Several garden enthusiasts have telephoned me to determine what they are doing wrong with their tomatoes, corn and other vegetables that enjoy heat, when in fact cool weather has merely inhibited growth and production. Unfortunately, while growth is inhibited, susceptibility to fungal diseases, such as powdery mildew, is enhanced. This would not be such a serious problem, except that weather has been unusually humid, promoting the proliferation of fungal organisms.

Regardless of resistance to the most common fungal pathogens that affect other vegetables and flowers, corn is detrimentally stunted by inhibited growth because it is on such a strict schedule. Most other vegetables can simply resume growth as weather becomes warm. However, corn insists on blooming and setting fruit at a precise time after germination. Stunted cornstalks that bloom on schedule will divert resources to production of corn and consequently remain stunted, compromising the quality of the corn, even if weather becomes very warm after bloom.

Most ash and sycamore trees that had been so severely defoliated by anthracnose fungus during spring and early summer have recovered somewhat, producing a second phase of vegetative growth during warmer and drier weather. The pathogen had proliferated during spring when weather was so variably rainy and warm. Although anthracnose becomes active during the currently humid weather, it is not what has been afflicting the London plane (sycamore) trees, causing foliage to be disfigured, fuzzy and white. Like zinnias, sycamores are now afflicted with powdery mildew, which had earlier been a minor affliction in conjunction with anthracnose. These unfortunate trees are certainly having a difficult time this year, almost recovering from one pathogen, only to be infested by another.


Tree of the Week: Red-Flowering Gum

I feel somewhat guilty about stealing clusters of dried inch-wide seed capsules from a red-flowering gum, Eucalyptus ficifolia, at a gas station while a colleague was in the mini-mart. The capsules were just not as impressive on the trees as I knew they would be when my neighbor had finishing arranging them with other dried "flowers."

Blooms may appear at any time, but are more prolific during late summer. The large, round floral trusses may be as wide as 10 inches and are almost always orange-red, but may be orange, pale orange, pale pink or pale white. Even the palest of the potential colors is impressive as it appears outside the dense and deep green foliar canopy. Individual leaves are approximately three to five inches long and wider than typical eucalyptus leaves. The reddish or grayish bark is quite fibrous. Mature specimens of red-flowering gum may be as tall as 35 feet.

Like most eucalypti, red-flowering gum tolerates many adversities, but may be damaged by excessive irrigation. Eucalypti grow like weeds if planted as seedlings, but have difficulty becoming established if installed as larger specimens. The smallest size that is practical is the best option. Susceptibility of the red-flowering gum to recently introduced pathogens that have afflicted other species of eucalypti is unknown.

Those on Rengstorff Avenue in Mountain View and a substantial collection used as street trees in Morro Bay exhibit remarkable uniformity. However, with only a few exceptions, eucalypti are grown from seed and may exhibit significant genetic variability, including variable floral color. Roots are innately complaisant to concrete unless irrigated too generously.

Horticulturist Tony Tomeo can be contacted at 408-358-2574 or at LGHORTICULTURE@aol.com.