EGARDENING   Friday, November 02, 2007

Resources

IPM Part 3: Deterring Insect Pests

Caterpillar....I have sworn perdition to thy race,    And recent from the slaughter am I come  Of tribes and embryo nations: I have sought
With sharpened eye and persecuting zeal, Where, folded in their silken webs they lay Thriving and happy; swept them from the tree
And crushed whole families beneath my foot; Or, sudden, poured on their devoted heads The vials of destruction....[Anna Lætitia Barbauld The Caterpillar (1743-1825)]

I must confess that I haven taken this excerpt out of context, and in fact the poem begins "No -helpless thing, I cannot harm thee now." I empathize with Anna Barbauld's struggle to know when and where it is appropriate to kill insect pests and when to let them be. Generally, I recommend tolerance, but there are times when action is imperative.

As many of you know, we have introduced into our ecosystem a number of foreign intruders for which there are few natural checks. The Canadian Food Inspection Agency has placed us on alert for some serious pests including the Emerald Ash Borer and the Asian Long-horned Beetle. Report any suspected evidence or sightings of these insects to the agency at 1-800-442-2342.

Less worrying foreign pests, like the gypsy moth (Lymantria dispar) introduced around 1869 to start a silkworm industry in the United States, will sometimes require our intervention. As can native pests whose populations swell to troubling proportion. How should we approach such pest problems?

Integrated Pest Management begins with identification. Learn about your pest. Does it merit action or will it simply cause a bit of aesthetic disfigurement and be gone? If you decide the pest must be controlled, here are your options:

  1. Cultural control - Keep your plants healthy and they are less likely to succumb to insects. Healthy plants and trees with strong immune systems are less likely to be targeted by insect pests. Prune out diseased or infested plant material. You can often manage insect problems by controlling the things they need to live: water, shelter, and food. For instance, sometimes fertilizing can exacerbate an insect problem by promoting more edible fresh growth. Sometimes watering can support insect development, as with white grub eggs and larvae in July and early-August. So its important to learn about your particular pest's life cycle and growing needs and change your practices where appropriate.

  2. Physical control - Prevent insects from accessing host plants by using traps, barriers and banding. Physically remove pests with hand picking, strong water spray, pruning, mowing or tillage, depending upon the insect and situation. For gypsy moths, a simple burlap band wrapped around the lower trunk of susceptible trees, from May to July, will attract the caterpillars which can then be removed.

  3. Plant variety and resistant species - Some plants are less susceptible to insect pests then others. Avoid plants that are likely to be infestation prone. If gypsy moths are a problem in your yard, plant trees that they will avoid like redbud, tulip tree or rhododendron. If you are fond of particular plant species, look for insect-resistant cultivars.  

  4. Companion planting- Companion plants can be used in several ways. First, plants that attract insect predators, birds and bats can be established to increase natural predation your garden. Next, some plants deter pests through the production of chemicals which are toxic, distasteful or which mask the scent of other plants. Finally, insect pests generally have a preferred food and can be attracted away from a prized plant. In agriculture, this is called a trap-cropping.

  5. Biological controls - Use predators, parasites and diseases of pests in a targeted way to suppress pest populations. Attract beneficial insects through companion planting and eliminating pesticide use.  You will find a variety of beneficial bacteria, nematodes and fungi in local garden centers. Use them cautiously. For instance, Bacillus thuringiensis var. kurstaki is a naturally occurring bacteria that is commonly used to treat gypsy moth infestations. However, timing is critical and overuse can lead to resistance and loss of non-target moths and butterflies. Remember natural does not mean benign.

  6. Chemical controls - There are many chemicals that can be used to control pests. They very greatly in their range of action, toxicity and persistence in the environment. Something like diatomaceous earth (a fine powder of silicon dioxide, from fossilized diatoms) physically abrades the exoskeleton of crawling insects, then acts to dehydrate and kill them. A different chemical approach is to use pheromones. These chemicals are produced by insects to attract their mates. They can be used to "confuse" the mating process and to attract insects to a trap. Horticultural oils, insecticidal soaps and azadiractin (sometimes called neem) are examples of low-toxicity pest deterrents.  For instance, dormant oil, applied to trees in late winter, will smother gypsy moth eggs before they hatch and reduce populations. While our Pest Management Regulatory Agency has approved such products as carbaryl and phosmet for domestic insect control, please inform yourself thoroughly about these insecticides and use them only if safer alternatives have failed and the risks to health and property outweigh the risks of use.

Let me know if you have a particular pest concern and I will try to provide you with an effective and environmentally-sound action plan.

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May toads nestle in your flower beds and help you tend your beauties in the spring.

Tidbits and Resources

Integrated Pest Managment Links

Common pests

Companion Planting Charts and Info 

Bat Friendly Gardening

Attracting Birds to the Garden

Insect resistance

Misc

The Caterpillar Anna Barbauld
 University of Pennsylvania Digital Library http://digital.library.upenn.edu/women/barbauld/biography.html
No, helpless thing, I cannot harm thee now;
Depart in peace, thy little life is safe,
For I have scanned thy form with curious eye,
Noted the silver line that streaks thy back,
The azure and the orange that divide
Thy velvet sides; thee, houseless wanderer,
My garment has enfolded, and my arm
Felt the light pressure of thy hairy feet;
Thou hast curled round my finger; from its tip,
Precipitous descent! with stretched out neck,
Bending thy head in airy vacancy,
This way and that, inquiring, thou hast seemed
To ask protection; now, I cannot kill thee.
Yet I have sworn perdition to thy race,
And recent from the slaughter am I come
Of tribes and embryo nations: I have sought
With sharpened eye and persecuting zeal,
Where, folded in their silken webs they lay
Thriving and happy; swept them from the tree
And crushed whole families beneath my foot;
Or, sudden, poured on their devoted heads
The vials of destruction.--This I've done
Nor felt the touch of pity: but when thou,--
A single wretch, escaped the general doom,
Making me feel and clearly recognise
Thine individual existence, life,
And fellowship of sense with all that breathes,--
Present'st thyself before me, I relent,
And cannot hurt thy weakness.--So the storm
Of horrid war, o'erwhelming cities, fields,
And peaceful villages, rolls dreadful on:
The victor shouts triumphant; he enjoys
The roar of cannon and the clang of arms,
And urges, by no soft relentings stopped,
The work of death and carnage. Yet should one,
A single sufferer from the field escaped,
Panting and pale, and bleeding at his feet,
Lift his imploring eyes,-- the hero weeps;
He is grown human, and capricious Pity,
Which would not stir for thousands, melts for one
With sympathy spontaneous:-- 'Tis not Virtue,
Yet 'tis the weakness of a virtuous mind.

Anna Lætitia Barbauld  (1743-1825)