AUGUST
2012

 

 

 

By
B. Rosie Lerner
 
Purdue
Extension
Consumer Horticulturist

 

Check out Rosie's book:Possum in the Pawpaw Tree

 

 

 

08-09-12

Question and Answer


Q. I had wanted hollyhocks for a long time. Finally I got some. The first year, they grew tall and strong and had nice blooms. The next year, it was more of the same except that I did notice that some leaves had some brown spots on them, which I promptly forgot about. This year - UGH! All of the various plants are infected with brown bumps on the backs of the leaves. The leaves die, and the disease travels further and further up the plant. Soon, there are no green leaves, and the whole plant looks dead. I know this has been an extreme summer, and I have not been watering, so that might even have something to do with the dead plants. I have been looking at others' plants and see that at least some people are having the same problem. I also noticed that one small plant, just coming up, had the "stuff" on its leaves. So, I need to know what to do: spray, pull them all up and start over, or use the seeds? - MH, Columbus, Ind.

A. Hollyhocks are susceptible to a number of different leaf-spot diseases, but, by far, the most common and destructive is known as rust. This fungus begins by causing tiny pinhead-sized brown spots on the undersides of the leaves. At the same time, the top of the leaf shows a larger yellow-to-orange-to-tan spot. Eventually, the spots enlarge and join together, as the disease spreads to the stems and even to the green parts of flowers. The leaves then shrivel and turn brown, giving the plants a blighted appearance. You can see photos and a brief discussion, courtesy of the Purdue Plant and Pest Diagnostic Lab.
     
The disease especially favors damp and/or humid weather. As dry as it has been, you would think it would be less of a problem this year. Gardens that have been watered regularly provide ideal conditions for this disease to infect, but morning dew and/or high humidity can also provide enough moisture for infection. Fungal spores are produced in the brown-raised spots on the lower leaf surface and overwinter in plant debris. Removing infected leaves promptly and cleaning up all plant residue at the end of the growing season is critical to reducing the spread of the disease.

Some fungicides that contain chlorothalonil, mancozeb or sulfur are labeled for use in controlling hollyhock rust. However, keep in mind that fungicides are preventative, not curative. They can only protect healthy foliage from becoming infected. If the plant is heavily diseased, it is too late to apply fungicides. Always consult the label for recommended rates and safety information before you apply.

June's Mystery Plant
In my June column, a reader sent the following question and photo:

Q. Enclosed are photos of my mystery plant. What is it? The local nursery did not know it. They guessed maybe a tropical, because of the look of the trunk. The plant started as a volunteer seedling among my plants with begonias. Can you shed some light on what the plant is?

papaya plant

The following answer was submitted:

A. The mystery plant photo submitted by the Columbus, Ind. resident appears to be a papaya plant. We are growing some papaya plants, and the leaves look identical. - Don & Connie, French Lick, Ind.

You are the winner! I agree that papaya is the more likely identity of the mystery plant. Compare the mystery photo to the papaya, courtesy of the National Junior Horticulture Association. Thank you for writing!

 

Writer: B. Rosie Lerner
Editor: Olivia Maddox,