Recommendations for the establishment & maintenance of a healthy peach orchard
Dr. John M. Halbrendt
Penn State Fruit Research and Extension Center
Peach stem pitting (PSP) is perhaps the most insidious, and potentially
costly disease affecting stone fruit in the northeast. In the most severe cases
this disease can completely destroy a peach orchard in as little as 4 years
after planting. Complete orchard loss is unusual but it is not uncommon for
PSP to kill several trees each year in mildly infested sites. As the number
of missing trees increases, orchards become less profitable over time and eventually
may justify pushing out an orchard prematurely. Because PSP is capable of significant
economic loss, every grower should be familiar with the biology and management
of this disease.
Biology of Peach Stem Pitting
Peach Stem Pitting is caused by the tomato ringspot virus (TmRSV)
and all peach and nectarine rootstocks are susceptible. Infected trees show
symptoms of stress and die within 2-3 years after infection. Trees may become
infected anytime after planting and there is no treatment that can "cure" infected
The natural hosts for TmRSV are common broadleaf weeds. Weeds
serve as reservoirs of the virus and spread the virus through seed dispersal.
Virus transmission to peach occurs only through feeding activities of the dagger
nematode (Xiphinema species).
Dagger nematodes are microscopic worms that parasitize roots
and they are efficient vectors of TmRSV. They acquire the virus when they feed
on infected weeds and transmit the virus when they feed on peach. Once nematodes
acquire the virus they may transmit it for the remainder of their life which
is estimated to be about two years. Dagger nematodes cause little damage to
fruit trees if they do not carry TmRSV. (A more detailed description of PSP
can be found in the Penn State Tree Fruit Production Guide.)
Principles of PSP management
It is difficult and in most cases not practical to control PSP after
an orchard has become infected. The key to control is prevention and this can
be effectively accomplished by practices which suppress dagger nematodes and
TmRSV. The optimum time to begin preventive measures is a year or two prior
to establishing a new orchard.
The first step should be a nematode assay and this can be done
even before the old orchard is pushed out. Knowing the population level of
dagger nematodes provides a clue as to the risk of PSP and whether nematode
control is recommended. Nematode control is a major component of PSP management.
The other component is weed control which limits nematode access to the virus.
Methods of control
There are several options available
for "cleaning-up" orchard
sites. The options include soil fumigation, nematicides, crop rotation and
green manure treatments. Each method has advantages and disadvantages that
need to be considered.
For many years the preferred treatment has been soil fumigation.
When properly applied, fumigation provides a quick and efficient method of
reducing both nematodes and weeds thus eliminating sources of virus and the
vector. It is a very effective treatment, however, a major drawback is cost
and it is the most expensive treatment for PSP prevention. Fumigants must be
applied by certified applicators and most growers must hire a fumigation service.
Fumigants are under review and their future availability is in question.
Nematicides are not as effective as soil fumigation but will
knock down nematode populations. This alone may not be sufficient to prevent
disease if virus reservoirs are available. A combination of nematicide treatments
and good weed control is more effective but TmRSV may reappear if a significant
number of virus infected nematodes or weed seed escape treatment.
Crop rotations can effectively minimize PSP if the alternate
crop is a non-host for either TmRSV, dagger nematodes or both. Graminaceous
crops such as wheat, oats, rye, corn or sudan grass are not hosts for TmRSV
but they are good hosts for dagger nematodes. Providing that broadleaf weeds
are controlled, these crops can effectively reduce the presence of TmRSV on
old orchard land. The nematode population, however, will remain unaffected
or increase. Thus there is a potential for reoccurrence of TmRSV.
Selected green manure crops have been
shown to effectively reduce the populations of both nematodes and virus.
Perhaps the best crop for this purpose is rapeseed. Dagger nematodes survive
on rapeseed but reproduction is low and TmRSV does not survive. However,
the greatest benefit is achieved after green rapeseed tissue is incorporated
into the soil as green manure and allowed to decompose. Decomposition releases
toxic byproducts which knocks-down dagger nematode populations. The nematicidal
activity of rapeseed green manure is not as effective as some commercial
nematicides but the combined effect of population reduction plus elimination
of TmRSV effectively provides a "clean" replant
site for the avoidance of PSP. Thereafter a routine program of weed control
and a periodic assays to monitor for dagger nematodes can maintain an orchard
free of PSP.
Comments on the use of rapeseed for PSP prevention
Rapeseed green manure can be an effective treatment to reduce dagger
nematodes and TmRSV in replanted orchards. Relative to nematicides, it is very
economical and can provide additional benefits such as helping to reduce subsequent
weed problems, increase soil organic matter, improve nutrient availability,
and erosion control. Green manure and rotation crops can also improve drainage,
aeration, and soil texture by creating soil channels after decomposition of
To get full benefit rapeseed must be grown in relatively pure
stands without many weeds. One season of rapeseed green manure is beneficial
but two summer seasons are highly recommended. A compromise between one and
two seasons is to grow two crops of rapeseed within one year. The problem with
this recommendation is that growers often find it difficult to keep to the
necessary timetable to accomplish this.
Suggested timetable for growing one or two crops of rapeseed:
Prepare a seedbed by late April–early May and
plant rapeseed by mid May.
A) If only one crop will be produced this can
be incorporated as green manure anytime in the fall but before the soil temp.
falls below about 50 degrees.
B) If a winter cover crop is planned, the rapeseed
must be incorporated by late August or early September. The seedbed must
be prepared and second crop planted by mid to late September to get sufficient
growth to survive the winter.
The winter crop can be incorporated in the spring
after growth has resumed and soil temperature has increased above
45 - 50 degrees.
Use only winter rapeseed varieties. A recommended
variety is 'Dwarf Essex'.
Rapeseed requires a firm, smooth seedbed that
is free of weeds, heavy residue, and large clods.
A preplant herbicide is highly recommended; Treflan® at
2 pints/Acre works well.
Seed may be drilled or broadcast. Avoid planting
too deep! A seeding depth of 3/8 inch is good or if broadcast, a culti-packer
may be used.
Use a seeding rate of 7 - 8 lbs/acre.
Rapeseed is sensitive to herbicide carry-over.
Fall planted rapeseed should have 8 - 10 true leaves and
a 5 - 6
inch tap root with a 3/8 inch diameter root neck before the ground freezes.
For optimum nematode control green manure should
be incorporated when there is adequate soil moisture and a soil temperature
above 50 degrees.