Post-bloom fungicide choices in blueberries

Controlling different diseases calls for a change in fungicide choice.

After bloom, the young, actively growing berries are susceptible to anthracnose and other fruit rots if they are wet for long periods during rain or irrigation. Fungicides can also protect the new shoots and leaves. Photo by Mark Longstroth, MSU Extension.

After bloom, the young, actively growing berries are susceptible to anthracnose and other fruit rots if they are wet for long periods during rain or irrigation. Fungicides can also protect the new shoots and leaves. Photo by Mark Longstroth, MSU Extension.

Early in the season, blueberry growers focus on controlling mummy berry and Phomopsis. Dormant and delayed dormant sprays of Lime sulfur or Sulforix aimed at these diseases also serve to reduce inoculum of fruit rot pathogens overwintering on infected twigs and remnants of last year’s fruit clusters.

Before and during bloom, fungicide protection is focused on preventing mummy berry flower infections. After bloom, there is no risk of further mummy berry infection. However, some of the fungicides used against mummy berry also have efficacy against fruit rots. In addition, bloom to early fruit set is also good time for management of anthracnose fruit rot because the pathogen becomes active at that time.

After bloom, the disease control strategy changes to protecting green fruit and young shoots. Later in the summer and early fall, protecting leaves may also be needed for controlling leaf rust.

Green fruit are susceptible to fungal diseases such as anthracnose, Phomopsis and Botrytis, the latter if the weather is excessively wet with high humidity. With respect to anthracnose fruit rot, some cultivars are resistant to the disease, e.g., Elliott, Draper, Liberty and Legacy, and won’t need as much protection as susceptible cultivars (e.g., Bluecrop, Bluetta, Blueray, Jersey).

Alternaria fruit rot becomes more of a concern when berries start to ripen, particularly in the cultivar Bluecrop. Be sure to change the mode of action of your fungicides to include these diseases and reduce the likelihood of fungicide resistance occurring in blueberries.

A recent survey has shown evidence of strobilurin resistance in the anthracnose fruit rot pathogen in Michigan. Thus, it is important to alternate fungicides with different modes of action and not rely solely on strobilurins for anthracnose fruit rot control. The anthracnose fruit rot prediction model on the Michigan State University Enviroweather website can also help improve fungicide spray timing.

Fungicide efficacy against fruit diseases in blueberries
FungicideDisease controlled
Trade nameActive ingredientFRACPhomopsisAnthracnoseAlternariaBotrytis
Systemics 
Abound azoxystrobin 11 Fair Good / Excellent* Good Poor
Pristine pyraclostrobin + boscalid 11/7 Good Excellent* Good Good*
Quilt Xcel azoxystrobin + propiconazole 11/3 Good Good Unknown Unknown
Omega  fluazinam 3 Unknown Good Fair Unknown
Quash metconazole 3 Good / Excellent Good Good Fair
Proline prothioconazole 3 Good / Excellent Fair Unknown Fair
Tilt propiconazole 3 Good Unknown Unknown Unknown
Inspire Super difenoconazole + cyprodinil 3/9 Good Unknown Unknown Good
Luna Tranquility fluopyram + pyrimethanil 7/9 Unknown Fair /Good Fair / Good Excellent
Switch cyprodinil + fludioxonil 9/12 Poor/Fair Good Excellent Excellent
Aliette fosetyl-Al 33 Fair / Good Good Good Unknown
Phostrol phosphorous acid 33 Fair / Good Fair / Good Fair / Good Unknown
Protectants 
Double Nickel Bacillus amyloliquefaciens 44 Fair Unknown Unknown Fair
Serenade Bacillus subtilis + terpene-based sticker- extender 44 Fair Poor Poor Fair 
Nu-Film
Oso or PhD polyoxin-D zinc salt 19 Unknown Poor Poor Good
Copper (various products) copper M1 Poor / Fair Poor / Fair Poor / Fair Poor / Fair
Sil-Matrix Potassium silicate NC Fair Good Unknown Unknown
Captan captan M4 Fair Fair / Good Poor Fair
Ziram ziram M3 Good Good Fair  Fair 
Vacciplant laminarin NC Unknown Unknown Unknown Unknown
Protectant and systemic mixtures 
CaptEvate captan + fenhexamid M4/17 Fair Fair Poor Good / Excellent

*If fungicide resistance is present, this product may be less effective than indicated. 

See related MSU Extension articles

Dr. Schilder’s work is funded in part by MSU‘s AgBioResearch.

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