Weather in its many manifestations, ice storms, heat, cold, drought,
and floods, can certainly be classed as a garden enemy. Some of its effects
are mechanical, as frost cracks in sudden cold or actual breaking of limbs
in hurricanes or by ice or snow, but almost everything else boils down
to a water relation.
We call the large brown areas that appear on rhododendron leaves in
late winter or spring SUNBURN or windburn. The cells that are exposed
to sun or wind lose water faster than it can be drawn up from the often
frozen ground and so they collapse, turn brown, and. die. Fungi may
appear in this spot secondarily, but this is primarily a physiological disease. It can be partially prevented by watering broad-leaved evergreens
very thoroughly late in the fall and by using a windbreak for too exposed
is the name for sudden death of foliage in summer heat, with
large areas in the leaves tan or brown. Sugar maples are subject to scorch,
reacting promptly when hot weather follows a period of cool cloudy
weather. Again it is a case of cells collapsing before the water evaporated
in the heat can be replaced from the roots. Copper beech is often damaged
(Figure 60A). Scorch on horsechestnut looks like a leaf spot, but it lacks
the black dots indicating fungus fruiting bodies.
of tomato, also occurring on pepper, squash, and watermelon, certainly looks like a fungous disease, but it is caused by irregular water supply, drought following excessive rainfall. Tissues at the
blossom end of the fruit shrink, and a dark leathery spot is formed that
may include half the fruit. Avoid excessive nitrogen, provide balanced
fertilizers, mulch to conserve moisture, water regularly in dry periods.
Frost cracks can sometimes be avoided by letting roses and other shrubs
harden of? early; do not feed after the middle of July; avoid excessive
watering in late summer.
When ice freezes into boxwood stems, the bark may slough off very
gradually with branches dying back for 2 years or more after the ice
storm or sudden cold.
Webworms are caterpillars which feed inside foliage they web or tie
FALL WEBWORM (Hyphantria cunea).
This is not a pest of evergreens but
appears on more than a hundred fruit and shade trees and shrubs.
The webs resemble tent caterpillar nests but are more loosely woven and
are at the ends of branches, often with several tied together, rather than
back at the crotch.