Organic Pest Control Techniques
June 27, 2013 at 9:44 AM
As organic gardeners, we’ve always taken the approach of keeping our plants as healthy as possible so they’re less vulnerable to issues, and then using the least aggressive approach possible to avoid collateral damage in the garden. What follows are a few techniques and products that are working for us now in our ongoing war against destructive insects and other critters.
A relatively mild winter and spring left us with an unwanted surprise: aphids. LOTS of them, in fact - way more than we would normally see this time of year. We’re seeing them on our brassicas, which doesn’t normally happen until fall. Our Damson plum tree is infested with them. The climbing rose is the least of our worries this year, as it turns out.
Aphids suck plant fluids and excrete a sticky, saplike substance. When leaves become coated with this substance, a fungus may grow in it, producing a sooty mold that interferes with photosynthesis. Heavy feeding causes leaves to turn yellow, curl under, and become distorted.
To combat this, we first use water, spraying as strong a stream as the plant can handle to knock the aphids off. Obviously, this won’t work on vulnerable young starts, on which we hand pick aphids. And this method is only partially effective on our 15 foot tall plum tree (hard to reach every leaf!). In needed, we follow the water treatment with a spray of Dr. Bronner’s soap (2 tablespoons in a gallon of water). This is just as effective as commercially available insecticidal soaps, but Dr. Bronner’s is cheaper, smells much better, and is environmentally sound. Other non-detergent soaps can also be used, but please don’t use detergent dish soaps, which have additives including colorants and perfumes, and are typically not organic or biodegradable.
Don't be tempted to apply at higher concentrations, as the soap can "burn" the leaves of the plants. It is best to apply in the veening and then rinse it off the next day if you expect hot, sunny conditions.
One caveat for using any soaps: what kill aphids can also kill beneficial insects like ladybug larvae and eggs. These larvae are particularly voracious consumers of aphids. So if you see evidence of ladybugs, don’t spray unless you have a particularly bad infestation.
Another pest deterrent we’ve recently started using with good success is diatomaceous earth (DE). Safe for earthworms and beneficial soil microorganisms, diatomaceous earth kills aphids, white flies, beetles, cabbage loopers or worms, mites, snails, slugs, leaf hoppers, and other harmful pests.
DE is the fossilized remains of microscopic shells created by one celled plants called diatoms. It is completely harmless to warm blooded animals, but it is also highly lethal to any creature that has an exoskeleton.
We apply DE only in dry conditions, as it’s ineffective when wet. To apply, we put it into a shaker jar, small sieve or flour sifter after the morning dew dries, and dust plants with the fine white powder. It does look a little odd, as if you coated your cabbages with powdered sugar. So far we’ve used DE on all of our brassicas (cabbage, broccoli, kale and the like) and lettuces.
Our client Kerry was the inspiration for this product, which she discovered when researching natural slug remedies. To say Kerry hates slugs is an understatement; she’s also happy that her brassicas are now free of cabbage worms. To quote her:
I'm applying the diatomaceous earth every couple of days when it's not raining, daily when it is. Basically, when I see it still covering plants and ground, I can skip that day; when it is gone or very diminished, I re-apply. I apply the stuff directly to the plants, and liberally on the ground surrounding them, and use a flour sifter to distribute. I am seeing a significant reduction in the slug population, particularly in my lettuce heads, where I used to find them nestled between the leaves. I realize it is early in the season, but so far, so good!
It’s very important to look for a food-grade, untreated product when shopping. Many products have added chemicals. After quite a bit of research, including this excellent blog posting, we sourced ours from Earthworks Health. It’s also important to continue to hand-pick pests and not to just rely on a product to kill them off. Regularly inspect brassicas for cabbage worms and eggs and remove them. Check under lettuces and remove any dead leaves, baby slugs and sow bugs you find as well.
Animal repellants and barriers
Larger critters - birds, rabbits and deer - can be devastating to a garden. Barriers can work well for specific issues, such as covering blueberry bushes with bird netting as fruit ripens, or installing heavy-gauge rodent screen under raised beds to keep burrowing animals out. We’ve also been known to construct temporary barriers to protect just-planted peas from the voracious spotted towhee, a pretty bird that decimates seeds just as fast as you can plant them (thanks to client Susan for discovering this one!).
Fencing is probably the best option in terms of effectiveness for both deer and rabbits. Unfortunately, as most of our clients have urban or suburban gardens in full view of their patios and living rooms, fencing isn’t always an option. So we turn to repellants.
The most effective repellant we’ve found for both deer and rabbits is Liquid Fence, a seriously smelly, eco-safe solution you spray on and around your garden. When we build new raised bed gardens in areas known to have these critters, we instruct our clients to spray their gardens the first day they’re planted. We spray the raised bed frames themselves as well as nearby pathways and access points. The idea is to let the animals know early on that your garden is not their salad bar. Once they’ve started foraging, it’s much more difficult to keep them away. In that case we’ll also spray the soil and even the plants themselves - anything that’s not being harvested in the next three or so days. It doesn’t harm the plants - or you - but makes them taste bad to invaders.
We do recommend using gloves and staying upwind when spraying this product. The good news is, you won’t be able to smell it after a few minutes, but it’s effective against deer and rabbits for up to two weeks.
While barriers and various products can be very helpful in your garden, the best defense is unquestionably maintaining plant health. Your regular involvement in and inspection of garden plants will give you the perspective you need to spot issues before they get out of control. If plants start looking yellow or sickly, or you see holes in the leaves or other changes, take a closer look. It might be that your plants need a dose of organic fertilizer, or more or less water. Sickly plants are more vulnerable to attack from any of the pests mentioned here, so keeping plants strong and healthy is the best approach.