We have a Linden tree beside our driveway. It is dropping a ton of sap creating a covering over the hostas and other plants. The plants are not thriving well at all. Is this normal? We have to wash the car windows and unstick the wipers before driving as well. We live in Burlington Ont
Thank you for contacting the Toronto Master Gardeners with your inquiry.
From your description it sounds as if your Linden tree is suffering from an infestation of Linden aphid, Eucallipterus tiliae. Aphids are tiny insects that feed by sucking sap from the phloem, the food-conducting tissues in plant stems and leaves. These pests secrete a sticky substance called honeydew which is what is coating your hosta leaves and your car windshield.
One of our earlier posts details the proper control of aphids:
A strong blast of water from your garden hose can dislodge the adults along with repeated application of insecticidal soap to catch the nymph stages can help control the population of this leaf sucking insect. When spraying with insecticidal soap, make sure to spray both the tops and underside of the leaves.
Natural enemies such as lacewings, and parasitic wasps may help to control aphids, but may not appear in sufficient numbers until aphids are abundant.
If the infestation is severe, you may which to contact a certified arborist to apply the soap. To find a certified professional arborist to help you with a tree problem, visit the Ontario branch of the International Society of Arboriculture here.
We also have a Gardening Guides on Controlling Insects without Pesticides and Integrated Pest Management which you might find of use.
Good Luck.