Flower Buds and a Few Thugs

yellow flowers on branches

Cornus mas (J. Llewellyn)

We’ve had such a cool spring that when we did start to get some “heat” a few weeks ago, it hastened the development of some of our earliest flowering plants.  Instead of there being distinct periods of bloom, many of them are blooming at the same time.  The cold weather this week has held plant phenology at a bit of a stand still.




Frost Protection. The surest way to protect tender new foliage and flowers is to cover them. Some growers use light weight thermal blankets and some use leftover poly. The coldest temperatures are usually experienced between the hours of 2:00 and 5:00 am. If you are irrigating to reduce frost injury, start irrigating before temperatures dip down below 0oC. The act of freezing releases heat from the irrigation water molecules and warms the surface of the plant so tissue does not freeze. Unfortunately, ice formation may actually physically damage tender new shoots because it is so heavy. You’ll have to use your discretion about night time irrigation. Another option is to increase air flow around the plants. By blowing away the cold air that settles around the plants, you can reduce some of the low temperature injury. Some growers have tried using fans from their airblast sprayers with some success.

Plant Phenology indicators this week, north of 401, include: Acer saccharinum (silver maple, many in late to finishing bloom); Acer rubrum (red maple, mid bloom); Cornus mas (Cornelian cherry dogwood, full bloom); Salix caprea (pussy willow, mid bloom); Acer saccharum (sugar maple, not yet blooming, will some bloom?). Most areas of southern Ontario in the range of 25-50 GDD base 10oC. If you are referring to the Phenology and Monitoring tables in OMAFRA publication 841, Guide to Nursery and Landscape Plant Production & IPM, look at the Tables starting with 2-3 on pg. 39.

PLEASE NOTE: The Following Pesticide Recommendations are meant for Exception Uses (e.g. agriculture) under the Cosmetic Pesticide Ban unless the active ingredient is listed under Class 11 pesticides in Ontario Regulation 63/09, effective April 22, 2009.

The Crop Protection Guide for Nursery and Landscape Plants (OMAFRA publication 840) contains the crop pest recommendations for nursery and landscape plants that was previously found in publication 383. Publication 840 is a .pdf file, accessible online and on cd.  The pest recommendations can also be found on our online, searchable database:  www.nurserytracker.com.  Check out NurseryTracker on your phone or tablet!!!

Nursery-Landscape Insect Pest ID: Dave Cheung’s Common Pests of Nursery-Landscape database to help ID your problem pests.

Once ash trees have leafed out, injectable insecticides may be used to protect the trees from new infestations of Emerald Ash Borer (Agrilus planipennis). Trees must be actively transpiring in order to maximize insecticide uptake into the cambium. Registered injectable insecticide products include: AceCap 97, Confidor 200 SL, IMA-jet and Tree-Azin.  The regulated areas for EAB outlines restrictions on the movement of all ash species (Fraxinus sp.) materials and all species of firewood from these regulated areas of Ontario and Quebec.

The Asian Long Horned Beetle was detected in the vicinity of Pearson International Airport in Toronto/Mississauga and efforts are continuing to eradicate this beetle from the area. The Asian Long-horned Beetle Infested Place Order is being enforced in the area encompassing: all parts of the City of Toronto and City of Mississauga, in the Province of Ontario, located within the area commencing at the point of intersection between Dixie Road (formerly Hwy. 4) and Derry Road (formerly Hwy. 5) and proceeding northeastward along the south side of  Derry Road to Bramalea Road. This means that tree materials, including nursery stock, trees, logs, lumber, wood, and wood and bark chips from tree species that are susceptible to the Asian Long-horned Beetle, may not move out of, or through, this area.


BuxusOWDes TaxusWinterDes Winter desiccation is evident on many evergreens this spring, but it doesn’t look as bad as it did this time last year. Drying winds and warm, sunny days in late winter caused foliage to lose water. Because the ground is (usually) frozen, roots can not replenish lost water from the foliage and the foliage dries out and becomes brown. Newly-transplanted evergreens are even more susceptible because of their reduced root systems and ability to store water. Quite often, the damage is on the afternoon-sun side of the plant. Take heart, as long as buds are not damaged, the emergence of new growth should hide most of the winter burn.

If you are bringing in SOD (Sudden Oak Death, Phytophthora ramorum) host nursery stock from high risk areas, you may want to monitor for SOD symptoms. Camellia, Rhododendron, Viburnum, Pieris, Kalmia and Syringa are considered to be high risk host genera, as they are most common genera found positive for SOD in retail and wholesale nurseries. Fungicides registered for SOD in nurseries include: Acrobat 50 WP, Chipco Aliette WG and Subdue Maxx.  For a complete list of SOD regulated hosts, check out: http://www.inspection.gc.ca/english/plaveg/protect/dir/sodspe.shtml

Where nursery stock continues to be maintained in a polyhouse, caution should be taken when applying pest control sprays. Temperatures in the polyhouse can spike on clear sunny days, causing the chemical to injure foliage. Ventilation holes should be cut to keep high temperatures and high humidity at bay. High humidity has been linked to distortion and stunting of new growth on vines and shrubs and should be addressed where these symptoms have been observed.

PseudomonasSyringaBloomerang In container nurseries, where Pseudomonas blight on lilac (and other deciduous shrubs) was a problem last season, you may want to consider an application of  copper as they bud out.  Research also indicates that the copper becomes more effective if combined with Dithane.  The bacteria overwinter next to the buds and can infect leaf tissue once bud caps split open.  Again, infection and spread of this bacterial disease can be reduced where temperatures and humidity levels are moderated (i.e. ventilation under poly) and new foliage is more gradually hardened off to outdoor conditions.

<a href="/clm/species/otiorhynchus_sulcatus"><em>Otiorhynchus sulcatus</em></a> (Black Vine Weevil) larva. In production nurseries where black vine weevil larvae are a problem in container crops (e.g. perennials, evergreens), monitor containers for larvae and pupae. Once soils reach at least a consistent 10-12oC and treat with Heterohabditis bacteriophora (H.b.).  This should result in a significant reduction in populations in under two weeks.  Order your nematodes in advance.  Since Heterohabditis nematodes require moist, warm soil, we find that they do not work well in the landscape/field unless ample, supplemental irrigation can be provided for the 2 weeks following application.  In the LANDSCAPE and GARDEN, check for overwintered larvae of black vine weevil on Rhododendron, Taxus, Thuja, Euonymus etc. in the garden.  When soils warm up you can try an application of nematodes to help reduce populations.

EuropeanChaferLarvaSoil  Take a look at the roots of poor looking turf and field grown ornamentals and look for populations of European chafer, May/June Beetle larvae and other white grub species in the soil. Preventative applications of Intercept (imidacloprid) are registered for white grubs (nursery production) and the application period is in June and July (during the adult flight period). Beneficial nematode applications are not recommended this time of year and are much more effective when applied to early instar larvae, mid-August to early-September.


Black Knot of Prunus (University of Minnesota Extension)

Black knot is easy to see on Prunus sp. at this time. Monitor gardens and adjacent wild areas for Prunus shrubs and trees for large black growths on previous years twigs. If you have the time to prune, prune the cankers out, back quite close to the main stem BEFORE LEAVES EMERGE. Destroy all pruned twigs. Pruning too shallow retains the undetectable, developing canker on the tree and does nothing to limit the disease. Fungicides may give some suppressions when sprayed at green tip, pre-bloom and blossom time. Fungicides include Daconil and Maestro. Fungicides need to be applied ahead of precipitation events during bloom and shoot emergence In the nursery/orchard, Daconil has been shown to be the most effective fungicide. (Fruit-bearing mature Prunus: Daconil cannot be applied after shuck split or fruit will be injured). For more information: http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2003/03hrt03a4.htm


Overwinter Cankers of Filbert Blight (Toronto Botanical Gardens)

Monitor ornamental Corylus sp. for signs of Filbert Blight. This is a fungal disease that causes rows of small, black, crescent-shaped cankers along dead stems. Remove cankered shoots, 20-30 cm behind visible cankers, when plants are dormant. Disinfect pruning shears between each cut. Do not prune once new growth starts emerging. Corylus avellena ‘Contorta’ is particularly susceptible. Spray fungicides to protect new growth, starting at bud swell to bud break. Registered fungicides for this disease include: Copper oxychloride 50, Copper Spray and Flint (Compass).

JuniperTipBlightClose Brown shoots on juniper may be a symptom of juniper tip blight (Kabatina blight). A small grey band or pinched grey canker can be found at the base of the infected shoot, this is where the spores come from. Where plants are still dormant, PRUNE OUT DEAD SHOOTS during DRY conditions (and remove shoots) to reduce disease spread. Disinfect pruning shears between each cut (e.g. rubbing alcohol, other sterilants) to reduce disease spread. 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.

Applications of horticultural oil should be finishing up soon (daily temperatures between 4oC and 12oC are ideal). Timing of dormant rate horticultural oil applications are critical since freezing temperatures, mixing with sulphur and applying at the dormant-rate on actively growing tissue may result in injury. Apply dormant oil on clear mornings to facilitate rapid drying. The oil provides a barrier that restricts both respiration and movement of overwintering insects. It is quite effective for the management of overwintering spruce gall adelgids, scale Nymphs and mite eggs (including spruce spider mite, European red mite, maple spider mite on silver/red hybrids). Keep in mind that most of these insects overwinter on the undersides of leaves and twigs. Since the oil droplets come out of solution so easily, frequent agitation is VERY important during application. Some plants listed as sensitive to dormant oil applications include: Japanese maple, red maple, sugar maple, hickory, walnut, blue junipers, blue Colorado spruce, white pine, red oak, and to a lesser extent: yew and cedar.

Keep in mind that dormant horticultural oil applications are not effective against Euonymus scale, Oystershell scale and pine needle scale and will have only very limited efficacy against Fletcher scale and Lecanium scale.  Dormant applications of horticultural oil are very effective against Magnolia scale and San Jose scale (on fruit trees).

<a href="/clm/species/oligonychus_aceris"><em>Oligonychus aceris</em></a> (Maple Spider Mite) eggs on maple. Remember the maple spider mite (Oligonychus aceris) injury you saw on the silver-red maple hybrids last year? The tiny, red, overwintering eggs of those maple spider mites can be found on the leaf scar, just below the bud for this years growth, on last year’s twigs. The mite eggs are tiny flat, red spheres and are just barely visible; you will need a hand lens to see them. Where populations caused damage last year, applications of horticultural oil prior to leaf emergence should help smother eggs and reduce the population.

img_2429 Birches with a history of bronze birch borer infestation should be pruned by now. Symptoms appear as branch tip death, branch death and death of the leader and progresses quite quickly. Destroy pruned material to prevent emergence of beetles. Natural resistance to this pest can be enhanced through activities that improve plant health, such as light fertilizing (May, October), irrigating and removing any weeds and grasses that provide competition for the tree. Betula pendula is most susceptible to this pest and should be avoided in areas of known BBB infestation. Betula nigra and its selections have been shown to be quite tolerant to BBB attack.

<a href="/clm/species/dasyneura_gleditschiae"><em>Dasyneura gleditschiae</em></a> (Honey Locust Pod Gall Midge) galls.<a href="/clm/species/dasyneura_gleditschiae"><em>Dasyneura gleditschiae</em></a> (Honey Locust Pod Gall Midge) adult.

Where honeylocust podgall midge was a problem in the past, monitor trees for overwintered adult midges soon. These adults will be emerging as the buds start to swell. Adults will be laying eggs on buds in early spring (reddish eggs on buds and new leaves). Recent research in Oregon suggests that delayed dormant oil applications targeting the first couple of egg clutches can help reduce the incidence of pod gall midge. This involves applications of product early in the season, starting before foliar emergence.

Egg Mass of Eastern Tent Caterpillar (Tom Hodgson, Waterloo Natural History Association)

Eastern tent caterpillars will be hatching at budbreak and these tiny, black fuzzy larvae will start feeding and making webby tents in branch crotches. Manually remove and destroy the egg masses of Eastern tent caterpillar where they are still dormant. The egg masses appear as swollen, shiny grey bands around small twigs of cherry, crabapples and hawthorns. They actually glisten in the sunlight. The larvae can cause severe defoliation in May, where populations are high. Young larvae hide in webby tents during the day, remove and destroy tents during daylight hours in the first week or two after their appearance. Where larvae start to feed, try an application of the biological insecticide B.t (Dipel, Foray) on the foliage during the evening hours. Larvae will turn black and die approximately 3-5 days after eating the B.t. residue on the foliage.

Gypsy moth egg masses can be scraped off and destroyed at this time. The egg masses appear as raised, buff coloured fuzz on tree trunks, fence posts, buildings and other sheltered locations. When larvae begin to emerge (when trilliums are in full bloom), some control can be achieved using Bacillus thuringienesis (Dipel, Foray) and spinosad (Success) insecticide in the first 2 weeks after egg hatch. 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. Sticky bands around trunks during the June/July flight period will help prevent females from laying eggs above sticky bands and will attract males to the sticky surface.

<a href="/clm/species/pyrrhalta_viburnicola"><em>Pyrrhalta viburnicola</em></a> (Viburnum Leaf Beetle) damage on viburnum.

Viburnum leaf beetle egg masses can still be pruned out and destroyed at this time (where leaves haven’t begun to emerge yet), to avoid destructive populations this spring. Look for raised bumps on the undersides of 1 and 2-year-old twigs. The bumpy caps can be picked off to reveal the yellow eggs underneath. Monitor these eggs as they will hatching into larvae as foliage emerges. The larvae are vulnerable to chemical control only during the first 7-10 days after hatch. Larvae feed on the interveinal tissue from the undersides of the leaves, keep that in mind if you are doing insecticidal applications (Success, Actara, horticultural oil).


Balsam twig aphid stem mother on swollen bud. (Photo credit: Rayanne Lehman, Penn. Dept. of Ag., Bugwood.org)


Monitor for overwintering Balsam twig aphid eggs on terminal buds on fir, white spruce, Colorado spruce and juniper, they are susceptible to dormant oil applications. Eggs will be hatching in the coming weeks and developing into stem mothers (nymphs). The tiny, bluish grey aphid stem mothers can be found on terminal buds as they break. Apply Diazinon, Malathion and Tristar on warm days (55 to 78 GDD Base 10oC OR before bud caps loosen off) to target these stem mothers and prevent the damaging generation that follows.
http://www.insectimages.org/browse/subimages.cfm?SUB=321 http://ctrees.cas.psu.edu/pdfs/PestsofTrueFir.pdf

<a href="/clm/species/pissodes_spp"><em>Pissodes sp.</em></a> (White Pine Weevil) adult. Overwintering pine weevil adults are active and are mating on young twigs of evergreens when the Forsythia starts to bloom. Monitor for small black/brown snout beetles around the foliage. Where populations are high, an application of contact and stomach poison insecticide (e.g. carbaryl) on foliage may help reduce numbers. Common weevil pests include white pine weevil (1/4 inch long, two white spots on the back), northern pine weevil and pales weevil (1/2 inch long, brownish black). Pine root collar weevils also overwinter as adults (developmental stages are overlapping), but they feed and lay their eggs at the root collar.  If you are applying insecticides to last years terminals to help reduce oviposition sites of white pine weevil (photo above), spray terminals with insecticides as the Forsythia is blooming.

Cooley spruce gall adelgid and Eastern spruce gall adelgid overwintering females appear as tiny (you’ll need a hand lens to see them), grey/blue fuzzy spots at the base of buds, on the undersides of twigs. They are just barely visible with the naked eye. Galls do not usually have much effect on plant growth but appear unsightly in summer when they turn brown. Where populations are high, the adelgids are susceptible to chemical control (or horticultural oil applications when dormant) BEFORE buds start to swell and while nymphs are still blue-ish. Target pesticide applications to the undersides of shoot tips. Use wettable powder formulations on blue spruce to prevent foliar discolouration. Once they are covered in a white, woolly material, they have begun egg-laying and are no longer susceptible to pesticides.  Heavy populations of spruce gall adelgid are often a sign of some other underlying cause of stress or root problem in the tree.  Where infestations are small, you can remove and destroy green galls in June to reduce populations.

Monitor for eggs of spruce spider mite on conifers with a history of mite damage. Spruce spider mite eggs appear as very tiny, round, reddish-brown spheres that adhere to the UNDERSIDES of twigs and foliage this time of year. You will require a hand lens to see them clearly. Monitor lower branches, this is where most of the feeding damage is done. These eggs are susceptible to dormant hort oil applications in the next few weeks, where temperatures permit and plant species are not sensitive.  Miticides will be effective once eggs hatch to nymphs.

Pine shoot beetle adults have emerged. The tiny beetles take flight after 2-3 days where temperatures reach 10-12oC (I know, it’s hard to believe we’ve had that). Adults lay eggs underneath the bark of stressed or dead pine trees and stumps. Those larvae will develop later in April and May. Remove brood material (i.e. trap (sentinel) logs, snags, dead/dying trees) before new progeny adults emerge (210 GDD, Base 10oC) to comply with the CFIA. All brood material must be burned, chipped (less than 2cm diameter) or buried (30 cm deep) to comply with CFIA standards.


About Jen Llewellyn

OMAFRA Nursery and Landscape Specialist @onnurserycrops
This entry was posted in Arboriculture, Diseases, IPM, Nursery Production, Weekly Nursery Landscape Report and tagged , , , , . Bookmark the permalink.

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