Pest Hunting: A Brassica Task

My many fall and winter Brassicas are sizing up nicely, but the ones not tented with floating row cover are showing a little chewing and some curling leaves. The culprits are cabbage butterfly larvae, snails and aphids.

Predator insects are still plentiful in the fall, but these pests can stunt the growth of young plants at a time when they need to be powering into winter with a strong growth spurt. To ensure robust, healthy plants, I am going hunting.

Cabbage butterfly

The larvae of the cabbage white butterfly or imported cabbageworm (Pieris rapae), often called the cabbage moth, are my first prey. Mostly what I’m finding right now are the slender green worms. They can hide — almost — by stretching out for an afternoon nap in the stem of a young leaf. They are further protected from my predatory grasp by secluding themselves inside the youngest leaves, the curled and furled ones sprouting from the plant’s center.

Cabbage butterfly larva

Cabbage white butterfly larva, on a fingertip.

Cabbage butterfly on leaf

Can you spot the green cabbage butterfly larva on this leaf? Hard to get a good camera focus, but it’s on the lower right edge.

Carefully, so as not to snap the tender growth shoots, I unfurl the rolled green shoots and lightly scoop through the inside with a fingertip.

Then I bend back the plant’s slightly larger leaves and unfold them one at a time, checking the base of the stem for the pale green body. Finally, I flip the leaf over between fingers and eye the back, in case one of them is on the move. (I look also for the elongated eggs, white or yellowish, on the undersides of the leaves. Those get squished too.)

Just the act of inspecting the plant can cause these critters to fall to the soil below, where they would pretty promptly inch under a leave and climb back on the plant, so I scan the soil surface too.

These pests can go through 3 to 5 life cycles per year, and can be in the garden from April through October. The jerky white butterflies with black wing dots flit around from plant to plant. Amazingly, they mate in the air. Their eggs take 4 to 8 days to hatch, and the green worm larvae lives for 3 weeks before pupating, where they cocoon themselves for a couple more weeks before emerging as a butterfly and beginning again.

I think — I hope — they’re on the year’s last life cycle.

 

Aphids

Green and grey aphids are a regular presence in my garden, and I’m finding small colonies on the broccoli, Brussels sprouts and kale. They take up residence on a stem or in the folded end of a leaf, and as they suck the juices out of the tender leave edge, it curls, providing them a cozy home.

Ones hiding in the leaves are fairly easy to spot, as the leaves also turn slightly purple on the edges when attacked in this way.

Aphids curling leaf

A colony of aphids on a fall broccoli start has caused the leaf to curl due to their feeding.

predator and aphids

Predator to the rescue! This native bee, just peeking over the leaf edge, happened to be checking out the aphid supply as I took pictures. I did not see him feed on them, but I hope he came back for dinner.

Again, my preferred method is to gently curl back the edges of the leaf and expose them. As they are also soft-bodied insects, they also will get quickly smooshed in between a thumb and forefinger. There is a little inevitable damage to the leaf area that was their home, but it’s much preferable to letting them form a stronghold there and begin to feed farther down the leaf and fill the stem, as they would like to do.

Aphids on Russian Red kale

These aphids crowding the stem of a Russian Red kale are doing plenty of damage.

When the aphids have colonized the base of a set of leaves, or the stem of a plant, a hard spray of water from the hose, straight down into the center of the plant, will wash them all off and drown a lot of them. Most of the rest are too weak to climb back onto the plant. I find that I need to return and do this again in 3 days to make sure I’ve gotten them all.

 

Snails

I used to see a lot more slugs, but the garden ecosystem has evolved to be more hospitable to snails. They are moving from my dying summer plants into my winter beds. It’s happening at a snail’s pace, but that’s fast enough for me to put on my camo gear and start stalking them.

These guys are a lot more visible than the others, as their brown shells stand out on a green leaf, even at a smaller size. They especially come out on a cool or rainy day, or right after dark.

Sometimes I’ll find their gelatinous, round white eggs in a cluster on the edge of a bed, usually near a rockery or some other good hiding place.

Snail eggs

These snail or slug eggs were found about six inches down along the inside edge of my stacked-stone raised bed.

But the hatched snails, or slugs, are most often found on the underside of the leaves, and they are quickly transferred to the underside of my foot on the path. Score another one (or ten) for the big guy.

These creatures are fascinating, and are all part of nature’s plan. And I don’t mind sharing a bit of my food with them. But this time of year, when the tastiest things on their menu are the young plants that will comprise my winter dinners, I am in a less permissible mood. Fall is for hunting.

 

One Response to “Pest Hunting: A Brassica Task”

  1. Cindy Riskin says:

    Thanks for the detailed information, Bill. I’ll get the waffle stompers and gardener’s soap ready.

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