Yellowing leaves and defoliation crabapple

Question: 30 yr old crabapple leaves turn yellow green fall off. Happens every June. I don’t see any bugs. What can you recommend to spray on it?

responder: Betsy, UVM Extension Master Gardener Volunteerwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention.When we include a link to a resource that recommends a chemical, it is for informational purposesonly; the chemicals may not be registered for use in Vermont. Replied June 19, 2024, 7:38 PM EDT
response: Dear Carlotta, Thank you for submitting your question to UVM Extension Master Gardener, and thank you for including the photos. Your crabapple leaves have brown spots that are indicative of a fungal infection, "apple scab" exacerbated by rainy springs and warm temperatures. Apple scab (Venturia inaequalis) is a fungus that infects crabapples apples, and pears. Generally the spots start as irregularly shaped light brown or olive green irregularly shaped spots on the underside of the leaf. The disease is less noticeable at this stage. As the infection progresses the lesions become more circular with the spots eventually turning black or brown. Infected tissue will thicken creating a bulge on the upper leaf surface. Leaves may curl and scorch at the margins, eventually leading to leaf and fruit drop. It is too late to treat the tree by the time this is noticed, but it is generally not lethal to the tree, unless it has occurred too many years in a row. There are still things you can do.  The fungus overwinters, therefore it is important to rake up fallen leaves and either burn them, bag them and take them to the dump, or bury them at least one foot deep. Pruning will also help air circulation.  The location of your crabapple is visually appealing but I do not think it is the best placement for this tree in terms of air circulation. It is quite crowded, close to the house, and close to the edge of the wooden planter and surrounded by other plants.  You may want to consider another more open location if you have this.  For a summary of management techniques see https://extension.umn.edu/plant-diseases/apple-scab Another option is to consider an apple scab- resistant variety of crabapple, if you would like to start a different tree. For a list, please see https://extension.illinois.edu/blogs/good-growing/2023-05-12-your-crabapple-losing-leaves-apple-scab-may-be-blame Please note if a new scab-resistent crabapple is again placed in an area that is too crowded, or the fallen leaves in the yard from the infected tree are not raked up and discarded, even a resistant variety can get apple scab. Good luck and I hope this is helpful.

responder: The Question Asker Replied June 20, 2024, 7:18 AM EDT
response: Oh dear. When should I spray this next year to hopefully prevent this from happening? Spray before any spring growth or after blossoming? What kind of  fungicide should I use?  Thank you so much for the explanation.  On Jun 19, 2024, at 7:38 PM, Ask Extension <<personal data hidden>> wrote:   ﻿

responder: Betsy, UVM Extension Master Gardener Volunteerwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention.When we include a link to a resource that recommends a chemical, it is for informational purposesonly; the chemicals may not be registered for use in Vermont. Replied June 20, 2024, 8:01 AM EDT
response: Hi Carlotta, Before any spring growth, but I cannot recommend a specific product. When we include a link to a resource that recommends a chemical, it is for informational purposes. UVM Extension Master Gardeners recommend non-chemical control, and do not generally have pesticide certification, but I will link to one of our collaborators to expand this answer. Stay tuned, It may take a few days for a response. Thanks.

responder: Betsy, UVM Extension Master Gardener Volunteerwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention.When we include a link to a resource that recommends a chemical, it is for informational purposesonly; the chemicals may not be registered for use in Vermont. Replied June 20, 2024, 11:35 AM EDT
response: Hi Carlotta, Our expert, Dr. Hazelrigg, who can recommend pesticides does not recommend it for this disease. She recommends the same management that I gave above and includes one other reference cited below. This is her response,"Apple scab is the disease commercial growers spray 15-20 times a season for. Since most backyard apples (and crabapples) do not get sprayed that much (for good reason!) pruning the tree to provide good air circulation so the leaves dry quickly is a good practice. Also cleaning up fallen leaves in the fall since that is where the pathogen overwinters. Here is more info on the disease and its control.https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/scabs/apple-scab"