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Diseases in the Nursery
Phytophthora infections
Occurrence and symptoms:
Phytophthora infections are noticed on leaves, stems and roots of cuttings in the
nursery. Dark spots with fimbriate margins appear on the leaves, which spread rapidly
resulting in defoliation. The infections on the stem are seen as black lesions,
which result in blight. The symptoms on the roots appear as rotting of the entire
root system.
Management:
Spraying Bordeaux mixture 1.0% and drenching with copper oxychloride 0.2% at monthly
intervals prevents the disease. Alternatively potassium phosphonate 0.3% could also
be used. The potting mixture may be sterilized through solarization. To the sterilized
mixture, biocontrol agents such as VAM @ 100 cc/kg of mixture and Trichoderma @
1.0g/kg of soil (Trichoderma population @ 1010 cfu/g) may be added at the time of
filling of nursery mixture in polythene bags. Pseudomonas fluorescens (IISR-6)
may be added to the potting mixture @ 1.0g of product containing 1010 cfu/g to enhance
growth and to suppress root pathogens. Since the biocontrol agents protect the root
system only, the aerial portion may be protected with chemicals. If Bordeaux mixture
is used, care must b taken to prevent dripping of fungicide to the soil. Alternatively,
systemic fungicide such as metalaxyl and potasssium phosphonate, which are compatible
with Trichoderma, may be used.
Anthracnose
The disease is caused by Colletotrichum gloeosporioides. The fungus infects
the leaves causing yellowish brown to dark brown irregular leaf spots with a chlorotic
halo.
Management:
Spraying Bordeaux mixture 1 % alternating with carbendazim 0.1 % is effective against
the disease.
Leaf rot and blight
The disease is caused by Rhizoctonia solani and is often serious in nurseries
during April-May when warm humid conditions prevail. The fungus infects both leaves
and stems. Grey sunken spots and mycelial threads appear on the leaves and the infected
leaves are attached to one another with the mycelial threads. On stems, the infection
occurs as dark brown lesions, which spread both upwards and downwards. The new flushes
subtending the points of infection gradually droop and dry up. Leaf spots caused
by Colletotrichum sp. are characterized by yellow halo surrounding the
necrotic spots.
Management:
A prophylactic spray with Bordeaux mixture 1 % prevents both the diseases.
Basal wilt
The disease is mainly noticed in nurseries during June-September and is caused by
Sclerotium rolfsii. Gray lesions appear on stems and leaves. On the leaves white
mycelia are seen at the advancing edges of the lesions. The mycelial threads later
girdle the stem resulting in drooping of leaves beyond the point of infection and
in advanced stages the rooted cuttings dry up. Small whitish to cream coloured grain
like sclerotia bodies appear on the mature lesions.
Management:
The disease can be controlled, if noticed early, by adopting phytosanitary measures.
The affected cuttings along with defoliated leaves should be removed and destroyed.
Later all the cuttings should be sprayed with carbendazim 0.2% or Bordeaux mixture
1 %.
Viral infections
Vein clearing, mosaic, yellow specks, mottling and small leaf are the most obvious
symptoms for identifying viral infections in the nursery.
Management:
As viruses are systemic in nature, primary spread occurs through planting material
since black pepper is vegetatively propagated. When infected plants are used as
source of planting material, the cuttings will also be infected. Hence selection
of virus-free healthy mother plants is very important. Secondary spread of the disease
occurs through insects such as aphids and mealybugs. Because of closed spacing of
seedlings in the nursery, chances of spread through these insects are more. Hence
regular monitoring of the nursery for insects and spraying with insecticides like
dimethoate @ 0.05% should be resorted to whenever they are seen. Besides, regular
inspection and removal of infected plants should also be done.
Nematode infestations
Root-knot nematodes (Meloidogyne spp.) and the burrowing nematode (Radopholus similis)
are the two important nematode species infesting rooted cuttings in the nursery.
The damage caused to roots by nematode infestations result in poor growth, foliar
yellowing and some times inter-veinal chlorosis of leaves. The establishment of
nematode infected cuttings will be poor when planted in the field and such cuttings
develop slow decline symptoms at a later date.
Management:
Soil solarization can be done for sterilizing the nursery mixture. The solarized
nursery mixture may be fortified with biocontrol agents such as Pochonia chlamydosporia
or Trichoderma harzianum @ 1 -2 g/kg of soil, the product containing 106.5
cfu fungus/g of substrate. A prophylactic application of nematicide is also necessary
to check the nematode infestation. A light irrigation may also be given to ensure
adequate soil moisture.
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