Growing Degree Days: 200-250 GDD Base 10C
1. Acer saccharinum (silver maple, dropping seed)
2. Aesculus hippocastanum (horsechestnut, late bloom)
3. Cornus alternifolia (pagoda dogwood, full bloom)
4. Spiraea vanhouttei (bridal wreath spirea, full to late bloom)
5. Syringa vulgaris (common lilac, finishing bloom)
6. Prunus serotina (black cherry, full bloom)
7. Ulmus pumila (Siberian elm, dropping seed)
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.
LO Nursery Scout Melissa Huntley has been really hard at work this spring monitoring nurseries for pests and other plant health issues! Her scouting reports are invaluable to growers and much of her findings are also reported in this ONnurserycrops blog! Thank you Melissa!
The imported willow leaf beetle has been found on both tree and shrub type Salix spp. this week! Black (and yellow) larvae can be found feeding on the undersides of leaves. They skeletonize leaves, leaving them looking lacy. This pest can really do a lot of damage in a short period of time. Apply insecticides (spinosad, malthion, acephate, carbaryl) where populations are at damaging levels.
Adults of the Imported Willow Leaf Beetle are metallic dark blue, convex-shaped beetles and eggs are yellow, laid on leaves.
Powdery mildew is starting to show up on a few hosts in the landscape (believe it or not). We found powdery mildew starting on Quercus robur ‘Fastigiata’ this week. Powdery mildew can lead to stunting and reduced photosynthesis on susceptible hosts like this one. Help protect healthy foliage with the application of fungicides (Daconil, Banner, Nova) and also keep host trees in well-aerated, fertile soil.
Woolly beech adelgid is still feeding on Fagus sylvatica leaves. You can find them on leaf undersides and all life stages are often interspersed together in the woollies! You can also find tiny, round balls of honeydew. This pest is very sensitive to insecticidal soap, as long as you can get good coverage on leaf undersides. This pest is usually of very little consequence to tree health.
Oystershell scale crawlers are actively feeding on new shoots of deciduous trees. The crawlers are tiny, yellow-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.
Gypsy moth larvae are feeding on several species of trees (oak, linden, hackberry, beech, Colorado spruce). Look for large holes in leaves, between veins. Turn over inspect leaf undersides for dark, fuzzy larvae (15-20mm long). Gypsy moth larvae may also hide in bark crevices during the day. Management of Gypsy moth larvae can be achieved using Bacillus thuringienesis (B.t., Dipel, Foray) and spinosad (Success) insecticide, with good coverage. Success applications should be finishing up as older larvae (>1″ long, yellow head capsule) are not susceptible to it. Some keen homeowners can install a burlap skirt at the base of the tree to create a shady, protected area for larvae to hide during the day (this behaviour usually peaks near the end of May). Homeowners will need to inspect burlap skirts and underlying bark crevices daily (1-3 pm is best) and remove/destroy larvae.
Fall cankerworm (Alsophila pometaria) larvae can be found chewing interveinal leaf tissue, especially on the leaf undersides. Larvae are pale green (although you’ll often see darker races too) and blend in with foliage. They are about 18-25 mm long right now and they are really hungry. Monitor for larvae on several hosts such as Acer, Tilia, Quercus, Ulmus etc. A foliar application of the bio-insecticide Dipel (Bacillus thuringiensis, B.t.). or traditional insecticide (e.g. permethrin) can help to significantly reduce populations and subsequent injury.
Potato leafhopper ADULTS are feeding on woody nursery stock and their eggs inside foliage are starting to hatch in the NURSERY. Monitor for potato leafhopper on nursery crops such as Acer (platanoides, saccharum), Quercus and Ostrya. Adults will fly away quickly but once nymphs hatch, they will scuttle SIDEWAYS, rather quickly, across the leaf and to the other side (they don’t have wings). Susceptible crops are those that are flushing new leaves (leafhopper’s favourite food source). Older, hardened off foliage is not usually as susceptible. Leafhoppers (and aphids) suck plant sap from soft, expanding foliage and cause foliage and stems/petioles to wilt, turn brown/black (‘Hopper Burn”) and become stunted and malformed.
Older, hardened off foliage will become flecked from potato leafhopper feeding but younger foliage is more severely damaged. Monitor populations and treat where new foliage is emerging. Leafhoppers are also attracted to yellow sticky cards, for monitoring. Registered insecticides include acephate, acetamiprid, carbaryl, permethrin.
Where new foliage has not hardened off yet, monitor for needlecast and blight diseases on spruce in the area.
Rhizosphaera needlecast (above photo) and Stigmina on blue Colorado spruce are our most common needlecast diseases in Ontario. Rhizosphaera appears as brown-purplish needles from the previous year’s growth (2-3 yrs old), symptomatic needles begin to drop in late spring. Stigmina appears on green and chlorotic needles, but doesn’t always lead to needle drop. To confirm it is Rhizosphaera, look closely at the needles. Those little white dots (stomata) will turn black and the black spots will protrude during sporulation. New, soft growth is especially susceptible to foliar diseases, but infection may also take place later in the season. Where there is a history of damage, treat with registered fungicides (copper oxychloride, Banner Maxx, Daconil) as new foliage continues to emerge Apply fungicides prior to precipitation events (spore dispersal). Unfortunately, most of these blights and needlecasts can be found sporulating for much of the year.
Protect emerging shoots (left photo) on 2 and 3 needled pines for Diplodia (Sphaeropsis) (right photo) tip blight. Diplodia tip blight appears as brown, stunted needles at the tips of branches. This fungal disease sporulates much of the season but needles are most susceptible when they emerge in spring. Protect emerging needles with fungicides (copper), especially before leaf wetness periods and continue to protect until needles harden off.
Euonymus scale crawlers are just starting to hatch in container nursery production. This is the most susceptible period for pest management. (They will be hatching in the landscape in about 2 weeks.) Crawlers are tiny, orange and they will take a week or two to emerge out from under the dead, brown female scale covers. Several insecticides are registered for the crawler stage (dimethoate, acephate). Kontos (spirotetramat) is registered both as a foliar and drench (which works well in containers). Crawlers are also very susceptible to insecticidal soap and the summer rate of horticultural oil.
Have white grubs (e.g. European chafer, June beetle) or Japanese Beetle phytosanitary restrictions been an issue at your nursery? Preventative applications of Intercept (imidacloprid) and Acelepryn (chlorantraniliprole) are registered for white grubs in nursery production and the application period will begin late June. Japanese beetle adults usually start to show up mid – late June in southern Ontario. Apply preventative soil drench applications for JB at the beginning of the adult flight period, usually when the Tilia cordata start to bloom you can monitor for them.
Monitor for spruce spider mite on conifers with a history of mite damage (Abies, Picea, Thuja). Spruce spider mites appear as very tiny, brown mites with black backs. You will REQUIRE A HAND LANDS TO SEE THEM CLEARLY. Monitor lower branches, on the North and Easter side of the tree, this is where most of the feeding damage is done. Miticides are effective against nymphs and adults (Floramite, Kanemite, Vendex). They are a cool season mite and have been increasing in some areas, they love this kind of weather.
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