Even though the calendar reads June, the adverse weather of May continues to plague the garden. Ordinarily, the days following Memorial Day mark the arrival of warm temperatures in the nation's capital, but no transition marked the past week. Unseasonably cool temperatures and off-and-on showers this past week intensified some of the lingering problems and delayed the onset of others.
Ordinarily, host shrubs and plants would be swimming with spider mites this first weekend of June, but cool, damp weather has held the population down to a minimum. However, with the expected arrival of hot weather, the mite population will explode. You should be prepared to deal with them.
The first of three generations of invisible lacebugs has already taken up residence on azaleas, pieris japonicas and rhododendrons, but again, cool, damp weather has kept the population in check. Leaf damage thus far has been minuscule.
However, May weather simply aggravated other problems, not the least of which were black vine weevil damage to rhododendrons, serious outbreaks of leaf blight on rhododendrons, on-time sprouting of yellow nutsedge weeds in the past week and an outbreak of brown patch disease on sunny lawns.
First, brace yourself for spider mites, basically European red mites on trees, spruce spider mites on evergreens and two-spotted spider mites on bedding plants. In all cases, you're looking at an invisible problem because mites can't be seen with the naked eye. Put a 10- or 20-power magnifying glass on a host plant and the mites are apparent; under a microscope, mites are almost prehistoric in appearance. They are so tiny that it takes 60 of them, placed end to end, to extend an inch.
As many as eight to 10 broods of mites are possible from now through late September during hot, dry weather. Mites generally feed on the bottom of foliage, siphoning off sugar from leaves and needles alike. Symptoms of mite feeding appear slowly, as much as three weeks after damage begins. Foliage slowly goes off color, from green to pale green to yellow and brown. Often, a bronze color separates the cycle from yellow to brown. Every outdoor plant is susceptible. If you have witnessed the death of a five-foot evergreen over one summer, know that mites were responsible. We let nature take its course with a four-foot dwarf Alberta spruce last summer, and mites destroyed the evergreen in only six weeks.
Organic controls do not work. We tried banana skins on the Alberta spruce last summer as an organic deterrent, but the bananas offered no resistance. Plain old Windex window washer works, but repeat sprays do not.
No matter what controls you try, keep records of what you use and when. Don't use the same product consecutively. Always rotate from one product to another, and stick to the timetables. Spray when no rain is in the forecast for 24 hours and when air temperatures are below 80 degrees. The best time to spray is in the evening when the foliage or needles will stay wet for the longest possible time. When foliage or needles dry, absorption stops.
Your best controls are Cygon and Orthene, occasionally making a spray of Kelthane to interrupt the alternating cycle of the previous products. Cygon and Orthene are systemics -- moving from leaf to leaf, providing protection throughout the entire plant -- while Kelthane works only on contact. The best method of application is with the hand-pump sprayer, but you should use the hose-end sprayer if you have dozens of shrubs and plants to protect.
Next, there are lacebugs. Also invisible to the naked eye, lacebugs are mostly attracted to azaleas, andromedas and rhododendrons. Washington has three generations: early to mid-June, late July and mid-September. Thankfully, some gardens never come under lacebug siege, but others see the pests without fail every year. The best controls are Cygon and Orthene because they are systemics. Spray June 16-17, July 14-22 and Sept. 8-9 for total lacebug control, always at night and after checking the weather forecast for rain.
Two weeks ago, we warned readers to check for sandwich-style bites on rhododendron leaves, but it appears as though few gardeners heeded the advice. We remind you again that record weevil populations are likely next year unless you control the adults now, before the July mating cycle begins. After that, the babies -- grubs of the black vine weevil -- will feed on rhododendron roots through the summer, weakening the shrub in the process. Flower buds produced in late August and September are likely to be fewer than in recent years.
Weevils climb over the plant only at night, spending the day in the top inch or two of soil under the plant canopy. Using liquid Orthene (1 1/2 ounces per gallon of water), sprinkle the solution over the soil in late afternoon or early evening, making sure that no rain is to follow. This soaking of the upper soil should control adult weevils quickly, but a second sprinkling a week later will catch any weevils missed on the first turn. This stops July mating as well as a new brood of weevils next year.
Rhododendrons should also be checked now for symptoms of a ravaging disease that decimates these shrubs. Look for brown leaves that are rolled-up like cigar wrapping. If you find any, take your pruning shears, go down to the base of that cane and prune it away. After this, disinfect the pruning shears by washing the cutting blades with a solution of one part chlorine bleach to five parts of water.
The disease, phytophthora, is in the soil, often arriving from contaminated soil on the rhododendron when it was planted. After entering the roots, spores travel up the cane, then reverse their path and destroy cells as the disease travels downward.
By pruning infected canes, you can eliminate the disease in the rhododendron, but you can only destroy the spores in the soil by a soaking application of Aliette or Subdue 2E, both costly. If you have lost a rhododendron in recent years, assume the reason to be this disease. Don't plant another rhododendron in this contaminated soil unless you soak the soil with Aliette or Subdue. One treatment usually kills any lingering spores in the soil.
If you find spotted leaves on your rhododendrons, blame May weather. Pick off badly spotted leaves, then plan on spraying the good foliage with Daconil (available as Ortho Multi-Purpose Fungicide). A small container of a commercial sticker-spreader product should be added to the Daconil spray; the spray will stick to the waxy leaves of the rhododendrons instead of running off as normally would happen.
Incidentally, major leaf damage in the form of bay spots won't occur on the rhododendrons until early August when rust returns to the shrubs. In late July, make a preventative spray to the foliage to kill rust spores blowing from any nearby hemlocks.
On a happy note, you can move most indoor plants outdoors this weekend. Plants will respond quickly to increased light as well as tropical humidity at night. If you maintain routine feedings through the summer, plants will grow substantially and will be better prepared to survive the winter indoors.
Plants taking full, direct sunlight include fruiting figs, gardenias and lantanas, but most houseplants require dense shade for the summer.
Among the shade-loving plants are Norfolk Island pines, weeping figs (ficus benjamina), scheffleras or Australian umbrella trees, palms, rubber trees (ficus decora), jade (crassula), holiday cactus (Christmas and Thanksgiving cactus), dracaena, poinsettias and fuchsias.
In all cases, plants should remain in their pots or containers, not transplanted to outdoor soil.
With gardenias, dig a hole two inches deeper and wider than the pot. Lay down an inch of stones at the base of the hole, move the pot to the hole and surround the cavity around the outer wall of the pot with stones. Scatter pine bark chips over the top of the pot. Keep the soil lightly moist, feeding every week with Peters's 17-6-6. You will enjoy flowers over the summer. Jack Eden is the host of "Over the Garden Fence" Sundays from 10 a.m. to 1 p.m. on WTOP Radio (1500 AM).