Control of Rhizoctonia Stem Rot in Propagation

Sanitation, sanitation, sanitation! As mentioned above strict sanitation to eliminate sources of Rhizoctonia from the propagation house is needed. Whether cuttings are taken from stock plants on site or brought in, care should be exercised to avoid contact of cuttings with a contaminated surface such as the ground, dirty bench or other non-disinfected surface. Since Rhizoctonia stem rot develops so quickly under favorable conditions, growers may be well advised to include a preventative fungicide treatment program in their crop production plans. Several fungicides are available for control of stem rot (see: Disease Management Strategies Table). Our research has shown that soaking dry rooting cubes in fungicide solution is an effective way to apply fungicide that uses about 50% of the fungicide volume needed when cuttings are sprayed with fungicide.

Recommended management strategies for poinsettia diseases.

Disease

Management Strategy

Bacterial Canker (Corynebacterium poinsettiae)

No fungicide controls available. Destroy all infected plant material.

Bacterial Soft Rot (Erwinia carotovora)

The bacterium is efficient at surviving on living plant surfaces without causing any disease problems. The primary control for bacterial soft rot is proper misting of cuttings and keeping greenhouse temperatures under 90^°F as much as possible. Apply a disinfectant to tools and propagation benches.

Botrytis

(Botrytis cinerea)

1. Good spacing;
2. Good air movement;
3. Minimize wounding and bruising;
4. Do not water overhead;
5. Watch temperature and watering carefully to avoid stress;
6. Use fungicide sprays or fumigants (Chipco 26019, Ornalin 50 WP [do not apply to bracts], or Exotherm Termil).

Phytophthora

1. Disinfect all growing surfaces;
2. Rouge infected plants;
3. Avoid high soluble salts in the root substrate (>3.0 mS/cm);
4. Use fungicides (Banrot 40 WP, Lesan 35 WP, Subdue 2E, Truban 25 EC, or Truban 30 WP)

Powdery Mildew

1. Good air movement to keep the foliage dry;
2. Good spacing to promote good air movement between the plants;
3. Scout for powdery mildew;
4. Rouge plants if only a few are infected;
5. Only use fungicides if mildew is found! (Avoid applications to bracts. Leaf burn possible. Captan 50 WP, Cleary’s 3336, Domain, Phyton 27, or Zyban WP)

Pythium

1. Disinfect all growing surfaces;
2. Rouge infected plants;
3. Avoid high soluble salts in the root substrate (>3.0 mS/cm);
4. Use fungicides (Banrot 40 WP, Lesan 35 WP, Subdue 2E, Truban 25 EC, or Truban 30 WP)

Rhizoctonia

1. Sanitation;
2. Use fungicides (Banrot 40 WP, Chipco 26019, Cleary’s 3336, or Domain)

Thielaviopsis (Black Root Rot)

1. Sanitation;
2. Avoid cool soil temperatures (55 to 60^°F)
3. Use fungicide drenches (Banrot 40 WP, Cleary’s 3336, or Domain)