because we need to kill the spores before
plants are wet. High disease pressure will occur when it rains for over 12 hours at temperatures
(>70F). Don’t use this mixture twice in a row. Use the Thiram PLUS Rhyme mixture instead if you
need consecutive applications. Until we have more crop safety data, this may be a good strategy to
minimize the PGR risk but maximize protection of your plants against Neopestalotiopsis.
During low infection conditions (temp <60F plus rain), use a less aggressive approach and apply
Thiram only.
Fall application recommendations:
First four weeks after planting and before low-disease-pressure situations:
Thiram SC at 2 to 2.5 qts per acre or
Thiram SC at 2.5 qts PLUS Rhyme at 7 fl oz (if you must apply a mixture during early plant
establishment)
Before high-disease-pressure situations
Thiram SC at 2.5 qts PLUS Tilt OR Inspire at labeled rates
followed by (if high-pressure situation persists)
Thiram SC at 2.5 qts PLUS Rhyme at 7 fl oz
Followed by (if high-pressure situation persists)
Thiram SC at 2.5 qts PLUS Switch at 11 fl oz