Click HERE for the AUDIO version of this blog post.
Um what happened to our crabapple trees? You know what happened, all that rain during leaf emergence made things pretty cozy for fungal and bacterial diseases. Crabapples tend to lose their leaves when they get infected with diseases like apple scab. Compartmentalization is a pretty common survival strategy in the plant world. But in the human world, it’s the thing that gets men in trouble 🙂
Growing Degree Days: 650-750 GDD Base 10oC
1. Daucus carota (Queen Anne’s Lace, full bloom)
2. Cirsium arvense (Canada thistle, full bloom)
3. Hydrangea arborescens ‘Grandiflora’ (full bloom)
4. Yucca filamentosa (Adam’s Needle, finishing bloom)
5. Sambucus canadensis (elderberry, late to finishing bloom)
Gymnosporangium rusts (e.g. cedar-apple rust, cedar-hawthorn rust, cedar-quince rust) are sporulating on Rosaceous hosts such as Amelanchier, Crataegus, Malus, at this time. These sporulating structures can be found on fruit and leaves and will be sending spores to the Juniperus hosts to cause infection and formation of tiny galls. This photo captures fruiting structures on Amelanchier berries. Where necessary, spray protectant fungicides to protect Juniper hosts (e.g. Nova).
Numerous lesions of pear trellis rust (Gymnosporangium fuscum) on ornamental Pear. Infection happened during leaf emergence. Although unsightly, usually pear trees retain their leaves and they are functional (photosynthesizing). Sporulating structures will be emerging from the undersides of these lesions in September/October, sending spores to the alternate Juniper hosts.
You have probably seen aeciospores of Quince rust (Gymnosporangium clavipes) on various rosaceous hosts before. Here it is on Crataegus crusgalli. What you may not know is that this is also Quince rust on Crataegus. I just noticed this myself a few years ago and it reminds me so much of immature galls of Black Knot (of Prunus). Nope this is a rust disease and these galls are quite apparent when the trees are dormant…..so prune them off then.
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 very susceptible to applications of contact insecticides, even insecticidal soap and the summer rate of dormant oil. Watch 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 June 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 with 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 are not curative.
Magnolia scale adults are white and will be turning pink-orange in the next week or two. They will developing dark-coloured crawlers under these protective shells, usually at the beginning of August or so. Pick the scale off and look for juicy flesh as a sign that reproduction has started yet. Insecticides are not very effective at this time and won’t be effective until crawlers emerge from under mother scales. However, you can scrub the fleshy scales off the undersides of twigs at this time 🙂
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, we often see copious amounts of sooty mold and twig dieback. You can also scrub this scale off of the twigs. This pest is also very vulnerable to dormant oil applications in late fall/early spring when no leaves are present (since 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 but where new growth is emerging, insecticides may be
Gypsy moth larvae are pupating and no longer susceptible to insecticides. Did you notice that there wasn’t very many caterpillars around this spring?
Sticky bands around trunks during the June/July flight period will help prevent adult female Gypsy moths 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 (TSSM) are feeding on several types of deciduous woody (Viburnum and Spiraea in container production) and herbaceous perennials. Look for chlorotic leaves with stippling, use your hand lens to see tiny, clear bodied mites with dark regions (may be faint black) on their backs.
Above photos: Salvia with TSSM damage, upper leaf and lower leaf. Note mites inhabit 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, Vendex, Kanemite, Floramite, Avid. Apollo is registered in outdoor nursery crops to knock down 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-bleaching damage to the foliage of 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 crash. It rarely causes significant damage to host trees. (Notice how they look a lot like spruce spider mites? They are of the same genus). (Photos: Lauren Stitt)
Taxus or Fletcher Scale crawlers (left) have settled on needles and twigs and are feeding (right). As they become older, they are more difficult to kill 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, with different modes of action, to avoid pesticide resistance and increase efficacy.
Monitor for black vine weevil ADULTS in the FIELD and LANDSCAPE for Rhododendron, Taxus, Thuja and Euonymus. Applications of nematodes in the field/landscape will be effective if you wait to early September to apply them. Strawberry root weevil 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) on Thuja (eastern white cedar). To scout for adult weevils, place a tarp or large piece of card board under the tree, shake branches vigorously 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 (CLM) 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. So, a sheering of 2017 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 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 are usually not very active until the cooler weather returns in August/September.
Click HERE for the AUDIO version of this blog post.