Introduction

Botrytis is a fungus that can cause gray mold and yield losses in berry crops.

While moldy fruit are the most upsetting consequence of botrytis, leaves can also be infected by this fungus. This is important because infected leaves can also serve as a source of mold spores for the following spring. Dr. Mike Ellis, a plant pathologist at Ohio State University, says that leaf debris is the primary source of botrytis infection in strawberry fields.

Botrytis spores will overwinter on plant debris and infect strawberries and caneberries when weather is wet and warm. The most devastating infection occur during bloom: infections will spread across a wide distance and will not make themselves known until fruit is formed and starting to ripen.

During summer, infection will spread during rainy periods but spread will be over a much smaller area. Summer botrytis infections will mostly affect berries that are in direct contact with spores, either by growing next to a moldy berry or by being touched by a hand that has mold spores on it.

Control of Botrytis during Harvest

Botrytis can spread from rotted berries to healthy berries. Touching healthy berries after touching rotted berries will spread the disease. The healthy berries will rot within 48 hours.

Another way the fungus spreads to healthy berries is through contact with soil or direct contact with infected berries. This is especially true in humid and rainy weather.

Here are some ways to prevent the spread of botrytis during the summer:

• Harvest rotted berries separately from marketable berries to prevent spread of botrytis.
• Pick all unmarketable berries into a “rot” bucket that you will not use for harvesting healthy berries.
• Dispose of rotted berries far away from your planting, so wind cannot carry the spores to infect flowers in the spring.
• Renovate your planting after harvest is completed, and remove leaves so that wind cannot carry spores to infect flowers in the spring.
• Plan to spray for botrytis next spring if you saw a lot of it in your fields this summer.

Here are some tips in case you know that you have a fair amount of botrytis in your planting, but cannot dedicate the labor to selectively remove the unmarketable berries:

• Encourage pickers not to touch moldy berries when picking, especially for quarts that will be sold fresh.
• Freeze or process your berries soon after picking.
• Encourage customers to refrigerate berries promptly.

Fungicides may be applied to raspberries and strawberries during summer as well.

Switch 62.5 WDG and Elevate 50 WDG both have a 0-day pre-harvest interval and are labeled for both of these berries. These are very effective fungicides, and Dr. Annemiek Schilder from Michigan State University recommends reserving applications of these sprays for very wet, rainy periods.

In caneberries only, Rorval Brand 4 Flowable can be used. It has a 0-day pre-harvest interval.

Control of Botrytis during Bloom

Controlling botrytis during bloom is critical, and there are several organic and conventional fungicides available. Rotating fungicides is important to avoid the development of resistance in the fungus. When rotating, it is helpful to avoid repeating a compound that is listed under the same FRAC Code.

If a fungicide is grouped into 2 FRAC Codes, do not follow an application with either of those FRAC Codes.

The following fungicide recommendations are based off of the 2021 Cornell Pest Management Guidelines for Berry Crops. These guidelines are accurate for New York State, but not all fungicides are listed. If you are in doubt whether the fungicide you have will do the trick, review the product label. Ensure that both the treated crop and the targeted pest are listed on the label.

Spring Botrytis Control in Strawberries

Start spraying strawberries for botrytis when 10-20% of flower buds are open. Spray again 10 days later with a different fungicide.

If the spring doesn’t have prolonged wet and humid periods, two applications of fungicide are enough to control botrytis. More fungicide applications are helpful if wet, foggy weather persists until harvest.

A couple conventional pesticides labeled for botrytis control in strawberry include:

• FRAC CodeM4: Captan Gold 80WDG, Captan 50WP, Captan 80WDG
• FRAC Code 17: Elevate 50WDG
• FRAC Code 17 & M4: CaptElevate 68 WDG
• FRAC Code 3 & 12: Switch 62.5 WDG
• FRAC Code 3 & 9: Inspire Super
• FRAC Code 7 & 11: Pristine

Many organic pesticides for botrytis control are not grouped by chemical class because they rely on living organisms rather than isolated compounds.

Organic pesticides labeled for botrytis control in strawberry include:

• Baccilus amyloquefaciens based fungicides:
  • strain # D747: Double Nickel 55, Double Nickel LC
  • strain # MBI 600: Serifel
• Baccilus subtilis based fungicides:
  • strain # QST 713: Serenade ASO, Serenade MAX, Serenade Opti
• Reynoutria sachaliensis based fungicides:
  • Regalia, Regalia CG
• Streptomyces Lydicus strain # WYEC 108: Actinovate AG
• Group M: Cueva Fungicide Concentrate

Spring Botrytis Control in Caneberries

Start spraying caneberries for botrytis when 5-10% of flower buds are open. Spray again 10 days later with a fungicide from a different FRAC Code.

• FRAC Code M4: Captan 80WDG
• FRAC Code 2: Rorval Brand 4 Flowable
• FRAC Code 17: Elevate 50WDG
• FRAC Code 19: OSO 5% SC
• FRAC Code 17 & M4: CaptElevate 68 WDG (only raspberries)
• FRAC Code 3 & 12: Switch 62.5 WDG
• FRAC Code 3 & 9: Inspire Super
• FRAC Code 7 & 11: Pristine

Organic pesticides labeled for botrytis control in caneberries include:

• Baccilus amyloquefaciens based fungicides:
  • strain # D747: Double Nickel 55, Double Nickel LC
• Baccilus subtilis based fungicides:
  • strain # QST 713:  Serenade Opti
• Reynoutria sachaliensis based fungicides:
  • Regalia, Regalia CG
• Streptomyces Lydicus strain # WYEC 108: Actinovate AG
• Group M: Cueva Fungicide Concentrate

Key Differences in Botrytis Control between Strawberries and Caneberries

• In Nassau and Suffolk counties, Switch 62.5WDG is only labeled for use on strawberries and onions.
• Captan Gold 80WDG and Captan 50WP are only labeled for strawberries.
• Rorval Brand 4 Flowable has a 0-day pre-harvest interval for raspberries, but can only be used on strawberries before the first fruiting flower.
• Serenade ASO and Serenade MAX are only labeled for strawberries.
• Serifel is only labeled for strawberries.

Cultural Management

Here are tips for reducing botrytis infection rates in a strawberry planting:

• Avoid planting crowns closer than 18 inches together to prevent a dense canopy.
• Grow on plastic mulch or raised beds instead of bare ground.
• Mulch in between rows with straw or other bedding to absorb moisture and prevent weed growth.
• Remove weeds. Focus on removing weeds that can catch a lot of moisture from the air. For instance, amaranth, sedges, and gasses will hold onto dew longer than purslane.
• Renovate after fruiting is over and move the old leaves far away.
• Apply most or all nitrogen after renovation, as spring applications will increase risk of infection. Apply nitrogen at a rate no greater than 20 lbs/acre in the spring.
• Use drip irrigation instead of overhead irrigation as the main means of water delivery.
• Plant resistant varieties, including ‘Earliglow’, ‘Jewel’, ‘Clancy’.

Here are tips for reducing botrytis infection rates in a caneberry planting:

• Prune out canes that are done fruiting promptly.
• Keep stands narrow, no greater than 1 – 2 feet.
• Prune the top 3-4 inches off of new canes to encourage branching and prevent rooting.
• Install new plantings in the direction of prevailing wind to encourage air flow.
• Install new plantings on sites with good drainage.
• Use drip irrigation instead of overhead irrigation as the main means of water delivery.
• Plant resistant varieties, including ‘Heritage’, ‘Crimson Treasure’, and black raspberries.

Additional Resources:

Management of botrytis gray mold in fall raspberries | Michigan State University Extension | Written by Annemiek Schilder

Botrytis Fruit Rot “Gray Mold” of Strawberry, Raspberry, and Blackberry | Ohio State University Extension | Written by Mike Ellis

2021 Cornell Pest Management Guidelines for Berry Crops | Cornell IPM | Written by Marvin Pritts, Elizabeth Bihn, Juliet Carroll, Kerik Cox, Michael Helms, Andrew Landers, Greg Loeb, and Laura McDermott.

FRAC Code List 1: Fungicides Sorted by FRAC Code | Fungicide Resistance Action Group

• This is a technical document with more information on how fungicide groupings are developed, to avoid the development of fungicide resistance.