DEAR JESSICA: I enjoyed your article about tropical plants and am very interested in growing hibiscus. I purchased a 4-foot tree in a supermarket about three weeks ago, and it has been blooming profusely. However, I now notice a sticky substance and white powder on its leaves and on the buds. Can you tell me what this is and how I can treat it?
-- Marilyn Parlato, Kings Park
DEAR MARILYN: What you describe sounds like an insect infestation. Look under the leaves for the presence of aphids, which look like small dots. Mealybugs are pink and waxy, and also might be to blame. Or it might be scale, another insect that clings to stems and other green parts of the plant. Aphids and scale don't move, so you might not realize they're insects. If you don't see any of those, check for mites by holding a white piece of paper under the plant and shaking it. If the paper gets specks on it, those are mites.
All of these pests excrete honeydew, the sticky substance you're seeing. This can be life-threatening to the plant, depending on the severity. A black, sooty mold often grows on the honeydew, blocking photosynthesis. It also attracts ants.
Depending on the type of insect, it might be easy to simply rinse them off. Others cling. The best way to eliminate them is to introduce a predator to do the dirty work for you. Ladybugs are sold by the box for just this purpose. A single adult ladybug can eat 1,000 aphids a day. Set them loose in the area, and let them get to work. If you cannot find ladybugs (nurseries and websites tend to run out by late spring), apply Neem oil or horticultural oil as directed on the package.
The white powder you report seeing is likely mildew and isn't necessarily fatal to the plant. But it is unsightly and is the result of excess moisture. Take care to water the soil directly and don't wet the leaves. Also, don't crowd the plant; allow enough room around it for air circulation, and place it in full sun.
To help fight the mildew, you can apply a mixture of 1 tablespoon of baking soda and 21/2 teaspoons of summer oil (available at most nurseries and garden centers), diluted in one gallon of water, on the leaves once a week.
If the white substance you're seeing is more waxy than powdery, then it's likely you're dealing with pink mealybugs, which lay their eggs in sacks of white wax, as depicted in the photo on this page. Cryptolaemus montrouzieri ladybugs are really the only effective defense against them because their waxy coating protects them from any chemical controls.
Being a friend to your lawn
DEAR JESSICA: I've been following your advice about when to fertilize my lawn, and it looks great! When should I use a fungicide? Should I use it before any fungus appears as a prophylactic?
-- Bruce Marcus, Merrick
DEAR BRUCE: If it ain't broke, don't fix it. There is no need to apply fungicide to your grass unless it's already infected. Instead, you should focus on prevention.
The best way to keep fungal and other diseases from plaguing the lawn is to keep it strong and healthy with good practices. Ensure adequate fertility, as you've been doing. Test your soil's pH every couple of years, and apply amendments if levels fall out of the 6.5-7.0 range. Excess moisture encourages the growth of fungi, so avoid overwatering, aiming for about an inch of water per week, including rainfall. Water only early in the morning, which affords an entire day for foliage to dry.
And remember, it's best to water deeply less often than to sprinkle every day. Persistent shade also encourages disease, as it fosters long-lasting moisture. You might consider pruning dense trees to allow more sunlight to reach the lawn, if necessary.
The Great Long Island Tomato Challenge
Challenge veteran Patrick Dean is trying his hand at growing grafted great white tomatoes this year. As of May 13, his outdoor plants were already growing fruit in his West Islip garden.
"Taste will tell, but I can't argue with early growth or flowering," he said. "Granted, I got a back hoe and replaced 4 feet of soil and regenerated my plot, but I'm insane!"
Are you in? The 8th annual Tomato Challenge will be held on Friday, Aug. 22 at 7 p.m. at Newsday headquarters (235 Pinelawn Rd., Melville).
Give your plants plenty of tender loving care all summer long, then bring your biggest, heaviest fruit to the event. I'll weigh your tomatoes personally and crown the 2014 Tomato King or Queen.
In the meantime, send a photo of yourself with your tomato plants and details about how you're growing them, and you might be featured next!