Blueberry Freeze Injury or Phomopsis?

This article was reviewed by the editor of The Ontario Berry Grower for technical accuracy and appropriateness.

Source: Michigan Fruit CAT Alerts, May 7, 2003

This spring, tip dieback is prevalent in some blueberry fields. In some cases, the damage seems to be due to freeze injury, while in other cases the Phomopsis fungus may be to blame. While the two symptoms are often difficult to tell apart, there are a few differences that may help you diagnose the problem.

If the dieback is due to Phomopsis, the infection would have taken place the previous year or the year before that if it wasn't pruned out. The infected twig or cane tends to be dark reddish brown with a gray-bleached area at the tip or farther down the twig or cane. Often, the border between the dead and live portions of the cane is fairly distinct. The bleached area may range from one to several inches long and may contain tiny black pimples, which are the fruiting bodies of the fungus. The fungus is most likely to sporulate in the bleached area. More recent twig infections may appear dark brown to almost black. The lesions may be enlarging down the twig from the tip or up and down the twig from an infected lateral bud, which will die before or during bud break. Also, if you notice that the lesions keep expanding, it is most likely Phomopsis and not freeze injury. The fungus can infect twigs and canes anywhere on the bush. Young green canes lower in the canopy often display reddish brown lesions (cankers) that may be flattened.

Freeze injury tends to turn cane tips a light reddish brown, without a bleached area, and the border between dead and healthy tissue is more gradual. Freeze injury may especially affect young green canes that did not harden off well last fall. Also, the damage may be widespread throughout the field and more severe in low-lying areas that are prone to frost.

Phomopsis twig blight incidence can be reduced by pruning out and destroying infected canes and twigs, which act as inoculum sources.

To see photos of this injury go to the Michigan State University Website.

Editor's note: Fungicides for controlling Phomopsis twig blight are Bravo 500 and Cabrio EG applied at green tip, pink bud and petal fall.

Related Links:

• Blueberry freeze injury or Phomopsis? Michigan State University
• OMAFRA Publication 360, Fruit Production Recommendations
• OMAFRA Berry Index Page
• OMAFRA Berry Bulletin Agriphone

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