Pest and Disease Management

The following information is based upon the Pest and Disease Management Workshop held in May 2011 by Jackie Robson. 

General Practices and Principles

Healthy Soil: The number one principle of organic growing is maintaining fertile, healthy soil.  Good soil produces strong, robust plants which tend to resist most pest or diseases.  It’s believed that weak plants might even give chemical signals that attract potential pests of diseases.

Observation: Even a beginner gardener can usually tell at a glance if something is wrong with a plant.  You may not always know what the problem is, but by paying attention you can stave off some of the worst effects from pests and diseases.

Companion Planting: some plants together can make each other taste better or grow stronger (tomatoes and asparagus) or make them weaker (beans with onions).  Review the companion planting list before planning your garden to give your plants every opportunity. letting some plants go to flower will not only allow you to gather seeds for yourself but are great magnets for benefitial insects.

Predator and Pollinator Habitat: Garter snakes and predaceous beetles will eat many garden pests, including slugs.  Make a snake habitat:

Another consideration is to plan your garden so that there is a succession of flowers to attract pollinators.   The Umbelliferae family are great nectar producers (ie. angelica, anise, arracacha, asafoetida,caraway, carrot, celery, centella, asiatica, chervil, cicely, coriander/cilantro, cumin, dill, fennel, hemlock,lovage, Queen Anne’s Lace, parsley, parsnip, sea holly) are would be a benefit to any garden.

Right Conditions: acid or alkaline; sandy or clay; sunny or shade; choosing the right plant for the right area will ward off many issues.

Crop Rotation: changing location of your plantings each year will keep disease organisms from building up in the oil.  Pests often have specific hosts that they attack by moving them around make it harder for them to find their favourite food source.  Some say that in a small plot with lots of diversity there is no need to rotate as everything gets mixed together.

Handpick Pests: This can be surprisingly effective.  Sometimes a plant is getting chewed down each night by as few as two or three cutworms which hide in the day.  Take a flashlight for a slug or cutworm hunt, dropping them into a bucket of soapy water.

Live and Let Live: 90 to 95% of all insects you encounter in the garden are either beneficial or neutral.  In addition, the remaining so-called pests do little damage in most situations.  Tomatoes and brassicas can outgrow flea beetles; ladybugs will only lay their eggs in the presence of aphids.

Sprays: Even homemade sprays using garlic or feverfew should only be used as a last resort as even organic sprays kills the beneficial insects along with the bad.  Observation and a water spay are usually sufficient.  40% of insect problems on crops are from pesticide use as predators are killed off.  If you don;t want to kill anything, then just overseed.  Instead of thinning your lettuce, the slugs will do it for you.  What you’re doing is mimicking nature…


Black or Grey Aphids: water or safer soap spray; encourage lady bugs or aphid midges.

Cabbage Butterly: handpick the worms and the eggs to prevent them from digging into the middle of the cabbage.

Carrot Rust Fly: once you have these, it’s very hard to get rid of them.  The fly is attracted to the smell, so use a thick layer of coffee grounds (at least 6″) of mulch and interplant with onions.  When harvesting, the smell is the strongest, so crush some mint or sage to confuse the fly. key to make it stinky; coffee layer needs to be at least 6″ thick.  Once you have the Rust Carrot Fly, you can’t get rid of it.

Coddling Moth: these are the worms you find in apples; throw out, do not compost, infected fruit. Use a dormant oil spray.

Cutworms: handpicking, plant

Earwigs: these insects are omnivores (eat plant and insects alike) and usually don’t cause a lot of problems, but if you need to reduce the population, earwigs traps are easy to make.  Stuff an old plastic pot or coffee cup with damp newspaper, and stick it upside with a stick in the garden.  They like tight, moist places and will hide there.  Shake the pot into soapy water.

Slugs: use barriers such as a bottomless tin can to protect new transplants.  Beer bait traps work best.  Use an old container filled with beer.  It needs to smell beery, not vinegary; keep adding water and sugar to keep it fresh.  Jackie’s Homemade Slug Bait: 1 c water, 1 tsp sugar, 1 tsp flour, ½ tsp dry yeast.  Add a little stick (ie half a paint stir stick) so that benefitial insects can climb out.

Sow Bugs: also know as wood bugs or pill bugs they don’t usually pose a problem, but if there are too many, they can attack small seedlings.  Use a sowbug trap, made from upside down cream cheese container filled with dry cornmeal.  The bugs eat the cornmeal, then the next time  they drink water, they pop.

Weavils: reduce population by spreading bedsheet out underneath the bush then shaking it.  Drown them in soapy water.

these are usually only a problem in gardens that have been made from lawns.  To see if you have a problem or to reduce the population, stick a chopstick in half a potato and bury it.  Dig up the dirt around the potato to see what’s there.


Clubroot: 7 years of non-brassicas;  throw out, do not compost.  The best prevention is to be sure where you are getting your plants from and not to borrow tools so as not to contaminate your yard. Bok Choy, Broccoli, Brussels Sprouts, Cabbage, Cauliflower, Collards, Colza, Hanover Salad, Kale, Kohlrabi, Mustard, Rutabaga, Turnip.  arreated compost tea will help the soil; as well as anecdotal stories that ½ c of lime at the bottom of the hole before planting the plant have staved off the disease.

Late Tomato Blight: a big problem in Victoria: airbourne, in the environment but it deosn;t show up until the conditions are right for it.  Which conditions?  Mosit, airless and cool; hence it’s usual appreance in late August to Early September when the rains start.  The key is airflow; the chance for the plants leaves to dry.  Protect your plants from rainfall, water on the ground not on the leaves and allow plants a chance to dry. What does Blight look like?  Starts with a single twig going black then the rest of it will follow.  Once you have the blight, harvest your tomatoes, your season is now done.  Cut off the entire branch and let them ripen.  How to get rid of it once you’ve got it – sorry to say, you can’t.

Powdery Mildew: sometime squash plants don;t sucuumb to the disease until late in the season, making it unnecessary to intervene as they have already produced and matured all their fruit.  A spray solution of 1-10 ration of milk to water or baking powder 1 tsp to 1 quart water can reduce the severity of the disease if used early or often.

White Rot: onions will be squishy and moldy, throw them out NOT compost.