Frost and Freeze Damage Update

Frost and freeze damage was minor in small fruits and grapes. Below is a review of general guidelines for when we expect damage to buds, flowers and fruit.

Over the last week many areas of the state have experienced minimum temperatures likely to cause bud damage. Generalized state maps (Figs. 1, 2, 3) show the minimum temperatures recorded in different parts of the state. As we all know, the temperatures required to cause damage depends not just on the low temperature, but on the stage of crop development when the cold temperatures occur. As you can see in Table 1, low temperatures of say 20F will likely cause significant bud damage to apples if crops are beyond the half-inch green stage. The same temperatures before this stage probably will not cause widespread damage.

So what happened this year? Based on the accumulation of growing degree days, we started out very early, about the same as 2012 (Figure 4). [Lori – this is the one called “Temperature figure.tiff”] This caused buds to start developing. By mid-late March the temperatures dropped and slowed the accumulation of growing degree-days and of course this also slowed crop development. Right now GDD are tracking about the same as 2011, 2013 and 2015 and thankfully behind 2010 and 2012. However note that like the last number of years we are still significantly ahead of “normal” (long-term average).

OK so what have we seen this year. As expected, we are seeing more damage in more southern areas where crops were at more advanced stages of development when the cold temperatures came. There has certainly been some bud damage to both apples and peaches, but pretty much full crops are still expected. Even in Lafayette at the Meigs farm we have seen a little bud damage to both peaches and apples, but only 20% or so of buds appear to be affected. Remember that even with 10% of buds alive (90% kill) we are often still looking at a full crop. So what’s the take home message? Mostly we dodged a bullet and will still need to thin.