Question
My marigolds that were once thriving are now totally dying. they are in pots but outside in a flower bed. first they stopped flowering. there were still buds but they never bloomed. if they did it was just barely and they looked wrong. now the leaves are all wilted and the whole plant is turning brown from the bottom up. i pulled one of them and the roots look fine. no bugs or mold or anything like that. i split open a stem and besides looking kinda empty, there was no discoloration or slime or bugs. my dahlia's are also drying out. they stopped flowering a long time ago but the leaves were still healthy. then all of a sudden it looked like they hadn't been watered in months. which is not the case. their leaves are also being eaten i think. how do you keep slugs away. i have no problems using chemicals at this point. there are other flowers,in pots and planted, in the same flower bed and they seem to be fine. i used to be so proud of my marigolds. can they be saved?

Answer
Hi Willow,

I am afraid that your marigolds and dahlias have typical symptoms of Southern bacterial wilt, caused by _Ralstonia solanacearum_, a widespread and destructive disease of numerous crops in the warm climates. It is a major disease of tobacco, tomato, potato, dahlia, geranium, hollyhock, hydrangea, marigold, nasturtium, zinnia and others. Bacterial wilt is the most frequent disease problem of marigolds.

Infected plants may become stunted with foliage light green to chlorotic (yellow) or grey green in color. The upper foliage may wilt slightly in the early stages of the disease but the plant rapidly wilts completely. Diseased plants often die within 7-14 days after the first symptoms are observed. Discoloration (necrosis) of the plant usually begins not in the roots, but rather near the soil level, so upon examination of the roots, typical root rot is not found.  

Southern bacterial wilt is a difficult disease to control. There are no chemicals that provide effective control before or after planting. The only control is to avoid susceptible plants or to grow resistant cultivars. The following marigold cultivars are resistant to bacterial wilt: Cupid; Irish Lace; Papaya Crush; Pineapple Crush; Pumpkin Crush; Rusty Red; Sparky; Sparky Mix; Bonanza Yellow; Choice Mix; Copper Canyon; Cupid Mix; Fort Knox; Golden Harmony; Goldie; Gypsy Dancer; Naughty Marietta; Orange Lady; Senator Dirksen; and Tangerine Gem.

If it is necessary to grow a susceptible cultivar in an area where the disease has been a problem in the past, plant the susceptible cultivar in another part of the area or plant them in new soil or a soil-less media in planter boxes.

I have not been able to find any information about dahlia cultivars that are resistant to Southern bacterial wilt.

At this point, it is wise to destroy (burn if possible) the diseased plants and try to minimize disease on other host plants.  _Ralstonia solanacearum_ has a broad host range which includes many plant families.

As far as slug problems, there are many ways to minimize slug-related problems.  First, try to reduce the size of the slug population by not providing good "homes" for them.  Being active primarily at night, they prefer moist, dark places (under boards, flower pots, etc.) which provide them protection from the sun.  If you can minimize the number of places they can "hide", you will have fewer problems.

Many gardeners have effectively used diatomaceous earth, the remains of exo-skeletons of small algae, as a physical barrier around flower pots, planter boxes, and such.  When the slugs crawl over this jagged, silica particles, the tissues are cut, and the slug dries out.  Others have placed a 1/2 inch of stale beer in a plant saucer overnight near the slug infestation; the beer attracts the slugs, and once in the beer, the slugs cannot get out.  There are slug bait available at the garden centers if you have a very large infestation.


Good Luck and Good Gardening!

John