|
|
How to Manage Pests
UC Pest Management Guidelines
Potato
Stem and Stolon Canker
Pathogen: Rhizoctonia solani
(Reviewed 8/07,
updated 8/07)
In this Guideline:
|
|
|
Aboveground symptoms of stem canker include uneven stands, weak
shoot growth, and aerial tubers. Foliage may develop yellowing, purpling,
and upward curling of leaves. Aboveground symptoms alone are not diagnostic,
however, because other diseases can cause similar symptoms. On belowground
stems and stolons, Rhizoctonia solani typically causes reddish-brown lesions that often develop into sunken cankers. Stolons can be girdled and killed,
resulting in a pruning effect and malformation and abortion of tubers.
If tubers in affected fields are left in the ground after vine death, they
often develop black scurf, an
accumulation of irregular black sclerotia of R. solani on the tuber surface.
The strain of R. solani that typically affects potatoes, called AG-3, is specific for potatoes and generally
does not cause damage in or reproduce on other species. Close relatives of
potato, such as black nightshade and tomato, may be exceptions. Rhizoctonia
solani is a soilborne fungus, but inoculum
of the fungus on seed tubers (visible as dark, irregularly shaped sclerotia) is
sometimes more important for disease development than inoculum in soil. In Kern
County, AG-3 types of R. solani apparently do not survive in soil between crops of potatoes; whereas in
Tulelake districts, R. solani AG-3 may overwinter in soil. The fungus only infects juvenile tissue. Disease
development is favored by relatively wet, cool (55° to 60°F) soils.
Reduce initial inoculum by using certified seed tubers that are
free from sclerotia of the fungus. Where R. solani AG-3 survives in soil between potato crops, rotate
out of potatoes for 2 to 3 years to reduce soilborne inoculum. Sugarbeet,
however, has been associated with increased severity of stem canker in subsequent
potato crops. Rhizoctonia stem canker can be reduced by practices that favor
rapid emergence, such as warming seed tubers before planting, planting tubers
at a relatively shallow depth, and avoiding early planting dates when soil
temperatures are cool. Black scurf development on daughter tubers is minimized
by harvesting quickly after vine desiccation rather than holding tubers in soil
for extended periods.
Fungicide treatment of seed tubers can reduce infection by R. solani from inoculum borne on the seed pieces. The
significance of this benefit may be small in fields where heavy soil
infestations of R. solani AG-3
persist between potato crops.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
|
| When choosing a pesticide, consider information relating
to the impact on environmental quality.
|
| |
| A. |
FLUDIOXONIL |
| |
(Maxim Potato Seed Protectant) |
0.5 lb/cwt cut seed pieces |
12 |
0 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Phenylpyrrole (12) |
| |
| B. |
FLUTOLANIL |
| |
(MonCoat MZ) |
0.75–1 lb/cwt cut seed pieces |
12 |
0 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Carboxamide (7) |
| |
| C. |
THIOPHANATE-METHYL/MANCOZEB |
| |
(Tops-MZ) |
1 lb/100 lb cut seed pieces |
12 |
0 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)/Multi-site contact (M3) |
| |
|
|
![[Precautions]](/IMAGES/btn-precautions_bul.gif)
![[UC Peer Reviewed]](/IMAGES/logo-ucpeerreviewed.jpg)
UC IPM Pest Management Guidelines: Potato
UC ANR Publication 3463
Diseases
R. M. Davis, Plant Pathology, UC Davis
J. Nuñez, UC Cooperative Extension, Kern Co.
B. J. Aegerter, UC Cooperative Extension, San Joaquin Co.
Acknowledgment for contributions to the disease section:
C. Smart, Plant Pathology, UC Davis
Top of page
|
