Good weed control is essential for rapid establishment and vigorous growth of young citrus trees. Eliminate all existing lawn grass and weeds for several feet around the tree. As the spread of the tree increases, widen the grass-free area beyond the tree canopy or drip-line.
Weed control can be accomplished by mechanical means such as hoeing. Herbicides such as Roundup(TM) are excellent for control of existing weeds and pre-emergent herbicides like Diuron at 3 kg/ha twice at 120 days interval is quite effective to control weeds up to 280 days.
Leguminous vegetables like cow peas, French bean, peas, etc., may be grown in citrus orchards. Intercropping is advisable only during the initial three years. Moreover, Leguminosae plants are compatible with the citrus root system. Besides, they are able to accumulate nitrogen in their roots.
The trees are trained to a single system and any shoot emerging from the portion below the bud union should be nipped off regularly. The first year growth beyond height of 0.7–1m should be punched off to develop side shoot. Only 4–6 shoots having wide angle with the main trunk, all around should be allowed to grow up to 3–4m. Thereafter no training is required. Training of plants should be completed in first 3 years so that plants attain a mechanically strong canopy. The pruning in pre-bearing trees may be done at any time.
Pruning of bearing trees though differs with variety. It consists of removal of dead, diseased and weak branches. Removal of water sprouts and suckers from each rootstock below the bud union is also essential and should be attended to regularly along with thinning of the shoots for better penetration of sunlight and aeration. The best time for pruning in bearing trees is after the harvesting during dry period ( June –September).
Citrus trees require more water because sap circulation never entirely ceases and transpiration takes place throughout the year. Being evergreen plant, Citrus requires good amount of water and water deficiency moisture stress at critical periods reduces fruit size and quality. Thus, moisture stress during the period of growth, flowering and fruit development should always be avoided.
During the first 6 months the trees should be irrigated twice a week and thereafter every 7 days. In young plants up to the age of 8-year, the irrigation should be given through basin system of irrigation. Drip irrigation system is gaining popularity.
A grown up citrus tree needs about 25–20 irrigations in a year, amounting about 1,325mm of water. Citrus plants have highest demand of water during fruit development. It is advisable to irrigate the orchard after the fruits have attained pea size. Moisture stress during tree flowering could result in excessive drop of flowers and fruitlets, and the resulting crop will be small. A serious drought followed by good rains could produce out-of-season flowering and fruit setting.
Fertilizer requirement of the plants is influenced by various factors like age of the plant, root-stock used, soil and climate along with the crop load in bearing trees. No uniform fertilizer recommendation can be made for all citrus cultivars in different agro-climatic regions. The fertilizer schedule commonly adopted is given below.
Table. Citrus nutrient recommendation per tree/year (g)
Table. Citrus Fertilizer recommendation per tree/year (g)
The fertilizers should be applied in a ring from below the canopy of the trees depending on age. For a mature tree, fertilizer is applied in a 30–40cm wide ring made at a radial distance of 100–200cm from the trunk as maximum feeder roots are located in the space below the tree canopy.
Though the requirement of major elements is by and large met by supplementing N, P, K fertilizers, farmers usually forget to apply micronutrients, the most essential part of citrus nutrition. Further, deficiency symptoms of Mn, Fe and Zn resemble very closely, making it difficult to judge which nutrient is really deficient.
It is often necessary to apply micronutrients. These elements are dissolved in water and applied as a spray onto the tree. Deficiencies of zinc, copper and manganese often occur and may be applied in 10 L water at the following concentrations:
• 15 g zinc oxide
• 20 g copper oxychloride
• 20 g manganese sulphate.
The micronutrient solutions should be sprayed when the leaves are actively growing. A boron deficiency can be rectified by spreading 20 g borax per large tree under the canopy.
1.7. Managing alternate bearing
Certain citrus types such as oranges or some mandarins have a tendency to have a year with heavy fruit production followed by a year with sparse production. This is called alternate bearing. You can reduce the potential of a tree to alternate bear by reducing the fruit load on a heavy fruit set year by thinning out some of the fruit. Pruning the tree will also help to offset alternate bearing. Also, fertilize less in light years and more in heavy years so that the trees needs are met according to the demands of the fruit load. Lastly, do not allow the old fruit to stay on the tree longer than necessary. Despite using these strategies, some varieties will just alternate bear.
1.8. Management of fruit drop
Some fruit drop is natural. Excessive drop may be due to drought stress, sudden high temperatures, low humidity, or nitrogen deficiency.
Heavy pruning, thrips, mites, or spray injury can also cause fruit to drop. Keep trees in good health to minimize fruit drop.
Fruit drop is a self-regulating mechanism in citrus trees. Too much fruit set will cause small fruit size. Additionally, excessive fruit set can also be damaging to trees.