Root Awakening: Brown spots could be scale insects

Pests could be scale insects

Since I moved to my 22nd-floor apartment, little white and brown spots have appeared on the veins and stems of my plants’ leaves. What is wrong with them? Are they infected and do I have to discard them?

Anita Chia-Jalleh

The brown spots could be scale insects, a type of sap-sucking pest that appears on long-lived plant parts. They can be scraped off easily with your fingernail or a plastic card.

You can also use summer oil, a pesticide sold at local nurseries, to kill the pests. Regular applications and complete coverage of the plant should resolve the issue. Test the pesticide on a small part of the plant to ensure there is no adverse reaction such as pesticide burn.

Since your plants are ornamental and not meant for consumption, you can also apply dinotefuran granules to the surface of the soil. This systemic pesticide will be taken up by the plant and kill any pests consuming the sap. This combination of pesticides should offer better pest control.

Snake plant could be infested or overwatered

My snake plant was healthy, but I recently noticed abnormalities on the leaves that I cannot remove. What is wrong and how can I protect my other plants from this?

Chan Tze Hua

Try scraping the defaced portions off using your fingernail or a plastic card. If you can do so, the pests are probably scale insects. Use a combined treatment: spray the plant thoroughly with summer oil and sprinkle dinotefuran granules on the surface of the soil. Both pesticides can be purchased via plant nurseries and online.

If the spots cannot be removed by scraping, it could be a case of oedema. This is a result of sudden intake of a large amount of water, followed by water retention. The tissue ruptures and heals over with corky brown tissue. If you are growing your plants indoors, ensure there is sufficient air circulation and sunlight. Water just enough to moisten the soil without making it soggy.  

Tree is the Common Sterculia

This tree in my neighbourhood has produced beautiful orange pods. What is it? 

Margaret Lee Kim Gek

The tree is most likely the Common Sterculia (Sterculia parviflora). It can be found not only in Singapore but also from North-east India to Peninsular Malaysia.

As it is a native tree species, the Common Sterculia is often planted locally. The seeds of its fruit can be cooked and eaten. The fruit is also consumed by fauna such as birds.

Dead leaf colonised by fungi

What are these crystals on the leaves of my plant? I trimmed them away, thinking they were mould, but they reappeared overnight at the base of the stem. Are the unaffected leaves safe to eat?

OK Wong

From the picture, the white needle-like fungal bodies can be seen only on the dead and rotting leaf tissue of your sawtooth coriander.

They could be saprophytic fungi that break down and recycle dead plant material. The wet soil and humid environment have likely been conducive for their growth.

You can remove the dead plant parts and discard them. The fungi are not likely to affect living plant tissue.

To avoid this happening again, promptly remove and discard any dying plant tissue. Grow the plant in a sunnier environment which will dry out the growing mix. Soil can be made more well-draining so it dries out faster. 

Pick healthy plants for food, and thoroughly wash and cook all harvested produce before consumption.

Plants grow as shrubs

I came across these two plants on my nature walk. What are they and how tall do they grow?

Andrew Wong

The rosetted plant with serrated leaf edges is probably the Star of Bethlehem (Hippobroma longiflora), which is not native to Singapore. It is a herbaceous, non-woody plant that produces white flowers. Its trailing stem can grow up to 60cm long. Note that the plant’s white sap is toxic.

The plant with reddish leaves is probably a young version of the Common Sendudok (Melastoma malabathricum). It is a native, woody shrub that can grow up to 3m tall and has traditional medicinal uses.