Week 6: An introduction to integrated pest management and the leek moth

This week brought the arrival our first guest teacher, Vic Izzo. Vic, an evolutionary ecologist, offered a new framework for pest management that begins with careful observation.

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Evolutionary ecologist, Vic,  with a wildflower bouquet cut from the Beneficial Insect garden on the north edge of our plot. The full and colorful bed does not only attract important pollinators, but also those insects that are natural predators to the unfavorable pests.

Evaluating whether or not a pest poses a threat is the second step in Vic’s framework. It is not always clear what presence and/or damage is within the tolerance of a given plant. The flea beetle, for example, will leave brassica leaves covered in tiny holes but cause no damage beyond the cosmetic imperfection.

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Flea beetles leave their mark on brassicas without affecting the health of the plant.        These greens are nutrient rich and fine to eat (though they may be a hard sell at market).

On the flip side, there are some pests (known as nectar-robbers) that can show up and appear to be causing no damage at all. While they may not be affecting the plant’s appearance now, they can use their sucking mouth parts to extract pollen from the plant, which, in turn, will cause the plant to be passed over by important pollinators. Without pollination there will be no fruit.

As a beginning gardener, the identification of pests, along with the determination of their harmful or non-harmful nature, requires a dependable resource. This is true of long-time gardeners gardening in a new region too. At the Community Teaching Garden we use two:

UVM Extension & Cornell Extension

A pest that has been successfully identified and determined to be a threat to the overall health of the crop can be managed in several different ways. In this third stage (management), Vic offered the Integrated Pest Management pyramid as a structure for decision-making.

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There are several methods that fall within each layer. Pest management strategy begins at the bottom and works its way up, as the tactics falling within the bottom of the pyramid will tend to be less invasive to the garden system as a whole.

Vic’s focus for the summer is on the leek moth. The leek moth is a pest of Allium crops with a hierarchy of dietary preference: leek, onion, garlic. We have no leek plants and only a few onions interspersed throughout the brassica sections of our garden. We do have a big and mature garlic bed right there in the center and, sure enough, Vic was able to point to the significant leek moth damage on the scapes of our garlic crop.

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The leek moth is relatively new to the region. The pest begins its life as a yellowish caterpillar, will experience a cocoon phase, and, ultimately, grow into the adult moth (about 1/2″ long).                  For more information, visit Cornell Extension

Pest identified and determined to be a threat to the crop. What to do next?

Choosing not to plant leeks, onions, and garlic could prevent the arrival of the leek moth. Too late! Cultural management often involves the strategic shifting of the physical location of a plant. Because the leek moths can fly, the garlic would not be helped by a move. In the case of the leek moth, intervening on the physical level is the best bet and, because the moths were feeding only on the garlic scapes, we decided that it was time for a harvest!

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Known as the scape, the flower bud of the garlic plant has a concentrated garlic flavor. Harvesting the scapes should help to manage the leek moth and support the continued development of the garlic bulb (to be harvested in late July).
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