By William Johnson
Q: My tomato plants have stopped setting fruit. What’s the problem?
A: This condition is due to a blossom drop. Blossom drop is a condition suffered by tomatoes, peppers, snap beans, and some other fruiting vegetables where the plant blooms but fails to set fruit, the blooms die and fall off. Tomato plants lose their blossoms for several different reasons usually related to some type of stress. The stress may be either nutritional, environmental or some combination of the two.
During this time of the growing season the most likely factor is temperature-related. Despite the fact that the ancestors of tomatoes evolved in the tropics, the flowering and fertilization process in tomatoes is quite sensitive to temperature conditions.
When day temperatures consistently exceed 85 degrees F. and night temperatures exceed 72 degrees F., tomato blossoms will start to drop. Since our daytime and nighttime temperatures have exceeded these upper limits over the past few days, gardeners across the county should expect blossom drop to increase over the next few weeks.
It is interesting to note that although the combination of high day and night temperature causes blossom drop, high night temperatures alone can be detrimental to flowering even if day temperatures are not over 85°F. Blossom drop caused by warm temperatures is primarily a problem on large-fruited tomatoes. Heirloom tomatoes are even more sensitive to the high temperatures that occur during the latter part of our spring growing season.
To help extend the tomato growing season, I always advise gardeners to plant one or several cherry tomato transplants. Cherry tomatoes have small, cherry-sized fruits often used in salads and for immediate consumption. Plants of cherry tomatoes range from dwarf (such as Tiny Tim) to seven feet or taller plants (such as Sweet 100).
Cherry tomatoes are easy to grow and will provide bountiful yields of flavorful and juicy fruits. Cherry tomatoes are less prone to many of the problems that plague larger-fruited varieties (such as blossom end rot) and they often produce fruit early.
Q: My citrus tree has black mold-like growth on the upper surface of some of the leaves? Should I use a fungicide to treat it?
A: You most likely have sooty mold, a fungus that grows on the sweet residue (known as honeydew) produced by sucking insects such as aphids and whiteflies. So don’t use a fungicide. That will not get to the cause of the problem. You need to treat with an insecticide to control the insects. Try using one of the horticultural oil sprays such as SunSpray Ultra-Fine Spray Oil or Green Light Neem Oil. Two or more applications about 7 to 10 days apart are recommended. Be sure to also apply either product to the lower side of all the leaves. Read and follow the manufacturer’s directions for use including conditions of air temperatures.
The horticultural oil suffocates the insects and greatly reduces their population while not harming most beneficial insects that also feed on the aphids and whiteflies. The horticultural oil will also help loosen the growth of sooty mold. Then rainfall and normal weathering will gradually cause the sooty mold to disappear.
Q: How can you tell the difference between a slicing type cucumber and a pickling type cucumber?
A: All pickles are cucumbers, but not all cucumbers make good pickles. Slicing type cucumbers are generally dark green in color and are from six-to-eight inches in length when mature. Pickling cucumbers tend to be lighter in color and are short and blocky in shape. An important point to remember is that if you intend to put up pickles, then you definitely should grow a pickling type variety. Pickling cucumbers were developed to go through the brining process and will generally produce a higher quality pickling product.
If you intend to use cucumbers mainly in salads, it is generally recommended that you use a slicing type cucumber. However, pickling varieties can also be used in salads–I rather like their crispness and flavor.
Q: The limbs on our young crape myrtle tree touch the ground after a rain. Is it safe to prune them now?
A: The weight of the old flowers and seed pods will cause the limbs to droop, especially when wet. You can safely remove the old flower and seed heads by clipping them off just below the flower bract. You can do this throughout the growing season. You can also remove any lower limbs that make it difficult to mow around.
However, I caution owners of large trees not to do any major pruning at this time of the year. Heavy pruning on crape myrtles in late summer and fall can cause winter injury to tender new growth. Postpone major pruning to provide size control until February and March of next year.
William Johnson is a horticulturist with the Galveston County office of Texas A&M AgriLife Extension Service.
Visit his website at aggie-horticulture.tamu.edu/galveston/index.htm.