How to Fertilize Areas with Winter Damage or Leaf Drop
Amaya Atucha, University of Wisconsin-Madison
Cranberry Crop Management Journal, July 29, 2020

Many growers experienced significant leaf drop this spring, probably due to an early cold event that occurred last fall. In addition, during our last virtual brown bag seminar, several growers and consultants commented on the occurrence of spring frost damage as well. One of the most common questions I get when we have these types of damages is 'What can we do to help the affected areas recover'?

1. If you have areas with significant leaf drop, do not apply extra fertilizer. The new upright will have enough nitrogen to support initial growth and if you apply additional fertilizer in the spring, it will only result in a longer upright and NOT in more and bigger berries. Fertilize the beds based on the amount of fruit set you see. The only instance in which I would recommend applying additional fertilizer before bloom would be if the new grwoth coming from uprights looks weak and yellow. In that case, apply ~5 units of actual N/ac before bloom. If you experienced leaf drop in the spring, but you had normal upright growth with good fruit set, then continue to fertilize your beds as normal.

2. If the beds have spring frost damage and most of the buds are dead or there are no flowers, do not apply extra fertilizer. If there is no fruit, the fertilizer will go into promoting vegetative growth and this will result in higher density of uprights, longer uprights, and delayed bud set for next season. To avoid the excessive vegetative growth, reduce the amount of fertilizer based on the fruit set you have (e.g., if you have 60% of the crop you would have expected, then reduce your fertilizer doses by 40%).

3. In areas with scarce vegetation due to leaf drop, weed control is more important than fertilizer application to make sure those areas are back into production the following growing season.