Citrus Nursery – part 2

Pathogen Status


Young citrus trees are sensitive to a number of root pathogens but the main problem in the nursery is the control of Phytophtora spp. Thus, use a new site to establish your citrus nursery. When possible, drench the soil with copper, fumigate the soil or burn dried leaves on the surface.




Regular supply of clean water throughout the year is very essential for a nursery. Depending on the rain for supply can compromise the success of nursery. In fact, water could be a source of problems in nurseries. To avoid such situation, be guided by the following:


a.       Pathogen status. Water may harbor pathogens such as nematodes and fungi. Thus, choose water from deep wells and springs over water from shallow ponds which may carry pathogens. However, note that spring water may possibly be contaminated with a pathogen as well. If Phytophtora spp presence is confirmed despite the use of water from clean sources, the water could be treated with chemicals especially in big establishments where risks could not be tolerated.


b.      Treatments. Filter out organic materials from the water first, as these may harbor or protect the pathogens against the treatment. Treat the water with 2-3 ppm chlorine for at least 30 minutes. Appllication during the night ensures a better result.


c.       Chemical properties. pH and salinity (amount of salts) of irrigation water could adversely affect the growth of seedlings. pH levels below 5.0 or above 7.5 will impair nutrient uptake. High levels of dissolved salt (above 500 mg/L or above 75 MS/m) will cause toxicity and retard growth. Hence, monitor pH and salinity regularly using reliable pH meters and electrical conductivity meters.


Growing Medium


For optimal growth at the shortest possible time, consider the following:


a.       Physical Properties. Air-filled porosity (AFP) of a growing medium is the percentage of its volume that contains air after the medium has been saturated with water and allowed to drain. It is a measure of how much air is available to the roots and is therefore an excellent means of determining the suitability of the physical properties of a growing medium.


A low AFP ranging from 15% to 25% (Hanneck and Black 1994) means that water has accumulated in the medium thus, driving out the air from the soil pores. This is a very conducive environment for Phytophtora spp., a major cause of root rot in nurseries. A very high AFP means that the soil pores are filled with air and, therefore, the soil will require frequent watering especially during dry season. The medium should be well drained but should retain enough water to sustain growth during dry season.


b.      Chemical Properties. As with water, pH and salt content of the medium should be determined before use. Adjust the medium composition to meet the desired chemical properties. The instruments used in determining these properties in water could be used as well for the medium. Determine the physical and chemical properties of prospective media prior to their use.


c.       Selection. The BNCRDC recommends a medium consisting of sand, compost and topsoil at 1:1:1 ratio. If no topsoil is available, modify the medium to 2 parts compost and 1 part sand. This medium with AFP of 15% has been successfully used at BNCRDC for a number of years. However, the porosity of the compost changes after some months, resulting in the compaction and hardening of the medium. The resulting lower AFP and water holding capacity becomes a problem in the later part of the budding stage.


Consider using readily available materials in the locality such as rice hull, coir dust, chopped corn stalks, composted pine bark, and saw dust. Moss can be used if available.


d.      Pathogen status and sterilization. Sterilized the medium to be used to ensure that it is free from pathogen. Ideally, all components should be fumigated together. This way, problem due to fungi in the nursery and later in the orchards can be avoided or at least minimized. However, fumigations are expensive and may be unsafe for the environment. Consider using the following methods instead:


·         Boiling treatment – Treat soil in pots and small seedbeds by pouring sufficient boling water directly into the soil. Shortly after pouring, cover the soil with canvass, paper or plastic to keep the heat within the treated thickness of the medium. Remove the cover when the medium has cooled. It is then ready for use.

·         Use of heat – Place the medium in an open pan and heat it underneath. Turn the medium occasionally with a shovel while temperature is rising. Maintain the highest temperature for at least an hour while sprinkling water to keep the medium moist. Allow the medium to cool after which it is now ready for use.

·         Burning straws or dried weeds – This is the easiest and most practical method that can be used to sterilize the growing medium. Pile and burn dried weed/grass straw on top of the medium – the thicker the pile the better. The medium could be turned over and the procedure repeated for better result.


e.      Storage Area. Storage areas should be protected with a low wall or raised above soil level. This serves to prevent contamination from run-off water.

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