5 Diseases to Look Out For This Summer

Many tree and shrub diseases thrive during the summer months. As hot, humid weather and evening thunderstorms create favorable conditions, these diseases can do a lot of damage to your landscape. Learn what diseases pose a danger to your trees and shrubs and what signs you should keep an eye out for on your property.

1. Phytophthora Root Rot

Phytophthora Root Rot is an extremely damaging and widespread fungal disease that will rot away root systems and eventually kill your tree if left untreated. In the worst cases, when left untreated trees can become structurally unsafe and uproot or snap possibly causing property damage and injury. The recent thunderstorms and hot, humid weather we have been experiencing have caused our soil to become warm and moist, conditions favored by Phytophthora Root Rot. The disease is also common in areas where run-off or rainwater collects around the roots of plants.


  • Suppressed growth
  • yellow or undersized needles/leaves
  • dieback
  • drooping and curling of leaves
  • leaves turning brown
Phytophthora Root Rot

Targets: Wide range of plants. The most susceptible include Azalea, rhododendron, dogwood, pieris,  yew bushes, deodar cedar, mountain laurel, heather, juniper, Fraser fir, white pine, shortleaf pine, camellia japonica, aucuba.

Learn more about Phytophthora Root Rot

2. Leaf Spot & Anthracnose

Leaf spot is a common term used to describe a number of tree diseases that leave spots on the foliage of trees and shrubs. These diseases are most commonly caused by fungi but can be caused by bacterial infections as well. One of the most well-known leaf spot diseases in our area is Anthracnose.


  • spots on foliage
  • spots can be brownish, tan, or black
  • concentric rings and dark margins
  • black dots in the spots, either in rings or in a central cluster.
  • spots may combine to form blotches
signs your tree is sick - leaf spot

Targets: Dogwoods, Ash, Oaks Sycamores, Maples, and other deciduous hardwoods.

Learn More About Anthracnose
Learn More About Cercospora Leaf Spot

3. Shot Hole Disease

Shot hole disease, also known as shot hole fungus, is a serious fungal disease that creates distinct BB-sized holes in leaves. With the warm weather and evening thunderstorms, we’ve been having the past couple weeks. Our Arborists expect to see Shot Hole Fungus popping up on lots of Cherry Laurels in this area in the next few weeks. Without treatment, this fungus will re-infect your shrubs year after year, not only ruining its aesthetic appeal but also weakening the shrub’s health.


  • Reddish-brown spots on leaves
  • Holes in leaves (can look like insect feeding damage)
  • Defoliation
Shot Hole Fungus

Targets: Cherry laurel, English Laurel, Cherry Trees

Learn more about Shot Hole Disease

4. Verticillium Wilt

Verticillium Wilt is a disease caused by the soil-borne fungi Verticillium albo-atrum and Verticillium dahliae. The fungus invades through the roots of susceptible trees and shrubs then spreads through the plant’s vascular system. Once the Xylem, the tree’s water transportation system,  is infected it becomes clogged and water can no longer reach the tree’s leaves. Verticillium is common and affects several hundred species of trees and shrubs.


  • leaf curling
  • dry leaves
  • small yellow foliage
  • leaf scorch
  • slow growth
  • Often the symptoms are seen on one side or section of the tree
Tree Fungus - Verticillium Wilt

Targets: Ash, Azalea, Cherry, Certain species of Dogwood or Linden, Locust, Magnolia, Maple, Oak, and Redbud.

Learn More About Verticillium Wilt

5. Bacterial Leaf Scorch

Discovered in New Jersey in the early 1990’s, this disease attacks shade trees and is caused by the xylem-clogging bacteria, Xylella fastidiosa.  Xylem is one of the two types of transport tissues in trees; by clogging these tissues the bacteria restricts the flow of water from the roots to the crown of the tree. This dehydration causes the tree to appear to be under drought stress even when it has access to enough water.

Diseased plants start to exhibit symptoms of infection in mid-summer. If left untreated this disease will cause dieback, secondary invaders, branch death, and ultimately death.


  • Marginal Leaf Scorch: Necrosis begins along the leaf margin and spreads toward the veins in an irregular pattern.
  • Green healthy tissue separated from the dead tissue by a yellow or reddish-brown band or halo.
  • Decline in vigor
  • Branch dieback
  • Defoliation
Bacterial Leaf Scorch

Targets: Oaks, Elms, Sycamore, Sweet Gum

Learn More About Bacterial Leaf Scorch

2 thoughts on “5 Diseases to Look Out For This Summer”

  1. Durinda Smith says:

    My 30 year old Yoshino cheery tree is in trouble. The leaves are turning yellow and dropping. What should I do?

    1. Rtectree says:

      Thank you for your inquiry, Ms. Smith. There could be multiple factors contributing to the symptoms you’ve seen in your cherry tree. One possibility is your tree may be experiencing shot hole disease, which typically recovers naturally by itself but may reduce its benefits (visual appeal, fruit or flower production, growth, etc.). We apologize about the belated response, however, if you are still interested in looking into the issue, you can book an appointment with one of our Certified Arborists by calling us at 703.573.3029 or scheduling an appointment through our online booking system. We also now have a Cherry Tree Care Package which will assist in providing proactive care and maintenance for your cherry tree to prevent the symptoms from showing up again. You can ask one of our Certified Arborists for more details about the program when you meet with them. Thank you!

      For more information on shot hole disease, check out our latest blog post on Cherry Trees.

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