All works related to rainguarding should be completed within the first fortnight. Any leakage observed during summer rain, on the already fixed rainguards should be corrected.
Application of stimulants:
The stimulant ethepon can be applied in panels under d/3, d/4, d/6 frequencies of tapping of the rubber trees in the first week of May as per the recommendation.
Plant protection measures:
Prophylactic disease control measures are to be undertaken against various diseases during this month, just before the onset of southwest monsoon.
Against abnormal leaf fall disease, 1% Bordeaux mixture or oil-based copper oxychloride (COC) is recommended. For protecting young rubber and nursery plants repeated rounds of Bordeaux mixture sprayed through knapsack sprayer, rocker sprayer or high volume power sprayer are preferred. For mature rubber, single round application of 1% Bordeaux mixture (3000 L/ha) may be sprayed. As an alternative, COC dispersed in agricultural spray oil is sprayed through micron sprayer from ground or helicopter, as aerial application. For micron spraying, the COC is mixed with oil in 1:5 proportion and 30-37 L/ha is sprayed. The machine should be carried through each row at a walking speed of 2-3 km/h. For helicopter spraying, 8 kg COC mixed with 40 L of oil is used. Fycop, Chlorocop, Parikh etc are oil-based COC powder formulations commonly used in rubber plantations. The spray oil is marketed mainly by Indian Oil Corporation. Care should be given to clean the spray equipment after each days use.
For shoot rot disease control in nursery and young field plants, 1% Bordeaux mixture is to be sprayed at 10-14-day-interval. If monsoon sets in early and tapping is continued during rainy seasons, the tapping panel should be disinfected at weekly intervals with mancozeb (Dithane/Indofil M-45-5g/L) or phosphorous acid (Akomin/Phosjet 2ml/L).
Spraying of 1% Bordeaux mixture on the trunk also along with the spraying against Phytophthora leaf fall ensures reduction in pink disease incidence. In high disease-prone areas, Bordeaux paste can be applied prophylactically. For 2-year-old plants, the top most brown portion of all branches is to be applied with the paste in a 30 cm band in addition to the forking regions. For 3 year old plants, application has to be made on all major forking regions, except the lower most, and also on all leaders of topmost brown regions.
Weeding should be carried out before the fertilizer application. The weeds thus removed may be kept aside for drying and the dried weeds can be used for mulching the plant basin.
Land preparation for new planting and replanting can be continued during this month. Large trees of economic value should be removed first followed by smaller ones. Slashing of undergrowth is needed only for new planting. Burning of dried debris facilitates planting operations. Lining, terracing and pitting also may be undertaken during this period. Rubber may be planted either by square (for level land) or rectangular (for level and near level lands) planting system. In undulating and hilly areas, contour lining should be undertaken and terraces cut along the contour to conserve moisture and prevent soil erosion. Instead of taking continuous terraces in the beginning, for economy, individual square platforms of size 1.25 m x 1.25 m can be made around each plant point which later on be joined together to form continuous terraces. Provision for proper drainage is to be given due consideration while preparing land for planting.
The density recommended for proper growth of rubber is about 420-445 plants/ha. In no case, the number should exceed 500/ha
Pitting and refilling
The standard size of the pit is 75 x 75 x 75 cm. In hard and stony soils, pits of size 90 x 90 x 90 cm can be taken. Filling should be done with top fertile soil. Well decomposed and powdered cow dung or compost at the rate of 12 kg and rock phosphate at the rate of 175 g per pit may be mixed with the top 30 cm soil in the pit.
Soil and water conservation
In slopes, soil conservation measures may be undertaken along with land preparation to prevent soil erosion and to conserve water. Construction of stone-pitched contour bunds (Edakkayyalas) and silt pits is the common conservation practices recommended other than contour terracing. Silt pits (trenches) of about 120 cm length, 45 cm width and 60 cm depth can be taken across the slope on the interspaces of rubber at the rate of 250 pits per hectares.
Cover crop establishment
In fields where planting is undertaken during this season, leguminous cover crop can be established. Pueraria and Muccuna are the popular cover crops.
Fertilizer application as per discriminatory fertilizer recommendation based on soil and or leaf analysis is more advantageous and economical. The central soil and leaf testing laboratory attached to the Rubber Research Institute of India and the Regional laboratories undertake analysis and offer recommendations.
Immature rubber up to 4th year of planting
For the initial four years, if the discriminatory fertilizer recommendation based on soil analysis is not available, the general fertilizer recommendation can be practised. Two types of fertilizer mixtures either with magnesium or without magnesium is recommended. In Kanyakumari district of TamilNadu, Thrissur, Palakkad, Malappuram, Kozhikode, Kannur, Kasaragod, Wynad districts of Kerala, Karnataka, Goa and Maharashtra regions the magnesium status of the soil is high and therefore 12:12:6 NPK mixture is recommended. For all other regions in the traditional belt of rubber cultivation, 10:10:4:1.5 NPKMg mixture is recommended. For Northeastern region 12:12:6 mixture is recommended. In the initial two years, fertilizer mixtures containing half the quantity of phosphorus in the water soluble form are more useful for better root development and plant establishment.