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Replant Problem
- Replantation pertains to the plantation of new plants of apple in the fields vacated by removal of old and declining trees.
- In India old trees in many apple orchards have either outlived their economic bearing life or declined due to the adverse effects of non-curable insect pests/diseases problems and/or natural calamities.
- Moreover, many growers want to introduce new improved and highly productive varieties in their old orchards, that too, sometimes under high density plantations.
- Because of land limitations, the growers the growers are mostly compelled to plant new apple trees on the old apple sites.
There has been increasing concern about poor growth, delayed fruiting and short life of apple trees planted in the old apple sites.. This problem being faced by the growers is termed as ‘Replant Problem’. It is also, sometimes, termed as ‘Replant Disease’ when only biotic causes are involved to develop such situation.
Causes of Replant Problem
- There are many causes of poor growth of young trees of apple and these vary from region to region or even orchard to orchard in a particular region. These can include weak or diseased nursery stock, poor planting and management techniques, water deficiencies or excessive, spray injuries or damage from insects, diseases, rodents etc. But our concern here is only with the soil related causes, which include biotic (harmful microorganisms) and a biotic (nutritional deficiencies or excessive soil pH, phytotoxins) factors in the soil.
- Various types of micro-organisms like fungi, bacteria, actinomycetes, nematodes and their interactions causes replant problem.
- When we remove the old plants, some of the root system (mainly fine roots) are left behind in the old site.
- The soil adhered to such roots consists a good population of micro-organisms which later almost rob the newly planted trees of their vital elements, thereby adversely affecting their growth.
- These micro-organisms can also directly affect the newly planted trees by causing some kind of maladies in their root system.
- A number of fungi belonging to oomycetes, hypomycetes and basidiomycetes have been reported as causal agents of replant disease.
- In England, Canada and U.S.A., many investigators have shown that species of Phytophthora and Phythium are the primary causes of replant disease, Phythium sylvaticum has been identified as cause associated with apple replant disease in Canada.
Management of Replant Problem
- Liming has been found effective in soils where Dermatophthora and Phytophthora are the causes of replant problem.
- The elements, N and P have been reported to suppress the growth of replant disease caused by fungi and bacteria and subsequently to promote the growth of bacteria antagonistic to these usual organisms.
- Replacing the soil at a replantation site with the steamed/fumigated old apple soil or some non-apple soil or potting soil mixture (containing peat, sand or soil, dolomite, lime, NPK fertilizer, minor elements) have also been reported as effective in attaining good growth of replanted apple trees.
- Inter-cropping with herbaceous crop and growing mustard and radish before planting greatly improved the growth of newly planted apple seedlings. Antagonistic crops like marigold (Tagetes pastula) successfully reduced the population of nematodes, Pratylenchus penatrans and the fungus, Phythium spp. In replant soil. Cultivation of red fescue (Festuca rubra) and red top (Agrostis alba) also reduces P.penetrans population.
- Soil sterilization by fumigation, steaming or even solarization checks the population of soil borne pathogens. Generally pre-plant treatments are more useful than the post-planting treatments.
- The recommendations to manage the replant problem in Himachal Pradesh include:
i) Dig out and destroy the stumps and roots of old/dead apple trees.ii) The fresh layout of the orchard be done by avoiding frequently/possibly the old pit sites.iii) New pits of bigger size (5 x 3 ft) should be dug and kept open for exposing to sunlight for about one month.
iv) Pre-plant soil sterilization by fumigation (early winter) or solarization (during summer) to check the population of soil borne micro-organisms. For fumigation, make 9 inch high heap of pit soil outside the pit, drench with formalin solution (1 litre of commercial formalin in 9 litres of water) and cover with transparent thin polyethylene sheet for atleast 48 hours. Remove the sheet and turn the soil daily for about a week so that formalin fumes escape from the treated soil. In case of solarization, 9 inch high heap of pit soil is covered with transparent polythene sheet for 2 months during summer before filling the pits.
v) Incorporate well rotten FYM along with 1 kg SSP fertilizer and 200 g Kanadane dust in treated pit soil and fill the pit upto one foot above ground level.
vi) Always use the healthy and strong rooted plants for replantation. In high problem areas preferably use tolerant rootstocks of apple like Merton793
vii) To improve the growth of newly planted apple seedlings, grow mustard, radish, marigold and red fescue (Festuca rubra) and red top (Agrostis alba) as decoy/biofumigation crops
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