When to Terminate Fungicide Applications in Strawberry
by Aaron Cato - May 29, 2020
Determining when you should stop spraying to protect strawberries can be a complex
issue. Here are some factors to consider which should help you come to a sound conclusion.
Strawberry production across the state is beginning to wind down as it starts to warm
up, but there are still many producers hoping to harvest more berries. A question
we often get is when you should stop applying preventative fungicides. This is a complex
question and there isn’t a one size fits all answer. Considering information related
to the disease cycle of our two main fruit rot diseases, Botrytis and anthracnose,
should give you a good idea of whether you need to continue applying fungicides.
Botrytis (Grey Mold)
Botrytis fruit rot (Grey mold) is usually the most serious disease of strawberries
in Arkansas (Picture 1). This disease occurs when botrytis spores infect flowers.
Spores cannot infect green or ripe fruit unless they are damaged from another source.
Infected flowers then either immediately present the disease, or it can present much
later and cause mold formation on green or fully ripe fruit. Considering it takes
around 30 days to get from a flower to a ripe fruit, we don’t need to be worrying
about this disease when we think we are less than 30 days from our last harvest.
Picture 1. Strawberry exhibiting Botrytis fruit rot.
Anthracnose
Anthracnose fruit rot is not always an issue for producers in Arkansas, but I would
argue that we have had a very serious anthracnose year in 2020 (Picture 2). This is
likely due to the early warm spell we saw this spring and the frequency of rainfall
events. Anthracnose spores can infect flowers, green berries, and fully ripened berries.
This means fungicides must be used until harvest to get full protection from this
disease. Consider two factors when deciding if you should consider protectant sprays
for this disease. First, if you have already had issues with this disease this year
it is likely that you have a high spore load in your field and are at a higher risk.
Second, rainfall events increase the risk of infection, and fungicides should be used
to protect fruit when there is rain forecasted.
Picture 2. Strawberry exhibiting anthracnose fruit rot.
Fungicide Product Considerations
I think many people in the state will have to continue to apply fungicides because
of the large amount of anthracnose issues we’ve observed, but we will need to augment
our normal programs to move the focus away from Botrytis. Products like Elevate only
offer control for Botrytis and should not be used anymore. Single MOA products like
Cabrio, Abound, and Intuity work great on anthracnose and are only fair on Botrytis
(Picture 3). Any of these products combined with Captan will offer excellent protection
of your strawberries at this late stage in production.
Product FRAC Group BFR Botrytis Resistance AFR
Captan; Captec
M04 G None
G
CaptEvate
M04 + 17 E Prevalent for 'Elevate'
G
Thiram
M03 G None
G
Fracture
BM01 P No data
No data
Topsin M
1 Not effective Widespread
Not effective
Rovral
2 G Prevalent
Not effective
Tilt; generics
3 Not effective Not applicable
F
Fontelis
7 E Prevalent
F
Kenja
7 E NOT prevalent
Not effective
Scala
9 G Prevalent
Not effective
Pristine
7 + 11 G Prevalent
E
Merivon
7 + 11 E Prevalent
E
Luna Sensation
7 + 11 E NOT prevalent
E
Cabrio
11 F Widespread
E
Abound
11 F Widespread
E
Intuity
11 F No data
P
Switch
12 + 9 E NOT prevalent
G
Elevate
17 E Prevalent
Not effective
Ph-D, OSO
19 G NOT prevalent
G
Picture 3. Common strawberry fungicides and their effectiveness in controlling Botrytis
fruit rot (BFR) and anthracnose fruit rot (AFR). This table is from the 2020 Southeast
Regional Strawberry Integrated Pest Management guide.
Product Use Rates
With the extended strawberry fruiting season many have seen this year we need to make
sure that late applications aren’t above label use rates. Listed below are a few of
the commonly used fungicides and use rates. Notice how the number of applications
can vary depending on the rate that you’ve used. Additionally, these product use limits
include applications made in both the fall and the spring, starting once plants were
transplanted.
Fungicide
Use Limit of Product/acre
Number of Applications per year
Switch
56 oz
4
Luna Sensation
27.1 fl oz
3-4
Captan (80 WDG)
30 lbs
8-16
Elevate
6 lbs
4-6
We need to be thinking about economics on top of everything mentioned here. When we
get to this time of the year it is not uncommon to push harvest to when it is no longer
profitable, mostly due to the low number of berries we are getting toward the tail-end.
Deciding if expensive fungicides are necessary are only one part of a very large equation
that should consider labor costs, irrigation costs, etc. If the conditions are ripe
for an extra profitable day of harvest, it’s generally going to pay to protect these
berries from anthracnose.
If you have any questions at all, give me a call at 479-249-7352.
