July Activities to Promote Plant Health Care

Issue: 
July-August 2006

WELL, SPRING IS OFFICIALLY OVER and hopefully you’ve had a chance to catch your breath! July is the month where your installations are slowing down and your maintenance clients are getting some much needed attention. Now that woody plants are fully flushed out, leaves are hardened off and conditions are staying consistently hot and dry, we need to start thinking about practices that will keep our landscapes healthy.

Infrequent, long irrigations will go a long way in replacing the soil moisture that plants need for transpiration. Irrigation is pivotal in helping newly-transplanted material establish more successfully, especially where soil conditions are dry and sites are exposed. Mulching landscapes will also go a long way in conserving soil moisture, suppressing weed emergence and also reducing soil temperatures to facilitate root growth.

Fertilizing woody plants is usually avoided from mid-July to the beginning of September since this is not a period of significant root growth for many deciduous species. Annual fertilizer applications should be split over multiple applications during the growing season. The first application taking place once the first flush of foliage is complete (late May), perhaps a second application in mid-June, and then a third application in late September or early October. By splitting the annual fertilizer application over 2-3 applications during peak root growth periods, we can maximize nutrient uptake (and minimize losses to the environment).

Hopefully the second flush of growth has helped deciduous trees recover from anthracnose and freezing injury that was suffered in May. Ash trees seemed to really suffer this spring, and the sycamores were looking pretty naked as they do most years. Some areas are going to have pockets of defoliated trees from Gypsy moth larvae. Last year we had numerous deciduous trees and evergreens moderately to severely defoliated. Repeated years of defoliation will result in dieback and mortality in the landscape and urban forest. We were starting to see a bit of Gypsy moth-related oak mortality in some pockets of Hamilton and Oakville last year. Time will tell just how extensive this damage is in 2006.

Scale Insect Crawlers are Emerging
July is a great month for managing the “crawler” stage of many common scale insects. Since many of us only have access to soft insecticidal products, we want to make sure that we are timing these applications for the most vulnerable stage of the insect’s life. In the case of scale insects, that would be the crawlers (newly-hatched eggs). These crawlers are quite vulnerable in the first few weeks of their life because they haven’t formed a protective waxy covering yet. Once they start to settle on a permanent feeding site, they develop that waxy covering and become much more resistant to pesticides.

Monitor common phenology plants in your area (see Table 3-3 of OMAFRA’s Nursery & Landscape Plant Production and IPM and refer to the tables on the following pages). When phenology plant development and Growing Degree Day summaries tell you its time for certain scale insects to be hatching, you should monitor host plants regularly. Manually pick off scale insects and examine their undersides. If the underside still looks fleshy, they haven’t laid their eggs yet and are still feeding. When tiny grains appear on the under sides, that means the adult females are essentially dying and leaving behind eggs under their protective shell.

Once the eggs start to hatch, you’ll see tiny, mobile “crawlers” that move over the foliage and twigs. It’s best to apply insecticidal products when most of the eggs have hatched. This is usually about 7-10 days after crawlers begin hatching. Multiple applications are usually necessary to knock down the population, but post application monitoring will provide the necessary feedback. This year, we have access to a summer oil called Landscape Oil (available from Plant Products). Be careful not to use Landscape Oil on emerging foliage, wait until foliage has emerged and is fully expanded. Landscape oil and insecticidal soap should help provide good management for newly-hatched crawlers where the use of more potent pesticides is restricted.

Juniper scale crawlers are settling and starting to develop a waxy covering. You’ll want to catch them early this month if you haven’t done so already. Spruce bud scale and cottony maple scale crawlers are hatching and they are still vulnerable. Spruce bud scale can be a bit of a problem on larger, established spruce trees that are under stress. European fruit Lecanium scale crawlers will be hatching soon and can be found commonly on deciduous trees such as ash. Look out for the second generation of Euonymus scale crawlers hatching out later this month. There seems to be a little disagreement as to when the 2nd generation of Euonymus scale crawlers will start to hatch, some say when the bottlebrush buckeye begins blooming and other say a couple of weeks later. Euonymus scale crawlers are bright orangey-yellow.

The second generation of pine needle scale crawlers will also be hatching later this month, around the time that the Rose-of-Sharon starts to bloom. Look for white flecks on needles of Austrian, Scots and red pine, those are the second generation of adult females with their egg masses. Pine needle scale crawlers are dark red and very mobile over the foliage and twigs. Magnolia scale is becoming quite obvious this month. Look for large, white, powdery looking bumps on the undersides of twigs. You can pick them off (they are still fleshy underneath) or prune out infested branches and destroy to reduce populations before egg-laying begins. As the adult females begin to lay eggs, they lose their powdery appearance, become orangey-pink and you’ll see the tiny eggs under them when you pick them off during your monitoring rounds. As with all other scale insects, treat crawlers at peak egg hatch with insecticidal soap, landscape oil or other registered pesticides that are permitted for use in your area.

Click here to view pdf table excerpts from this publication.

— Jen Llewellyn, Ontario Ministry of Agriculture and Food and Rural Affairs (OMAFRA) Nursery Crops Specialist

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.