Something on my serviceberry leaf

(Question)

I planted a serviceberry shrub about 1 year ago. It came through the winter with flying colours and flowered nicely this Spring. Today I noticed that some of the new leaves, at the tips of branches, have curled up. There is a white crystalline coating on the underside of the leaves. Please help ASAP, with identifying and ways to treat this problem. I don’t want to lose this fabulous bush.

(Answer)

Serviceberry, Saskatoonberry, Shadbush, and Juneberry are all common names, often regional, of the same genus, Amelanchier spp..  I add this tidbit of information, as it is often important to know what the scientific name might be, as there are often so many common names, some of which cross with a completely different plant.

There are two species of insects that can cause the sticky coatings on the new leaves or bark: aphids and scale insects. The crystalline coating you note is probably due to the heat we’ve been having and it has dried out some of the honeydew left by the insect.

The first, aphids are likely the culprit. Aphids of several type suck juices from Amelanchier spp. Heavy infestations cause distortion of the foliage and new growth, and deposit large amounts of sticky honeydew (the undigested portions of the sap) on lower foliage. It is attractive to certain ant species, who will often protect the aphids by rolling the leaves along their margins, or the new leaf growth at the terminus of the new branches. They do this in order to “farm” the honeydew to use as food for their colony. Severe honeydew secretions can attract Black sooty mold. Black sooty mold can spread thickly and cause the death of the plant.There are a number of sooty molds,  genera causing sooty molds. The most common in our area is the Cladosporium group. In order to control the mold, the insects must be controlled first.

For more information on control of Black sooty mold: http://baker.ifas.ufl.edu/Ag/documents/BlackSootyMoldonLandscapePlants.pdf

First, check your shrub more closely, particularly the underside of the leaves, the crotches of the twigs and  where the leaf meets the twig. Small, oval insects that come in many colours (green white, black, orange, yellow) may be colonizing there, particularly underneath the leaves.  If they are visible, a good blast from your hose can dislodge most. Insecticidal soap, available at any nursery, can help remove the pests too – follow the directions. Checking every week and treating with the hose or soap will stem the tide of this pest. A good watering and mulching will help keep the shrub hydrated as well.

Scale insects are usually small, brownish in colour and can be found at the margins of leaves or along the new twigs where sucking the sap is easiest. Infested branches can die back completely. As with aphids, sticky, clear honeydew is produced as a by-product of undigested sap. Scale insects are difficult to irradicate in their adult form,as they have developed a hard shell. If there are a few, scraping them off will kill them. I use my fingernails, but some people are squeamish about that. Heavily infested branches should be pruned out.

The best time to beat the insect is when it’s still in it’s larval form. The newly hatched nymphs are white, and are not yet protected by the hard shell. Dormant oils are not effective, when the eggs are still snug under their mothers. Early June is a good time to monitor for newly hatched  nymphs. Insecticidal soap will kill the nymphs.

 

Keep an eye out every week, look for these insects and keep them in check. Keep your plant watered to prevent dehydration. Mulching around the tree, being careful to keep the mulch away from the trunk(s) will keep moisture in. Keeping mulch away from the trunk will prevent moisture buildup on the bark, thereby stemming another potential problem, mildew.

Good luck, the tree is worth the effort.