Q. What is the dark round parasite on the undersides of the leaves my Rose of Sharon? It’s just starting to bloom with beautiful pink flowers, so I hate to cut it down, but the leaves are really grossing me out. What can I do to save the plant?
A. The dark brown raised structures on the undersides of the leaves is not a parasite or bug. It is a fungus called Rust. Rust can be a problem on a variety of hosts. On roses, and turf, it’s a bright orange color. Typically, the dark reddish-brown type is found on Snapdragons and Hollyhocks; however, it will infect Rose of Sharon, Flowering Maples, and Mallows. Rust is an air bore disease that infects only when the right conditions are present. The fungi spread from plant to plant or area to area mostly by the wind; however, insects, rain, and animals may help spread the problem. While the spores are circulating, they’re dormant. It takes moisture on the foliage of a host plant at night to germinate the spores along with mild temperatures. Usually, three to four hours is sufficient. With some plants overhead watering late in the afternoon can be problematical, but I don’ t think this was the case with your plant. The trigger here was the wet condition we had in May. The fungus always shows up after the fact. You could apply a fungicide, but I probably would do nothing. The rainy season is over for the year, so the dry conditions limit the infection. I’d pick off the worst of the infected leaves and feed it with all-purpose plant food to encourage the new growth. Besides, remove any of the debris that may have fallen at the base of the plant.
Note: Rose of Sharon or Hibiscus syriacus is a widely cultivated deciduous ornamental shrub. It’s native to Asia and is the national flower for South Korea. But it is often mistakenly thought of as a biblical plant. The biblical reference is for a different plant, Pancratium maritimum, which blooms in the late summer on the ‘Sharon Plain’ on the coast of the Mediterranean Sea just above the waterline.
Q. I’ve been told that I planted my Bok Choy seeds a little too late this year. They are just over an inch tall right now. Will I have any luck with them or should I replant in the fall?
A. I wouldn’t give up on them just yet. The odds of them reaching maturity is not very good with the long days. Bok Chop is a cool-season, short day oriental vegetable. With mild conditions along the coast, you’ll be okay; however, with warm temperatures inland, they’ll go to seed or ‘Bolt.’ Bolting is a survival mechanism in annual plants. When the growing conditions are unfavorable, they’ll produce the next generation, seeds, prematurely as quickly as possible. This also occurs at the end of their normal life cycle.
Q. What could be easier than growing radishes? My recent crop sprouted within two weeks, and now they are flowering! The foliage is very lush with tall stems, but the radishes are tiny and thin. I’ve never had this happen before. What do you think is the problem? Were the seeds planted too shallow or too deep, is there too much Nitrogen in the soil?
A. Lush top growth with little or no root development is the typical growth pattern with radishes, carrots, and other root crops from too much Nitrogen. Nitrogen stimulates the top growth. The plants grow rapidly at the expense of the underground plant parts with short-term crops. The excessive Nitrogen occurs from commercial fertilizers, animal manures, and from blended, soil amendments used as organic matter. Of the three, the soil amendments are the least problematical. With clay soils, they are critical for drainage and to help with soil compaction. For a ten by ten area or one hundred square feet, two cubic feet of animal manure and five pounds of Vegetable Food plus the soil amendment is sufficient. Many times the area is underestimated while the nutrients are over-applied. It’s the ‘if a little is good then a lot more is even better,’ rational. Superphosphate is often substituted for Vegetable Food, where root crops are to be planted. Superphosphate has no nitrogen but plenty of phosphorus for root development that is the edible portion of the plant. This situation is easily corrected by adjusting the Nitrogen-based nutrients at the time of planting. Nitrogen is a mobile element, so it leaches out of the soil over time. I wouldn’t hesitate to plant a new crop of radishes right away, but I wouldn’t add any more nutrients. I would cultivate the soil and may add more amendments before sowing the seed.
