As the rainy season is over, young rubber seedlings in the nursery should be irrigated in the morning and evening. Irrigation, sufficient to drench the nursery, once in four days is enough. In large nurseries, the area may be divided into different quarters and irrigated on rotation. Polybag plants also should be irrigated preferably in the evenings.
Summer season is favourable for occurrence of Corynespora leaf spot disease in young rubber plants. Several small and large spots appear initially on the leaf surface which later join together resulting in shot holes and the leaves fall off when severe. Spraying of 1% Bordeaux mixture or Dithane (Indofil) M45 0.2% can effectively control the disease. The intensity of the disease can be reduced by providing shade in the nursery.
Another leaf disease occurring in young rubber plants, during this period is the birds eye spot. This disease can also be controlled by the fungicide mentioned above.
Powdery mildew disease
As many of the plantations are in the initial stages of refoliation, during this period, occurrence of powdery mildew disease is common. It can also be intense in polybag grown plants. Misty days and intermittent rains of low intensity forms the ideal condition for the spread of this disease. Initially tender leaves develop white fungal spots which later turns into ash colored powdery spots. Affected tender leaves gets dried up and drops off after curling. Under favorable climate repeated incidence of the disease may occur.
Application of 11-14 kg 325 mesh size Sulphur dust, 3-5 times at an interval of 7-14 days from the time of sprouting of leaf buds in at least 10 % trees in the plantation till the wintering is over will effectively control the disease. Sulphur is available as a mixture with talc powder in a 70:30 ratio. Dusting should be done using tree dusting machines. Sulphur dust can be most efficiently applied in the early hours of the days when the leaves remain wet due to presence of dew, which favour sticking of the dust on the leaves.
For seedlings and polybag grown plants, wettable suphur at the rate of 10 g in 4 liter water can be applied using sprayers, at an interval of 7-10 days. An alternative is the applications of Carbendazim (Bavistin) 0.05% solution (1 g in 1 litre water). Wettable sulphur and Carbendazim may be applied alternatively for more effective disease contorl.
From the second year of growth till the canopy covers, application of lime on the brown stem portion from the bud union up to the first fork is advised in order to protect the stem from sunburn. Copper sulphate need not be added in the preparation of lime solution. Application of lime is more effective than application of china clay.
Branching of the rubber plants up to a height of 2.5 m should not be allowed. As the tapping commences at a height of 1.25 m in budded trees, any branching below this height will create difficulty for tapping. Hence branches up to this height should be pruned off close to the main stem, using sharp knives.
As the plantations are more prone to fire damage in summer season, precaution be taken against it from the beginning of the summer season itself. A fire break (fire belt) should be provided around the plantation for a width of 5-7 meters by clearing off all plants and dried leaves in this area. As the defoliated leaves may keep on accumulating in
the fire break it has to be regularly removed and the area kept clean.
Mulching of small rubber plants using dried leaves, grass or cover crop is recommended before the onset of dry season to prevent loss of soil moisture from the plant base, to increase the soil organic matter content and to control the growth of weeds. It may be done at a distance of 5-7.5 cm away from the base of the plant.
If the rainguards fixed on the trees for the rainy season has not been removed till now, it should be removed. If tapping shades are used they should be carefully removed to prevent any damage so that they can be reused next year.
Shade in nurseries
To prevent drying of polybag plants during the severe summer season, nurseries should be provided with partial shade with plaited coconut leaves which allows partial sunlight for the growth of the plants.
If the crop production during the summer season is found to be economical, no tapping rest is needed during this period and tapping may be continued once in three days.