Regardless of the few complaints heard when the temperatures have exceeded eighty-five degrees or so, there has not been much ‘hot’ weather here this summer. This weather has certainly been more pleasant for those of us without home insulation, shade trees or air conditioning; it has not been so for species that enjoy heat.
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 and anthracnose, 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 corn stalks 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 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.
Ask Tony Tomeo a gardening question at www.AskTonyTheGardener.com