Apr 4, 2016

Prepare for cold temperatures tonight

Potential freezing weather is approaching Michigan’s Fruit Ridge the night of April 4-5. Amy Irish-Brown, a Michigan State University Extension educator, gave growers some context for how to prepare.

On the Ridge, most apples are still in the silver tip stage with a little green showing, but not enough to call it green tip for most varieties on most sites. Apples at silver tip can handle 15˚ F before there is fruit bud kill. At green tip, it’s 18˚ F. Forecasted low temperatures might dip to 20˚ F or slightly below that in low areas, so there should be little damage based on the forecast as of noon, April 4. The dew point is 24˚ F for tonight, as of noon, according to Irish-Brown.

For growers thinking of running their fans tonight, Irish-Brown gave them a few things to consider:

• There is a giant mass of cold air aloft, and as long as the winds stay up overnight, running fans will be not be of use as there will not be the necessary calm conditions to set up an inversion.
• There is some indication that winds could die down late at night or early morning. If that happens, it does take some time (a few hours) for an inversion to build.
• Watch the situation closely – if there is no inversion, fans won’t help. In fact, they could hurt, as you will be moving cold air around which could create a “wind chill” factor and cause tissue damage that otherwise would not happen. Not to mention issues with running mechanical equipment at low temperatures.
• Also, the cold air aloft is very cold, so if you do run fans watch your temperature around them closely. If you were to tap into that cold air aloft, you could bring that down to the surface and cause a great deal of cold injury.
• Sprinkler irrigation systems are not designed to protect below the mid-20s and should not be used for this freeze event.

For more information, click the links below.

http://msue.anr.msu.edu/news/what_are_radiation_freezes

http://msue.anr.msu.edu/news/what_is_the_difference_between_a_frost_and_a_freeze

http://msue.anr.msu.edu/news/freeze_damage_depends_on_tree_fruit_stage_of_development

http://msue.anr.msu.edu/uploads/files/PictureTableofFruitFreezeDamageThresholds.pdf

http://msue.anr.msu.edu/uploads/files/TreeFruitCriticalTemperatures.pdf

http://msue.anr.msu.edu/news/monitoring_for_the_risk_of_frost_and_freezing_temperatures

http://msue.anr.msu.edu/news/spring_freezes_and_fruit_bud_damage