> Does anyone know of an organically-accepted method of dealing with
>Brown rot of peaches caused by the fungus Monilinia fructicola?
Some biocontrol methods/observations I've heard from organic growers
at different stages of the stone-fruit cycle:
--Remove rotted/dried fruit from trees to decrease inoculum.
--Cultivate the orchard floor to bury the mummies.
--Choose early maturing cultivars.
--Take care not to injure fruit on the twig.
--Refrigeration, or cool storage, for harvested fruit.
--Excessive nitrogen makes canopies thicker, thus shading the fruit
more and increasing conditions that encourage the bacterium.
On the institutional front, I turned up some stuff in a VERY quick search.
Here's a summary of cultural approaches research from UC-Davis's IPM program:
Cultural Approaches to Control Brown Rot of Stone Fruits in California.
Principal Investigators: T. J. Michailides, Plant Pathology,
Davis/Kearney Agricultural Center, Parlier; B. A. Holtz, UC
Cooperative Extension, Madera County; C. Hong
Objectives: Determine the importance of Monilinia fructicola
apothecia as a source of primary inoculum in stonefruit orchards in
the San Joaquin Valley.
Study the conditions that favor the stromatization of mummified fruit
by M. fructicola that enhance the production of apothecia capable of
initiating blossom infections in the spring.
Determine the importance of thinned fruit as a source of inoculum
during the season; and whether thinned fruit can become stromatized,
overwinter, and produce apothecia in the spring.
Summary of Accomplishments: Apothecia of the brown rot pathogen,
Monilinia fructicola, of stone fruit were commonly observed in
February and March in commercial orchards during a disease survey and
in experimental orchards where stonefruit mummies were added. Several
millions of ascospores can be released by each apothecium at the
beginning of the season. Conidial sporulation of M. fructicola was
not observed either on mummified fruit, peduncles, or blighted
flowers and twigs.
Mummies, however, produced conidia under laboratory conditions.
Blossom blight was less severe in research plots where mummies were
removed than when mummies were left on the ground. Subsequently,
preharvest fruit brown rot was also less severe in plots where
mummies were completely removed than where infected fruit were left
on the ground. A similar relationship was observed for postharvest
fruit brown rot in both 1995 and 1996. In addition, preharvest fruit
brown rot was reduced in plots where the orchard floors were disced,
herbicides were applied to berms in the tree rows, and mummies were
removed in comparison with plots where no till, no herbicide, and no
removal of mummies were practiced. These results suggest that
apothecia can function as a main source of primary inoculum for
initiating brown rot epidemics in stonefruit orchards of the San
Joaquin Valley; and that blossom blight and fruit rot can be reduced
by removing mummies from orchard floors or by preventing the
development of apothecia after discing and/or applying herbicides
Apothecia were produced in February and early March from stromatized
mummies that were placed in the orchard soil only in October,
November, or December. Stromatized mummies placed in the field in
August/September and January/February did not produce apothecia,
presumably because they did not have the proper conditions for
apothecia development. Apothecia were never produced from
nonstromatized or fresh fruit mummies, and laboratory results
confirmed these field studies. Therefore, growers who knock infected
fruit to the ground before October (preferentially immediately after
harvest) can break the life cycle of the brown rot fungus by
preventing fresh mummies to become stromatized and by subjecting the
mummies under conditions favorable to destruction.
Field fruit brown rot was less severe in plots where thinned fruit
were removed than where thinned fruit were not removed and where the
thinned fruit were added in five orchards in both 1995 and 1996.
Postharvest brown rot was also less severe in treatment plots, from
one nectarine orchard in 1996, where thinned fruit were completely
removed than where thinned fruit were not removed. No difference was
observed in both pre and postharvest brown rot of fruit from
treatment plots where thinned fruit were racked from "dry" berms into
"wet" irrigation drenches than when thinned fruit was left untouched
in two nectarine orchards. Our results suggest that thinned fruit can
function as a significant source of secondary inoculum for M.
fructicola and brown rot disease can be reduced by destroying thinned
From the Good Fruit Grower (Yakima, WA):
Researchers have yet to find a biological fungicide effective against brown
rot, although they have identified cultural practices that can increase
disease incidence, and are studying yeasts as potential combatants.
The influence of excessive nitrogen, composted waste, thinning practices,
and yeasts upon brown rot have been studied by Dr. Themis
Michailides, associate professor of plant pathology for University of
California (UC), Davis. Stationed at UC's Kearney Agricultural Center
in Parlier, he has examined many approaches to reduce brown rot
Although it has long been recognized that fertilization practices
affect levels of plant diseases, until recently, there were few good
examples reinforcingthat concept.
Data from research studying the effects of nitrogen on Fantasia nectarines
show that blossoms from unfertilized trees resulted in the lowest levels of
disease infection. More stamens were infected on blossoms from trees
receiving high nitrogen rates (250 and 325 pounds of nitrogen per acre per
year) than from trees that were unfertilized, or received 100- and 175-pound
Additionally, the higher nitrogen treatments also showed higher disease
incidence from the research inoculations in green and mature fruit. Positive
correlation was also found in overwintering mummy fruit, which had higher
disease incidence from trees in the high nitrogen category.
Evaluation of the fruit cuticle weight showed that cuticle thickness was
greatest in the unfertilized fruit, decreasing in thickness as the nitrogen
rates increased. High nitrogen treatments resulted in denser canopies,
which shade fruit to cause thinner cuticles. Postharvest storage potential
and brown rot susceptibility are both affected by cuticle thickness and
potential water loss.
The interdisciplinary research conducted by Michailides, and others,
showed that nitrogen fertilizer rates higher than 100 pounds per acre per
year on Fantasia nectarines produced no beneficial effects and increased
brown rot infection.
Michailides is also studying the potential of yeasts to fight M. fructicola,
although he said it is too soon to report upon results. When comparing
brown rot in a trial of peach trees treated with traditional fertilizers and
composts to a plot treated with composted waste from urban yards, he
found that the urban compost did not increase or make worse the incidence
of brown rot, and may have reduced its severity.
He is further studying what may be a connection between the "green waste"
and the many yeast spores that were found on the fruit surfaces.
Growers frequently overlook the significance of thinned fruit as a source of
secondary inoculum in the spread of brown rot. Results from recently
completed research show that brown rot was less in nectarine orchards
where thinned fruit were completely removed than on those from plots
where thinned fruit were left on the floor of the orchard.
Lisa Skog at U. of Guelph was working on the use of "natural fruit
volatiles for reduction of postharvest rot of stonefruits and pears."
"Sponsored by the Ontario Research Enhancement Program. Co-operators:
Brian McGarvey, Agriculture and Agri-food Canada and Dennis Murr, U.of Guelph.
"Various fruit volatiles which are produced as part of the plant's
natural volatile profile or in response to mechanical injury,
microbial attack or environmental stress are being evaluated as
antimicrobial agents. Research is being focussed on reducing brown
rot (Monilinia fructicola) and blue mould (Penicillium expansum) of
Ontario stonefruits and pears. Once effective compounds have been
determined, investigations into the mode of action and application
methods appropriate for Ontario industries will occur."
Whether "natural fruit volatiles" would qualify under certification
standards is not something I know.
Hope this helps.
Center for Integrated Ag Systems, UW-Madison
UW voice mail: 608-262-8018
Home office: 415-504-6474 (504-MISH)
Home office fax: Same as above, phone first for enabling
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