OCTOBER
2008

 

 

 

By
B. Rosie Lerner
 
Purdue
Extension
Consumer Horticulturist

 

 

 

 

 

10-02-08

Question and Answer

Q. Hello, I have 4 hydrangea plants in my yard that are over 5 years old and have never bloomed. Two are in total shade, one is in part shade and the last is in full sun. The plants themselves continually get bigger every year and thrive. I have tried not removing the 'sticks' or 'spines' left at the end of the season, as the plant goes dormant, to see if it would maybe cause the plant to bloom. I don't think there is a problem with the acidity in the soils because I have other acid-loving plants and bush near each plant, and they bloom annually. Please help!

A. Ah, if only I had $1 for every time I was asked this question! There are a number of species of hydrangea, each with their own flowering habits and peculiarities. While most hydrangeas flower best in full sun or partial shade, I suspect you have the bigleaf hydrangea, Hydrangea macrophylla, which traditionally flowers only on old wood. But because this species dies back to the ground each year in our area, the flower buds are also killed. So it rarely flowers in the upper two-thirds of Indiana unless in a very protected location. The plant is root hardy, so it re-grows new foliage, but no blooms. Even in areas where the plants do not die back, it breaks dormancy quite early and then the flower buds are killed in subsequent frosts. One possibility would be to provide winter protection as you would for tender roses, but then you would still have the spring frosts to deal with.

There are a few cultivars of H. macrophylla nowadays that also bloom on new wood, the so called "everblooming" or "remontant" types, such as "Endless Summer," "Blushing Bride," "All Summer Beauty," "Mini Penny" and the "Lets Dance" series. Next year, look for a new rebloomer from Bailey Nurseries called "Twist 'N Shout" with burgundy red stems and fall color.

For more information on bigleaf and other types of hydrangeas, see my article at http://www.hort.purdue.edu/ext/hydrangea.html.

Q. I purchased a Snowbird Hawthorn in 2004. There is hardly a branch on the tree that is not covered with the cedar rust and little round fuzzy ball-like things. I have tried using different kinds of fungus sprays to no avail. A lot of the stems and leaves appear to be dying and have turned completely brown. Do you know of anything short of cutting the tree down that I can do to get rid of this? I was wondering, should cut off all the dead branches and burn them? Would that kill the tree? I really want to save this tree if at all possible.

The nursery where I got the tree from gave me a bottle of "Fung oil," which calls for 3 Tablespoons per gallon of water and spray it on, and also a bottle of "Infuse," which calls for 1/2 teaspoon per gallon of water and spray it on. I was to do this in the spring, when the flowers have opened, and again 10 or so days later. I even sprayed it on at other times, but it hasn't helped one bit. In fact, the rust seems to be getting worse with each passing year. I would appreciate any advice you could give. Thank you.

A. There are two species of Cedar rust that can infect hawthorns: both require two plant species to complete its life cycle. The symptoms on your hawthorn would include small, whisker-like structures that contain rust-colored spores on fruits and young twigs. These spores are blown to susceptible species of Juniper (cedar) and subsequently produce galls that remain dormant until the following spring, when they produce orange, gelatinous horns that release spores that, in turn, infect hawthorns. In addition, Cedar-hawthorn rust causes yellow spots on the foliage, while cedar-quince rust generally does not. Cedar rust is not typically expected to kill the tree, but it can weaken the tree, making it susceptible to other diseases, insects and winter injury that can deal the final blow.

Removing dead branches is appropriate anytime, regardless of the cause, but by itself will not be enough to control the disease, unless you remove the alternate host. But there are many juniper around, so removing just the ones on your property will not likely be effective.

I am not familiar with "Fung oil," but wonder if perhaps the product is the one called "Fungonil," a fungicide containing the active ingredient chlorothalonil. This fungicide is labeled for use on a wide variety of garden plants for control of many different fungal diseases, including cedar rust. Infuse is a systemic fungicide labeled for control of a number of diseases including cedar rust. These fungicides need to be applied to the hawthorn starting around blossom time and reapplied every 10-14 days until the orange horns on the juniper's galls have dried up. (Infuse's label states every 14-21 days). Spraying the junipers is not recommended, but pruning out the juniper galls will reduce the amount of spores that would otherwise infect the hawthorn.

Although the cultivar "Snowbird" was bred for disease resistance, it has not proven to be so and has been noted for disease problems in Michael Dirr's "Manual of Woody Landscape Plants," among other sources. It might be wise to consider a disease-resistant replacement, rather than have to continuously prune and spray to keep this one going.

Take a look at Purdue Extension bulletin BP-138 for more information on cedar rust of landscape plants. The publication is online at http://www.extension.purdue.edu/extmedia/BP/BP-138-W.pdf.

 

Writer: B. Rosie Lerner
Editor: Olivia Maddox,