This deadly disease causes stems to become mushy and rotted. Stem and tuber rot Rhizoctonia solani Thanatephorus cucumeris [teleomorph] Cottony stem rot Sclerotinia sclerotiorum: Vascular wilt Fusarium oxysporum Verticillium albo-atrum. 2. The infection causes pith to blacken and rot with an … You didn't mention what area of the country you're in but I'm wondering if you've had a lot of rain followed by excessive heat. Could be rot (fungal disease), but I suspect thrips. Most dahlia varieties should form roots within 10-14 days when the proper environmental conditions are provided. Symptom: Cuttings turn black and rot at the soil line. Bacterial Diseases. Viral diseases – Viruses are often transmitted by thrips, which burrow deep into the stems and buds. This helps to cure them and to prevent rot during storage. It might re-sprout. Stem rot – Dahlias planted in poorly drained, soggy soil are highly susceptible to stem rot. After your tubers have dried, cut back the rest of the dahlia stem with pruners or a sharp knife. Viral diseases; Mosaic Cucumber mosaic virus: Dahlia mosaic virus Tomato spotted wilt virus: Ringspot Impatiens necrotic spot virus: References. Root and stem rot is not an uncommon problem, nor is it the end of the world. If a dahlia gets infected during the growing season, overwintered tubers can carry that bacteria on to the next year. Choose a location – either indoors or out – that won’t dip below freezing, has good air circulation, and indirect sunlight. If it were mine I'd dig down to see if the tuber was rotted. 1. Below is a list of some of the problems that might be encountered while taking dahlia cuttings. A dahlia succumbing to bacterial stem rot. Treating, controlling, and preventing root rot can be an arduous process, but anything worthwhile takes a bit of blood, sweat, and tears. Bacterial wilt - this makes the stem droop. These nuisances feed on bud tips, flowers and leaves and then, left unchecked, burrow down inside the dahlia stem. Viral diseases. If not, I'd trim any sign of rot around the stem area and replant it. Dahlia diseases and what to look for. 1. Stems that are affected will be wet and subject to rot. Bacteriosis – if the stem is brown and soft, this can be the cause. This causes the plants to wilt. Welcome to the dahlia forum! However, now that the problem has been identified, it’s time to work on a solution. To treat borer attacks, spray BT (Bacillus thuringiensis) on the dahlia foliage when the worms are feeding. Typically, bacteria enters plants through a wound or natural opening. Look for small holes in the underside of the bud; thrips chew in and eat the inside of the bud killing the flower and not allowing it to open (what you see as rot is a symptom and not the problem). Bacterial diseases are difficult for a home gardener to diagnose.