Apple Tree Diseases: Powdery Mildew

Diseases play an important role in low productivity of any crop in the form of yield losses. Generally about 33% losses are due to diseases and insect pests. There are some diseases which not only impair with the yield losses but these also contribute towards poor quality of the produce. The question now arises that, What is Disease?: 

Disease is an impairment of health or a condition of abnormal functioning.

Diseases of Apple

Powdery Mildew
Collar rot
White Root Rot

Premature Leaf Fall
Sooty Blotch and Fly Speck
Apple Scab
Apple Mosaic Virus

In this post we are going to talk about the powdery mildew disease of apple. This disease is very common in Kinnaur district of Himachal Pradesh as dry weather plays an important role in the appearance of the disease.

Description: The disease infects leaves, blossoms, green shoot, and the fruit. On the leaves, the fungus can appear as felt-like patches or as a solid mat on the surface, particularly on the undersurface of the leaf. Initial infections on the underside of the leaf may cause chlorotic patches or spots to occur on the upper side of the leaf. This symptom, however, is not unique to powdery mildew so inspection of the underside of the leaf is necessary to confirm that powdery mildew is the cause of these symptoms. Under favorable environmental conditions, the disease spreads over the entirety of the leaf and progresses down the petiole on to young, green shoots. Infected leaves tend to crinkle, curl, or roll upwards along the edges giving them a narrow appearance. If the infection is severe, infected leaves will usually drop prematurely during the summer.

Shoot infections are the typical result of overwintering infections of the fungus in buds. When the terminals push in early spring, the fungus grows along with the new succulent growth and infects this tissue immediately. These shoots may be killed outright in the spring, or may survive throughout the season and die in late fall or winter. The initial growth of the fungus on newly infected twigs appears powdery white but eventually turns a darker brown. Small black fruiting bodies, called cleistothecia, can appear in the mycelial mat and function as the source for sexual reproduction and the eventual production of ascospores.

The blossoms, petals, sepals, receptacles, and peduncles may become infected and covered with the fungus. Blossom infections are less common but are important because infected blossoms will either fail to set fruit or produce small, stunted and/or russetted fruit. These fruit are unmarketable for fresh market consumption. 

In my next post I shall be talking about the 
Disease Cycle of Powdery Mildew, 
Management of Powdery Mildew

Apple Tree: Training Systems in Intensive Apple Cultivation: Vertical Axis

This post is in continuation of the series on Training Systems in Intensive Apple Cultivation This post explains about the Vertical Axis or French Axis training system 

The vertical axis (VA) system

The vertical axis (VA) system has been touted by some growers as the next logical step from free standing central leader trees to high density supported systems. The main reason cited is the great similarities between the systems and the low emphasis on limb manipulation by tying. There are ladders used in picking, but with a flat tree wall at ladder height it is quite fast and simple to manage ladders.

Even though the VA system is one of the taller systems used in high density supported systems, there is still a critical need for lower limb development. These lower limbs will form a fruiting table yielding perhaps 60% of the crop and must be established before the trees should be allowed to grow taller. Proper development of the bottoms of the tree will allow 75% or more of the fruit to be picked from the ground. Cultivars that have a high requirement for light (e.g. McIntosh) are well suited to this system. Other cultivars like Gala, Goldrush, Golden Delicious and Empire have a growth habit highly suited to this system.

VA systems allow trees to grow taller than SS systems. The system basically consists of one or more high tensile steel wire(s) drawn tight and supported 2 - 3 m above the ground by a series of in-line posts spaced 9 to 15 m apart. The closer the spacing for the inline posts, the higher the degree of stability of the support system under strong wind or high cropload conditions. 

Individual trees in the row are supported by vertical leader supports that reach up to the top support wire. The tree consists of a conical, or "Christmas tree" shape and grown up to 3.5 - 4.0 m tall. The leader is not pruned until the tree reaches its full height. Shoots arising on the side of the axis or trunk close to and competing with the leader are removed as they arise or during the dormant pruning season. Side branches on the leader are renewed on a periodic basis.

The VA support system is somewhat more complex than the SS to install. It does require a high level of skill to build the support system and be sure it is adequate to hold the trees and crop load. A post failure in this system can result in the loss of several trees. The standard anchoring system now in use is the "auger anchor" which is screwed into place. Posts are generally pounded or watered (water gun) into the ground.

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Apple Tree: Training Systems in Intensive Apple Cultivation: Slender Spindle

This post is in continuation of the previous post on Training Systems in Intensive Apple Cultivation: Trellis. This post explains about the Slender Spindle training system further modification of spindle bush training system.

Slender Spindle:

This is the system preferred by growers who wish to work exclusively from the ground and are not confident in building wire support systems. The slender spindle (SS) consists of an individual support post at every tree.

Slender Spindle Support System:

The post should be 2.4 - 3 m in length and of pressure-treated wood, concrete or metal to ensure it lasts the life of the orchard (perhaps 12 - 18 years). A diameter of 4 - 6 cm is preferred, since risk of frost heaving increases with larger diameters. The depth of the post in the ground should be 60 - 90 cm for stability leaving 1.5 to 2.5 m above ground. A common mistake is to have insufficient post height above ground.

Slender Spindle Training Pruning:

The tree is trained to a slender bell, or pear shape with the bottom whirl of branches acting as a permanent fruiting table. The leader and top of the tree is kept quite weak to contain height. Renewal pruning of mature trees consists mainly of removing 2 - 3 of the largest diameter branches on an annual basis during the dormant season.  Tree height does not exceed 2 - 2.5 m.

In the next post I shall be discussing about the Vertical Axis or French Axis training system. This system is followed mainly in France having average productivity of about 42 Tonnes per Ha.

Apple Tree:Training Systems in Intensive Apple Cultivation: Trellis

This is in continuation to my previous blog on Training Systems of Apple Trees in Intensive Orchards where I mentioned about three basic training systems of apple trees in intensive cropping i.e. high density apple plantations. Today I am going to discuss about trellis.

Trellis:

Why trellis or any other support system based training system should be adopted for the HDP on clonal rootstocks. As you are now aware of the fact that the production can be optimized by harvesting 70 per cent of available light. Further the wood produced and fruit produced ratios are to be optimized. Why we produce wood? Wood is produced for structural strength. This is the reason for growing larger trees on strong scaffolds. If we want to grow HDP we must understand that support system is necessary to reduce wood production. This helps us in growing the trees with more fruiting wood than the structural wood. Therefore the production can be started at early stage of the plant/ orchard life. If the production can be taken as early as two to three years of planting, the breakeven point of orchard establishment can be met earlier.

The system basically consists of one or more high tensile steel wire(s) drawn tight and supported 2 - 3 m above the ground by a series of in-line posts spaced 6 to 10 m apart. The closer the spacing for the inline posts, the higher the degree of stability of the support system under strong wind or high crop load conditions.

The trellis support system is somewhat more complex than the Slender spindle and vertical axis to install. It does require a high level of skill to build the support system and be sure it is adequate to hold the trees and crop load. A post failure in this system can result in the loss of several trees. The standard anchoring system now in use is the "auger anchor" which is screwed into place. Posts are generally pounded or watered (water gun) into the ground.

The key problems of trellis systems are varieties with excessive vigorous or strong rootstocks that result in excessive pruning to contain the tree. Also, trellis systems support the total weight of the crop load and, as a result, must be exceptionally sturdy with posts for wire support located every few trees in the row.

In coming posts I shall be discussing about Slender spindle, Vertical Axis and Super Spindle training systems.

Apple Tree: Training Systems of Apple Trees in Intensive Orchards

The number of apple trees per acre in new orchards has gradually been increasing. Orchard intensification is motivated by the desire to produce fruit early in the life of the orchard to rapidly recover establishment costs. Intensification is possible by using dwarfing rootstocks that control tree size, induce early cropping, and produce large quantities of fruit relative to the amount of wood produced.

Apple trees grown on dwarfing rootstocks have shallow or brittle roots systems and trees grew poorly and often leaned or fell over. Therefore these plants require support systems. However, Intensive orchard systems are more profitable than traditional low-density orchards on semi-dwarfing rootstocks. However, because the establishment costs for intensive orchards are high, trees must be trained and pruned properly to induce and maintain high yields.

Motivation for orchard intensification.

The primary reasons for orchard intensification include:

1.) early fruit production, and
2.) reduced pruning and harvest costs of mature orchards.

Yield is positively related to the amount of sunlight intercepted per acre. Profit, which is influenced by yield as well as fruit size and quality, is probably at an optimum when an orchard intercepts about 70% of the available light. Traditional orchards, using vigorous rootstocks, were typically planted at a spacing of about 22 feet x 16 feet with 132 trees per acre. For the first five or six years after planting, fruiting was discouraged to promote vegetative growth so trees would fill their space as rapidly as possible. The first crop was usually harvested four or five years after planting, but high yields were not obtained until trees finally occupied their allotted space. Maximum yields did not occur until about 12 to 14 years after planting.

Intensive orchards are typically planted at narrow spacing depending upon the training system adopted but one thing is very clear that a small crop is often harvested the year after planting, because trees have so little space to fill, peak production is usually achieved during the 6th or 7th year after planting. Once trees fill their allotted space, maximum yields are similar for all types of orchard systems. Because the primary advantage of intensive orchards is early fruit production, these orchards should be planted only on excellent sites with a low probability of crop loss due to frost or hail.

Intensive orchard training systems.

The three basic types of training systems used for intensive orchards are

1. "Trellis,"
2."Slender Spindle," and
3."Vertical axis or French Axis."

There are many modifications of each system, and orchardists will need to adapt a system to suit their own particular situation. The basic systems will be discussed in coming posts

Apple Tree: High Density Apple Plantations: Why?

In my previous blogs I discussed about high density plantation and rootstocks, clonal rootstocks. Though I have written about the productivity, but farmers must understand what does this productivity means? For this purpose I tried to compare the area harvested, production and yield for 2006 to 2010 (five years) for six countries Viz. China, France, India, Italy, New Zealand and USA. Graphs prepared for visualizing the impact of high productivity. You can go through these graphs and then decide why HDP is necessary? The data was obtained from www.fao.org (FAOSTAT).

The data presented above indicates that India possesses second largest acrage under apple plants among the six countries compared, where as Italy possesses only one sixth of its acrage but when production is compared with, India and Italy has at par production. France shows maximum productivity and India shows lowest productivity. Further our orchards are becoming old and senile that warrents us to move with a planing and that too we have to face replant. We have only one option if we want to maintain our production or enhance the production and quality i.e. HDP.

In coming posts I shall be discussing about training systems for HDP Apple.

Apple Tree: High Density Plantation: Apple Rootstock

This post is in continuation to my previous post on High Density Plantation: Advantages of smaller trees.

What is rootstock?

Rootstock is the root system and a small proportion of the lower trunk of most apple trees. Grafting the genetically distinct fruiting part of the tree, the scion, on the rootstock forms whole tree. Occasionally a third genetically distinct component, an interstock or interstem, is grafted between rootstock and scion.

Why rootstocks are used?

Its really difficult to propagate the scions directly, but the rootstocks can be propagated easily that’s why rootstocks are used in apple propagation whether seedling or clonal rootstocks. Next question comes to the mind that why clonal rootstocks when seedling rootstocks are available and are propagated easily. Its true that seedling rootstocks can be propagated easily but these vary in genetic make up because its a sexual propagule, therefore it is bound to produce a different reaction to the scion. This means that you can not expect the plant to produce the same quality as of the parent. Whereas the clonal rootstock is produced through vegetative means thus have same genetic print that gives assurance that reaction to the scion will be the same that means there is most likely same quality of the plants and fruits can be produced.

In coming post I shall be discussing about Advantages of clonal rootstocks