Azaleas & Rhododendrons:
What's Been Eating My Poor Azaleas??!!
Q. Love listening to your show on Saturdays! I planted some light violet-flowered Azalea bushes last spring. All was going well until I noticed small silvery dots that seem to go deep into the tops of the leaves, and black dots (bug poop?) that can be wiped off with light finger pressure on the bottoms. I also noticed an insect on the stems; half as big as a house fly, with translucent wings. Can you tell me what these bugs are? Are they causing the leaf damage? What's the best way to keep them off the plants? (I was using my garden hose to physically blast them off.) They disappeared when the cold weather settled in, but I'm worried that they'll return next year. Help!
----Don Hatosy; (live near Nazareth, PA; work in Joisey)
A. Well, a disease called "leaf spot" causes silvery-gray discoloration on the tops of leaves AND black dots (the "fruiting pustules" of the fungus). If your dots are only in the center of the discolored areas, prune out and trash the diseased parts, and then follow my basic azalea advice.
But more likely that bug is doing the damage. The Rhododendron Lace Bug (azaleas ARE rhododendrons) is a lacy-winged sap-sucker that causes whitish discoloration on the tops of leaves, and yes, does deposit black bug poop on the undersides. ("Frass" is the preferred term for bug poop, by the way, and a great word to know. You can tell somebody "you're full of frass!" and get away with it, unless they're an entomologist...)
Anywho, if they are lace bugs, they WILL be back. In fact they never left! If you look closely, you should see a "protective cone-like cap" overtop of where the winged adults laid eggs on the undersides of the leaves, and little spikes of plant sap that oozed out of the injured areas. You can spray a light horticultural oil on those leaves to try and smother the eggs, but you'd be better off pruning out and destroying the infested parts instead.
Come Spring, check the undersides of the leaves for the 'nymph' form of this pest, a wingless, spiny insect that walks sideways, like crabs and drunks. Blast 'em off with sharp sprays of water or squish 'em personal-like, by sliding the leaves betwixt your thumb and forefinger. Spraying the undersides of the leaves with insecticidal soap kills nymphs and adults. (Spray late in the day, then rinse the plant off with water early the next morning, before the sun can hit the sprayed leaves.)
The Best Defense: Healthy Plants!
But the REAL answer is to grow those puppies in the conditions they require. While it's true of all plants, it's TRIPLY true for azaleas: Keep them happy, and you won't be plagued by pests or pestilence. Treat them wrong, and bad bugs and blights will barge in like politicians to a payoff.
Their soil should drain well, and it MUST be acidic, a pH between 5 and 6 (if it tests higher than that, add sulfur or mulch the plants with pine needles or shredded oak leaves). Azaleas love a rich soil, but can't stand harsh chemical fertilizers, so top-dress them with a gentle organic plant food like Holly-Tone (which also acidifies the soil) or, even better, an inch of compost, right after they finish blooming. They need to grow in 'filtered' or 'dappled' sunlight (which in English means 'partial shade'); they can't take full sun. AND their roots practically grow ON the surface, so they MUST be heavily mulched, four inches deep is not extreme, to prevent the thirsty plants from drying out.