Tip Blight on Blue Atlas Cedar

Pest and Life Cycle – (Sirococcus conigenus / Kabatina sp.) Tip blight is a fungus that affects both Atlas (Cedrus atlantica) and Deodar Cedar (Cedrus deodara), with the Sirococcus being the most common. It has a one year life cycle with the fungus overwintering  in dead shoots and infecting the base of new needles from spring to summer – especially during periods of prolonged rain with temperatures between 60-70F. Atlas Cedar is a North African species and is accustomed to a drier climate.

Symptoms – Needles change colour from blue to tan or pinkish and drop, with tip dieback being quite common.

Management – Fixed Copper sprays applied regularly (at label rate) through periods of wet warm weather from spring to early summer will help control its spread.

Prevention – 1. Prune out all dead or diseased branches once the rains have subsided and dispose of in the garbage (do not compost). 2. Rake up all fallen needles at the base of the plants.

Rhododendron Bud Blast

Pest and Life Cycle – (Pycnostysanus azaleae, syn. Seifertia azaleae) – Although often attributed to the above-mentioned fungus, Rhododendron Bud Blast can be caused by other Saprophytes that thrive on dead or decaying plant material. It is now believed that leaf hoppers act as vectors to spread this fungus, as the female lays its eggs in the buds (through slits) of rhododendrons and azaleas in late summer. This allows entry for the fungus which infects and kills the buds from autumn through winter.

Symptoms – Flowers buds often discolor by autumn and progressively brown through winter. These are usually dead (and dry) by spring and covered with black bristle-like fruiting spores that can remain viable for up to 3 years. Occasionally, damage will spread to adjacent twigs.

Management – Fungicides are usually unnecessary, as the best course of action is to physically remove all dead (or discoloured) buds and any nearby twigs exhibiting dieback. Both of these should be discarded in the garbage (do not compost).

Prevention – 1. Monitor for leaf hoppers (using yellow sticky traps) from spring (when larvae emerge) to late summer (when adults are active) and control  with an organic contact pesticide such as Trounce. 2. Bud Blast can also be caused by environmental factors such as drought, winter damage, sunscald and poor fertility – so be sure to provide adequate irrigation during dry spells and use mulch to help retain this moisture, plant your rhododendrons in suitable locations (not all cultivars or species tolerate sun), choose rhododendrons that are hardy for your region and make sure they are adequately fertilized and provided an appropriate soil pH (which is acidic) so they can access those nutrients.

Mossy Rose Gall

Pest and Life Cycle – (Diplolepsis rosae) The Mossy Rose Gall Wasp are small dark wasps that emerge from the old galls in late winter (April to May) as the weather turns warmer. There are few males produced and the females lay eggs for about 3 weeks in the dormant buds of specific roses. When the larvae hatch they feed on the buds, causing them to distort and grow large galls. The larvae live within the gall feeding, pupating the following year. There is one generation per year.

Symptoms – The primary symptoms are large (up to 4 inches wide) mossy galls commonly known as Robin’s Pincushions or Bedeguar (Persian for ‘wind-brought’) Galls. These are usually located on the stems and may be yellowish-green to rose in colour, fading to brown. The galls start appearing from June to July.

Management – Although the galls look rather ominous, they tend to do very little physical damage to the rose, although in severe cases the stem portion above the gall may decline or die-back. Organic pesticides are ineffective as the gall serves to protect the larvae inside, so the only viable management practice is the physical removal and disposal of the galls as they appear.

Prevention – This wasp species tends to target only species (such as R. canina) roses, Rosa rugosa and some old garden roses – rarely affecting modern hybrids. So your best prevention is to avoid planting the target species.

Aphids on Helleborus

 

 

 

 

 

 

 

 

 

 

Pest and Life Cycle – (Macrosiphum hellebori) Actually, many different types of aphids feed on Hellebores but this genus does have its own aphid species. They are most active from March to April attacking flowers and foliage, although they are commonly found on the reverse of leaves throughout the summer. The more serious problem with an aphid infestation is the possibility of the spread of virus diseases such as Mosaic and Helleborus Black Death.

Symptoms – Affected leaves and flowers are encrusted with aphid colonies – usually on the face of the flower and the reverse of the leaf. Secondary symptoms (often found on the leaves just below heavy infestations) include glossy patches or black sooty mold (growing on the undigested honeydew secreted by the aphids) often flecked with white molted exoskeletons.

Management – Plants can be sprayed with a contact pesticide containing insecticidal soap and Pyrethrin (Trounce), making sure that you thoroughly cover the affected areas (such as the reverse of the leaf). If the plants are in bloom, spray in the early evening when pollinators are not present. For small infestations you can either squash them or remove the leaf entirely and discard. When dealing with mass plantings, a release of predatory ladybugs should be considered (if they are available at the time).

Prevention – 1. Aphids reproduce quite rapidly so regular monitoring is essential (every 7-10 days) starting in early spring. 2. Remove any weeds growing near Helleborus as these can serve as alternate host or overwintering plants. 3. Many gardeners remove the older tatty foliage (particularly on Lenten Rose or Helleborus x hybridus) as the new leaves emerge. This makes it easier for you to monitor the plant for aphids and it also controls fungal problems such as black spot.

Currant Sawfly

Pest and Life Cycle – (Nematus ribesii) Sawfly (a dark fly-like insect related to wasps) overwinters in a cocoon in leaf litter or just below the soil surface. Adults emerge as the foliage flushes on host plants (around April) and lay eggs on the underside of the leaves. The eggs hatch into caterpillar-like larvae (up to 1/2″ long, green with dark spotting) which feed on the plant for 2-3 weeks, often causing defoliation, they then drop to the soil and pupate. A second generation (up to 3 a year) is produced midsummer and it is the latter one that overwinters. This pest affects gooseberries, currants and Jostaberries.

Symptoms – The damage begins as small central holes in the leaves and can progress to the point where nothing is left but a skeleton of leaf veins. The Sawfly larvae begin feeding  lower down on the shrub, usually near the center of the bush and work their way outwards.

Management – Hand-pick and discard badly infested leaves or spray with a Pyrethrin or insecticidal soap-based product (Trounce) on both the upper and lower leaf surfaces. BTK sprays do not work on this pest, as the larvae are not true caterpillars.

Prevention – 1. Check plants frequently (twice a week) beginning in early April for any signs of foliar damage and treat immediately. This will lessen the chances of future infestations. 2. Remove mulch and leaf litter at the base of host plants where Sawfly can overwinter.

Dogwood Anthracnose

Pest and Life Cycle – (Discula destructiva) This fungal disease is prominent during prolonged wet springs accompanied by cool weather, but it may also be prevalent in the fall. It usually begins in the lower part of the crown and works its way up, commonly affecting trees that have experienced drought stress or winter injury. Fruiting bodies overwinter on infected leaves (dead leaves can remain on the tree over winter) and branches, initially releasing spores anytime from May to July (can also be active in the fall) – these are spread by water droplets and wind. Both Eastern (Cornus florida) and Pacific Dogwood (Cornus nuttallii) are very susceptible to this disease.

Symptoms – Tan to brown spots appear on foliage and flower bracts, with the tips and margins of leaves often dying back completely. Severe infections may cause premature defoliation and branch tip die-back, eventually forming cankers on bark and stems.

Management – Pick-up and discard (do not compost) any foliage that drops prematurely and prune out dead branch tips once the wet weather has subsided.

Prevention – 1. Plant only resistant species or cultivars such as Cornus kousa, Cornus mas, Cornus x ‘Eddie’s White Wonder’ and Cornus florida / kousa hybrids such as ‘Stellar Pink’. 2. Provide ideal growing conditions of good soil drainage, adequate moisture during dry periods and planting sites with good air circulation. 3. Prune and discard (do not compost) any dead or infected branches, as well as the fallen autumn leaves. 4. Do not over-fertilize to try to compensate for poor plant vigor, as this will only result in lush foliage that is more prone to infection.

Blueberry Chlorosis

Pest and Life Cycle – Blueberry chlorosis is not caused by pests or fungi, but is strictly a cultural problem resulting in an iron deficiency. Highbush Blueberries (Vaccinium corymbosum) prefer an acidic pH range of 4.5 to 5.2 and when the pH is higher some nutrients, such as iron, are unavailable to the plants.

Symptoms – Affected plants have leaves (occasionally stunted) with prominent green veins surrounded by pale yellow plant tissue. If the whole leaf is yellow (no green veins) you probably have a nitrogen or sulfur deficiency, or possibly poor soil drainage.

Management – You should test the soil pH around affected plants and if it is too high, add elemental sulfur (at label rate) or iron sulphate (faster acting) to the soil in order to lower the pH and allow plants access to essential nutrients. You can temporarily rectify the deficiency by working chelated iron into the soil around plants or dissolving and using it as a foliar spray – symptoms should subside in about 30 days.

Prevention – 1. Be careful not to situate blueberries near fresh concrete or masonry, as the water runoff from these will raise the soil pH levels. 2. If your blueberries are in close proximity to your lawn, be careful to keep any lime or dolomite applications to the grass away from the blueberry roots as this will also raise soil pH. 3. When planting blueberries, incorporate some peat moss (about 20%) with the existing soil as this will both acidify and help retain moisture during dry periods.

Vine Weevils on Rhododendron

Pest and Life Cycle (Otiorhynchus sulcatus) Black Vine Weevils are nocturnal snout-nosed beetles (greyish-brown to black). The adults emerge from the soil in early June and feed on plant foliage. After about a month they begin to lay eggs in the soil, usually near the base of the affected plants. The larvae that hatch feed on roots and the bark of stems at ground level. These overwinter underground, pupate in May and emerge from the ground as adults. Adults will also occasionally overwinter in the root system or above ground in leaf litter.

Symptoms – Small notches begin to appear on the foliage margins with leaves becoming lacy with severe infestations. Ground-borne larvae feed on roots and bark (near soil level), often girdling the stem and killing the plant outright. Vine Weevils also attack Azalea, Viburnum, Yew (Taxus), Kalmia and Salal (Gaultheria shallon).

Management – As soon as leaf damage occurs (usually in early June) spray affected foliage with a Pyrethrin-based pesticide and repeat with signs of fresh injury. This spray acts as a deterrent leaving a residual botanical poison on the leaf surface. If the Rhododendron is free-standing (not touching another plant, walls or fences) you can use a sticky paste band (Tanglefoot) on the main stems to trap the night-feeding adults.

Prevention – 1. Use a soil drench that includes parasitic nematodes around plants in May (as soon as the soil warms) and again in late August – being sure that the area has been well watered prior to application. 2. Lay traps of rolled corrugated cardboard (held with rubber bands) near the base of affected plants. Adults will lodge in these during the day, at which time you can simply tap them out into a bucket of soapy water. 3. Plant weevil-resistant Rhododendron cultivars which have rolled-under edges that are difficult for them to feed on. Some of these include ‘Point Defiance’, ‘Virginia Richards’, ‘Jock’, ‘Dora Amateis’, ‘Crest’, ‘Odee Wright’, ‘Moonstone’ and ‘Graf Zeppelin’.

Powdery Mildew on Garden Phlox

Pest and Life Cycle – (Erysiphe cichoracearum) In summer, spores of this fungus are carried to healthy foliage by wind, water droplets or insects – usually during periods of high humidity and moderate temperatures (60-80F) – occasionally brought on by drought stress. This fungus overwinters on native plants, weeds and old stems and foliage. While the vigor of individual plants is reduced, this disease seldom kills Garden Phlox outright.

Symptoms – White or powdery-grey blotches covers healthy foliage and stems, usually starting at the base of the plant. Badly infected leaves eventually turn yellow and die, with these latter symptoms also starting near the base of the plant.

Management – For minor infections simply remove the affected foliage and discard in the garbage (do not compost). Alleviate drought stress by watering the soil deeply around plants showing symptoms. Copper or sulfur-based fungicides (used at label rate) as well as horticultural oil (do not spray within 2 weeks of a sulfur treatment) may also provide some control, although the cultural methods below will probably prove to be more effective.

Prevention – 1. Space and locate plants in full sun in order to provide good air circulation. 2. Do not over-fertilize as this causes lush foliage which is more prone to this disease. 3. Water deeply during dry periods (in the morning) and try not to get the foliage wet. 4. Remove plant debris (fallen leaves, dead stems) at the end of the season and discard (do not compost) to prevent the fungus from overwintering. 5. Only plant mildew-resistant cultivars of Phlox paniculata such as ‘David’, ‘Orange Perfection’, ‘Delta Snow’, ‘Starfire’, ‘Bright Eyes’ and ‘Prime Minister’. Please note that none of these selections is impervious to powdery mildew and may exhibit symptoms when conditions are less than ideal.

Aphids on Water Lilies

Pest and Life Cycle – (Rhopalosiphum nymphaeae) Aphids overwinter as eggs on fruit trees, usually members of the Prunus genus. They hatch in spring as wingless females and keep reproducing. With the onset of warmer weather some of the females develop wings and migrate to feed on other plants, such as water lilies. They travel back to the plants they overwinter on late in the season and lay fertilized eggs for next year’s generation. Waterlily Aphid also feeds on marginal plants such as Typha (Cattail), Sagittaria (Arrowhead) and Pontederia (Pickerel Weed) and is capable of walking on the surface of the water.

Symptoms – Waterlily Aphids are sucking insects which attack both leaves and flower stems (particularly those above the water surface) and may cause premature yellowing, distortion or stunted growth. They are even capable of feeding underwater by crawling down stems and trapping air with specialized hairs on their bodies.

Management – Knock the aphids off plant parts using a hard spray from the garden hose. Once they are in the water, Koi and Goldfish with readily feed on them. If you do not have any, consider purchasing a few inexpensive feeder fish (also good for eating mosquito larvae) for this purpose. Do not use pesticides or oil-based products in your pond (particularly those with Pyrethrin, which is highly toxic to fish), as these can adversely affect the aquatic environment. If only a few leaves are affected, they can be removed entirely and discarded.

Prevention – 1. Monitor your waterlilies, marginals and plants around your pond frequently, as it is much easier to deal with a minor infestation. 2. Treat nearby fruit trees (particularly Prunus fruits such as cherry and plum) with dormant oil to kill overwintering aphid eggs.