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Cornell Fruit Resources: Berries

Resources for Commercial Berry Growers

May 6 Berry Update

Strawberries: Warmer weather over the weekend helped move things along – now seeing flower buds pushing in the crowns of early varieties. I’m finding strawberry aphids and spider mites in low numbers, most may still be the overwintering population. Noticed some cyclamen mite damage under low tunnels in a 2nd year planting. This week will be a roller coaster of temperatures – warm(ish) days and cold nights. Frost risk predicted in many areas may hurt crop potential, especially as flowers start to push.  Many growers have put out their irrigation equipment and are geared up for frost protection. All of the extra water and impact from the sprinklers can spread or exacerbate diseases like angular leaf spot and red stele root rot. Consider following up with fungicide applications.

showing aphids on a leaf
While a little out of focus, there are 2 aphids on this leaf. A hand lens helps with ID, but it is possible to spot them with the naked eye.
showing insect pest damage
Cyclamen mite feeding causes malformed leaves and fruit. Picture taken May 4.

Table 1. Critical temperatures of strawberries based on stage of development (Perry and Poling, 1985)

Stage of Development Approximate Critical Temp. (°F)
Buds internal 10
Tight bud 22
“Popcorn” 26.5
Open blossom 30
Fruit 28

Frost can kill flowers or cause damaged, misshapen berries.  Leaf tips and edges can also be injured.

show stage of crop development
Strawberry crown with flowers at tight bud stage.

Overhead irrigation provides the most protection but is a challenge to manage and for heavy ground will result in wet soils exactly when you don’t want moisture.  Many growers are relying on heavy weight row cover to protect blossoms, then in a critical frost event, will irrigate directly on top of row cover – which does provide protection.

For more information, see the comprehensive OMAFRA fact sheet on frost protection in strawberries:

showing crop development
Blueberry flowers at early pink stage.

Blueberries: Colder areas still at tight cluster, but milder areas moving to early pink, and in warmest areas bloom is starting.  Buds become increasingly susceptible to frost damage the closer they get to bloom. Some growers have set up frost protection (sprinklers) in their blueberries, which can help on a windless night.

Mummyberry risk continues, and with bloom approaching, we add botrytis blossom blight and anthracnose risk to the mix. The fruit rots often don’t become apparent until the fruit ripens, but many infections start at bloom, so this is a critical time for management. Anthracnose has become a perennial problem in some fields and should be managed more aggressively in these sites. The same fungicides will usually manage all the fruit rots – be sure to rotate between FRAC groups!

showing crop stage
Raspberry flowers at tight bud stage.

Brambles: Now seeing closed flower buds peeking out on floricane (summer-fruiting) raspberries and primocane shoots are several inches tall. I haven’t seen any yet, but this is the time to start looking for raspberry fruitworm, raspberry sawfly and tarnished plant bug on young leaves and flowers.

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