I have an expert on growing citrus coming into town for a seminar Tuesday at the University of Nevada Cooperative Extension’s Lifelong Learning Center located on South Maryland Parkway at East Windmill Lane. He will be speaking from 6:30-8:30 p.m. This seminar is free and open to the public; reservations are not necessary. Seating is limited. For more information, call the master gardener help line at 257-5555.
Q: We have had fantastic results with tomatoes for many years. We put them in a planter we built to grow them. Last year, we cut them back again in late summer and had a second batch. This year, we changed the dirt out and put in some bagged soil from a local nursery. The plants really grew and we are getting lots of tomatoes. We put a powder on them so they wouldn’t get tomato worms.
We have been getting good production of tomatoes for a few weeks now, but the plants are getting brown leaves with gray spots. First, they go yellow, then brown with spots and finally dry up. I feed them with Miracle-Gro for tomatoes as directed on the box. I do not want to lose these plants. What should I do to get rid of the dying leaves?
A: There are several tomato diseases but only two are relatively common here in the desert; they are early blight and late blight.
In early blight, leaf spots usually begin on the lower leaves and are circular, up to one-half inch in diameter, brown and contain dark concentric rings like a target.
This is most likely what you have, but without seeing it or having a pathologist identify it, I can only guess.
Usually the leaves turn brown and then dry up. Entire plants can be defoliated thus exposing the fruit to sunburn. This is a fungus disease and is spread by wind and insects.
The disease stays on dead plants and debris left over the winter. It is very important when growing tomatoes to completely clean up the growing bed at the end of each season and plant them in a different bed the following season. In other words, we should be moving our plants to new locations or different beds each growing season.
When you see this disease beginning to develop on younger plants, an organic chemical control is copper fungicides such as Bordeaux. Read the label and follow it precisely.
A less likely foliar disease is late blight of tomato. This disease can be characterized by its rapid and destructive nature. This disease is probably less likely in our climate since it usually requires mild, moist weather for development. However, considering our recent weather, I cannot rule it out.
Late blight usually can be identified from a pale green halo that surrounds leaf spots as they are enlarging and looks very different from early blight. Again, copper fungicides will give some measure of control if caught early. Bordeaux can be hard on plants so apply it cautiously and only when necessary.
If you suspect that your tomato plants have succumbed to either early or late blight, do not compost the vines; destroy them instead. Make sure you clean up all debris from areas where tomatoes were growing. Move your tomato, pepper, eggplant and potato plantings into new areas of the garden each year. Try not to plant in the same area for at least two or three seasons or longer if at all possible. Try to avoid planting these plants close to each other since they share similar diseases.
Q: I moved a small Meyers lemon tree that was growing in a large pot to my porch and put it inside a larger pot to help insulate it. Now, the sun is only on it from sunrise until about 10 a.m. Is this enough sun? I have very few choices of where to move it and now it seems like it is dropping leaves.
A: Whenever we give a plant less sunlight, it will receive less energy for growth. Technically we can divide growth into two types: vegetative growth or growth that goes into the development of leaves, stems and roots, and reproductive growth for flowers and fruit.
For sure you will see a decrease in flowering and fruiting. Will the tree survive? Probably, but with decreased growth and the type of vegetative growth will change. Because the tree was in strong sunlight, it produced leaves that were smaller, darker green and thicker. These are referred to as sun leaves.
When a plant is taken from strong sunlight into shade, it frequently will drop some or all of its sun leaves. The plant will subsequently try to put on a whole new set of leaves called shade leaves. These leaves are larger, lighter in green color and thinner. These new leaves are more efficient at capturing light in shade.
But, shade leaves are not as tough as sun leaves and can be easily damaged in strong winds and strong sunlight. When plants are grown in the shade and then plunged into strong sunlight, their response is usually to drop the shade leaves and put on new and more efficient sun leaves.
This is why it is usually recommended to put plants transported from nurseries in Southern California under shade cloth for a few weeks to acclimate them before planting them in full desert sunlight.
Plants’ leaf drop usually signals panic in homeowners and their response is typically to give them more water. This is not a wise thing to do if a leaf drop was due to a change in sunlight rather than a lack of water.
Q: Is there a list of flowers that benefit from deadheading besides geraniums? I have canna lilies. Do I cut the stalk to the ground with the dead flower removal? What about zinnias?
A: All flowering annual and herbaceous perennial plants will benefit from deadheading.
Deadheading is the removal of spent flowers from plants after they have bloomed. In most plants, deadheading removes the potential of the flower for producing seeds.
Seed production in plants, although it doesn’t appear so because they’re so small, requires a lot of energy. Removing flowers immediately after they bloom allows the plant to redirect this energy into other growth. Deadheading is very important in plants that are repeat bloomers as this will encourage more production of flowers during the season.
In many plants that are not woody, deadheading can be done with your thumbnail by just pinching off spent flowers at the base. Other plants that are tougher may require sharp scissors or pruners. And still in other cases where many flowers are borne along a single stem like your cannas, removal may have to be done by completely removing the stem at its base.
Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at firstname.lastname@example.org.