Are you seeing black marginal necrosis on the newest growth of Pear (Pyrus) trees? We saw the same phenomenon back in 2016 and after several attempts at culturing pathogens failed, we determined that the necrosis was the result of extreme weather. Southern Ontario has seen its fair share of sweltering heat and humidity this summer. Ten out of the last 23 days in Toronto have been recorded to exceed30 degrees C. Those extreme temperatures have been taking their toll on plants, especially newly emerged foliage that hasn’t developed a thick protective cuticle yet. In the pear industry, this marginal leaf necrosis is known among farmers as “pear blast” and is common on foliage that emerges during high heat and humidity. The phenomenon usually lasts only a few days and will not worsen or spread to other healthy foliage.
Supplemental irrigation will be very important to support tree health during the summer of 2018.
Growing Degree Days: 750-900 GDD Base 10oC
1. Daucus carota (Queen Anne’s Lace, full bloom)
2. Cirsium arvense (Canada thistle, full bloom)
3. Hydrangea arborescens ‘Grandiflora’ (white flowers turning green)
4. Yucca filamentosa (Adam’s Needle, finishing bloom)
5. Sorbus aucuparia (fruit turning yellow).
Fall webworm (Hyphantria cunea) nests are starting to become more numerous already this year. Look for larval nests on deciduous trees such as Juglans, Betula, Fraxinus and Prunus. Larvae can be found feeding on foliage inside the strong webbing. Larvae are light yellow with dark spots and will flick their abdomens conspicuously when a predator approaches. Where possible, manually remove webby larval tents and destroy them. Larval tents expand to encompass more and more foliage every few days so it is possible to spray infested trees with Dipel/Foray to suppress populations where pruning is not possible. There are multiple generations of larvae per year.
Euonymus scale is starting to produce a SECOND generation of crawlers at this time. Look for tiny, orange crawlers or brown nymphs in among the adult scale populations on leaves and stems. Crawlers are the most susceptible life stage and are sensitive to applications of contact insecticides, even insecticidal soap and the summer rate of horticultural oil. Mind the high temperatures as some pesticides can burn foliage when its hot and humid out. Kontos is one of our newest insecticides registered for scale insects in the nursery. It can also be used as a drench.
Are you seeing webbing around the ends of branches on deciduous trees such as ash, birch and cherry? Look inside the webbing and look for yellow, fuzzy caterpillars. These are fall webworm caterpillars and they usually start to show up on the ends of branches this time of year. Prune out nests and destroy them to prevent future colonies from infesting your trees. Pole loppers are an awesome tool for managing fall webworm caterpillar nests! Spraying is not necessary or necessarily effective unless there are high populations of nests.
Have white grubs been an issue in your nursery? Preventative applications of Acelepryn (chlorantraniliprole) and Intercept (imidacloprid) are registered for white grubs (nursery production) and July is a good time to use these products (during the adult flight period). [Beneficial nematode applications for white grubs (e.g. European chafer) will be effective in early-mid August where there is regular irrigation].
Japanese beetle adults are flying and feeding on leaves of woody plants (Syringa, Tilia, Ulmus, Prunus, Rosa). Look for metallic, coppery-green beetles with white tufts of hairs along the edge of their abdomens.
Adulticide insecticides for JB in the nursery include Sevin XLR and Imidan. Pheromone traps for JB are extremely good at attracting the adults. Always place traps far AWAY (I mean away) from susceptible host trees and shrubs (e.g. Rosa, Prunus, Tilia, Syringa, Ulmus etc.).
DECIDUOUS WOODY AND HERBACEOUS PERENNIALS:
We have seen lots of powdery mildew on deciduous flowering shrubs (Amelanchier, Rosa, Physocarpus) and herbaceous perennials. Monitor for white, powdery residue on the tops and bottoms of leaves. Protect new foliage with fungicide applications [e.g. Switch, Milstop, Regalia (biofungicide), Tivano] but where the disease pressure is moderate to high, fungicides are not going to be very effective as they have limited curative action.
Magnolia scale adults are white and will be turning pink-orange in the next couple of weeks. They will producing dark-coloured crawlers under these protective shells, usually at the beginning of August. (Magnolia scale do not produce eggs but give birth to live young). Pick the scale shell off and look for juicy flesh as a sign that reproduction has not yet begun. Insecticides are not very effective at this time and won’t be effective until crawlers emerge from under mother scales in August. However, you can scrub the fleshy scales off the twigs at this time to give immediate management of this pest.
European elm scale (Gossyparia spuria) crawlers have hatched and can the tiny bright yellow nymphs can be found on new twigs of elm (e.g. ). Adult females are 2 mm long (tiny), oval, brown with a whitish fringe around their body. This can be an injurious pest on elm, we often see copious amounts of sooty mold and twig dieback. You can also scrub this scale insect off of the twigs. This pest is also very vulnerable to dormant horticultural oil applications in late fall/early spring when no leaves are present. The overwintering nymphs migrate to the bark crevices at the end of the growing season.
Injectable insecticides may be used to protect ash trees from new infestations of Emerald Ash Borer (Agrilus planipennis). Trees must be actively transpiring in order to maximize insecticide uptake into the conductive tissue. Registered injectable insecticide products include: AceCap 97, Ima-Jet and Tree-Azin. Check out the Management Strategy for Emerald Ash Borer and Bronze Birch Borer at: http://www.omafra.gov.on.ca/english/crops/insects/eab-bbb-manage.htm.
Potato leafhoppers NYMPHS and ADULTS are still feeding on woody nursery stock on the newest growth (2nd flush). Above photo: PLH damage on Rhus aromatica by Lauren Stitt. Monitor for potato leafhopper on nursery crops such as Caragana, and Acer (platanoides, saccharum). Nymphs are about 2 mm long and scuttle SIDEWAYS, rather quickly, across the leaf and to the other side (they don’t have wings to fly away). Susceptible crops are those that are flushing new leaves (leafhopper’s favourite food source). Older, hardened off foliage is not usually as susceptible. Leafhopper adults are winged, are very mobile, tiny, pale yellow-green jumping insects that are easily disturbed when you approach infested foliage. It almost looks as though they are being flicked off of the foliage. Potato leafhoppers suck plant sap from soft, expanding foliage and cause foliage to wilt, turn brown/black (‘Hopper Burn”) and become stunted and malformed. Older, hardened off foliage will become flecked from leafhopper feeding. Unfortunately, most of the damage has been done by now.
Gypsy moth larvae are pupating and no longer susceptible to insecticides. Adult Gypsy moths are just starting to emerge in southern Ontario.
Sticky bands around trunks during the June/July flight period will help prevent adult female Gypsy moths (above) from laying eggs above sticky bands and will attract males to the sticky surface. Pheromone-baited sticky traps are also available to help reduce populations of adult males. GET YOUR TRAPS OUT NOW!
Two-spotted spider mites (Tetranychus urticae) are feeding on several types of deciduous woody (Viburnum and Hydrangea in container production) and herbaceous perennials. Look for chlorotic leaves with stippled appearance. The leaf undersides will have a “dirty” appearance. Use your hand lens to see tiny, clear bodied two-spotted spider mites with dark regions (may be faint black) on their backs.
Above photos: Salvia with Two-spotted spider mite damage, upper leaf and lower leaf (right). Note mites inhabit the lower leaf surface giving it a “dirty” appearance. These mites are small but the damage is significant so catch them early. Miticides registered for this mite in the greenhouse include: DynoMite/Sanmite, Vendex, Kanemite, Floramite, Avid. Apollo is registered in outdoor nursery crops to target the egg stage and newly hatched nymphs. In the greenhouse, biocontrol agents should be brought in to coincide with the first sign of TSSM. Phytoseiulus persimilis is a predatory mite that feeds on TSSM when temperatures are below 26oC and it is a good choice when TSSM populations are low-moderate. Amblyseius californicus is a predatory mite that can be brought in ahead of TSSM appearance (because it can find other sources of food). Stethorus punctillium is a new beetle that is a good predator of TSSM.
You might notice some bronzing and yellowing on the foliage of white oak species, caused by the Oak spider mite (Oligonychus bicolor). This mite becomes active in mid summer and feeds for a good 6 weeks before populations start to die down. It rarely causes significant damage to host trees unless infested trees are very juvenile. (Notice how they look a lot like spruce spider mites? They are of the same genus). (Photos: Lauren Stitt :))
Taxus/Fletcher Scale crawlers (left) have settled on needles and twigs and are feeding (right). As they become older, they cover themselves in waxy material and are more difficult to manage with insecticides. Several contact and systemic insecticides are registered for this pest in the nursery. Be careful to rotate pesticides with others belonging to different groups (i.e. different modes of action) to avoid pesticide resistance and to instead increase pesticide efficacy.
Monitor for Black Vine Weevil (Otiorhynchus sulcatus) ADULTS in the FIELD and in CONTAINER PRODUCTION on Rhododendron, Taxus, Thuja, Picea and Euonymus and several other ornamental hosts. Applications of nematodes will be effective if you wait to early September to apply them. Strawberry root weevil (Otiorhynchus ovatus) can also be a problem in field production of evergreens, adults have emerged.
Signs of strawberry root weevil adults include brown, flagging shoot tips (and small girdling marks at the base of the flagged shoot) . The most common host for this type of damage is Thuja occidentalis (eastern white cedar). SRW flagging is common on Thuja and does not usually negatively impact tree health.
To scout for adult weevils, place a tarp or large piece of cardboard under the tree, shake branches vigorously over the board and look for brown-black weevils “playing dead”. Insecticides for adult weevils in the nursery include Pounce, Sevin and Thiodan. Remember, adult weevils feed at night. Spray insecticides in late evening to target adults and reduce UV degradation (e.g. Pounce, Scimitar).
Cedar leaf miner next generation larvae are starting to feed on tender new foliage. A light sheering of tips in early August should give good knockdown of CLM larvae. Cygon is registered as a foliar application for CLM larvae in early August in the nursery.
Remember all that boxwood leafminer you were trying to manage this spring in the landscape? Well the next generation of larvae are feeding on this year’s growth NOW, although you can’t see any signs of them yet. A sheering of 2018 growth will eliminate many of the lovely, leafy homes they’ve found. They will die of desiccation in those clippings over the next several weeks.
Monitor for nymphs and adults of spruce spider mite on conifers with a history of mite damage (Photo: Dave Cheung). They can be found in blocks of Thuja, Picea and Abies and are more common in evergreens receiving regular irrigation. Spruce spider mite nymphs and adults are brown with black backs and found on new foliage this time of year. Click HERE for a short video. Miticides registered for SSM include Floramite and Shuttle/Kanemite, Vendex. Miticides may be required where pest pressure is moderate to heavy (container grown conifers with overhead or drip irrigation). Populations in field production and in the landscape can really explode with the cooler nights of August/September.