Mango tree may be suffering from a bacterial disease
I notice a black sticky substance (above) at the tips of the branches of my young mango tree, where new young leaves are growing, and at the dividing parts of the main stems. I have tried to cut off the end of the young branches, but the black substance reappears. Will this cause subsequent flowers to dry up? A friend has recommend using chalk powder on the black parts - will this help?
Ong Sze Lan
It appears that your plant shows symptoms of a bacterial canker that is reported in mango trees. Symptoms include the death of the growing tip with production of a black exudate. The infection can extend outwards from a bud to the central vein of mango leaves. Extensive dying back of branches can also occur.
Prune infected stems to prevent the disease's spread. Note that this disease can be difficult to manage.
Copper-containing fungicides that are available for sale in some local nurseries may be able to provide some control of this bacterial disease. The fungicide should be applied during the rainy season to contain the spread of the disease. Avoid getting too much copper into the soil as excessive copper can be toxic to plants and beneficial soil micro-organisms.
Boost the plant's health by promoting a healthy root zone that permits the plant to absorb nutrients and develop resistance against disease. Mulch the roots with shredded dry leaves and incorporate good quality organic matter.
Spraying the leaves and drenching the soil with a product containing chitosan, which is reported to induce systemic acquired resistance, may help.
Fruit of Eggfruit Tree is best enjoyed when ripe
What plant or tree (left) is this and are the fruit edible? Several trees are grown on a rooftop garden in Toa Payoh.
Yu Chin Hsia
The fruit tree is commonly known as the Eggfruit Tree or Canistel. Its botanical name is Pouteria campechiana. Pick the fruit when it is ripe to enjoy it.
When unripe, the fruit can be hard, gummy and astringent.
Ripened fruit are orange on the outside and the flesh is yellow with a pasty texture, which somewhat resembles the texture of the yolk of a hard-boiled egg or the flesh of pumpkin.
Aglaonema does best under filtered sunlight
I left this plant (left) in the sun and the leaves got burnt. I brought it into the patio and sprayed insecticide on it. It has grown better. What plant is this and should I cut away the burnt leaves?
The plants can be regarded as fancy leaf cultivars of the aglaonema. Aglaonema is commonly called the Chinese Evergreen.
These plants are best grown in a location where they can get four to six hours of filtered sunlight. Direct sunlight can be intense and can bleach and burn the leaves.
The plants should not be grown in dense shade as they will not be receiving enough light to grow well. Plants will be lanky and produce weak, floppy stems.
Burnt leaves should be pruned promptly. Under optimal light conditions, new leaves will be produced and these will replace those that have been removed. There is no need to apply insecticides as there are no pests involved.
Echeveria, Marsh Pennywort are common houseplants
Can you tell me what plants are these? Marie Nicolette Kongx
The plant on the left is a succulent belonging to the genus Echeveria. There are many cultivars for sale in local nurseries.
However, not all are easy to cultivate in tropical Singapore.
They need good light to maintain their colour and a tight rosette growth habit, as well as cool nights to thrive.
These plants grow best in well-drained soil that dries out between each watering. Prolonged wet feet can cause the plants to rot and die.
The plant on the right is botanically known as Hydrocotyle verticillata.
Commonly known as the Marsh Pennywort and Frog's Joy, it is a herbaceous ground-cover plant with a creeping growth habit. This plant thrives best in a sunny and moist spot.
If you have an outdoor garden, avoid growing this plant in the ground as the creeping stems (called stolons) can quickly invade the area and be very difficult to remove.
• Answers by Dr Wilson Wong, an NParks-certified practising horticulturist and park manager. He is the founder of Green Culture Singapore and an adjunct assistant professor (Food Science & Technology) at the National University of Singapore.
• Have a gardening query? E-mail it with clear, high-resolution pictures of at least 1MB, if any, and your full name to stlife@ sph.com.sg