Plants will help gardeners who help themselves. Especially those with natural pest resistance. But a gardener has to do his part by selecting and planting wisely.
Plants have evolved fascinating strategies to thwart insects and diseases: Complex chemical compounds discourage feeding in some species. Others place physical barriers in harm's way; hairs, spines and waxy coating protect leaves from infection.Frequently, plants will simply tolerate the damage, surviving despite repeated attacks. Birch trees, for instance, can live for many years under siege from birch leaf miner. (Not so with bronze birch borer, however, a bug that kills its host.)
The dilemma for plants is that they can't always adapt fast enough to outwit insects and fungi, which have an amazing capacity for change. As a result, the bugs are winning.
Horticulturists at Cornell University confirm that many of our "traditional" landscape plants have serious pest problems today that they didn't have just 20 years ago. They also estimate that 50 percent of all plant losses occur because a gardener fails to plant a specimen in the right location.
Plants are doing their part, but gardeners must help out by selecting varieties with natural pest resistance. From trees and shrubs to flowers and vegetables, alternate choices are available for almost every landscape situation.
Benefits to the gardener are significant: less maintenance, lower costs, fewer pesticides. Not to mention that resistant plants will look better - and taste better - than those struggling to survive.
Selecting for pest resistance sometimes requires compromise, as in the case of birch trees. Ravaged by borers in many parts of their range, the lovely white-barked varieties have become a landscape liability.
River birch is similar in habit but resistant to borers, making it a good substitute. The trade-off is that its bark is not quite as dramatic as that of its relatives. "Heritage" has the prettiest bark of the river birches.
In crabapples, consider varieties that resist apple scab, fire blight and rust. New and better varieties are being introduced at an astonishing rate and now come in every variation imaginable: pink flowers or white, green leaves or red-tinted, fruits golden or red. Form can be upright, broad and spreading, oval, weeping, dwarf or in-between.
Take the road less traveled. Along the way discover a host of beautiful trees and shrubs, many with unfamiliar names, but all with likable personalities. White fringe tree, sweetbay and "Galaxy" magnolias, serviceberry, maakia, Heptacodium, Japanese tree lilac and Carolina silverbell are willing and able to replace ailing dogwoods and disease-prone cherries.
If a dogwood it must be, substitute a kousa dogwood for our native species or plant one of the new hybrids, "Constellation" or "Stellar Pink," both of which display good resistance to the anthracnose fungus. Try Corneliancherry dogwood for super-early yellow blooms and attractive summer fruits.
Within the maple family are at least a dozen patio-size varieties that offer gorgeous bark or carefree shade. Some do both. Paperbark maple, hedge maple and amur maple are available now; but coming soon to American gardens will be a cadre of wonderful Asian and striped-bark species.
Need something a little larger? Research yellowwood, Katsura tree, Korean mountain ash, Turkish filbert and golden-rain tree to see if one or more would suit your landscape conditions.
Smaller, as in shrub size? Rarely have I seen witchhazel, Japanese kerria, Carolina allspice, oakleaf hydrangea, bluemist shrub, pearlbush, weeping peashrub or ornamental blueberries defoliated by insects or spotted by disease.
Whatever you do, mix things up a bit. Monoculture (planting lots of one variety) is risky. If you need three trees, for instance, select three different varieties, or two of one and one of another. Diversity is a certain way to avoid catastrophic losses.
Pest resistance works in the vegetable patch, too, at least to some degree. Insects avoid tomatoes with hairy leaves and thick skins. Most cherry tomatoes exhibit such traits.
"Viva Italia" paste tomato is unattractive to tomato fruitworm (experts don't quite know why) as are Roma, Tiny Tim, Chico, Ace and Yellow Pear. Gardeners with fungus problems on tomatoes should be growing VFN varieties, with built-in resistance to verticillium and fusarium wilts and nematodes.
Member of the cabbage family are less likely to be attacked by cabbage worms and aphids if they're the purple cultivars. Purple cauliflower, kohlrabi and cabbage curiously repel these pesky insects.
For fewer pea aphids, grow tall, loose varieties such as "Sugar Snap" or "Green Arrow." They offer fewer places for the insects to hide than dwarf bushy varieties.
And finally, try thwarting squash vine borers by planting varieties that root readily along stems on the ground. Winter squashes, especially butternut, do quite well in borer territory. "Sundrops" is the most borer resistant of the summer squashes.