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CROP CULTIVATION OF WALNUT
CROP CULTIVATION
Climate and Soil
Walnut is sensitive to low temperature during spring and high temperature during summer. Walnut should be grown only under such climatic conditions which are free from frosts during spring and extreme heat during summer. Early frosts also injure young shots causing them to fail to leaf out in the ensuing spring. At boom, temperature of even 2o  -3o C below freezing  results in killing of a large number of young flowers. Hot summers with low humidity result in blank nuts. They grow well in areas with well-spread rain of about 75cm or more. Temperature of 29o – 32o C near harvesting results in well-filled kernels. Areas where the trees do not receive adequate chilling cause them to leaf out and bloom late.
A well-drained silt loam soil having abundant organic matter is ideal. The soils should be free from rock, impervious clay, coarse and sandy soil with hard pan, layers of gravel and fluctuating water table.  Alkaline soils should also be avoided.
Planting
The seedling plants should be planted 10m apart, while for budded / grafted plants it should be 7- 8 m apart. December – March is ideal time for planting. Square/hexagonal or contour systems (on undulating soils) are followed for plantation. The seedling plants are to be planted @ 100/ha . whereas vegetatively propagated plants @ 200/ha. In square system. In case of hexagonal system, the number of plants are 15% more.
Training and purning
Modified central leader system is most ideal for training since it provides very good strength to its framework. Trees should be trained on a single stem up to 1-2m, on which 5-6 scaffold branches should be retained at almost uniform distance spirally. Excess buds should be pinched during first year. Pruning is not being practiced in our country, as almost entire plantation is of seedling origin, attaining giant size which makes pruning in later years almost impossible. However with grafted plants, pruning is practicable which can help increase the productivity and improve the quality. Trees of seedling origin receive some kind of pruning while harvesting by thrashing the limbs with wooden poles. It is however a crude method which needs to be modified
Manuring and fertilization
Although walnuts are not generally being applied with fertilizers, for achieving higher yields of quality fruits, application of fertilizers is very essential. For Jammu and Kashmir areas, a dose of 250g of N, 60g of P2O5 and 250g of K2O is recommended to 10 year old trees.
Full dose of P and K half of N is applied 2 weeks before expected bloom. Rest of the half quantity of N should be applied into 2 equal doses, 3 weeks after fruit set and during early July.
For correcting Zn deficiency, 0.4% zinc sulphate should be applied as a foliar spray.
Aftercare
Where staking is required, the plants need to be tied loosely to the stake to prevent wind damage . Water sprouts developing from the rootstock should be pinched bank.
Irrigation
Generally walnuts are grown under rainfed conditions, but they need adequate water during  5-6 weeks after bloom. Inadequate moisture results in poor quality. Due to lack of lack of plumpness of kernels, yield is reduced considerably. In absence of irrigation facilities, sod culture in conjunction with mulching helps in moisture conservation. However, if irrigation is available it should be applied at 1-2 fortnightly intervals depending upon dry spell period and water-holding capacity of the soil.
Harvesting and Postharvest management
Walnuts are usually harvested when hull colour changes from green to yellowish with cracks or when splitting starts at suture from pedicel end.
Nuts should be harvested at PTB stage (when packing tissue turns brown). If harvested earlier, the hulls remain stick tight and under over mature conditions, insect pests harbor within the hulls. Vegetatively propagated trees can be sprayed with Ethenphon ( 2 chloro- ethyl – phosphonic acid) (1,000 – 1,500 ppm) at PTB stage. By doing so, fermentation of hulls can be avoided and hulling becomes easier.
For better nut recovery, the orchard floor should  be cleared and tarpaulin or polythene sheets may be spread on the floor beneath trees prior to knocking of the nuts. After harvesting, nuts should be properly dehulled, washed and dried. In case nuts are not dried properly there is every apprehension of mould development which impairs the quality of the fruit.
In Himachal Pradesh harvesting commences from August and extends up to last week of September, whereas in Kashmir walnuts are harvested in September.
Dipping of nuts after harvesting in Ethephon 2,000 ppm solution at PTB stage reduces dehiscene of walnut hulls from 13 days (in untreated fruits) to 6 days
Plant Protection – Diseases and Pests
Walnuts are susceptible to several diseases and pests, and even though most of them do not threaten the life of plants, they may however ruin a sizable portion of the edible nuts and the visual appearance of the plant
Walnut trees can be infected by diseases specific to this plant, the most common are:
  • Walnut Blight
  • Walnut Leaf Blotch
Walnut Blight
Also known as bacterial blight, it is caused by Pseudomonas juglandis or Xanthomonas campestris pv. juglandis. It usually causes black spots on leaves, holes and blotches on fruit, and possibly dieback of shoots. Fruits are usually damaged extensively, especially when the male catkins are affected
Walnut Blight affects mainly young growth and nuts, and is the most damaging when it occurs during cool and wet periods, around flowering time (so it is most dangerous to species which leaf early). The bacteria will overwinter in seemingly healthy buds, launching a new attack when new growth is at hand.
Treatment consists of cutting out damaged parts (cutting too much is better than cutting too little) and burning them. Bordeaux mixture may help too. Prevention may be attained by using a soil with a pH above 6, avoiding excessive nitrogen, excessive wetness and allowing for good aeration by pruning
Walnut Leaf Blotch
This disease also goes by the name of Walnut anthracnose, its scientific names being Gnomonia leptostyla, Marssonina juglandis or Marssoniella juglandis.
This widespread fungus, it causes nuts to turn black and then fall, as well as brown blotches on leaves and fruits. It also causes a great number of leaves to fall.
This disease spreads well in wet weather, usually during May and early June and will overwinter on leaf litter. The only treatment consists of burning fallen leaves and maybe using a Bordeaux mixture
Other diseases are common to several plants, including walnut trees, and the most common are:
  • Honey Fungus
  • Blackline
  • Crown Gall
  • Downy Spot
  • Nectria
  • Botrytis
Honey Fungus
Also called Shoestring fungus, Mushroom root rot and Oak root fungus, this disease is caused by Armillaria mellea
This is a fairly dangerous disease: it enters through roots and wounds, affecting and rotting roots, butt and collar. It can also spread through the ground to neighboring trees. Eventually, the plant may suffer defoliation, dieback and death
It should be noted that American Walnuts (in particular J. hindsii, J. nigra and hybrids) are resistant to Armillaria mellea and using them as rootstock may be useful in preventing the disease (even though they suffer increased probabilities of contracting Blackline). Diseased plants should be removed carefully to prevent spreading of the disease
Blackline
This is a dangerous disease caused by a virus (a strain of the Cherry Leaf Roll virus - CLRV-W), and it only affects non-regia rootstocks.
Plants affected by blackline suffer yellow drooping leaves, stunted growth and early leaf fall. The name of the disease comes from the typical dark line between the stock and grafted tissue. The tree may suffer dieback and death
The virus spreads through pollen, seed, and infected grafts, so it tends to spread fast
Crown Gall
This infection, caused by the bacterium Agrobacterium tumefaciens, causes swellings on the lower trunk and roots. It is not dangerous
Downy Spot
This common disease only causes leaf blotches, namely yellow blotches on the top of the leaves and mildewy patches below
Nectria
Walnuts are affected mainly by two types of Nectria, namely Nectria galligena (Nectria canker) and Nectria cinnabarina (Coral spot). N. cinnabarina is the more dangerous, since it can lead to rot, wilting and dieback, while N. galligena causes cankers. Any infection should be cut and burned
Botrytis
Botrytis can affect both plants and even harvested nuts if they are left in wet conditions. Plants are more frequently attacked during wet periods of the year. Also known as Botrytis cinerea or Common Grey
Mould
Walnut Tree Common Pests
These pests generally do not cause the death of walnut trees, but they may damage them and reduce their visual impact or fruit yield
Walnut Leaf Gall Mite
Aceria erinoea, previously known as Eriophyes erineus. This disease causes raised bumps (around 1,3cm/0.5 inch long) on the leaves resembling a caterpillar's body. The mites are only 0.1mm wide, lurking in the winter in young buds and damaging them before they even develop the leaves. It is difficult to get rid of this pest, but fortunately the damage dealt is usually small and not life-threatening for the plant
Codling Moth
Laspeyresia pomonella is a moth that usually attacks nuts, staining shells and kernels and even destroys them in the fruiting season. Sprays are recommended to get rid of Codling Moths
Walnut Tree Minor Pests
These pests are not encountered frequently, but it might be useful for you to know them
  • Panonychius ulmi - Red Spider Mite
  • Lecanium coni - European Fruit Lecanium
  • Pratylenchus vulnus - Root Lesion Nematode
  • Chromaphis juglandicola - Walnut Aphid
The following pests are (usually) only found in North America
  • Conotrachelus juglandis - Walnut Weevil
  • Amyelous transitella - Navel Orangeworm
  • Datuna integerrima - Walnut Caterpillar
  • Husk Flies - these are found in the USA and Canada: they may spoil the flavor of the kernel and feed in the husk. They may also stain the fruits. Sprays are a good way to control them
Walnut Profile Package of Practices - Seed Profile

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