This post is derived from the collaborative efforts of Guido Schnabel (Clemson University), Bill Cline and Caleb Bollenbacher (North Carolina State University), and Phil Brannen (University of Georgia).
Whether or not Neopestalotiopsis will damage your strawberries this season depends on several factors – including the quality of the transplants, the cultivar, sanitation practices, soil inoculum levels, weather conditions, and the fungicides you use. Below, we discuss aggressive chemical options for newly planted transplants coming in with Neopestalotiopsis or clean transplants being introduced into fields with a recent history of Neopestalotiopsis infestations (e.g., last year). In fields that haven’t had Neopestalotiopsis problems in the past two years and were planted with symptom-free plants (and with no word from the nursery that there were issues), these aggressive options are not likely necessary. In such cases, broad-spectrum fungicides like thiram or captan can generally be applied as needed or every 10 to 14 days during the fall. However, if Neopestalotiopsis does appear, then more aggressive programs should be adopted immediately.
To reiterate, this post focuses on chemical management options for fields affected by Neopestalotiopsis last year and for fields now being planted with Neopestalotiopsis-contaminated transplants. These options include fungicides with proven effectiveness against Neopestalotiopsis, such as thiram, fludioxonil (found in Switch, Alterity, and Miravis Prime), and the DMI fungicides propiconazole (Tilt, Topaz, and Propi-Star), difenoconazole (Inspire and Inspire Super), and flutriafol (Rhyme). Here are some key points to consider:
- Spray fungicides every 10-14 days when weather conditions are dry, and when conditions are wet, your spray program should be tightened to include a fungicide application every 7-10 days.
- One can apply four applications of Switch (or any of the labeled generics such as Alterity) per crop cycle if applied at the full rate of 15 fl oz per acre. If you use the lower rate (11 fl oz per acre), you may apply it five times. Most, if not all, of those applications should be reserved for spring or early summer to prevent fruit rot. And no, you cannot legally use four more applications of Miravis Prime after reaching the maximum number allowed under the Switch label restrictions.
- Thiram solo applications should form the backbone of your spray program to maintain low inoculum levels. It is an effective material against Neopestalotiopsis and Botrytis.
- Before an infection event (significant rainfall at temperatures over 70°F), spray a mixture of Thiram with a demethylation inhibitor (DMI) fungicide. Research has shown that propiconazole (found in Tilt, PropiStar, etc.) can be applied once to planted plugs without affecting plant growth. However, propiconazole-containing fungicides should not be used multiple times in a row, as they may cause slight stunting over the course of the season. There is no data on cut-offs, but they may be more vulnerable to propiconazole stunting as compared to plug plants. For cut-offs, we recommend flutriafol (Rhyme) or difenoconazole (Inspire and Inspire Super), which have not shown any inhibition of plant growth on transplants.
Fall application recommendations:
First three weeks after planting and during 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)
After three weeks and before high-disease-pressure situations
Thiram SC at 2.5 qts PLUS Rhyme at 7 fl oz OR Inspire at labeled rates
followed by (if high-pressure situation persists)
Thiram SC at 2.5 qts PLUS Tilt at label rates (use Rhyme at 7 fl oz if you planted cut offs)
followed by (if high-pressure situation persists)
Thiram SC at 2.5 qts PLUS Switch at 11 fl oz
Additional information can be found in the Strawberry IPM Guide (www.smallfruit.org) and in the MyIPM app, all supported through the Southern Region Small Fruit Consortium. Feel free to reach out to your local Extension county agent if you have questions about this post or any other aspect of strawberry production.
