Wednesday, September 14, 2011

tomato hornworms


This year I became acquainted with a new garden pest, the Tomato Hornworm. This large bug is actually a caterpillar that chomps away on tomato plants, in a perfectly green disguise. My first clue they existed was actually the frass (bug poop), because it is dark and stands out against the leaves. The ‘horn’ is fake, and meant to scare predators.

These bugs can defoliate an entire tomato plant overnight, so let’s discuss prevention and control. One way to prevent these pests is to cultivate the top few inches of soil wherever tomatoes have/are being grown. This will expose the pupa to predators, like birds. It’s helpful to have a birdbath in the area where your tomatoes are growing.

Another environmental control are parasitic wasps (Braconidae) that lay eggs, hatch, and spin cocoons on the backs of the caterpillars that end up looking like grains of rice. These tiny wasps slowly eat the caterpillar as they grow into adults. If you find a caterpillar covered in these cocoons, place the bug and some leaves in a jar with large-holed screening to enable the wasps to escape and infect more caterpillars.

I have only seen a few of these caterpillars (each with the parasistic wasps present), but should the issue become worse, the next phase of control is targeted insecticide. Bt (Bacillus thuringiensis kurstaki) is a naturally occurring bacterium which targets caterpillars specifically. After eating the Bt sprayed leaves, they lose the ability to feed and die within a few days.

Bt is one of the safest insecticides on the market, sold under the names ‘Dipel’, ‘Green Step’ etc. and is certainly preferable to broad-spectrum insecticides. Lady Bugs and other beneficial insects will not be affected, and neither will the birds that eat caterpillars who have consumed Bt.

Some plant damage on plants has to be acceptable when gardening in an eco-friendly way; the Tomato Hornworm is after all the larvae of the Five-Spotted Hawkmoth (Manduca quinquemaculata). But, if you are dependant on your tomato crop for food, spraying Bt every few weeks will prevent crop loss and is an environmentally sensitive means of pest control.

The image above is a Tomato Hornworm parasitized by wasp larvae.

Tuesday, September 13, 2011

Buttonbush [Cephalanthus occidentalis]



This plant ‘labors in obscurity’ says Dr. Dirr in his Hardy Trees and Shrubs manual; which may be why I wasn’t able to readily identify it when a friend asked me what it was last month. Except for these strange, creamy white flowers that appear in August, this large native shrub remains fairly anonymous. Its habit and texture remind me of Viburnum.

The temperatures are falling and the days are getting shorter. The garden is growing well and we received some much needed rain last week. Unfortunately that wind and rain bent over my smaller butterfly bush and I had to cut it back several feet. I still have blooms in the garden, but they are growing fewer. It’s time to think about fall annuals and select spring bulbs.

I’m turning my attention to planning and possible garden renovations this fall. I’ve decided to grow fewer tomatoes and increase my pepper varieties next year. I’ll remove some of the sedum and ultimately have more room for perennials. I’d like to include cut flowers and increase wildlife/pollinator habitat/food sources where possible.

Thursday, September 8, 2011

Pop Culture meets Horticulture: reason’s Madonna should love, not loathe, hydrangeas…

Pop culture comes up in the world of horticulture and landscape architecture about as often as Madonna injects herself into that world, or hardly ever. This week we all learned of Madonna’s contempt for Hydrangeas, as seen in this viral YouTube video. But if Madge would take the time to see how similar the maligned flower is to her chameleon-self, she may actually come to appreciate this long-loved garden treasure.

A top-selling shrub, hydrangeas are extremely versatile, thriving in sun or shade with appropriate moisture. The more refined of the two most popular Hydrangea species is the Bigleaf Hydrangea (H. macrophylla) which can be found in hortensia (mop-head) or lacecap varieties. These pink and blue hydrangeas bloom on new wood and can change color over time in relation to the soil pH (acid=blue, alkaline=pink); ‘Nikko Blue’ is a popular Bigleaf variety.

The Oakleaf Hydrangea (H. quercifolia) has coarser textured leaves, can grow much larger (up to 8’ tall and wide) and has considerable fall color. Typically, Oakleaf blooms develop a pink hue with age. ‘Snow Queen’ is a popular Oakleaf Hydrangea variety, all of which bloom on old wood. A good rule of thumb is to prune all Hydrangea varieties directly after flowering; they make fantastic cut and dried flowers for arrangements.

There are more than a handful of species outlined in Dr. Dirr’s Hydrangeas for American Gardens, and that is a wonderful resource to learn more about them and their care. To be sure, there is a Hydrangea for every gardener and landscape architect regardless of sun exposure, hardiness zone, and design style much in the same way there is a Madonna album or phase we can each remember fondly and relate to.

As Madonna revives her image and career time and again, Hydrangeas continue to appeal to new gardeners taking shape as vines, shrubs, small trees, and even perennials. Indeed, they are the ‘Madonnas’ of the woody plant world, constantly being reinvented and always in the spotlight. Hopefully both the flower and the pop-diva will interest us for generations to come.