As I wrote in my earlier post about the trials and triumphs of fall gardening, one of the primary challenges we’ll face in the fall garden this time of year is insect pests. (And boy have I been dealing with some of those lately.)
Protecting Your Fall Garden from Insect Pests
By late summer, insect pests are everywhere. Though established summer crops can weather the assault, young fall plants are especially susceptible to predation right now. And pest pressure will remain high until the first frost, so gird your loins and prepare to do battle.
Grasshoppers, cabbage worms, armyworms, aphids, and cutworms are some of the big late summer pests in my garden, though your “most wanted” list can vary depending on where you live and what you grow. My first line of defense when it comes to pests is physical barriers, my second is handpicking, and my third and final line is an organic pesticide.
Pest Control Method #1: Physical Barriers
Physical barriers like floating row cover are a great way to exclude pests from your plants. Floating row cover is a lightweight, spun-bond polypropylene fabric that allows water and most sunlight (depending on the weight) through while keeping pests out. It also provides a few degrees of frost protection, making it useful for season extension later in the fall.
Floating row cover does come with a few drawbacks. First, you’ll need to order it online as it’s not carried in big box stores or local nurseries. Second, you’ll need to fashion supports for your row cover–the most common choice being wire hoops. Third, floating row cover lives up to its name and can be hard to secure. (And if it’s not properly secured, pests can get under it and have a field day in an environment where they’re protected from their own predators.)
My row cover tactics have been cobbled together from several sources plus personal experience. I use Agribon AG-19 floating row cover, which is one of the lightest weights available. There’s an even lighter weight–AG-15–that’s specifically for insect control (with no frost protection), while there are several heavier grades that provide even more degrees of frost protection.
I mulch very heavily with straw when I first set my plants out, so for the first week or two I let my row cover rest on top of the straw and anchor the sides with pieces of untreated scrap lumber. When the plants start touching the row cover, I install 1/2″ PVC hoops and use specially-made clips to secure the row cover to the hoops. This system originated with Herrick Kimball of Whizbang Gardening, who once sold kits with templates for the necessary pieces. He’s now compiled the plans, along with instructions, in a book called The Planet Whizbang Idea Book for Gardeners. (Since making the clips is rather laborious and requires specialized woodworking equipment, I have some commercial clips on the way that may work with my PVC hoops.)
Cutworms, which live in the ground and come out at night to mow down your tender little plants, can’t be excluded by the use of row cover. But they can be stopped by protecting the stems of the plants. I mentioned my “toothpick trick” in my last post, and wanted to include a photo here because I’ve gotten a number of questions about it.
It’s a really basic technique, but it works. Take one toothpick and stick it into the ground right next to the young plant’s stem. (Do this gently, because I don’t want to jam it in there and accidentally damage the stem underground.) Then insert another toothpick on the opposite side of the stem, again as close as possible to the stem. You can add more toothpicks if you’d like to have even more protection (I used three for the Brussels sprouts pictured above), but two is the bare minimum.
Cutworms kill plants by wrapping their bodies all the way around the stems and chewing through them, so having a toothpick barrier on either side makes this impossible. Instead of toothpicks, some people tear little strips of newspaper, fold them in half, dip them in water, and then wrap them around the stem several times. I’ve done that before and it also works, but I find it’s more time-consuming than the toothpicks.
Pest Control Method #2: Handpicking
When I can’t exclude pests, like when I’m growing young transplants out in our open-sided hoop house, I rely on handpicking. Handpicking is very simple: examine your plants, paying attention to the tops and bottoms of leaves, tender new growth, and the base of the stem. If you see any insect pests, gently remove them from the plant and destroy them. Soft-bodied insects like aphids and caterpillars can be crushed, while hard-bodied insects like Japanese beetles can be crushed or drowned in soapy water.
Handpicking is a very effective method of pest control because it ensures the death of the pests that you find–a few pests will always get past a barrier no matter what you do, and some pests will inevitably find a place to hide from and survive an organic spray. Sometimes, handpicking is the safest way to manage pests on fragile seedlings and delicate plant parts. If you have a keen eye and inspect your plants daily, you can prevent an enormous amount of insect damage.
Handpicking does have a few downsides: first, it’s labor-intensive for large numbers of plants and second, it’s time-consuming–for maximum effect it should be done on a daily basis. The untrained eye may also have a difficult time picking out certain pests, like aphids, that are small and able to blend in with their surroundings. Caterpillars are usually easier to find because they do damage on such a large scale.
Pest Control Method #3: Organic Pesticide
If you’re like me, you’re committed to an organic garden and want to avoid pesticides as much as possible. I also avoid many organic pesticides for two reasons:
First, even organic pesticides can be harmful to beneficial insect predators and pollinators, so it’s important to know exactly what kind of activity a pesticide has before using it in your garden.
Second, I want to encourage the proliferation of beneficial insect predators, like ladybugs, lacewings, and parasitic wasps, in my garden. To do that, I have to leave at least some pests to do what they will, because otherwise these beneficial insect predators (and birds) won’t have anything to prey on. Without anything to prey on, they’ll have no reason to frequent my garden.
But sometimes, despite my best efforts, a pest situation gets out of hand and I turn to an organic pesticide. My personal choice is to use only OMRI-listed pesticides. The OMRI Product List is published by the Organic Materials Review Institute, a non-profit organization that evaluates soil amendments, fertilizers, pesticides, herbicides, and other agricultural inputs and determines if they conform to the USDA National Organic Program’s certified organic rules and regulations.
A product isn’t required to be OMRI-listed to be acceptable for certified organic production, but it’s a useful metric for home gardeners who want to grow organically but don’t have time to research individual products and compare them against the NOP standards themselves. OMRI-listed products will bear the OMRI logo on the packaging.
For cabbage worms, I use Dipel dust, which is composed of Bacillus thuringiensis (Bt) spores. Bt can be applied as a dust or a liquid spray. Unlike other pesticides, Bt is not neurotoxic, not a broad-spectrum pesticide, and will not harm pollinators. It has a very specific effect against leaf-feeding caterpillars and won’t harm warm-blooded animals or humans. However, Bt degrades in sunlight, so it needs to be re-applied weekly. If you dust plants with Bt, be sure to wear a dust mask or respirator to avoid inhaling the powder, which can irritate the lungs.
For aphids, I use insecticidal soap. Insecticidal soap is thought to disrupt the cellular membranes of small soft-bodied insects like aphids, spider mites, and thrips. Insecticidal soap is made the same way as any other type of soap: by combining a strongly alkaline compound with plant or animal fats. Because it’s so concentrated, it’s diluted in water before being sprayed onto plants. While it’s an effective and safe pesticide, it can damage plants if it’s applied too heavily. Light, frequent applications (every 4-7 days) are best.
1. “Bacillus thuringiensis,” W.S. Cranshaw. Colorado State University Extension. http://www.ext.colostate.edu/pubs/insect/05556.html
2. “Insecticidal Soaps for Garden Pest Control,” Joyce D. Ubl and Carolyn Munnerlyn. Clemson University Cooperative Extension. http://www.clemson.edu/extension/hgic/pests/pesticide/hgic2771.html
What’s your go-to type of insect control? Which pests pose the biggest threat in your garden?