Thank you for contacting the UVM Master Gardner Helpline with your question and including pictures. How frustrating to have your blueberry bushes dying after all your hard work. What a great way to teach your daughter about gardening.

I asked the Director of the Plants Diagnostic Clinic for her advice and this is her response:

“I would suspect something more abiotic if they have lost so many bushes. I would ask if they have tested the pH of the soil to see where they are on that. Blueberries struggle if the pH is not between 4.5 and 5.5. I also would be curious to know what the root systems look like on the dead plants. They may have not become established well.

“Have they irrigated the plants? Drought stress may also play a role. BB are really shallow-rooted plants and benefit from regular irrigation and at least a 2-inch layer of mulch. We have had a lot of late season drought in the past few years although I don't know where they are located.

“The other thing that may be involved is winter damage. If the bb were already stressed, they may have some dieback from low winter temperatures. I saw A LOT of winter kill this past year all over the state where the plants would leaf out then large sections would dieback. There was also a fungal disease involved in the dieback. In these cases, the grower pruned out all the dead tissue to the soil line and now the plants are bouncing back. If you are not seeing ANY resprouting at the base of your dead plants, then I suspect the roots are actually dead. This would be something other than winter damage.

“They should do a soil test, prune out all dead wood, assess whether there is any basal shoot growth and if not, dig up a plant to look at the root system. Those with dead root systems will not come back but if they were just killed back from winter, they should have resprouted.

“The insect is a moth and is not causing or contributing to any of the dieback. Hope this helps.”

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This website has information about how to collect and submit a soil test to the UVM lab: https://www.uvm.edu/extension/agricultural-and-environmental-testing-lab. While you have correctly been applying sulfur in the spring, it is possible it was not the correct ratio or that your soil is low on some other nutrient. It is a good idea to test the soil every few years to make sure it’s in the correct range for blueberries.

Also, you want to prune out the dead branches when the bush is dormant and either burn them or dispose of them in the trash. UVM Extension has this article available with guidelines on pruning high bush blueberries. https://www.uvm.edu/vtvegandberry/factsheets/PruningHighbushBlueberries.html. Make sure you disinfect your pruners. This article entitled “Disinfecting your Garden Tools” written by University of Florida provides a few options: https://blogs.ifas.ufl.edu/polkco/2019/08/16/disinfecting-your-garden-tools/

To determine if the plants that appear dead will come back, trim off a dead branch to look for a live core. Also, you can carefully dig up the roots and see if they are still alive. Look for fine white tips on the roots. Make sure that the roots are spread out evenly. Plants purchased in pots will maintain the pot shaped roots if you don’t spread the roots out eventually killing the plant. I'm sorry, but if all the branches are dead, no new shoots are forming, and the roots are no longer viable your plant did not survive.

To find a good mulch and making sure you are putting it on correctly this article entitled “Mulches” written by the University of Missouri Extension about mulching: https://extension.missouri.edu/publications/g6960. Also, this article entitled “Volcanoes Kill Trees” written by the University of New Hampshire Extension gives good information about mulch depths and proper application.

Finally, you might find this article entitled “Growing Blueberries in your Home Garden” written by the University of Minnesota Extension interesting: https://extension.umn.edu/fruit/growing-blueberries-home-garden

I hope you find this information helpful. Please feel free to let us know if you need further information or have additional questions. Good luck with your blueberries.

Laura, UVM Master Gardner Helpline Volunteer