Allen Owings, research coordinator of the LSU AgCenter Hammond Research Station, discusses ornamentals being grown in trials at the Margie Jenkins Azalea Garden horticulture lecture series and industry open house on May 15. Photo by Olivia McClure/LSU AgCenter

Plants with Potential, which are unfamiliar ornamental plants, sit on display at the Margie Jenkins Azalea Garden horticulture lecture series and industry open house on May 15. Photo by Olivia McClure/LSU AgCenter

Jason Stagg, instructor at the LSU AgCenter Hammond Research Station, tells attendees about Plants with Potential at the Margie Jenkins Azalea Garden horticulture lecture series and industry open house on May 15. Photo by Olivia McClure/LSU AgCenter

News Release Distributed 05/18/15

HAMMOND, La. – Many Louisianians have watched dogwoods gradually disappear from the landscape in recent years. While environmental factors are partially to blame, some gardening mistakes can also hinder dogwood health, said Mark Windham, professor in the University of Tennessee’s Department of Entomology and Plant Pathology.

Windham’s discussion of dogwood, rose and hydrangea health highlighted the Margie Jenkins Azalea Garden horticulture lecture series and industry open house on May 15. The event is held annually at the LSU AgCenter Hammond Research Station in recognition of Margie Jenkins, a longtime Louisiana nursery owner. The azalea garden at the station was named for her in 2006.

Dogwoods were once common along the I-10/I-12 corridor, but that range has been shrinking northward since 1995, Windham said. The heat in the South combined with an uptick in cases of powdery mildew and clearwing moth infestations led to many trees’ demise.

It is difficult to spray dogwoods with fungicides to get rid of powdery mildew, Windham said. But resistant varieties such as Cherokee Brave and the Appalachian series are available.

“Healthy dogwood foliage looks like a highly polished car,” he said. “If it looks dull, that’s powdery mildew.”

As for clearwing moths, future infestations of larvae can be prevented by avoiding tree wounds, Windham said. Place mulch around trees and don’t get too close to them with lawnmowers or string trimmers.

Spot anthracnose causes reddish spots on dogwood flowers in spring and summer but does little harm to the tree’s health. Windham recommends just dealing with it. Spot anthracnose usually does not return the following year.

A host of other issues with dogwoods can be avoided with proper transplanting. Choose a location where the dogwood won’t have “wet feet,” Windham said, and plant it so that the top of the root remains visible. Dogwoods have soft bark, so too much soil around the trunk will cause it to rot.

Roses in the South have been facing two diseases – black spot and Cercospora leaf spot – that look similar and are controlled by the same fungicides. The likelihood of black spot can be reduced by irrigating between 10 p.m. and 10 a.m. to avoid extending the wetness period caused by dew, Windham said. Cercospora likes hot, humid weather and is more prevalent in wet years, which 2015 is shaping up to be.

Hydrangeas benefit from careful selection of their location. Full sun can essentially burn them and is ideal for Cercospora and spot anthracnose, Windham said. Too much shade can increase the chances of powdery mildew.

“Just because your auntie or grandma grew a hydrangea at their house and it looked great does not mean you can if your environment is different,” Windham said.

It is also important not to incorrectly prune, over-fertilize or over-irrigate hydrangeas, he said.

Rick Webb, owner of the Louisiana Growers nursery in Amite, talked about native plants and their value in Louisiana landscapes. In Louisiana, many underappreciated and underused natives are available, such as switchgrass, little bluestem, irises, seashore mallow and pickerelweed.

Though Louisianians are accustomed to seeing some of those plants along roadsides and in ditches, they still offer something special in gardens.

“It’s about what these things do for us, what they do for our environment, what they do for the things we live around,” Webb said. “Natives remind us of our place. It’s a sense of where you’re from when you have the elements of the world around you.”

Pawpaw is a good example, he said. Those trees offer edible fruit for people and wildlife, an attractive, manageable shape and beautiful gold foliage in the fall.

Allen Owings, research coordinator at the Hammond Research Station, gave a tour of the Sun Garden, which is used for evaluations of both annual and perennial flowers as well as woody ornamentals. Some current selections are Louisiana Super Plants, including the BabyWing begonia, Mesa series gaillardia and Tutti Fruitti buddleia.

Jason Stagg, instructor at the station, told attendees about a new program called Plants with Potential, which is designed to introduce unfamiliar but good-performing ornamental plants to the nursery and landscape industry. Ten Plants with Potential being grown at the station for distribution to area growers for trials are:

– Kapioloni Bronze copper plant

– Masaica copper plant

– Barbara Rogers begonia

– Aureoreticulata iresine

– Belle Starr Gold lantana

– Mary Helen geranium

– Nova pentas

– Florida dwarf rose purslane

– Silke’s Dream salvia

– Trailing yellow turnera