LADYBUG: HIGH HEAT, HUMIDITY INFLICT STRESS ON PLANT

High heat and high humidity are often some of the most dangerous stress factors that can be inflicted upon plants. Mid-August has given a long stretch of temperatures that have risen into the high-90s and stayed there. Night temperatures also stayed high and so did the humidity with no moisture, unless is was applied.

Most plants in our area grow best when night temperatures are in the lower-60s and day temperatures in the 70s. As both day and night temperatures rise, a series of problems may develop.

Leaf scorch is a common midsummer symptom of a tree or shrub in trouble. Leaf scorch is most common on newly planted trees. The plant may be saying that its roots have been injured, and it has not grown enough new ones to repair the damage. Or it may be saying that because of the abundance of rain received this spring that without proper drainage, the roots are still soaked.

Scorch develops when water is lost from leaves faster than it can be replaced. As a result, the cells die and the leaves either wither or completely dry up.

The first readily noticed symptom of scorch is a slight yellowing of leaves. As the problem becomes more serious, browning, and often death, of the leaves occurs. This has happened on our tree peonies, which are shade lovers. In this prolonged drought they have been watered, but have lost some leaves anyway.

Sometimes shade trees fake false fall leaf drop, and all may not be well with them. However, sometimes they may develop a premature color or leaf drop for no apparent reason. Some trees, such as tulip poplar, maple, birch, sycamore and linden, may respond this way.

A sudden drop of healthy leaves is often hard to explain. It usually occurs during a period of hot, dry weather that follows a spring with lots of rain. Newly planted trees may have limited root development because of the wet spring.

Trees under substantial stress may respond by developing fall color prematurely, says Dr. Ray Rothenberger of the horticulture department of the University of Missouri. Some maples and oaks are apt to respond this way.

In the vegetable garden, one of the first problems of high heat is the failure to produce. Such plants as cucumber, squash and melons often fail to pollinate properly during hot weather. Plants under stress may begin fruit formation, but as water demands are shifted to the vegetative portion or to already developing fruits, new blossoms or small fruits drop off.

When night temperatures are higher than 70 to 75 degrees, peppers fail to pollinate. Blossoms may drop off when daytime temperatures are higher than 90 degrees.

Tomatoes are another garden crop in which pollination can be influenced by high temperatures. This sometimes results in "blossom drop." While materials can be purchased to improve blossom set in cool weather, they are not effective during high temperatures.

Blossom end rot seems to appear on tomato fruits at this time of the year. If the problem is severe, have the soil tested this fall. It may be that the soil acidity or calcium content needs to be adjusted for next season.

Tomatoes with a tendency to rot, are often abundant, at this time of the season. The best control for this is the quick removal of any fruits as soon as spots are seen. Prompt harvest of ripe fruit will also slow development of this problem.

Cloudy spots is a condition in which numerous, small whitish areas develop just under the skin of the tomato and can be seen on the surface. This is caused by a stink bug feeding on the young tomatoes. Garden insecticides that kill sucking insects will be effective in controlling them. The tomatoes are still less usable and may need to be peeled.

Hot weather can prevent fruit set in many tomato varieties. If fruit formation has been reduced, this may be the cause. Set will gradually improve as days and nights become slightly cooler.

Not only garden produce, but also many flowers are suffering from heat-related problems. Geraniums are often hungry and need fertilizer during the summer. The size and color of the leaves are generally good indicators of fertilizer needs. A complete garden fertilizer, such as 5-10-5, or special geranium food are good.

Long periods of high temperatures are hard on plants, animals and humans.