Collar Rot and Root Rot in Apple

Collar Rot of Apple

The disease was reported in 1960 in India. In Shimla district of Himachal Pradesh, 13.27 percent of apple trees are affected with this disease and 8.31 percent in Kinnaur district alone.

Causal organism

This disease is caused by Phytophthora cactorum, a soil born fungus. The disease pathogen can survive in soil where a soil temperature remains between 12 to 20 degree Celsius and pH should be 5-6. The infection starts in the month of March to April and August to September from the infected leaves or previous year’s fallen fruits present in the plant debris and soil. Infection starts from the collar region of tree which is nearer to the soil and goes to roots of the plant. Pathogen can enter into the tissue from pruning wound, injury or crack near the soil or from the graft union.

Symptoms

• Collar region of the plant near soil shows death of tissue (necrosis), moist rot turns brown colour in phloem and cambium.
• Stem after rotting converted into canker. The performance of the infected tree decreases over the years and leaves become less dense.
• Tree shows poor terminal growth with loss of vigor of plant and stunted.
• Reddish coloured leaves are produced in late summer months. The leaves show chlorosis and purple discoloration in the rainy season to autumn months.
• The tree looks different with stress symptoms in the orchard and can be identified from a distance. Sometime, the tree dies suddenly.
• One of main cause of the disease is water logging or regular saturation of water near the stem.
• Death of tree occurs where the tree is girdled.

Management

1. Root stocks such as M2, M4 and M9 are resistant. MM103, MM104, MM106, MM107, MM109, MM110, MM111, MM113, MM115 are moderately susceptible. M2, M7 and MM112 are intermediately resistant.
2. The distance of the graft union from the ground should be at least 30 centimeter or above.
3. Good orchard management practices such as planting of tree should be done in well drained soil, improved drainage system around the tree trunk, avoid injury to the stem during field operations, should be followed.
4. The sand can be placed up to one foot area with 10 cm depth around the stem to avoid standing of water and to avoid chances of infection.
5. Scarification of wound near the collar portion should be done and then any fungicidal paint such as Bordeaux paint or any other copper paint must be applied.
6. Drenching with Mancozeb (0.3 percent i.e. 600 gm in 200 L water) or Copper oxychloride 500 gm or mixture of Ridomil MZ 400 gm + Carbendazim 200 gm in 200 L of water at the radius of 1.5 feet around the trunk, during the month of March and August to September can be done as precaution against this disease.
7. The foliar spray of Fosetyl - Aluminium completely controls the disease.
8. Isolates of Trichoderma and Gleocladium species are act as bio control agents for the control of this collar rot disease.

White root rot in Apple

This disease is caused by Dematphora necatrix. The fungus remains alive in the debris of infected branches in the form of Sclerotium. The ideal temperature for growth of fungus is 14 to 17 degree Celsius. Due to this, this disease affects the orchards located at the height. Clay and loamy soils with 5.5 - 6.0 pH and high water content are very helpful for infection.

Symptoms

• The rotting starts from lower roots which further advanced to upper portion of roots, ultimately reaching to tree trunk. After few days of infection, the roots are covered with white mycelial growth of fungus. Later, fungus on roots turns greenish grey or brownish black in colour.
• White fungal growth spreads around the infected roots due to high humidity. In the rainy season, that white fungal growth looks like the flat ribbon like structure.
• In advance stages of infection, black mustard like structure of fungus appears on the surface of dead tissue of the plant.
• The leaves show premature chlorosis, number of leaves on the plant decrease. Bronzing of leaves occur with premature defoliation. The growth of branches also stops. The fruit size also remains small in infected tree and fruits are also decrease in number.
• The plant becomes weak due to infection in root stock and dies within two years. The diseased seedling or trees are easily uprooted from the soil.

Management

1. Disease resistant root stocks for example:- Malus prunifolia (Crab Apple) or Malus floribunda can be used, where there are chances of infection.
2. The infected area should be avoided for new plantation. If it is necessary to reuse the area, then proper sterilization with formalin or chloropicrin should be done.
3. Infected tree can be saved through “approached grafting” technique. Infected soil should be kept fallow with frequent cultivation to starve the fungus.
4. Isolation trenches should be digged around the infected trees.
5. Fungicidal paste should be applied after the removal of infected rotten roots from the plant.
6. There should be provision of proper drainage of water because water logged soils are more susceptible to the infection.
7. Lime application (500 to 1000 gm per tree) may be done in infected trees for some years for acidic soils.
8. Organic methods such as neem cakes or lantana leaves or deodar needle or green manures are also useful for this disease.
9. Nitrogenous fertilizers application should be reduced because it increases the disease incident.
10. Drenching with Carbendazim (100 gm in 100 L of water) or Aureofungin (40 gm) + Copper Sulphate (40 gm per 100 L of water) at the start of rainy season in June- July should be done. This fungicide mixture should be applied in 15 - 20 cm deep holes, done at a distance of 25 - 30 cm each.  The basin should be brought to soil moisture of 30 - 40 %. This should be repeated 3 – 4 times every year during rainy season.