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We are seeing wind tattering damage on tender new foliage of trees and shrubs. Ontario springs are often characterized as windy with extreme temperature shifts leading to low temperature injury and wind damage. High winds in the Barrie area last week caused damage to large trees with full canopies as well as property damage.
Plant Phenology Indicators: GDD Base 10C: 150-200
1. Aesculus hippocastanum (horsechestnut, full bloom) 2. Cornus alternifolia (pagoda dogwood, early bloom) 3. Spiraea vanhouttei (bridal wreath spirea, full bloom)
4. Syringa vulgaris (common lilac, full-late bloom)
5. Prunus serotina (black cherry, early-mid bloom)
The Crop Protection Guide for Nursery and Landscape Plants (OMAFRA publication 840) contains the crop pest recommendations for nursery and landscape. Download it onto your phone or computer for easy reference.
Nursery-Landscape Insect Pest ID: Dave Cheung’s Common Pests of Nursery-Landscape database to help ID your problem pests.
Seeing malformed, stunted leaves with brown-black marginal necrosis on container grown lilac (Syringa spp.)? This is due to a combination of low temperature injury and a weak bacterial pathogen, Pseudomonas syringae. It is quite common on the first flush of leaves of container grown lilac and plants usually grow out of it to put on a more normal-looking second set of leaves. Where cool, wet conditions are still an issue, bactericidal sprays of copper can help protect new leaves from the pathogen.
Leaf spots on deciduous flowering shrubs are showing up everywhere because of the cool, wet conditions we had during leaf emergence. Leaf pots appear as purplish to brown, with yellow to brown necrotic margins. Several fungi (Colletotrichum, Septoria etc. ) cause leaf spots on ornamentals. When the second flush of leaves start to emerge in overhead irrigated containers, you may want to protect new growth with a foliar application of fungicide (Banner, Daconil, Dithane, Nova). Once container grown stock is planted in the field, the disease symptoms diminish.
Fireblight is a systemic bacterial disease that causes twig and branch dieback and bark cankers on large limbs and the main stem. It infects apple and pear trees through flower or through recent wounding (e.g. pruning). It is a serious disease in juvenile trees. Below are the links to the updated Risk Maps For Fire Blight. It is important to watch for late blossoms, called ‘rat tail’ blossoms, which are very susceptible to infection by this bacteria. Click on the risk map for either apple or pear to help you decide what management precautions you need to take to reduce fireblight infection.
[The Fireblight risk prediction maps for May 29 -June 4]:
WOOLLY BEECH APHID are feeding on beech. These aphids are small and green but they cover themselves with bright white, woolly strands and produce honeydew droplets that cling to the woolly masses. Populations are usually not threatening to tree health but applications of Insecticidal Soap can be very effective at reducing populations of young nymphs, especially when adequate spray coverage on LEAF UNDERSIDES.
Where HONEYLOCUST PLANT BUG was a problem in the past, monitor trees for tiny, green, wingless, nymphs (see above image). Plant bug nymphs and adults were a problem in many areas last year as these sucking insects caused stunting, malformation, chlorosis and senescence of leaves (see lower image). Shake new leaves over a white surface to assess populations of plant bug nymphs. Most contact insecticides work very well against this pest.
Reducing populations of honeylocust plant bug now is important since multiple generations will be cycling over the next few weeks.
Crawlers of Oystershell Scale have hatched in container production and are starting to hatch in the field/landscape (adults shown above). These crawlers are tiny and brown and very susceptible to insecticides including insecticidal soap and the summer rate of horticultural oil. This scale species can be found on several deciduous trees including lilac, ash, magnolia, maple, hackberry, willow etc.
Brown shoots on juniper may be a symptom of juniper tip blight (Kabatina blight). A small grey band or pinched grey canker with black fruiting structures can be found at the base of the infected shoot, this is where the spores come from. Pruning is not suggested once new growth appears, as it will help spread this disease. Where cankers are found, copper and Dithane are registered to protect emerging new growth this spring and summer.
Fletcher scale (Taxus scale) nymphs are actively feeding on Thuja and Taxus and are getting larger. They have a distinctive white stripe down their backs. You will probably notice the honeydew first. This scale is difficult to manage at this size but an application of systemic insecticides may help reduce populations in hot spots. It is entering its most rapid growth/feeding phase.
Crawlers (photo above) and nymphs (photo below) of Pine needle scale can be found on white/mugo/Scots pine at this time.
Pine needle scale crawlers and nymphs are susceptible to applications of acephate, carbaryl, dimethoate, horticultural oil, insecticidal soap, malathion. Good coverage is required to effectively reduce populations of this armored scale insect pest.
Pine bark adelgid eggs (photo above left, Melissa Huntley) have hatched into tiny yellow nymphs (photo above right, Dave Cheung). Look for small, woolly-white masses with eggs and nymphs underneath.
These pine bark adelgid nymphs will be moving to feed on emerging foliage and will cover themselves in a woolly coating soon, making them much less susceptible to contact insecticides. Avoid using horticultural oil on white pine as it will dull the glaucus sheen to the needles. Other options include insecticidal soap, acetamiprid, dimethoate, malathion.
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