Mealy bugs infesting succulents

I have a few pots of plants in my office and some have a white substance on their stems (above). The plants are grown near the window with direct sun. Why is this happening?

Ellen Choo

The pests infesting your succulents appear to be mealy bugs.

First, use a gentle jet of water to remove them, taking care not to break the leaves of the plants or overly wet the growing media.

Organic pesticides such as summer oil and pyrethrins obtained from some species of chrysanthemum may be used to manage the population of the pests.

Follow the instructions on the label on how to administer these pesticides.

Repeated spraying every three days or so is needed to manage the pests.

Ants are known to "farm" mealy bugs for their sugar-rich honeydew secretions, so you should also manage the ant population that may be moving mealy bugs around the growing area.

Weed is not known to be edible

This plant (below) is growing in my garden. What is its name and is it edible? Does it have any benefits?

Lucy Kie

The plant often occurs as a weed and is botanically known as Gymnopetalum scabrum. It is a member of the melon family (Cucurbitaceae). It commonly occurs in wastelands and is not known to have food uses.

Rainbow Tree needs sunlight to thrive

The leaves on my plant (above) are wilting. I have another pot of the same plant, but its leaves are spread out and they look healthy. What can I do to improve the condition of the first plant?

Quay Suan Tee

The plant is a cultivar of the Rainbow Tree (Dracaena reflexa var. angustifolia).

From the leaves' lack of colour and floppy appearance, it is a sign the plant is lacking sunlight needed for healthy growth.

It should be situated in a location where it can get at least six hours of direct sunlight daily for optimal growth and for its foliage colours to be exhibited.

Lack of blooms may be due to insufficient light

The protrusions in my orchid (above) do not turn into flower buds. Why is this so?

Grace Tong

The identity of your orchid is not apparent from the picture. It is important to know the species - in terms of its botanical name - characteristics and growth requirements of the orchid.

There are various reasons for orchids not blooming.

First, ensure the plant is one that will thrive in Singapore's tropical conditions.

Some cool-growing orchids require cooler temperatures to grow well. Others need a distinct temperature change to trigger flowering.

Another reason for the lack of flowers may be insufficient sunlight. Plants grown under overly shady conditions tend to be shy in terms of flowering. Their leaves also tend to become long and floppy.

You may want to look at your fertiliser regimen: Avoid using plant food that is rich in nitrogen as that will promote the production of lush leaves over flowers.

Fresh leaves of some Gynura species are eaten as a salad vegetable

I got cuttings of this Gynura bicolor (above) from a community gardener. I was told the plant can be eaten as a salad, so I ate some. Subsequently, I chanced upon a research paper that mentioned that this plant has substances called PAs (pyrrolizidine alkaloids), which are harmful. I also read online that PAs can be destroyed by heat, but their decomposition temperature is usually beyond normal cooking temperatures. I am concerned about the long-term health effect of consuming such a plant. What is your advice?

Alex Quek

The Gynura is probably not Gynura bicolor and is likely an unidentified Gynura species.

The fresh leaves of some Gynura species are eaten as a salad vegetable and there is a study that reported their safe consumption in the short term. As a plant with health benefits, Gynura is known for its anti-hypertensive and anti-diabetic properties.

Pyrrolizidine alkaloids are natural-occurring compounds found in many plants.

It is heartening to know you take the effort to get to know the plants you eat, rather than blindly consuming them due to purported health benefits.

As with plant foods that contain natural toxins and anti-nutrients, it is advisable to know how to prepare them to ensure they are safe for consumption as well as to consume only appropriate amounts.

It is important to know one's body and avoid consumption of pyrrolizidine alkaloid-rich foods if one has liver issues. Long-term consumption of a large quantity of Gynura plants should hence be avoided.

Check with a doctor before self-medicating.

• 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