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Nursery diseases

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NURSERY DISEASES

Phytophthora Infections

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. Spraying Bordeaux mixture 1 per cent and drenching with copper oxychloride 0.2 per cent at monthly intervals prevents the disease. Alternatively, metalaxyl 0.01 per cent (1.25 g/litre water) or potassium phosphonate 0.3 per cent 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 @ 1g/kg of soil (Trichoderma population @ 1010  cfu/g) may be added at the time of filling of nursery mixture in polythene bags and at regular intervals. Pseudomonas fluorescens (IISR-6) may be added to the potting mixture @ 1 g of product containing 1010  cfu/g to enhance growth and to suppress root pathogens. Application of Trichoderma and IISR-6 in the potting mixture at the time of planting and drenching IISR-6 at 1st  and 2nd  months after planting is recommended for producing disease free cuttings. Since the biocontrol agents mainly protect the root system, the aerial portion may be protected with chemicals. If Bordeaux mixture is used care must be taken to prevent dripping of fungicide to the soil. Alternatively,
systemic fungicides such as metalaxyl (1.25 g/L) and potassium phosphonate (3 ml/L) 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. Spraying Bordeaux mixture one per cent alternating with carbendazim 0.1 per  cent 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 mycelia threads appear on the leaves and the infected leaves are attached to one another with the mycelia 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. A prophylactic spray with Bordeaux mixture one per cent prevents both the diseases.

Basal Wilt

The disease is mainly noticed in nurseries during June-September and is caused by Sclerotium rolfsii. Grey lesions appear on stems and leaves. On the leaves white mycelium are seen at the advancing edges of the lesions. The mycelia 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. 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 per cent or Bordeaux mixture 1 per cent.

Viral Infections

Vein clearing, mosaic, yellow specks, mottling and small leaf   are the most obvious symptoms for identifying viral infections in the nursery.  As viruses are systematic 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 placing of seedlings in the nursery, chances of spread through these insects are more.  Hence regular monitoring of the nursery for insects and spraying with insecticide like dimethoate 0.05 per cent should be resorted to whenever they are seen.  Besides, regular inspection and removal of infected plants should also be done.

Nematode Infestation

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 interveinal 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. Nematode infestations tend to be more in rapid multiplication nurseries. 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  cfu fungus/gm of substrate. Alternately, rhizobacteria like IISR 853 can be applied @ 1 g/bag (formulations containing 108  ñ 1010 cfu/g) at monthly intervals. A prophylactic application of nematicide is also necessary to check the nematode infestation. For this, make three equidistant holes of 2-3 cm depth in the bag around the cuttings and place phorate 10 G @ 1g/bag or carbofuran 3 G @ 3g/bag in these holes and cover with soil. A light irrigation may also be given to ensure adequate soil moisture. In rapid multiplication nurseries where the rooted cuttings are retained for a longer duration nematicides may be applied at 45 days intervals as described above.


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