Cover crops, row covers on readers’ minds

Posted April 23, 2010, at 6:56 p.m.

On the heels of last week’s column about no-till gardening, I received an e-mail from Bangor gardener Jane Marasco. “Last fall I planted winter rye in my vegetable garden as you recommended. Today’s article says not to till. How can that be when now my garden is all grass?”

According to the Rodale Institute (http://newfarm.rodaleinstitute.org/features/0104/no-till/chart.shtml), winter rye is compatible with no-till gardening. Its use does, however, rule out the use of the cover-cropped area for early-season crops.

Used in a no-till system, the winter rye cover crop should be cut to ground level after it flowers, in mid-June, at the earliest, for the Bangor area. A scythe would be a good tool for this job, considering the bulk of a winter rye cover.

The gardener then should wait two weeks before planting, allowing growth-inhibiting allelochemicals produced by the rye plants to dissipate. After this waiting period, summer crops, such as tomatoes, peppers and squash could be transplanted through the mulch formed by the decomposing rye.

This schedule leaves little margin for disruption of our short growing season. For crops that require more than 70-75 days to mature, it would be best to forgo the no-till approach and dig in the winter rye in early spring. While this digging disturbs the soil, life will rebound and be nourished by the increased organic matter.

Oats would be the better cover crop for no-till gardens in Maine. Sown in mid-September, the oat plants will grow until winterkilled and then form a mulch over the surface of the soil. Beds can be planted as soon as the soil can be worked in spring without concern for allelochemicals. (Do not let oats go to seed in the fall garden. If a killing freeze is delayed and the plants start to flower, cut them back.)

Row covers and insects

Larry Sanford of Orono e-mailed a question about controlling the Colorado potato beetle without using pesticides. “I want to grow a few potatoes this summer but am concerned about attracting the potato beetle to my garden. I garden without chemical pesticides, so what can I do?”

I believe in row covers (available from most garden supply companies) as the best defense against the potato beetle and other vegetable garden herbivores, including the cabbage moth, a major feeder on broccoli, cauliflower and other brassicas. Made of spun-bonded polypropylene, row cover fabric is light in weight, allows 90 percent light transmission and is permeable to air and water.

Row covers work best when floated over the top of plants, anchored to the ground on all sides with wire pins, soil, rocks or boards. Crops should be covered immediately after planting, applying the fabric loosely so plants can lift it as they grow. For small seedlings or transplants, the cover can be supported initially with wire hoops.

Leaf beetle predator

Invasive insects arrive in this country without their natural predators and consequently wreak havoc with native ecosystems, including our gardens. The viburnum leaf beetle, for several years now a major threat to several species of native viburnums, is no exception; the gardener is its only predator.

In Marjorie’s garden, we have several maple leaf viburnums, Viburnum acerifolium, scattered about. It is one of the beetle’s favorite hosts, along with arrowwood viburnum, V. dentatum, and cranberry viburnum, V. trilobum, all favorites of Maine gardeners. I know of several large plants of the latter two species that were killed within two years, defoliated each summer by the adult beetles and their larvae.

Now is the time to play the role of predator. Scout the upper twigs of your viburnums for clusters of beetle egg casings. They appear as small raised “warts” on the surface of the twig. Often the portion of the twig above the casings is dead. If you scrape away the raised portion of a casing, you can see the yellowish eggs inside.

When you find casings, prune off the infected twig with a cut just above a pair of leaves below the infected area. Gather all such prunings and burn them.

Believe me, you don’t want to let those eggs hatch.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.

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