Chiku's lichen is harmless, desert rose is ageing

Our family has had this chiku tree for many years and it produced large, sweet fruit. However, in the last two years, large algae-like patches have been developing on its trunk and seem to be growing thicker and bigger. The tree has also stopped fruiting. What are these patches and how do I eliminate them?

We also have a desert rose plant which is flowering very well, but the leaves of the lower branches keep turning yellow and dropping. What is the cause?

Josephine Howe

The bluish-green growth on the bark of your chiku tree is probably a lichen, which consists of algae or cyanobacteria living among fungi in a mutualistic relationship.

These grow on the surface of the bark and do not pose any danger to your tree. Their presence is regarded as an environmental indicator of air quality that is good enough to support their growth.

For your desert rose, if only a few older leaves fall off, it is usually not a cause for concern. The plant produces new leaves and sheds older ones over the course of its growth.

Do note that although the desert rose is a drought-tolerant plant, it should not be allowed to dry out totally. When experiencing moisture stress, the plant will wilt and older leaves may turn yellow and drop off. Water it regularly and let it dry out slightly before watering again.

Plant may be dill or fennel

What plant is this? It is special to my family, as we received the seeds from a Taoist priest after my maternal grandfather's funeral in 2019.

The plant germinated and has been growing for the past year or so. It is now about 70cm tall and has some yellow flowers.

Goh Wee Gin

The plant may be either dill (Anethum graveolens) or fennel (Foeniculum vulgare). They are easily grown from seeds which are often sold as spices.

Both plants produce feathery leaves and yellow flowers. They are annual plants which die once they finish flowering and fruiting. You can collect the seeds and grow new plants.

The dill plant is generally smaller and produces bluish green leaves. The fennel plant, on the other hand, is slightly larger and its leaves are a lighter green. It may not form the characteristic bulbous base.

Regular maintenance needed for weed-free turf

There are two large patches of weeds (above) of the same kind in my garden. Please help me identify the weed and the weed killer I need to eradicate it.

Ho Foong Keng

The weed appears to be the White Kyllinga (Kyllinga nemoralis). It is a common weed in Singapore.

Applying commercially available weed killers will kill or damage nearby plants.

You may want to engage a landscape company to remove the infested area and also some soil beneath to get rid of any rhizomes. New turf can be installed after that.

Do note that regular maintenance of your turf is essential to ensure it remains weed-free.

Neem plant infested with scale insects

What are these on the neem leaves (above)? How should I deal with them?

Mah Yee Leong

Your neem plant appears to be infested with scale insects. The white mass on one of the leaves is the egg case of this pest. Scale insects suck sap from a plant and can weaken it if the infestation is severe.

Environmentally friendly methods of control involve removing heavily infested parts of the plant and spraying it with pesticides such as summer oil, which can suffocate the insects.

Pyrethrins extracted from chrysanthemum flowers may be used in rotation. Regular applications are needed to reduce the pests' population. Chemical pesticides may also be used. They can be more potent, but may affect beneficial fauna in the garden.

Rainy season may hinder pollination

I was so proud my pumpkin plant (right) had finally started to bear fruit. However, one by one, the fruit turned brown and dropped off. It cannot be due to a lack of water, since it has been raining almost every day lately.

Thomas Lee

The large yellow flowers of the pumpkin plant are usually pollinated by bees.

During the rainy season, they are less active and natural pollination may not occur. As such, flowers with incomplete pollination may be aborted. Excessive moisture at the roots may also be the cause of the issue.

The surface of one of the young fruit seems to have been eaten. Snails and slugs are often the culprits, and are more active during the rainy season. You may want to plant your pumpkin during a drier and sunnier time of year.

Also, try to train the pumpkin vine to grow on a trellis off the ground to prevent pest problems such as snails and slugs, as well as diseases such as mildew.

Direct sunlight, water

My plant has produced flowers for the first time in six years. At the same time, many of its leaves are turning pale green and then yellow. Nearly half of the leaves have fallen off in the last few weeks, while flowers are appearing.

What is this plant and what is happening to it?

Ed Aw

The plant looks like the Caricature Plant (Graptophyllum pictum).

From the picture, the pot seems a little too small to support the growth of the plant. You may want to move it to a larger pot.

When a plant is grown in a small pot, its supply of water will run out quickly. When experiencing moisture stress, the plant will wilt and older leaves may turn yellow and drop off.

Also, if the plant has been growing in the same pot for a long time, its nutrients may have been exhausted.

Fertilise it regularly to support healthy, robust growth.

The plant also looks a bit lanky. You may want to prune it to promote a more bushy growth habit.

The stem cuttings can be used to propagate new plants.

• Answers by Dr Wilson Wong, an NParks-certified practising horticulturist, parks manager and ISA-certified arborist. 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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