Root Awakening: Build a light trap to manage millepedes

ZZ plant
ZZ plant

ZZ plant does not release toxic gases

Recently, we bought a few pots of the ZZ plant for the office. However, we received feedback from a colleague that this plant is poisonous and could emit poisonous gases. Even after researching on the Internet, we are still uncertain whether the plant is safe. Is it?

Stephanie Tee

To date, there are no peer-reviewed, reputable, scientific research reports to back claims that the ZZ plant (Zamioculcas zamiifolia) releases toxic gases that are harmful to humans.

However, do note that this plant belongs to the yam family (Araceae). Similar to many plants from the same family, such as the money plant and common edible yam, the ZZ plant has minute calcium oxalate crystals in its sap and tissue.

People with sensitive skin should avoid touching its sap and tissue as the crystals can cause skin irritation. Do not eat the plant as well, as these crystals can cause inflammation of mucous membranes in the body.

Plant may be sunburnt

The leaves of my plant are turning yellow (above). But the plant continues to grow and new leaves are formed. I water it regularly, making sure that the soil is not dry. What is the cause of the yellowing leaves and how can I treat it?

Summer Low

The plant is botanically known as Schismatoglottis wallichii. The leaves of the plant appear bleached and burnt at the edges. It could be a case where the sunlight is too intense for the plant, leading to sunburn. The environment may also be a little dry with low humidity.

It usually grows as an understorey plant in a rainforest where there are gentle rays of sunshine and the humidity is rather high.

As such, you may want to move the plant to a more shady location that is not windy.

Build a light trap to manage millipedes

What is the best way to eradicate these millipedes without harming the plants and environment?

Ben Yeo

There are several ways to reduce the population of millipedes in the garden. Millipedes are decomposers and are attracted to organic matter. As such, it is necessary to use good-quality compost that is mature and low in carbon content, which serves as a source of food for millipedes.

Use dried leaves cut into small pieces as a mulch to reduce the millipede issue. Small leaves are preferred as they are less liable to collect water which can lead to mosquito breeding.

You can make your own pitfall trap, where a container is buried in the ground with its rim at surface level. Fill the container with a diluted garden insecticide. Install a light source, such as a garden solar light, next to the pitfall trap.

Millipedes attracted to the light will fall into the container and be killed by the insecticide solution.

Periwinkle may be lacking in nutrients or infected by a disease

Some of the leaves of my periwinkle plants (above) turned yellow, even though the plants still produce flowers, albeit tiny ones. The plants grew well before and produced lots of flowers and were exposed to at least six hours of sunlight. Do they suffer from a severe iron deficiency called chlorosis?

Oei Khoen Hwa

You are right - your periwinkle plant (Catharanthus roseus) may be lacking in nutrients. In this case, it is a mobile nutrient - such as nitrogen, phosphorus, potassium or magnesium - which can be moved from old to new leaves by the plant. This results in yellowing leaves at the lower portions of the plant.

You may want to check the soil pH level to ensure it is in the right range so that the nutrients can be absorbed by the plant.

Once the soil pH is corrected and nutrients added, the symptoms should gradually disappear.

Another possibility is a phytoplasma disease caused by a micro-organism that is spread by sucking insects like leafhoppers. If this is the case, there is no cure for your plant and you need to remove and discard it.

If you are to grow periwinkle again, take note that there is a need to manage the population of sucking insect pests in the garden and to sterilise cutting tools used.

Kuan Yin bamboo is infested with scale insects

I planted this Kuan Yin bamboo (above) about a year ago. In the beginning, I just put it in water. Later, I pierced some holes at the bottom of the bottle and put soil in it. The plant was growing well for some time, but a month ago, I noticed spots appearing on the leaves. They began with old leaves at the bottom, but now they are spreading to younger leaves as well. I place the plant on my window sill, but put it indoors for a few hours midday to avoid strong sunlight.

Tan Pin Ho

It appears that your Kuan Yin Bamboo plant (Dracaena braunii) is infested by scale insects. They are a common pest in this plant when it is grown under insufficient light.

To ensure that your plant is healthy and able to ward off pests like scale insects, it is necessary to provide sufficient light for its growth. The Kuan Yin bamboo prefers to be grown in a location where it can get at least four hours of filtered sunlight.

You can use a very soft toothbrush to remove the pests, but take care not to scratch the leaves. After that, you can use summer oil, neem oil or a soap solution to spray on the plant.

Ensure that all surfaces are covered and repeat the application to make sure the pest population is kept at a low level.

Follow the instructions on the label to dilute pesticides before application. Repeated applications may be needed to keep the pest population at a level that is not detrimental to plants.

Apply pesticides during the cooler part of the day to reduce the likelihood of them burning the leaves.

• 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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A version of this article appeared in the print edition of The Straits Times on July 21, 2018, with the headline 'Root Awakening'. Print Edition | Subscribe