Root Awakening: Jambu plant may have spider mites

Spray the plant thoroughly with dilute sulphur soap or a lime sulphur solution, which will suffocate and kill the mites. PHOTO: NG WAI LAM

Jambu plant may be infested by spider mites

What is the reason the leaves of my jambu plant keep dropping and turning yellow?

Ng Wai Lam

Examine the affected leaves closely using a magnifying glass, if necessary, and see if you can spot small red moving dots. These are spider mites that may be causing the speckled marks on the plant’s leaves. Spider mite infestations are common on plants grown in dry high-rise environments, which are also devoid of natural predators of the pest.

If they are indeed spider mites, spray the plant thoroughly with dilute sulphur soap or a lime sulphur solution, which will suffocate and kill the mites. Several applications are often required to provide adequate control.

On a regular basis, hose your plant down to remove pests. This is a chemical-free method to keep plants pest-free.

Stem of curry leaf plant may be infested by scale insects; okra has nutrient deficiency

Curry leaf plant (left) and lady’s finger plant. PHOTOS: PADMA ADHIKESAVAN

The stem of my curry leaf plant has a white layer, and the leaves of my lady’s finger plant have changed to light green. Why is this happening?

Padma Adhikesavan

Use a soft toothbrush to try to gently scrap the white coating off the stem of your curry leaf plant.

Check the material using a magnifying glass to see if they are scale insects, which are common pests found on woody perennial plants. If they are, use the toothbrush to remove them, but take care not to injure your plant.

After that, apply summer oil insecticide all over the plant to suffocate the remaining pests. Several applications on a regular basis should provide some control.

As for your lady’s finger, the chlorotic older leaves are a sign the plant has a mobile nutrient deficiency, most likely that of magnesium. Use a fertiliser that contains magnesium. A chemical salt-based, water-soluble fertiliser or Epsom salt solution may help.

Also, ensure your soil has some organic matter, is aerated, well-drained and not compacted for optimal root growth and function.

Protect hibiscus flowers from drying winds and grow the plant under direct sunlight

Hibiscus are heavy feeders and require iron and a slightly acidic soil pH level for good growth and health. PHOTO: SOOCL

I have been caring for this hibiscus plant for some time. The flowers bloomed beautifully initially and the plant received water daily and fertiliser monthly or once in six weeks. However, the flowers have stopped blooming as beautifully and, sometimes, the bud would wither without flowering. The edge of the petals also curls up when the flower is blooming, and there is a darker red ring in the centre. The bloom cycle is also much longer. I have moved the plant from its spot in the balcony, where it had full sunlight, to a shadier area and two flowers bloomed on consecutive days. How can I make the plant bloom brightly again?

Soo C.L.

Hibiscus are generally considered high-light plants, thriving and blooming when they get at least six hours of direct sunlight. But they can tolerate a little shade.

The lack of sunlight can cause plants to remain vegetative or decline. Hibiscus are heavy feeders and require iron and a slightly acidic soil pH level for good growth and health.

The burning of the flower petals could be due to drying winds, which is common if plants are grown in windy high-rise environments such as balconies and corridors. Ensure the plants are well-watered and grown in a protected location to reduce damage to flowers.

Black leaf surfaces may be brought about by sooty mould

Sooty mould can be removed by spraying leaves with a very dilute soap solution and then wiping the leaf surfaces with a soft cloth. PHOTO: AUDREY LIM

My hydrangeas were growing well for the last nine years, but the leaves are turning black lately. The plants are grown in the ground and under a transparent shelter, so they get light but not direct rain.

Audrey Lim

For the blackened leaves, do they feel sticky and can the residue be scraped off? If so, it could be a case of sooty mould.

The damage caused by sooty mould is mostly aesthetic, but is a sign of a sucking pest infestation. Check for the presence of scale insects, aphids, mealy bugs or whiteflies – these are common sap-sucking pests. They excrete honeydew, which is a sugar-rich liquid, and this falls and coats leaf surfaces which sooty mould will then grow on.

Sooty mould can be removed by spraying leaves with a very dilute soap solution and then wiping the leaf surfaces with a soft cloth. At the same time, the soap solution can also suffocate the sap-sucking pests.

Apply the soap solution on a small part of the plant first to see if there is any adverse effect. Dilute the soap solution further if it burns leaf tissues and apply it late during the day when it is cooler.

Grow plants that are less susceptible to awl snail damage as a more sustainable approach

I am making compost using leftover raw vegetables, dried leaves, eggshells and banana peels. I have found beetle larva and, now, awl snails in it. I am told both are harmful to plants. Does my method of processing compost need improvements? Can such compost be used as fertiliser? My new xiao bai cai has been eaten up by the awl snails.

Lee Chee Chee Thomas

The feed materials used to make your compost are generally low in nutrients, so the resulting compost is a source of organic material that is best treated and used as a soil amendment to improve soil structure. The nutrient levels are too low for the material to be regarded as fertiliser.

As for the awl snails, you may want to scatter tea seed powder, a low-toxic plant-derived material that can help to kill the pests. Several applications over time can help with the infestation.

But tea seed powder can affect beneficial fauna like earthworms. Consider adding watermelon skins to attract the snails to the bait, so they can be removed subsequently.

Beetle larvae are part of the fauna that helps with the breakdown of organic materials. They should leave the system once the organic matter has all broken down.

Note that the infestation of awl snails can also come with the material you use to make compost. The constant addition of compost to planting beds made from such materials will mean that the infestation may continue even with measures taken. A more sustainable growing approach is to grow plants that are less susceptible to awl snail damage.

  • 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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