Causes of Raywood Ash Trees and Dying Branches

Q. We have two Raywood ash trees that are loosing whole branches and more from either a systemic disease or insects. The trees are about 23 years old and well cared for. Damage starts at the terminus of the branches and soon involves the whole branch leaving the leaves a light tan color over the entire branch and limb.  We have used Bayer systemic pesticide topically over the area of irrigation.

Ash tree planted  with rock surface mulch surrounding it and leaf scorch.. Probably too hot in this location and perhaps not enough water applied.

A. Three possible problems exist for that tree; drought, borers and a disease called ash decline. It is not a good tree if it is surrounded by rock mulch. It is more of a “mesic” tree which means it is better off in a mixed landscape, or a part of the landscape, that has a mixture of higher water using plants.

Drought

Sometimes this tree is put in a part of the landscape surrounded by rock and water delivered from drip emitters. Rock surrounding this tree is not a good idea. As the tree gets bigger it needs more water. If more emitters are not added or more water provided during summer months it can become droughty and you will see dieback of limbs.

Smooth bark of some trees can lead to sunscald. The orange discoloration on the trunk is light sunscald. It helps if ash is not planted in rock.

Sunscald and borers

The bark on the tree when it is young is fairly thin so it doesn’t do well with intense sunlight on the trunk for long periods of time. It can get sunburned fairly easily when in west or south exposures of intense sunlight particularly surrounded by rock on the surface of the soil. This frequently leads to borer problems in the sunscald areas of the trunk. You will see dieback of limbs and a loosening of the bark on the trunk on the West or South sides of the trunk. The area under this loosening is dead due to intense sunlight (sunscald) and this is wear the borers are typically seen. Bayer helps but the real problem is its location in the landscape.

This is sunscald (sunburn) on the trunk of an ash tree. Most likely the trunk is dead on that side where sunscald occurs. This damage is thought to attract borers like the flatheaded apple tree borer which attacks many different plants.

Ash  decline

This is a disease that is common on many ash trees including Raywood. The damage resembles drought because the disease plugs the vessels inside the tree that carry water. The limbs begin dying and the tree dies a slow death over years. It is best to remove it if this is the case.

What to do? 

Look for damage to the trunk from sunscald and borers. If you see it then this could be the problem or part of a problem. Make sure the tree is getting enough water when it is watered. At 23 years old it should be getting 30 to 50 gallons each time it is watered. You can supplement water given to it by putting other plants that require water near it so they can share water. If you don’t see any improvement in the tree by giving it more water and you find no borers then it probably has ash decline and consider removing it.

The link below is accurate info on this tree. Other info could be sales hype.