Q: My hosta leaves have a strange pattern on them, and after looking around on the Internet, I wonder if the problem is from foliar nematodes. The veins are browning, like short stripes, with yellow areas in between the veins. The rest of the leaf area is green. Only a few plants have this pattern, but I’m worried it may spread and kill my other hostas.
A: The problem you describe (and the accompanying sample) does indeed point to foliar nematodes. Hosta, fern, peony, brunnera, lily, Solomon’s seal and strawberry are other common hosts of foliar nematodes. These pests are found in the leaves, crown and stems of plants, and while they can cause significant damage to the leaves, they rarely cause the death of plants.
Plant parasitic nematodes are microscopic, segmented round worms which are very hard to control. On hostas and other plants with parallel leaf veins, the symptoms show up as patterns that run along the leaf length, in between the veins. On brunnera or anemone (and other plants with branching veins), the symptoms show up as angular splotches between leaf veins.
Nematodes depend on a film of water to spread from plant to plant, entering leaf tissue through the stomata (gas-exchanging pores on the leaf). Nematodes find it difficult to cross vein tissue, so they exit the leaf and re-enter through nearby openings, provided a film of water is present.
After this summer’s frequent rains, the nematodes have found many films of water to spread from place to place and plant to plant. Inside the leaves, female nematodes can lay up to 30 eggs, which hatch in about 10 days.
To manage foliar nematode populations, thoroughly remove and destroy all infected plant debris in the fall. No chemicals are available to control nematodes in the home landscape.
Q: I planted a magnolia this spring, and it bloomed beautifully. Now I notice a black discoloration on the stems as well as on the mulch under the stems. What might be causing this?
A: Magnolia scale is an insect with a piercing-sucking mouthpart that removes plant sap from its host, in this case magnolia trees. When the scale insect processes the sap, much of the sugar is excreted as “honey dew.” Sooty mold is a harmless fungus that grows on this sugary excrement. This is the black discoloration you see on and under your tree.
Most adult scale insects can resist contact insecticides because their bodies are coated with a waxy covering. They are vulnerable, however, after the eggs hatch out into the crawler stage. These crawler insects are very easy to kill with insecticidal soaps and horticultural oils, or synthetic pesticides. Crawlers can even be dislodged with a sharp jet of water (or a gloved hand).
Magnolia scale crawlers are active now, so treat infested trees in the coming week to 10 days to manage this pest. Over time, scale insects can significantly weaken trees, causing branch die-back and even tree death.
Q: I’ve noticed several huge wasps around my patio, digging into the soil. When I get close to them, they behave aggressively, and I’m worried someone will be stung if I don’t get rid of them. They must be 2” long! What are they?
A: In late summer, we typically get several questions concerning this interesting wasp, the cicada killer. These large solitary wasps have black bodies and white or yellow markings on the abdomen.
The female constructs a nest in the ground, often preferring sandy soils. As any loving mother would, she provides only the best food for her young, in this case cicadas. She stings cicadas to paralyze them, then drags them to the nesting area and lays an egg inside the cicada.
While each wasp constructs only one burrow, several wasps may be attracted to a site, particularly if the soil is very sandy.
Male wasps are extremely territorial, and will behave aggressively toward anyone getting close to a nesting area. The males can’t sting, since female wasps sting with their egg-laying appendage, but they make up for their impotence with attitude.
Unless the cicada killers are a great nuisance, they should be left alone. Changing the soil environment may help discourage the wasps from nesting in the same location next year. Consider adding compost to the bed, and mulching with several inches of good-quality bark mulch. In rare cases, an insecticidal dust may be used to destroy existing wasps.
Denise Ellsworth directs the honeybee and native pollinator education program for Ohio State University. If you have questions about caring for your garden, contact her at 330-263-3700 or click on the Ask Denise link on her blog at www.osugarden.com.