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Mr. Smarty Plants - White spots on Hibiscus leaves

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Wednesday - August 06, 2008

From: Wichita Falls, TX
Region: Southwest
Topic: Non-Natives, Pests, Edible Plants
Title: White spots on Hibiscus leaves
Answered by: Barbara Medford

QUESTION:

My hibiscus trees have white spots or splotches on the leaves. What is it and what can I do to get rid of it? Also, the birds are eating my tomatoes faster than i can grow them. I've used the owl & snake tricks which work about a week & then they're back eating again. What do you suggest?

ANSWER:

Again, we have to figure out what plant we are talking about. There are literally hundreds of plants typically referred to as "hibiscus", some annual, some perennial. There are some native hibiscus and many that are non-native, but all belong to the mallow family, so hopefully even if we pick the wrong one to discuss, the same advice will apply. Since you refer to hibiscus "trees" we believe that what you have is a Hibiscus syriacus, native to Asia, and often called Rose of Sharon. There are other mallows called Rose of Sharon, as well, adding to the confusion. A synonym to the current name is Althea syriacus, and lots of people have what they call altheas.

Since the Hibiscus syriacus is non-native to North America, we have no information on it in our Native Plant Database. At the Lady Bird Johnson Wildflower Center, we urge the use of plants native to the area in which they are being used, because they are already adapted to the environmental conditions there and thus will require less fertilizer, water and maintenance. However, we have done some research and will try to answer your questions on the leaf spot. This USDA Forest Service website on Rose of Sharon will give you general information on care for the plant as well as pests and diseases. It is hardy in Zones 5 to 8, and Wichita Falls is in Zone 8, according to the USDA Zone Hardiness Map.

Aphids may cover leaves with sticky honeydew. Over-fertilizing increases aphid infestation. However, we believe what you are asking about is bacterial leaf spot; the only treatment we found for that was to pick off and destroy the infected leaves. Don't leave fallen leaves or blooms on the ground as they may harbor the bacteria.

Now, on to your tomato question. Once more, we are talking non-native plant. Most food plants are either non-native to North America or so intensively hybridized that they bear little resemblance to the original form. Tomato, Solanum lycopersicum, is a member of the Solaneaceae or Nightshade family, closely related to tobacco, chili peppers, potao and eggplant. It is native to Central and South America from Mexico to Argentina. With reference to keeping birds out of them, if we could devise a fool-proof method to keep all the little beasties that love tomatoes, too, off of them we would be zillionaires. See this excellent Texas A&M Horticulture site on Tomato Questions. One which addresses your question is quoted below:

"Tomatoes should be supported. Whether you cage or stake them is personal preference. Regardless of the method, plants with foliage and fruit supported off the ground will produce more than unsupported plants. Caging has several advantages. It involves less work than staking. Once the cage is placed over the plant there is no further manipulation of the plant - - no pruning, no tying. The fruit are simply harvested as they ripen. In many areas, staking and pruning of the plant to a single or multiple stem results in sunburn when the developing fruit is exposed to excessive sunlight. Other advantages of caging over staking include protection of fruit from bird damage by more vigorous foliage cover and less fruit rot. Caged tomato vines produce more fruit of a smaller size, but staked and tied plants produce less fruit which mature earlier yet are larger."

 

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