Let’s follow up last month’s discussion of the European Chafer Beetle with some thoughts on a couple of other “problem” issues this summer. The last few summers the main problem has been drought. That seems to have been remedied this summer, but cool rainy weather brings its own set of issues.
Many have been noticing a problem with brown and drying leaves on lilac bushes. The most likely culprit is Bacterial Leaf Spot disease. This is very common in Minnesota and most common in cool, wet weather. The blight begins to manifest with small brown to black spots with a halo of yellow tissue on the leaves. The center of the leave may dry up and fall out, leaving what is often called a ‘shot hole.’ With long periods of favorable weather the spots can grow together and the entire leaf can dry up and fall off. Leaf spot disease can weaken the plant by interfering with photosynthesis, but most of the time only a small percentage of the leaves are affected and so it is a minor stress for the plant. But repeated leaf loss in several consecutive seasons can result in less growth and susceptibility to pests and other diseases. Major leaf loss in two to four consecutive seasons should be taken seriously.
There a few things you can do to reduce the impact of leaf blight. Bacteria can survive in leaf litter and the soil and re-infect your plant next year, so rake up fallen leaves and destroy them before the snow falls. Prune your lilac to increase light penetration and air flow throughout the bush. (Lilacs set their buds in spring shortly after they bloom, so don’t prune now or you will cut off the flower buds. Prune after they bloom next spring.) Wet conditions promote disease so always water a lilac at the base of the plant; try to keep the leaves dry.
Another problem that has cropped up this summer is the explosion of Creeping Bellflower. Creeping Bellflower is an invasive plant introduced into the United States from its native habitats in parts of Asia and Northern Europe. You probably have seen it in many yards and gardens this year because it survived the drought years and loves the rain! It is prolific because it spreads by both seed dispersal and root propagation. It grows to 2ft to 3ft tall and produces a tall spire of blue-purple bell shaped flowers. It is often confused with other bell flowers and could be considered an attractive addition to the garden but the problem is it is that it out competes other plants by choking them out. After flowering each plant produces as many as 15,000 seeds!
You can easily spot and pull the flowering plant before it produces seeds, but Creeping Bellflower also spreads through its root system. Small pieces of root can produce new plants. Once it takes hold is not easy to eradicate and requires dedicated removal. Small sections can be controlled by digging out and removing all the roots and stems, but a larger invasion might require more intense measures. You can possibly effectively manage the spread by smothering the plants with a tarp or newspaper, but it may be necessary to resort to a broadleaf herbicide. Only certain herbicides are effective and may require multiple applications. Also be cautious because broadleaf herbicides can be harmful to desired garden plants. For more info on effective herbicides for the control of Creeping Bellflower refer to the Minnesota Extension Service Yard and Garden News at
extension.umn.edu/weeds/creeping-bellflower.
Creep Bellflower can continue to bloom through early fall, so keep on pulling the flowering plant you see. You can contain the root propagation to your own yard or garden, but those seeds can disperse to your neighbors and across the whole landscape. Keep up the good fight!