were all observed with moderate to high levels of canker.
In addition, earlier observations have shown Blake,
Golden Jubilee, Raritan Rose, Derby, Rio-Oso-Gem,
Early-Red-Free, Slaybaugh, Jerseyqueen, Triogem, and
Redgold to also be quite susceptible. Sunhigh, Dixired,
Harken, J.H. Hale, and Coronet are less susceptible.
There are no completely resistant varieties.

Peach Decline.Peach trees can die from many
causes. The most prevalent loss occurs from winter injury
to weakened trees. The problem is most severe where
peaches follow peaches, and preplant fumigation for
nematode control is not practiced. However, the effect of
the preplant treatment lasts only for about 1 year, and a
postplant application is needed in the fall following the
second growing season. Additional postplant treatments
are needed yearly through the sixth growing season for
maximum control. Other cultural practices required to
maintain strong trees are also highly beneficial.
One practice, which should be avoided, is pruning 1-
to 6-year-old trees prior to February. Also, see the section
on "Nematode Control."

Phytophthora Root and collar rot, caused by
various species of the fungal pathogen Phytophthora,is a
serious problem on peach as well as on apple. It is most
troublesome in orchards where the internal soil drainage is
poor or where water lays. No varietal resistance is known
for peach rootstocks, and the problem frequently develops
from the use of infected nursery stock. However, the
pathogen survives well in the soil and newly planted trees
could just as easily become infected from resident
inoculum.
The most effective control consists of ridging the
planting row to ensure that water does not lie in the area
of the tree roots and crown. Since the disease can be
introduced with infected nursery stock, a careful
examination of trees received from the nursery is required.
Ridomil Gold at 2 quarts per treated acre can be used
on both nonbearing and bearing trees. Apply in a band
corresponding to the weed control strip or apply as an
under-the-canopy spray using a handgun to drench the
soil. Use enough volume (e.g., 1 gallon of spray for 1-4
year old trees) to provide good penetration into the root
zone or irrigate 0.5" to 1.0" after application.
Alternatively, perform the application just prior to a
rainfall. Two applications in spring (April and May) and
one in September are recommended for sites known to
have poor drainage or past problems.
Aliette 80WP can be used on nursery and nonbearing
trees within the Orchard. It is applied as a series of foliar
sprays. Consult label for specific rates and timing
schedule.
Fixed copper containing fungicides and maneb may
also be helpful in preventing infection. They must be
applied prior to infection to be of value. Use 4 pounds per
100 gallons of either fungicide and add to the borer spray
in the fall to reduce costs. When applied with the borer
spray, make sure the entire root zone is covered (area
under the canopy) and not just the tree trunk. Another
application is needed in the spring to increase the

effectiveness of these materials.

Powdery Mildew.The fungus Sphaerotheca
pannosacauses powdery mildew of peach and nectarine.
This is the same pathogen that causes mildew on roses.
Sporulating colonies of this fungus have been observed on
multiflora roses growing wild along woods adjacent to
orchards.
Since the fruit becomes resistant to infection shortly
before pit hardening, infections generally occur between
pink-bud and third cover sprays. However, once lesions
are established, they will continue to expand in size.
Sulfur (4 lb) provides reasonably good control. Funginex
and Nova are extremely effective.

Prunus Necrotic Ring Spot Virus.This disease has
been present for many years in this region. The disease is
pollen transmitted and transmitted through the seed and
by grafting with buds from infected trees.
For many years the virus was considered to be a
latent virus, one which was present but producing no
symptoms. The strain of the virus present in this region
did produce raised blisters on scaffold limbs, a fine net
cracking of the bark on older wood, a canker similar to
Cytospora Canker and a slight reduction in size.
We now apparently have a more aggressive strain of
the virus present. Symptoms consist of the development
of black, sunken cankers on the present year's growth in
mid-summer. The canker development weakens the
terminals and they break-off during periods with heavy
winds.
The disease generally occurs throughout the tree,
with all of the terminals dying. The tree appears to be
dying but new shoots eventually develop. The initial
symptom is the "Shock Symptom" which develops when
the plant first becomes infected. Symptoms rarely appear
on the same tree the following year, but other trees in the
block may exhibit these symptoms.

Rhizopus Rot. This disease, caused by Rhizopus
stolonifer, is very rarely seen in the orchard because
healthy, uninjured fruit in the tree are not susceptible to
infection. However, the fungus often colonizes any
injured, fallen fruit. Airborne spores from these diseased
fruit contaminate fruit on the tree. Then, once fruit fully
ripen, usually after harvest, the inoculum is already
present on the fruit, ready to infect and cause disease.
Rotted fruit is identified by a mass of white, thread-
like mycelium covered with an abundance of black spore-
producing structures, called sporangia. The Rhizopus
fungus produces an enzyme that dissolves the tissue,
which holds the skin to the flesh. Thus, the skin "slips"
easily from the flesh when pressure is applied to the skin
in the area of the rot.
Although preharvest control is usually not necessary,
the application of fungicide, such as Botran 75WP, may
be necessary in very wet years. For postharvest control,
the fungicide Allisan can be used in conjunction with the
wax spray. Also, care should be taken to prevent
mechanical damage during harvest and packing.

1998 New Jersey Commercial Tree Fruit Production Guide

107