TALK ABOUT PLANT DISEASES

Plant diseases are caused by FUNGI, BACTERIA OR VIRUSES. This pathogen lives on or inside the plants as a parasitic organism by consuming the host plants for their source of food. The pathogen pant disease affect the health of the plants and reduce the yield production as well as kill the plants. So there must be a factors determine the severity of the disease attack to the plants or there must be a suitable condition for the pathogen to multiply tremendously in the plant tissues. Although the disease may be introduced in the clean area but climatic and soil condition favour the establishment of the disease organisms. This article I would like to share knowledge about factors determines the severity of plant disease based on my observation and experience in food crop extension activities for about 30 years in the field. Factors that determine the severity may due to Soil Condition, Climate, Irrigation, Planting Distance and Planting Time.

1. Soil Condition
As I visits most of vegetable production area in Malaysia, most of the vegetable area are fertile, well-drained soils with plenty of organic matter to ensure high productivity. The soils also balance in the supply of plants nutrients and adequate moisture stand and excellence chance of withstanding attacks by most disease. Most lowland vegetable area are located near the water supply such as rivers, lakes and ponds. One of the largest vegetable area in Muar located at Sengkang B1 19 and Kg Solok Tangkak are peat soils with modern infrastructure. From my observation some seeds are slow to germinate due to unsuitable soil condition for roots to establish or take a longer time for the crop to establish. Some cases may be infected by damping-off fungi at early stage.

Leafy vegetable need a significant amount of water from sowing to harvesting season especially on peat soils that are porous and lack of important nutrients. The acidic soil favour the disease and it is important to apply lime (GML etc) to improve the soil pH and increase the ability for the plants to absorb the nutrients from the soils. Soil humidity, CEC, acidity, salinity, texture, pH and others may results the plants growth. Some vegetable farmer apply more organic matter and compost to improve the soil fertility.

2. Climate
Although soil temperature can influence the growth of soil-borne fungi, the main effect of the climate is on those diseases developing above ground level. High temperature and high humidity in most lowland vegetable area in Malaysia may favour for certain diseases to establish such as Downy Mildew fungi attack watermelon, melon, cucumber and their family groups. Other disease such as leaf spot disease, mould fungi are associated with the climate and environmental factors. From my observation in large vegetable area in Tangkak and Johor Bahru area seems that the wet season (in November to January) the chances for leafy vegetable are frequent and affect yield quantity and quality.

3. Irrigation
Irrigation system in vegetable growing area are critical because the spread of plant disease pathogen related to the distribution of the water. There is a report saying that if the farmers watered their vegetable in the late day may cause the leaves remain wets and this condition allow the spores to germinate in infect the plants. Overhead irrigation ( by sprinkler system) is the most system applied in Johor, Malaysia because it was practical, cheap maintenance, effective and applicable. Some disease may start from water source, water flow , spraying , contact and many others. Drip tape, micro-sprinkler, mist system, open over-head sprinkler and many other supply the water according to type of crop, varieties, plan age and planting system.


4. Planting Distance
From my observation in commercial vegetable farm in Buloh Kasap, Segamat, Johor seems that the densely planted crops can create condition of high humidity and less wind movement which encourage the growth of many diseases. The normal planting distance for bitter gourd (Momordica charantia) is 1.5 m x 0.5 m to provide 8,540 plants/ha and if planted in closer will cater more than 10,000 plants/ha. More numbers of plants per hectare may not produce more fruits but more plant diseases as I observed.

5. Planting Time
Crop Calendar and matrix Production calendar is a planning program for the farmers WHEN is the best time to grow vegetables. Watermelon growers would not grow during November to January in Johors and most east coast due to wet season and possibility of flood, water-logged and poor drainage. Farmers has their own planting time date to suit the market demand, best climate, high demand, suitable land area and practical.


By,
M Anem
Agronomist
Johor
Malaysia