Stunted Tips & Invasion of the Leafhoppers

Issue: 
September-October 2009

LOOKING AROUND THE LANDSCAPE, you’ve probably noticed all the stunted leaves at the tips of branches on our street trees. Take a closer look at sugar, red, red-silver hybrids and Norway maples and you may see stunted, bushy leaves that look like they never fully emerged. In the summer, you may also have noticed that these leaves were quite chlorotic and the margins were often black. What gives? Most people attribute this to hot, dry weather in summer… but not this year. Would you believe that tiny leafhoppers are to blame?

Leafhoppers blow up from the south every spring and infest plants as they migrate north. Leafhoppers arrive in southern Ontario around the middle of June each year. Their arrival quite often coincides with the emergence of the second flush of growth on our deciduous shade trees. Leafhoppers are most attracted to soft, succulent new growth as it is expanding. This is because 1) they can insert their sucking mouthparts into it easily and 2) they can lay their eggs into this tissue. The result is an explosion of flightless leafhopper nymphs that feed on leaf tissue until they pass into the adult stage and disperse.

Leafhoppers suck out plant sap from several points on the leaf resulting in chlorotic (yellow) spots and larger areas of chlorosis on the leaves. Feeding injury also causes stunting and distorted tissue. Like other sucking insects, leafhoppers can be vectors for plant pathogens (e.g. viruses) and this can have significant impacts on plant disease for some crops. Leafhoppers are also known to inject toxins into leaf tissue as they feed, which probably explains the marginal necrosis (blackening).

I had a lot of neighbours and other homeowners asking me about leaf stunting on their trees this year. Leafhoppers are such tiny, yellow-green, mobile insects that it takes a tenacious person to detect them. So why did we see so much injury in 2009? The answer lies in the weather. It was cooler than average for extended periods of time. Which means leaf emergence was slower than usual and that favoured feeding and egg-laying activity of leafhoppers. They were extremely successful this year and the result was greater than average injury on deciduous trees in the landscape and nursery.

How does leafhopper injury impact the health of the tree? Generally speaking, the injury is mostly aesthetic on older landscape specimens and the trees tend to grow out of it. In cases where trees are withstanding several years of repeated attacks, there may be some long term stunting and dieback.

Fire-Red Lesions on Pear
Pear trellis rust has been found in the landscape at several locations in southern Ontario in the last few years. Given the cool, wet spring, it’s not surprising to see it on so many ornamental pear trees in 2009. This disease causes very striking, orange-red lesions on ornamental and fruiting pear trees by mid-summer. Tiny, crème-coloured string-like lanterns appear on the undersides of these lesions in September and October and these structures send spores to infect juniper hosts. Once leaves drop, these structures die and are no longer a source of this disease. It is the alternate host, juniper, that carries the disease from year to year.

Pear trellis rust is caused by the fungus Gymnosporangium sabinae (G. fuscum). You may know the genus Gymnospor-angium since other species of this fungus cause cedar-apple rust, cedar-quince rust and hawthorn rust on ornamentals. Like many rust diseases, two hosts are required to perpetuate pear trellis rust from year to year. Juniper is the perennial host and pear is the summer host. The disease can be particularly damaging on pear, resulting in complete defoliation and crop loss if the disease is not managed.

The disease overwinters as subtle branch swellings on juniper. Try pruning out branches with suspicious swellings in the winter to reduce sporulation the following spring. Another alternative is to keep juniper and pear hosts separated as far away from each other as possible. Where fungicides are permitted to protect pear leaves, applications should take place in the spring when the disease is sporulating on the juniper host (during warm, wet conditions). In the Ontario landscape, tree care specialists will need to obtain permission from the Ministry of the Environment before applying non-exempt pest control products.

Contact Information

This column is written by Jen Llewellyn, Ontario Ministry of Agriculture and Food and Rural Affairs (OMAFRA) Nursery Crops Specialist

Email any questions you have directly to Jen and we'll publish her response.


P: 519-824-4120 ext. 52671 • F: 519-767-0755
jennifer.llewellyn@ontario.ca

OMAF website: http://www.omafra.gov.on.ca/scripts/english/crops/agriphone/index.asp

Nursery Landscape Agriphone: 1-888-290-4441

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.