Preventing Measures for Coffee Leaf Rust in Coffee Plantations

Jayarama

Coffee leaf rust was first noticed in Africa in 1861 and in Srilanka in 1868. It showed its first presence in India in l869.Later it appeared in arabica coffee field in the middle of cocoa plantation in the State of Bahia in Brazil in 1970 and since then this fungal disease is prevalent in most of the arabic a coffee growing countries world wide. In India this is the major coffee disease which has the potential to cause a crop loss to the extent up to 70% in severe infected conditions. CLR is considered as the most severe foliar coffee disease known to date. Coffee arabica L. is the most receptive of all coffea species to CLR however, its reception depends on the different varieties. Robusta coffee is also receptive to CLR but the damage caused is negligible.

CLR is caused by the fungus Hemileia vastatrix which normally lives as an obligate parasite in the leaves and sometimes also in the young shoots and fruits of coffee plants only. Young delicate leaves of coffee show generally stronger susceptibility than the older ones. CLR is very specific to coffee and no other host of propagation has been identified for this parasitic fungus since its first appearance in Srilanka about 14 decades back. As on today 41 different physiological forms of this hemileia are known.

Favourable conditions for the development of CLR

The fungal spores germinate in damp conditions in the presence of water. Epidemics therefore are prevalent during the wet season. Rainy spells show an increase in the spread of the fungus. The most favorable temperature for the germination of fungal spores is between 21°C and 25°C. Below 15°C or above 28°C temperature the spores generally do not germinate. Light intensity falling on the coffee plants has also a direct influence on the germination of the CLR spores. When the environmental conditions are cloudy and the coffee trees growing under shade trees or have dense foliage, the light intensity on the undersides of the coffee leaves is low, under these conditions the germination of the fungal spores are hindered.
Therefore, there is a strong interrelationship between light and temperature on the extent of spore germination. This is why plantations at higher altitudes hardly ever suffer from being severely attacked by the leaf rust disease. The temperature at higher altitudes is generally low which does not permit spore germination. Even if the temperature at these altitudes is favorable there is often inadequate moisture which does not provide favourable condition for germination. In addi tion to these parameters, researchers showed that low soil pH combined with high yield can also predispose coffee trees to the disease. The coffee leaf rust fungal spores are carried by wind to a longer distance while rain water splash, animals or plantation workers will spread them to shorter distances like on the neighboring plants.

Therefore timely control measures have to be taken to avoid the spread of the disease with the test proven chemicals. Bordeaux mixture (prophylactic) and other organic fungicides (systemic) could be used to control the CLR disease. The fungicides like Bayleton (triadimefon) and Contaf (hexaconazole) have systemic action combined with preventive, curative and anti-sporulant properties generate good results with minimum application and hence such systemic fungicides can be used but judiciously. The application of Bordeaux mixture should be done on time with adequate coverage underneath the leaf surface for the effective control on the spread of the fungus to newly generated young shoots. Spray of Bordeaux mixture during the pre-monsoon period is very essential which protects the younger leaves from getting contaminated from the fungus

Some useful steps to prevent CLR Preventive measures are as important as curative measures in the control of CLR. One should always remember the following points.

· Sufficient space should be created between the individual plants to avoid cross contamination.

· Good aeration for rapid drying of the leaves.

· Sufficient moisture content should be maintained in the soil through proper mulching.

· No weeds should be allowed which may act as bridge between the individual plants.

· Good fertilizer programme should be practiced to induce more vigorous growth of young tissues especially with nitrogen fertilizers.

· At the end of long dry period and well before the onset of monsoon, preventive measures should be initiated as at this point of time there will be least number of germinable spores.

· Preventive action has to be taken by the use of Bordeaux mixture spray immediately after the receipt of first rain.

· The coffee plants have to be sprayed in such a way that the entire underneath portion of coffee leaves are covered with the spray solution in right quantity.

Rising Cost of Copper sulphate and whether Bordeaux mixture spray can be avoided?

Any estate operations which are mandatory in nature like leaf rust control/prevention in arabica plantations should not be compromised with the cost of chemicals. If compromised, in the long run the results will be devastating as the plants shed the leaf compliments due to higher incidence of CLR, inviting higher incidence of white stem borer also. Therefore, control of CLR is very crucial. Now, since the cost of Copper Sulphate is constantly rising, many enquiries have come about either skipping the BM spray or reducing the recommended quantum of spray solution per acre. It is also noted that the sprays are given untimely in inadequate volume due to higher cost of copper sulphate. Few planters are resorting to sprays of systemic fungicides in the place of BM spray. It is advised that continuous use of systemic fungicides in the coffee plantations for the control of rust may lead to the development of irreversible resistance in the fungus. If, once the fungus develops resistance, it may lead to a position where no product will be effective for disease management especially in the control of obligatory parasitic fungus like Hemileia vastatrix.

Skipping of BM spray will also lead to the development of black rot, stalk rot and other disease problems in arabica plantations. There should not be reduction in the spray volume and recommended quantity of spray solution should reach the target area for the effective prevention of the spread of the CLR disease in coffee. For the grown up plants with 6X6' spacing, 1200 liters (6 barrels or 7) of 0.5% BM spray is essential (ie @ the rate of one litre per plant). If we use high volume sprayers, the wastage will be more and hence planters can use DSP sprayers with 8 to 10 lances. Small planters can use gator sprayers with long hose (60 - 70 feet length). It is specially advised that the Copper Sulphate procured by the growers have to be tested for its content and composition before use as there is a risk of adulteration with other cheaper chemicals including sugar (it takes the same colour as Copper Sulphate and is cheaper) which has been experienced some years back. The pH of the BM should be adjusted in between 9 and 10 for maximum efficiency of the sprayed solution in preventing the CLR spread to other tissues. It is recommended that, it is not advisable to skip BM spray during the pre monsoon period as well as during the post monsoon period (those who use 2 BM sprays in a year instead of systemic fungicide use during post monsoon period). Other planters who use systemic fungicides during the post monsoon period are advised to use them sparingly. Those who could not take up pre-monsoon BM spray due to the early setting of S.W. monsoon, the spray could be taken up during the break in the monsoon. Wherever, leaf rust and black rot problems are noticed, Bayleton plus Bavistin or Tilt plus Bavistin (160g/ ml + 120g) can be sprayed to reduce CLR as well as black rot disease on arabica in the heavy rainy fall areas.

Presently the cost of Copper Sulphate is Rs 145/- per kg as against the last years cost of Rs 60/ - and is unlikely to come down immediately. The total cost of spray solution per acre (7 barrels) will be therefore around Rs 1050/(including spray lime cost) which is about Rs 600/- more when the chemical cost was low. If this spray is skipped, there is a definite risk of heavy proliferation of leaf rust fungus affecting the entire plant leading to heavy defoliation, black rot incidence as well as stalk rot problem. Heavy defoliation causes higher levels of white stem borer problem and imbalance in fruit development and ripening. In any case, in the absence of pre-monsoon BM spray, there is a chance of 2030% defoliation leading to 10-15% crop loss or sometimes more in Indian conditions. Although, there is no definite correlation worked out between extent of defoliation and crop loss, research done else where in Brazil have shown that 1 % of the damaged foliage can lead to 1 % crop loss in the following year. Depending on the location and variety, the crop reduction could be 25 to 45% due to disease attack.

As an example, if in a estate picking 300 kgs of clean coffee per acre this will lead to a loss of 30-45 kg of coffee( at the rate of 10-15% crop loss) and the estate is losing approximately Rs 2400 to 3600 (Rs. 80/- per kg of Coffee) per acre on account of skipping the Bordeaux Mixture spray. If, the spray volume is brought down to 5 barrels or lower, the percentage infection level may come down marginally, but may cause greater loss in the long run. Therefore, skipping or reduction in spray volume is not suggested. In the mean time increasing the spray concentration to 1 % by decreasing the spray volume considerably is also not recommended.