Possible fungus on King Hawthorn leaves

Question: Hello, I think we might have a fungus on a King Hawthorn tree.  It is only 2 years old but we had a very wet spring.  It was healthy earlier in the spring.  I would like to know which fungicide will work best to contain the fungus and the best method to apply it. Since the tree (sapling) is so young I'm hoping we don't have to remove all the leaves. Thank you, Christine Scanlan

responder: Colorado Master Gardener, Denver County Replied June 22, 2023, 12:37 PM EDT
response: It looks like the hawthorn tree has Entomosporium mespili leaf spot, which is a fungus.  Wet conditions such as rain and spray irrigation can spread the spores from the soil or from other infected areas of the tree to the leaves.   Rain can't be prevented, so keeping the site clean around the tree is important by raking and disposing of leaves as well removing plants beneath the tree and replacing them with mulch.  Fungicide is often used as a preventive, but can be use to treat.  Please see the sites below for more information.     If you choose to use a fungicide, be sure to carefully follow the product use directions - the label is the law.

responder: Colorado Master Gardener, Denver County Replied June 22, 2023, 12:54 PM EDT
response: It looks like the hawthorn tree has Entomosporium mespili leaf spot, which is a fungus.  Wet conditions such as rain and spray irrigation can spread the spores from the soil or from other infected areas of the tree to the leaves.   Rain can't be prevented, so keeping the site clean around the tree is important by removing, raking and disposing of leaves as well removing plants beneath the tree and replacing them with mulch.  Fungicide is often used as a preventive, but can be used to treat. Please see the sites below for more information on cultural practices and specific fungicides.  If you choose to use a fungicide, be sure to carefully follow the product use directions - the label is the law.  https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/entomoslfspt.html#:~:text=Raindrops%20and%20overhead%20irrigation%20splash,coincide%20with%20new%20plant%20growth.  https://www.lsuagcenter.com/NR/rdonlyres/26F24BD5-4C73-470B-B1D1-94469C027FA8/74736/pub3171EntomosporiumleafspotHIGHRES.pdfhttps://ag.umass.edu/landscape/fact-sheets/hawthorn-leaf-spot  https://ag.umass.edu/landscape/fact-sheets/hawthorn-leaf-spot

responder: The Question Asker Replied June 22, 2023, 1:44 PM EDT
response: Thanks so much for getting back to me. Can you also please tell me:1.  Can this spread to other trees?2. If we don’t treat it with fungicide will the tree health be in danger?Chris  On Jun 22, 2023, at 10:54 AM, Ask Extension <<personal data hidden>> wrote:﻿

responder: Colorado Master Gardener, Denver County Replied June 22, 2023, 2:39 PM EDT
response: Thanks so much for getting back to me. Can you also please tell me:1. Can this spread to other trees?2. If we don’t treat it with fungicide will the tree health be in danger?  Chris   On Jun 22, 2023, at 10:54 AM, Ask Extension wrote:   The Entomosporium mespili fungus seems to cause "spotting and premature drop of leaves in most plants in the Pomoideae group of the rose family. Hosts include apple, crabapple, evergreen pear, hawthorn, loquat, photinia, pyracantha, quince, Rhaphiolepis, serviceberry, and toyon." According to https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/entomoslfspt.html  If you have trees or shrubs within this group, it's possible it could spread.  Although once the weather becomes hot and dry again, fungus spread is reduced.  Be sure to follow the cultural recommendations to reduce fungus spread.  A serious infection of the fungus will weaken the plant making it potentially susceptible to other diseases. More information on the University of New Mexico State University site. https://plantclinic.nmsu.edu/documents/entomosporium-leaf-spot.pdf  The unusual frequent rain pattern we've been experiencing this spring has caused plant challenges that we don't normally see.    Just as a side note, there are some varieties of hawthorn that are supposed to be more resistant to leaf spot than others.  Please check the websites included in this and the earlier posting for more information.  Hello, I think we might have a fungus on a King Hawthorn tree. It is only 2 years old but we had a very wet spring. It was healthy earlier in the spring.  I would like to know which fungicide will work best to contain the fungus and the best method to apply it. Since the tree (sapling) is so young I'm hoping we don't have to remove all the leaves. Thank you, Christine Scanlan   Thanks so much for getting back to me. Can you also please tell me:1. Can this spread to other trees?2. If we don’t treat it with fungicide will the tree health be in danger?  Chris   On Jun 22, 2023, at 10:54 AM, Ask Extension wrote:     Hello, I think we might have a fungus on a King Hawthorn tree. It is only 2 years old but we had a very wet spring. It was healthy earlier in the spring.  I would like to know which fungicide will work best to contain the fungus and the best method to apply it. Since the tree (sapling) is so young I'm hoping we don't have to remove all the leaves. Thank you, Christine Scanlan

responder: Colorado Master Gardener, Denver County Replied June 23, 2023, 9:43 AM EDT
response: Chris, I shared the photos of your Hawthorn with my colleagues and they have diagnosed the leaf spots as a different fungal disease. This one is called Juniper-hawthorn Rust. It is a common on hawthorn. It's also very interesting because it requires two different species to survive 1) hawthorn, apple or crabapple and 2) juniper. That means, in theory, you could control the fungus if you removed one of those hosts from your yard to interrupt the cycle; however, in an urban environment like Denver where practically every other house has either a juniper or a crabapple that method of control simply wouldn't be effective; even if you didn't have the alternate host, one of your neighbors would.  We see a lot of rust in years where there has been a lot of spring moisture which we certainly have had this year. Here's a link to a short fact sheet from CSU Extension with additional information. It lists a couple of fungicides you might use but note that fungicides need to be applied when the tree first starts bloom so it's probably too late to start this season.  https://planttalk.colostate.edu/topics/insects-diseases/1450-juniper-hawthorn-rust/

responder: The Question Asker Replied June 26, 2023, 10:31 AM EDT
response: Hello,  Thank you for this follow-up.  The rain has certainly affected so many areas of our gardens.     From what you're telling me I think I need to contact our arborist.  Especially if it's too late to apply a fungicide. This tree is very close to our thriving crab so I'm wondering if it's just best to remove the hawthorn to prevent further spread.   In any case, I appreciate the thorough information and details you provided.  As always, the extension is so valuable to all of us in the state.   Best regards, Chris Scanlan  -----Original Message-----From: Ask Extension <<personal data hidden>>Sent: Jun 23, 2023 7:43 AMTo: thomas1991 <<personal data hidden>>Subject: Re: Possible fungus on King Hawthorn leaves (#0106591)

responder: Colorado Master Gardener, Denver County Replied June 26, 2023, 4:20 PM EDT
response: Chris, Juniper-hawthorn rust can be bad some years but not a problem in others. For that reason, I'd advise against removing your tree. This is one of those years that it is bad due to all the moisture this spring, but next year there might be hardly any or none.