Emergency Registration for Emerald Ash Borer

March-April 2008

JUST BEFORE CHRISTMAS, the Ontario Ministry of Natural Resources applied for an emergency use registration for a product that may help protect un-infested ash trees against emerald ash borer (Agrilus planipennis). The proposed product is TreeAzin, an injectable version of neem (azadirachtin) using their patented Ecoject™ system. Neem is a plant-derived insecticide that comes from a tropical tree species (Azadirachta indica) found in Africa, Asia and India.

Neem works by interfering with the molting process of immature insects. This means that the insects will discontinue feeding and eventually die. Neem is both an anti-feedant and a systemic insecticide, which means that it has to be absorbed by the plant and insects need to feed on/suck juices from plant tissue that contain neem in order for it to work. Neem seems to have a huge range of uses; everything from traditional medicinal properties, to cosmetic, to insecticidal. I even found a reference where neem was used as a spermicide for rabbits, monkeys and some human volunteers (I guess regular methods of contraception must seem tame for some!).

The Ecoject™ system was developed by Bioforest Technologies Inc. who has been working with the Canadian Forestry Service to carry out efficacy trials on the system and various insecticides (imidacloprid, azadirachtin) over the last few years. Holes are drilled into the trunk of the tree and TreeAzin is injected into the tree using an enclosed canister and plunger system. The granting of this emergency use is significant because neem is not yet registered as a pesticide in Canada. The niche for this product will most likely be for high value trees such as ornamentals and golf courses. It could also be used as part of control programs, such as to treat trees on the perimeter of a known infestation.

Horticultural Oil in Spring
I know I mention this every year, but the effectiveness of the correct use of horticultural oils can not be downplayed. They provide a physical barrier which restricts both the respiration and movement of many overwintering insects (e.g. adelgids, scales, mite eggs). To avoid foliar damage, horticultural oil is best used when daily min/max temperatures remain somewhere between 5 and 15oC during the first week or so after application. This is especially important on evergreens since their foliage is always present and always susceptible to injury.

Try to make applications when conditions will facilitate rapid drying of treated twigs. A horticultural oil suspension that remains wet on the plant can cause phytotoxicity under freezing temperatures or hot, sunny conditions. Avoid mixing oil solutions with sulphur and other fungicides as plant damage may result. And above all, keep solutions of horticultural oil agitated as often as possible to prevent over application, especially on evergreens.

Applying the dormant rate of horticultural oils provides an excellent opportunity for surpressing populations of many overwintering insects and mites. Spruce spider mite, maple mite and European red mite all overwinter as eggs on twigs and buds and are susceptible to horticultural oil applications at bud swell. Several species of scale insects (magnolia, euonymus, lecanium scale, etc.) will also be smothered by horticultural oils, especially where application equipment has been adjusted to target the undersides of twigs and stems (where the scale insects can be found).

Always read the label carefully since many plant species are sensitive to horticultural oils (see below). Avoid spraying red delicious, mutsu or empire cultivars of Malus as bark injury may result (I’ve actually seen this). Do not apply to Malus or Pyrus after green tip. I’ve had professionals tell me that they have used horticultural oil on Taxus and Thuja for years and never had a problem. Others have seen quite a bit of burn on those two genera – yikes. Remember, oil and water do not mix. You will need to agitate the mixture constantly in order to ensure even coverage (yes, I know I already said this so it must be important!). If over-application occurs and extreme temperatures are experienced within a week or two, damage may result. Applications should be made during mild mornings when no rain is in the forecast to facilitate drying.

Plants Sensitive to Dormant Oil
Acer palmatum (Japanese maple), Acer rubrum (red maple), Acer saccharum (sugar maple), Carya (hickory), Cryptomeria, Juglans sp. (walnut), Juniperus (blue cultivar selections), Picea pungens glauca (blue Colerado spruce), Pinus strobus (white pine), Quercus rubra (red oak) Taxus (yew) and Thuja (cedar).

Other, Less-Sensitive Plants
Cercis canadensis (redbud), Fagus (beech), Ilex crenata (Japanese holly), Picea abies (Norway spruce), Picea glauca (white spruce), Pseudotsuga menziesii (Douglas fir).

Contact Information

This column is written by Jen Llewellyn, Ontario Ministry of Agriculture and Food and Rural Affairs (OMAFRA) Nursery Crops Specialist

Email any questions you have directly to Jen and we'll publish her response.

P: 519-824-4120 ext. 52671 • F: 519-767-0755

OMAF website: http://www.omafra.gov.on.ca/scripts/english/crops/agriphone/index.asp

Nursery Landscape Agriphone: 1-888-290-4441

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.