The mango quick decline due to sudden death syndrome or tree mortality is a new emerging problem. Agronomists have researched to find its exact causes and suggested several measures to overcome the problems to save the orchards and improve mango productivity.

Those growers, who followed these suggestions, have achieved good results. However, most of the growers are still facing these problems as they have not followed the agronomists' recommendations.

Water shortage at the critical flowering and fruiting stages is one of the reasons behind this problem. Some progressive growers, to overcome the problem, have changed the irrigation strategies and are applying modern micro-irrigation methods. They are installing drip irrigation systems to apply water to their mango orchards.

The government provides drip system to growers at subsidised rates. The drip irrigation method, also known as trickle irrigation or micro-irrigation, saves water and fertiliser by irrigating through a network of pipes, laterals and emitters. The system allows water near the plant roots either onto the soil surface or beneath the soil surface directly to the root zone area and thus water shortages at critical flowering and fruiting stages of mangoes can be avoided.

In drip irrigation, the drippers operate at a slow rate; usually the discharge matches the soil infiltration rate which neither allows surface flooding nor the runoff making water losses minimal. Fertilisers and nutrients are also applied through this system and their losses made minimal by localised application and reduced percolation. The system can irrigate irregular shaped fields without proper land leveling as it is a prerequisite for basin, border and furrow irrigation methods.

It also minimises soil erosion and labour cost by regulating water through valves and drippers. The foliage remains dry thus reducing the risk of diseases. This method is usually operated at lower pressure than other types of pressurised irrigation systems such as sprinkler, thus energy costs are also reduced.

Many growers have installed drip irrigation system in their orchard and are deriving its benefits. However, some of them have reported problems of immature fruit drop and poor fruit quality under drip irrigated mangoes. They contacted experts at the Sindh Agriculture University, Tandojam, to know the reasons for it.

The university formed a team of prominent horticulturists to find the reason behind such anomaly. The team visited mango farms irrigated by drip irrigation method and explored the possible reasons.

A significant portion of the mango orchard, the experts visited, was being irrigated by drip irrigation system, while the rest of the orchard by basin flooded method. The farm contractor informed them that the drip irrigated mangoes had a significant immature fruit drop rate and defoliation (falling leaves) problem as compared to those irrigated by basin flooded method. The contractor also informed the experts that the quality of drip irrigated fruit was inferior to fruits of basin irrigated trees.

At maturity, the drip irrigated mangoes lost their freshness and quality within few hours of harvest, thus significantly affecting their market value and rejection by exporters. A sound of the stone inside the fruit could easily be heard with a small shake/movement.

The team investigated the possible causes and offered the following preliminary observations and recommendations

A tree was irrigated by four small drippers (Jet sprinklers), installed at near about two feet from the main trunk/stem. The number of drippers was not sufficient (especially in the trees of spread canopy), to provide adequate quantity of irrigation water to meet its requirement.

It was observed that the orientation of the drippers was inappropriate which failed to irrigate outer edges of the whole canopy of the tree/plant. This might have resulted in dry stresses to the plant roots, located in the vicinity of outer edges. The dry stress could be avoided by increasing the number of drippers and through their proper placement around the canopy. The lateral pipe should be placed along the circumference around the canopy and more drippers be installed or water application time be increased.

Until the number of drippers is increased, the irrigation application time with available drippers be significantly increased to an extent that the entire canopy is fully saturated. This will compensate the water deficit and save present fruit set.

The damage caused by wet stressed could also be reduced by flooding the entire area at least once a month, till the number of drippers is increased and the system properly managed and operated.

The present drip system did not apply water to the trees hence they experienced the dry stresses. Apparently, the entire plant canopy was not fully wet; hence the roots located at the outer edges were not receiving water. The system should be operated for additional hours so that water could reach the dry area around the canopy.

Further, it seemed that there was a water application and management problem at farm level. It is suggested that either the frequency of irrigation may be increased or irrigation application time should be enhanced.

The basins around the drip irrigated trees should also be formed; they should be properly irrigated so that discharge should match the infiltration rate. The system should be operated for longer periods until entire canopy area was wetted.

Most of the land between rows of the mangoes was very dry and hard, that also causes temperature to be higher during this time of the year, as compared to basin/flood irrigated lands. This expedites evapo-transpiration that results in high differential in moisture gradients between roots and leaves. Since transpiration demands were not meet due to sharp gradient thus plant leaves did not look fresh and green, particularly during afternoon hours.

It was apparent that the plant leaves were yellow (wilted) while they were lush and green in basin irrigated trees. In order to reduce this dryness effect, either the entire area should be irrigated couple of times or a small channel/furrow between rows should be made and irrigated. This may be allowed in them at least once a month during fruiting and their maturity periods, to avoid the dry effect.

There was no serious problem of any insect pest or disease. However, mango midge and scale insect infestation observed were very rare. Some leaves were found infected with tips die back and bacterial leaf spot diseases, whereas, some symptoms represent inadequate water and nutrition deficiency.

Further, the team suggested a detailed study of the site during next fruiting season. The study should focus on soil characteristics, soil profile texture, water application timing, application rate, soil infiltration, hydraulic conductivity, moisture distribution pattern, soil fertility level, fruiting behavior, and other relevant parameters. The impact of these factors along with water through drip system could then be related to the yield and quality of mango and a final conclusion could be drawn.

Young and poor quality mango plant with two drippers (Jet sprinklers). The healthy plant may be replaced and there should be provision of more number of drippers, when canopy of the tree increased on age.