Monday, September 12, 2011

Kale IPM

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Excuse me, but there’s a worm in your pesto.
Kale leaf foliage,
stripped from the leaf 'rib'.
The finished product: kale pesto!
The finished, finished product:
kale pesto on homemade pizza.
Yesterday afternoon, my husband and I harvested kale and basil to make pesto. The basil did quite well this season – with nary a pest blemishing its leaves. The kale, on the other hand, came with several added bonuses that I didn’t want in the pesto:
  • Cabbage worm larvae (caterpillars) and eggs
  • Aphids - with signs that an infestation was imminent
  • Spiders and their webs
We harvested the kale, and I carefully inspected and washed each leaf before cutting the flesh of the leaf blades from the rib. We made a tasty kale pesto, that was delicious on pizza with homemade crust and sauce (shout out to my husband, who is the cooking brains in this operation).

But as I was making the pesto (or, cleaning the leaves, so my husband could make pesto), I knew it was time to go out into the garden to manage the cabbage worms and the aphids, before they got out of control.

Cabbage worms are the larvae (young) of the ubiquitous cabbage butterflies (Pieris rapae) that you see flying around everywhere. The adult butterflies lay their eggs on cruciferous plants: broccoli, cabbage, collard greens, Brussels sprouts and kale. The larvae can’t feed on non-crucifers. Thus, females who make a ‘mistake’ and lay their eggs on a non-cruciferous plant basically doom their young to death by starvation.

I've dealt with the cabbage worms all summer long. Every day when I watered, I carefully picked their eggs off of the kale leaves. I searched the leaves and picked off the caterpillars that hatched from eggs that I missed. I was happy when my husband cleared out a nearby tangle of grape and blackberry canes (i.e. stems), and the spiders promptly migrated from that area and into my vegetable garden. The spiders surely helped to keep the cabbage worm population down - pouncing on caterpillars as they munched on my kale, or entangling the caterpillars in their web. They might even munch on an aphid or two (although, spiders really prefer and need the protein rich meal that the caterpillars offer - much more nutritious than the sac of sugar that is an aphid).

Two cabbage worm eggs
on kale. I picked these off of
kale leaves, as I watered the
A late-instar cabbage worm,
almost ready to build a cocoon.
I pick these off of leaves, as well.
Spiders munch on cabbage worms
and other insect pests. I leave
these be in my garden.  They're my
pest control buddies.
But, the spiders couldn't do it all themselves. After harvesting and cleaning this batch of kale, I knew that I needed to go out into the garden and use chemical controls. My conundrum, however, is that I wanted to control the cabbage worms and the aphids, but not harm the spiders. I needed to use pesticides that had a 'narrow spectrum' of activity. Narrow spectrum insecticides harm a relatively few types of insects and other arthropods. Broad spectrum pesticides harm a large array of insect types, and are thus more likely to harm both your pest (which you want) and your beneficials (which you don't want).

I went to my pesticide storage container, and decided on 2 products. Both products are organic. When I need to use a pesticide, I prefer using organic pesticides, over synthetic pesticides in my vegetable garden. The major benefit of using an organic pesticide over a synthetic pesticide is that organic pesticides degrade quicker than synthetics, after they are applied. I hate the idea of eating pesticide residues with my vegetables, so when I am treating edible plants, I almost always use an organic product. I want that extra assurance that the vegetables will be pesticide free when I harvest, cook and consume them.

The products are also formulated, so that they will help manage the cabbage worms and the aphids, but that they are unlikely to harm other insects and arthropods. I wanted to protect my garden spiders, afterall. They're my caterpillar eating buddies.

Label of a narrow-spectrum insecticide with the active
ingredient Bt-k (Bacillus thuringiensis kurstaki).
To control the cabbage worms, I chose a dust formulation of a product whose active ingredient is Bacillus thuringiensis kurstaki (also called Bt-k). The insecticide only works against the larvae of butterflies and moths (like, the cabbage worm caterpillar I am trying to manage on my kale). In addition, this insecticide must be eaten in order for it to be effective. Thus, if I sprinkle the dust only on my kale leaves, only those caterpillars that are eating my kale will get a dose of the insecticide. The brand name of the product doesn't matter. Look for the active ingredient (Bt-k), formulated as a dust.

Pay attention to the directions for use. You only need 0.5-1 oz per 50 square foot of garden. One ounce = 2 tablespoons. Thus, for a standard sized 3 foot by 5 foot garden bed, you only need one third to two thirds of a tablespoon. Since this product often comes as a dust formulation, and is packaged in way that you can simply 'shake out' the pesticide, much the same way you might sprinkle Parmesan cheese on top of spaghetti, it's unfortunately easy to over apply this pesticide. To avoid over applying, set the dispenser so that the pesticide will lightly sprinkle out of the packaging. Don't open the dispenser all of the way when applying.
Note that you only need 0.5-1.0 ounces
per 50 square feet of garden.  This is a
very small amount!  Be careful not to
over apply.
Instead, apply a fine dusting, with the
container open only the tiniest amount.
If you apply the dust with all of
the holes open, you're likely to over
apply this insecticide in your garden.
To control the aphids, I chose a ready to use spray formulation of insectidal soap, which has an active ingredient name of 'potassium salts of fatty acids' (or something similar). Insecticidal soaps work by degrading the exoskeleton of the insect. Thus, they best against small, soft-bodied insects, such as aphids, whiteflies or thrips, and tend to have little effect on larger, harder-bodied insects such as beetles, caterpillars, grasshoppers. Insectidal soaps must contact the aphids in order for the insecticide to work. Unlike Bt-k, insectidal soaps do not require the insect to eat the toxin. Instead, the insectidal soap must contact the aphids in order for the insecticide to work.

Label of an insecticidal soap product, with the
active ingredient 'Potassium Salts of Fatty Acids'.
I had another option available to me. When my flea beetle (and my aphid) problem became too big for me to manage using physical controls (i.e. picking the beetles off of the plant) or biological controls (i.e. relying on parasitoids to help me control the beetles), I needed to incorporate a chemical control into my integrated pest management approach. I decided to use an organic pyrethrin. Pyrethrins are an organic insecticide that works against a wide range of insects. Even though it is an organic insecticide (and thus has the advantage of degrading rapidly in the environment), I avoid using this product when I can. It surely helped me to control the flea beetles and aphids on my potatoes, but if I had accidentally sprayed the pesticide onto a parasitoid or a bee, it would have probably killed those beneficial insects. Because the aphid problem on my kale could be managed with insecticidal soaps, I chose not to use this broader spectrum and combination product.

Note that the product below has two active ingredients: pyrethrins plus potassium salts of fatty acids (i.e. insectidal soaps). This is an example of a combination product. The product above has only one active ingredient: potassium salts of fatty acids.
Label of a combination insecticide, including broad
spectrum pyrethrins, as well as insecticidal soap.