Thursday, March 5, 2020

Ten Percent Rule*

No matter how much insecticidal soap I sprayed, the aphids came back stronger than ever. Finally, so frustrated, I stuck the head of our giant three year old jalapeno out the window, shaking the plant vigorously to dislodge the aphids and shed the leaves on which they congregated. Although only outside for a minute, it was about 10° F, and not thirty minutes later, the remaining leaves had turned black -like frost-damaged basil. I was ready to toss the whole deal, but I hesitated. The following day, I pushed the head of the pepper out the window yet again and pruned the branches hard -all the way to the woody, tan stems.

This sweet pepper had been pruned hard in December, yet the aphids continue to show up. You can see their shed skins and the stunted condition of its remaining leaves.

About a week ago, the jalapeno's woody stems sprouted vigorously. I had hoped it would do so slowly -those new leaves such easy sucking and still three months before any pepper can be reliably placed outside.

This week, leaves twice as big but still tender, the aphids have returned. I put my ugly, fat thumb in the picture to show how tiny the aphids are. I rely on my camera and macro lens to spot new aphids since my eyes can no longer focus so closely.

Closeup of the three aphids.

It has been warmer than average recently. Although we are far from a Minnesota spring, which typically arrives in May, the warmth brings out a few Asian lady beetles that worked their way into the walls last October. Attracted to the light, they usually make their way to windows, and die. Outside, they wouldn't make it at all, given that nights drop to the single digits at times.

Aware that predation is the best way to control aphids outdoors and in greenhouses, I haven't been willing to release ladybugs in the house. So when the warmth brought this one to a window near the peppers, I coaxed it onto my hand and then the sweet pepper. The lady beetle is a reluctant helper, it seems to only want to hide, but the following day I didn't observe any aphids and the lady beetle was still on the pepper, alive.

*The 10% Rule is an ecosystem function where energy passed on from one trophic level (position of an organism in the food chain) to the next, only ten percent of the energy is available to the consumer. An example: the pepper plant passes on only ten percent of the energy to the aphid and the aphid only ten percent to the lady beetle who consumes it. To receive the full energy consumed by the aphid, the lady beetle needs to eat a lot of aphids -something for which gardeners should be thankful.