How to Identify and Manage Pests in the Garden

by: EJ on 03/11/2016
Posted in: Gardening

There is nothing more frustrating that seeing your seedlings sprout from the ground, only to return the next day to find some devilish creature has destroyed them!  One year, a mouse carefully dug up every pea I planted, leaving only little holes just the right size for cute tiny paws.  Or, equally as likely, I find leafless stalks with the tell tale shiny trail of slug slime.  Today's blog is an excerpt from Backyard Bounty:The Complete Guide to Year-Round Organic Gardening in the Pacific Northwest  by Linda Gilkeson which takes us through the basics of garden pest management.

Although you are probably concerned about pests in your garden, in my experience, more plant damage is caused by something wrong with the growing environment than by pests. Of course, that assumes your garden is well protected from deer!

The advantage of organic gardening, based as it is on building healthy soil, is that it produces healthy, resilient plants. By minimizing the use of insecticides and by planting to attract beneficial insects, organic gardeners can count on substantial help from the many insects that feed on pests. In fact, the more your food garden resembles a natural ecosystem — with mixed plantings and mulched soil — the easier gardening becomes.

Among the many possible insects and diseases that can occur, few regularly plague vegetables and fruit crops on the coast. In any one garden, you will likely see only a handful of these problems and most garden pests can be prevented, once you know what you are dealing with.



Photo Credit: Dale Calder

Prevention is the key. It is the first line of defense against insect pests, diseases, weeds, mammals and other pests. Preventative methods are safe, mostly cheap, and they do a good job of avoiding damage altogether. Many provide solutions that last for the whole growing season. Here are some examples:

  •  Covering crops with floating row cover fabric to stop insects from laying eggs.

  • Planting varieties that are resistant to diseases.

  • Mulching the soil to prevent weeds from coming up.


Growing healthy plants is part of prevention because they are less susceptible to disease and more likely to survive pest attack and quickly replace dam- aged leaves.

Plants become stressed when they don’t get enough sunlight, water or nutrients. Sometimes there is no shortage of any of these in the environment, but conditions that the gardener can control, such as acid soil or poor drain- age, prevent plants from getting what they need.

Another aspect of prevention working in favor of home gardeners is the fact that we grow so many different kinds of plants in a small area. Quite the opposite of a grower with a huge field of one vegetable, which gives the pests of that crop an unlimited supply of food. Insects and disease organisms stick to their particular host plants, so the mixed plantings in a small garden limit their ability to spread. For example, even if every one of your carrots were damaged by carrot rust fly, you could still have fine beets, onions, radishes and other roots, because they are not acceptable food for that particular pest.


Basics of Garden Pest Management

Think pests are causing problem in your garden? Here are some steps to follow that will help you decide.

1. Make sure the problem is correctly identified. If you don’t know what the problem is, there is no point in spraying or taking other action. You may never know what caused some kinds of the damage. However, because many things that go wrong with plants are caused by poor environmental conditions, you can always work on improving the growing conditions and see what happens.

Whether a problem is caused by insects, disease or other pests, the cause must first be correctly identified before you can know what controls will work and how to prevent it in future. The use of the bacterial spray BTK (Ba- cillus thuringiensis  kurstaki) is a good example: it only infects caterpillars, which are the immature stage of moths and butterflies. It doesn’t affect other pests, including the sawfly larvae that look just like caterpillars. So, reaching for the BTK will do you no good if your problem is sawflies.

The individual pest entries in this chapter describe the most common pests of food plants in this region, but not every problem that could possibly occur. If you need help identifying a problem, try the following (see Re- sources for details):

• reference books and websites (especially university cooperative extension departments);

• local Master Gardeners;

• gardener hotlines for phone queries and online forums;

• staff at local garden centers.

If you can take a picture of the problem, you can e-mail it to someone to help with identification (much better than a verbal description!). If you can’t bring a specimen to a Master Gardener clinic or garden center for help in identification, bringing a photo on your cell phone is the next best thing.


Photo Credit: Todd Petit

2. Keep an eye on the problem. Regularly checking on a problem after you notice it can tell you whether a problem is getting worse or not and help in identification. People often notice leaf damage, for example, only after the critter that did the chewing has finished feeding and crawled away. By checking on the plants for several days, you can tell whether or not new dam- age is occurring. If you don’t see new damage, there is no point in spraying. You can, however, note the date when you first saw the problem. Next year, start looking a few weeks earlier than that for the first signs of damage so you can track down the culprits.

Get a magnifying glass to help you see, and keep notes (sketches, photos)so you have a record for next time.


3. Decide whether treatment is needed. It is important to distinguish between the kind of damage that reduces your crop or could kill plants and damage that doesn’t really affect your harvest. A parsley worm caterpillar chewing on carrot leaves isn’t really doing much damage because it isn’t at- tacking the part of the plant you want to eat. Anyway, you might be happy to allow the caterpillar to feed, knowing it will become a beautiful Anise swallowtail butterfly. On the other hand, a codling moth caterpillar boring into the center of an apple is directly ruining the crop (though even in this worst case, the good parts of that apple can still be salvaged for applesauce or juice).

What you consider “damage” can be a matter of personal taste and practicality. This is where the home gardener has a great advantage over the commercial grower. Because produce in the commercial system is graded for perfection of appearance, growers control pests that merely do cosmetic damage. Home gardeners, on the other hand, don’t need to waste food that has scars or marks, because they can simply trim off the blemished bit and use the rest. After all, how perfect does the skin of an apple need to be, if the apple’s fate is to become apple pie?

The size of a pest population is another thing to consider in deciding whether you need to take action on pests in the garden. Pests are naturally kept in check by weather conditions, natural enemies and other factors. In some years, some pests appear in high numbers; in other years, numbers are low or nonexistent. It is by no means certain that a small infestation of insects will grow or that a disease you see on a few leaves will spread — the problem may die out. By regularly checking, you will be able to see whether the problem is getting worse.


Potato Bugs Photo Credit: Gene Perry

4. Use least toxic and non-toxic controls. There are many effective methods for managing garden pests that do not involve using pesticides:

• Physical controls: These are measures that remove pests or kill them directly. For example, blasting aphids off plants with water sprays, pruning out diseased branches, picking off leaves that have insect eggs, or mulching to smother weeds are all physical ways to control problems.

Biological controls: Most insect pests have natural enemies that can be relied on to keep numbers down to non-damaging levels. Birds are important predators of insects, especially in the spring when they are feeding chicks, but most insects are kept in check by other insects and spiders. You can increase the number of beneficial insects to your garden by planting flowers that attract them (see page 183).

• Pesticides: Most pesticides are chemicals (though a few contain micro- organisms). Low-risk pesticides contain low-toxicity chemicals, such as soaps or compounds extracted from plants (see table 9.1). These are only “safe” from the human point of view, of course, not for beneficial insects or other creatures. Most pesticides made from plants and other natural sources are permitted for use by certified organic growers.

Some people make homemade mixtures on the assumption that these are safer than commercial pesticides. This is a mistake! Ingredients such as soap, oil, salt or mouthwash that don’t harm people, can damage or kill the plants you spray them on. And remember that any mixture that actually works to control pests, will also work to kill beneficial organisms, such as the insects that eat the pests or the “good” fungi that control disease-causing fungi.

The best thing you can do is avoid using pesticides of any kind. When some type of action is called for, try non-pesticidal methods first, and use pesticides as a last resort. You can minimize the harm from pesticides by choosing the least toxic product that will do the job. For example, if insecticidal soap will work, use that instead of pyrethrins (a nerve toxin extracted from pyrethrum daisies), which are more toxic and lasts longer on leaves. If you are spraying insecticides, spray only the plants, or parts of plants, that need treatment. Spraying where it isn’t required isn’t just a waste of time and money; it also needlessly harms other organisms.

Many municipalities have passed by-laws restricting pesticide use within their jurisdiction. The by-laws allow gardener sto use low-risk products on their garden pests but restrict more toxic chemicals.

In the pest entries beginning on page 187, I have only included recommendations for pesticides that are acceptable for organic growers and people living where there are pesticide restrictions.


5. Follow up. Whether you take action or not, keep checking on the garden pest situation and keep making notes. Your notes will tell you when problems appeared or disappeared, and how well your approach worked. If you know when to expect a particular pest, you can prepare to deal with it while the infestation is still small.



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