Hand Fern has fungal disease
I bought this fern (above) at the Singapore Garden Festival. What is its name?
The fern is botanically known as Doryopteris pedata and its common name is Hand Fern, which refers to the shape of its fronds.
Your plant appears to have black fungal spots on its fronds. You may need to use a fungicide to control its spread while allowing new fronds to develop before pruning them.
Do not prune all the fronds as this will kill the plant. In future, avoid injuring the fronds so they do not get infected again.
Pomegranate plants need full sun, less water
My pomegranate plants (above) are lanky and sparse and some branches have turned bald. I regularly snip off the bald branches and prune the overgrown ones, hoping to make the plant more lush, but to no avail. The plants also do not bear fruit. They get three hours of direct sunlight a day, fertiliser every two months and water every day. What is wrong with them?
The pomegranate plant (Punica granatum) requires full sun to grow well. The amount of light your plants get may not be sufficient.
Next, this plant is best grown on slightly drier soil. Allow the growing media to dry out a little before watering again. Excessive moisture can lead to root issues and promote soft, lanky growth.
Finally, avoid pruning the plant excessively because flowers are produced on new growth.
Guava fruit borer infesting plant
My guava plant is growing quite well. But about a month ago, it was attacked by mealy bugs. This stopped after I sprayed the plant with insecticide.
The fruit I collected a few days ago looked quite good on the outside, but when I cut it open, it was rotten (above) and worms could be seen wiggling. How did this happen and how can I prevent it from happening again?
Lee Chee Chee
Your guava appears to be infested by the guava fruit borer, which is the caterpillar of a moth. In a home garden, it is not advisable to spray pesticides that can affect your neighbours and damage beneficial fauna, which may, in turn, help to manage pests.
It is more practical to inspect the plant for eggs of the moth that are laid on flowers and developing young fruit and remove them promptly. It is also important to wrap developing fruit with plastic bags to prevent the adult moths from laying eggs on them.
Finally, remove infested fruit and discard them with household trash to break the life cycle of the moths.
Lithocysts common in rubber plant
The leaves of my rubber plant (above), which is more than 10 years old, look diseased. There are white bumps and brown dots on the front and "rusty" stains on the back. Are these signs of a scale insect attack? Should I remove the diseased leaves or prune the stem and hope for new leaves to grow? The plant is grown in a large pot on a balcony facing the south.
The white dots on the leaves of your rubber plant (Ficus elastica) are typical of the species. These spots are called lithocysts, which are specialised enlarged cells containing crystals of calcium carbonate. They cannot be rubbed off and there is no cause for worry.
Yam refers to different plants around the world
Is the yam sold in supermarkets here called taro? I understand that yam plants have vines and are creepers, such as sweet potato or Chinese yam.
Common names can be confusing as the same name can be used to refer to different plants in different regions.
The term "yam" is a good example. It refers to the underground storage organs that a number of plants produce. This is the reason botanical names of plants are used to pinpoint particular plants.
In Asia, the term "yam" is used to refer to the plant from the Arum family (Araceae) that produces edible underground corms which are used to make desserts and cakes. Its botanical name is Colocasia esculenta and it grows as a herbaceous plant with a bunch of shield-shaped leaves.
Also in the same plant family as the common edible yam is the elephant foot yam whose botanical name is Amorphophallus paeoniifolius. The large brown corms of this plant can be seen being sold in the fresh produce shops in Little India here.
The underground storage organs from plant species from the genus Dioscorea are also called yams. In Singapore, you can see the Chinese yam (Dioscorea polystachya) and Ratalu Purple Yam (Dioscorea alata) on sale. Plants in this genus are climbers.
In parts of the United States and Canada, the term "yam" is sometimes used to refer to the common sweet potato (Ipomoea batatas). It is a relative of the morning glory and is often grown as a groundcover, although it can also take on a climbing growth habit.
• 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.
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