Hi,

I heard some discussion on the radio about Trees dropping leaves, and the consensus was that it was fairly common for older trees. Here is our situation:

I have a weeping crabapple tree located in full sun. IN the spring, it has beautiful pink blooms. After the blooms are gone, it slowly starts dropping leaves. Here we are in the middle of July, and it is half bare. By the time October rolls around, we don't have to rake any leaves because the tree is totally bare. This has happened every year for the 6 years we have lived on the property, and we estimate the age of the tree to be about 20 years old.

I do not see any bugs or holes in the trees, nor do I see any type of fungus that I can see.

Is this typical for most crabapple trees?

Crabapples are very susceptible to apple scab. Even with that,



CRABAPPLES


Crabapples are probably one of the most popular ornamental trees in this area. And with good reason, they have beautiful spring flowers, a variety of shapes for any garden, and they look great in the winter months.

Flowering crabapples are great choices for the typical small suburban yard. They will stay well under 30 feet or so tall, so they make a good choice for planting under power lines.

Flowering crabapples have a wide range of leaf color—there are greens of course in lighter shades and deep dark shades. There are also purple leaved types.

Flower colors range from pure white to pinks to deep reds. Some are single petalled others are double.

But one of the best features is the winter berries. Some flowering crabapples will have red berries almost an inch in diameter. Most berries however are smaller like these. There are also varieties that sport yellow berries.

Crabapples are prone to sucker from the base of the trunk, remove these suckers as soon as they appear so that they don’t get a chance to grow large enough to mar the tree’s appearance.

Unfortunately, crabapples can be affected by a variety of leaf diseases and insect pests. Apple scab will cause the leaves to yellow and darken. In severe cases the entire tree will defoliate annually and may even result in death. But with over 600 varieties to choose from, you can certainly find one that has built in disease resistance.


Here’s a list of Crabapples varieties that have shown resistance to apple scab:

CULTIVAR NAME FLOWER/FRUIT COLOR
‘Adirondack’* White w/red tinge/red-orange
‘Candymint Sargent’ Pink w/red edge/deep purple
‘Donald Wyman’ White/glossy red
‘Hargozam’ Harvest Gold* White/gold
‘Jewelcole’ Red Jewel* White/cherry red
‘Lanzam’ Lancelot* White/gold
‘Louisa’ Pink/yellow
‘Mary Potter’ White/red
‘Molazam’ (Molten Lava) White/red-orange
‘Prairifire’ also exhibits Japanese beetle resistance Purplish red/red-purple
‘Purple Prince’* Bright red/bluish purple
‘Red Jade’ White/glossy red
‘Strawberry Parfait’ Pink w/red margins/yellow
‘Sutyzam’ (Sugar Tyme) White/red

I looked up apple scab on the net and found this info, hope it helps broadripple.


Rake up all apple scab infected leaves as they drop. Throw the infected leaves away or burn them.

Do not use apple scab infected leaves in compost as the fungal spores can survive winter and will increase the spore count around your yard the following spring!




Apple scab disease is caused by a fungus (Venturia ineaqualis) that survives winter on previously infected leaves and twigs. In spring, the spores are released and may be blown by the wind or splashed by rain onto tender emerging leaves. Signs of apple scab infection include yellow/brown lesions on the leaf surface and leaves dropping prematurely. The leaf drop is usually seen mid-August, but in the case of a severe infection, new leaves will fall as early as May. In order for the apple scab fungus to infect your tree, three factors must occur simultaneously. The “disease triangle” for apple scab includes: wet, cool weather; available spores; available leaf surface.
Apple scab affects trees in the genus Malus which includes ornamental crabapples and eating apples. It is a species-specific fungus and will not be transmitted to your other landscape trees or shrubs. Apple scab is not considered to be a serious threat to a healthy crabapple or apple tree; however, repeated annual infections of apple scab will progressively weaken the tree and leave it susceptible to attack by secondary disease or insect problems. Apple scab can also disfigure fruit from your eating apple tree.*
CONTROL:
Prevention is the best control. Two fungicide applications spaced 2-3 weeks apart as the leaves are emerging in spring will achieve about 80% control for that season. Pruning in the winter following a severe infection can help to remove any twigs killed by the apple scab fungus. Removing excessive sucker growth from inside the canopy as well as proper structural pruning will improve the air circulation and appearance of your tree. Because the apple scab fungus is transmitted by water, don’t allow your sprinkler system to hit the leaves. Water only in the early morning hours so the foliage can dry by nightfall. If possible, install a soaker hose around the critical root zone. A soaker hose will use less water as well as irrigate only the targeted plants.

Plant growth regulators have shown promise in treating apple scab fungus. Growth regulators such as Cambistat™ work inside the tree and last 3-5 seasons. Cambistat™ benefits your tree by promoting more root growth during times of stress, such as a heavy infection of apple scab. Cambistat™ may be the correct solution for your landscape.

Thanks for the replies. I've got the suckers under control and have pruned it over the last two years, so I hope it is still healthy enough to save. However, the leaves do turn yellow, then brown. So, Apple Scab is probably the right answer.

Since the leaves have been mulched into the lawn over the last few years, I am sure there are spores everywhere. I will look for fungicide treatments.

If not, then it looks like I'll have to eventually find a more disease resistant variety.