How to Manage Pests
UC Pest Management Guidelines
Phytophthora Root Rot
Pathogen: Phytophthora spp.
In this Guideline:
Field symptoms of Phytophthora root rot
are first noticed when new primocanes (first-year
canes) wilt and the shoot tips die back. Floricanes (second-year canes) of affected plants have weak lateral shoots. Leaves turn
yellow or scorch from the margins. Often severe wilt and dieback occur during
the first hot spell of the season. Roots and crowns are dark brown in color and
lack fibrous roots. If the outer surface is scraped from the crown or main
roots of recently wilted plants a reddish brown color can be seen with a
distinct line where infected and healthy tissues meet. Infected tissue will
eventually turn dark brown as the tissue decays.
Phytophthora is a soilborne pathogen that survives in the
soil as a resting spore (oospore). When soils become saturated with water for
prolonged periods, infectious motile spores (zoospores) are released into the
soil and can infect raspberry roots or crowns. Phytophthora species other than P.
fragariae var. rubi may be involved in root rot
of raspberry. (Generally, Phytophthora does not cause economic damage to blackberries.)
Not all root rots are due to Phytophthora. Raspberry roots are very sensitive to
excessive moisture in the soil for long periods of time. Root death from lack
of air can also occur and result in similar foliar and root decay symptoms.
Control is best achieved by planting in noninfested soils that have good drainage. Avoid low-lying areas that collect excessive
water or clay soils that are poorly drained. The use of raised beds can improve
drainage as can proper irrigation management; this in turn can reduce disease
incidence and severity. Carefully monitor and control irrigation. Use clean
plant stock, plant in noninfested soils, and use cultivars
suitable for local conditions that are less susceptible to root rots.
blackberry cultivars appear to be highly tolerant to Phytophthora,
whereas red raspberries are in the main fairly susceptible, with the varieties
Latham, Killarny, Caroline, and Nordic most tolerant
and the varieties Ruby, Heritage, and Polana most
Proper site selection with good water
management and the use of clean stock and appropriate cultivars are acceptable
management tools in an organically certified crop.
Preplant fumigation can reduce initial
disease inoculum to allow for plant establishment in heavily infected sites,
though the pathogen will recolonize the area with time. Properly timed
fungicide applications may also reduce disease incidence in established
|When choosing a pesticide, consider the general properties of the fungicide as well as information relating to
environmental impact. Not all registered pesticides are listed. Always read
label of product being used.
||COMMENTS: Fumigants such as
1,3-dichloropropene are a source of volatile organic compounds (VOCs) but are
minimally reactive with other air contaminants that form ozone. Fumigate only
as a last resort when other management strategies have not been successful or are not available.
||(Ridomil Gold EC)
||0.25 pt/1000 ft of row
||MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)
||COMMENTS: For use on raspberries. Apply in fall after harvest and before rains. Repeat in spring if conditions are severe.
||(Aliette 80 WDG)
||MODE OF ACTION GROUP NAME (NUMBER1): Phosphonate (33)
||COMMENTS: Apply in fall after harvest and before rains, repeat if
necessary 3–4 weeks later. In spring apply when shoots are 1–3 inches, repeat 3–4 weeks later.
UC IPM Pest Management Guidelines: Caneberries
UC ANR Publication 3437
S. T. Koike, UC Cooperative Extension, Monterey County
M. P. Bolda, UC Cooperative Extension, Santa Cruz County
E. J. Perry, UC Cooperative Extension, Stanislaus County
W. D. Gubler, Plant Pathology, UC Davis
L. J. Bettiga, UC Cooperative Extension, Monterey County
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