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How to Manage Pests
UC Pest Management Guidelines
Carrot
Cottony Soft Rot
Pathogen: Sclerotinia sclerotiorum
(Reviewed 1/09,
updated 1/09)
In this Guideline:
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Sclerotinia infection
may occur at any stage of growth, and extensive root decay may occur before
symptoms of wilt and collapse appear on the upper part of the plant. Infection
is always accompanied by a characteristic cottony, white mycelium that appears
on the surface of the infected tissues. On or inside the white mycelium appear
black, round-to-irregular-shaped structures (sclerotia), which are about 0.1 to
0.4 inch wide. Sclerotia are survival structures of the fungus. The fungi Pythium or Rhizoctonia may also produce cottony growth, but will not
produce sclerotial bodies in the mycelium. Sclerotinia soft rot is usually soft
and watery compared to Rhizoctonia rot, which tends to be firm and dry.
Bacterial soft rot tends to be slimy and malodorous and is often secondary to
cottony soft and other fungal rots.
Sclerotinia is most
active when soil temperatures are 55° to
77°F. Moist soils are necessary for
fungal activity. However, once infection is established, moisture from the
carrot root tissue is sufficient to maintain fungal growth.
Cultural Control
Deep plowing once per year to bury sclerotia 8 to 10 inches into the
soil will reduce disease incidence, but not eliminate it completely because
spores may be blown in from other fields. A 3-year rotation to cereals, corn,
or cotton will also help reduce sclerotial populations in the soil. Trimming
the sides of the foliage after the canopy closes may increase ventilation
between rows and allow leaves to dry. Avoid planting into fields with a history
of cottony soft rot.
Organically Acceptable Methods
Cultural controls and the use of the biological fungus, Coniothyrium
minitans, are
acceptable for use on organically grown produce.
Monitoring and Treatment Decisions
Begin applications when disease first appears and conditions favor
disease development.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
|
| When
choosing a pesticide, consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used. |
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| A. |
BOSCALID |
| |
(Endura) |
4.5 oz |
12 |
0 |
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MODE
OF ACTION GROUP NAME (NUMBER1): Carboxamide (7) |
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COMMENTS: Do not make more than 2
applications before rotating to a fungicide with a different mode of action (i.e., group designation). |
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| B. |
IPRODIONE |
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(Rovral) 4F |
1–2 pt |
24 |
0 |
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MODE
OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2) |
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COMMENTS: Do not make more than 4 applications of iprodione/season. |
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| C. |
CONIOTHYRIUM MINITANS# |
| |
(Contans) WG |
1–2 lb |
4 |
0 |
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MODE OF ACTION: A fungus that kills
sclerotia of Sclerotinia sclerotorum and S. minor. |
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COMMENTS: Apply before planting. |
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UC IPM Pest Management Guidelines: Carrot
UC ANR Publication 3438
Diseases
J. Nunez, UC Cooperative Extension, Kern County
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Fresno County
Acknowledgment for contributions to Diseases:
B. W. Falk, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara County
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