Q: I like the look of fountain grass and want to plant some in our landscape. I’m wondering if it will drop seed and become a weed in our garden. I sure don’t need any more weeds.
A: Fountain grass, Pennisetum setaceum, has become a popular landscape plant because of its graceful appearance, ease of cultivation, and ability to thrive in low-irrigation settings. However, in some areas of California’s Central Valley, fountain grass has become an invasive weed in natural habitats because its seed is easily spread by wind, rain, and even animals. Our local nurseries carry several selections that are designated sterile and these selections should not present a problem in the garden. Nevertheless, even those sterile selections may produce seed occasionally according to University of California Cooperative Extension Advisors. By selecting varieties clearly labeled sterile, you should be able to minimize any possible problems and still enjoy their graceful appearance.
Q: Some of the leaves on my lemon tree are covered with a dusty black material, and the undersides of the leaves are white and sticky. Can you tell me what this is?
A: The black material you describe is sooty mold. This is an unsightly fungi that grows on the excreta of insects and on plant exudates. From your description, I suspect your tree probably has an infestation of white fly, a common insect pest here. White flies congregate on the underside of leaves where they suck plant juices and lay their eggs. While the weather is warm, the number of natural predators of white fly in the environment is low and the white fly infestations are high.
Right now, you can manage white fly infestations with several tactics. If the white flies are only on a few leaves, simply pluck the leaves from the plant and dispose of them. That may take care of the immediate problem. If the white flies are on many leaves, use your garden hose to wash the underside of the leaves to remove the white flies. You may need to do this on a weekly basis to get the problem under control. This tactic has been shown to be as effective as spraying with pesticides, and helps remove the sooty mold too.
Spraying with pesticides is undesirable because there are a number of insects present in our landscape that are predators of white flies, but they would be killed by the pesticides too. The population of these biological control insects tends to increase as the weather cools, so you should…