Fungus and sod webworms are summer problems
Q: For the past three years, I have had healthy and robust ruellias. The plants are virtually indestructible and easy to grow and maintain. However, over the past few months each has suddenly developed a white fungus on the leaves. The fungus has not affected any other types of vegetation in the immediate area. The plants are in sunny areas, well-ventilated and have never shown any kind of distress before. What causes this fungus, and what can be done to abate its growth? I have extensively trimmed each plant back, gathered up and tossed out the clippings, and they have no problem growing back again with healthy leaves. Then the fungus reappears. Gary Gano, Houston
A: Powdery mildew could be the problem; however, since sun and good air circulation do help discourage this fungal problem, I’m curious why it would appear on your plants. Avoid overhead watering. If you determine powdery mildew is the culprit, applications of neem will provide control.
Other options: Apply a fungicidal soap spray with sulfur. Or spray plants weekly with a baking-soda solution of 1 teaspoon per 2 quarts of water.
If you see white woolly patches/felty growth on plant leaves, perhaps it is mite damage. Examine the leaves carefully with a magnifying glass or microscope to identify the tiny creatures. Or take damaged leaves in a sealed bag to a nurseryman for identification. A horticultural oil can help with control.
Q: I have a hydrangea I will transplant from a pot to the flower bed. Unfortunately, some of the leaves are turning black although the plant has fresh leaves. Elenor Crixell, Houston
A: This may be a water-related problem. Black or brown leaf margins can be a sign of too much water. Black spots are an indication of a moisture-encouraged fungal problem.
Perhaps the abundant rain we have had has encouraged fungal spots on the leaves. Overhead watering also promotes leaf spots, so avoid watering the foliage when possible.
Since you see healthy new foliage, your shrub likely will recover. Remove any fallen infected leaves to prevent fungus from lingering.
Hydrangeas like water, especially during the hot, dry summer. But good drainage is a must. The shrubs like some sun for good blooms; however, avoid the hottest direct sun to prevent leaf scorch. Plant in a well-draining area with morning sun and afternoon shade or filtered sunlight.
Neem is one organic treatment for black spots on hydrangeas or the familiar small brown-purple spots that grow and develop tan/gray centers with purplish edges.
Pruning turk’s cap
Gardeners recently have asked how to prune turk’s cap, a hummingbird favorite.
This is a personal decision. I prune my turk’s cap to control the gangly look. So for a natural, loose look, prune the longer branches to neaten the appearance a bit.
Large shrubs often can be pruned up like small trees. As the larger trunks gain height, the lower side branches are removed to reveal the trunks, and you create a more treelike canopy.
Sod webworms
There are various active sod webworm species going about their summer work. If you spot moths hovering over your lawn, or if they fly up when you walk across the grass, you may see their handiwork — patchy brown areas with chewed blades in your turf — in the days/weeks ahead.
Depending on the species, the moths may be white to gray or the dingy-brown tropical sod webworm that’s plagued Houston-area lawns in recent years.
There can be multiple generations of sod webworms during the warm months, and we often see the early rounds this time of year.
The moths fly over a lawn, depositing scores of eggs that hatch into larvae/caterpillars. These caterpillars set up homes in silken tunnels built in the thatch of the grass. The night feeding creatures chew off pieces of grass and return to the small tunnel to eat. You may see the silky tunnel threads in early morning.
To test for sod webworms, soak an area of the lawn with a highly diluted soap solution. They should rise to the surface. Ask your nurseryman for pest identification.
To control the caterpillars, spray the biological pesticide Bt (Bacillus thuringiensis) according to label instructions. Be careful; avoid spraying butterfly plants.
Spinosad, another biological treatment, also is effective. And beneficial nematodes can help control sod webworms.
Texas A&M University experts say webworms prefer sunny, hot, dry lawn areas, so water these deeply as needed. Cut the grass high during hot, dry periods. Gather the clippings during infestation as the moths lay their eggs on the grass.
It’s beneficial to rake up dead grass and thatch. After the next mowing, rake again. Since the webworms don’t eat grass roots, new green blades may reappear, especially in wellmaintained lawns.