Check olive tree for root issues

My olive tree, which is planted in the ground, has been growing well for the past seven months until recently, when the leaves started to drop. Some leaves dried up and took on a lacklustre colour and the whole tree seems to be dying. There is no visible insect attack and the watering schedule has remained very much unchanged. What is the likely cause of the problem and what should I do? The tree gets four to five hours of sunlight every day and is watered every evening.

Joshen Ooi

The closing and browning of leaves often point to an issue related to water uptake and hence the health of the roots.

When did the issue start to appear and did it occur during the rainy season late last year? The waterlogged root zone could have caused root rot or disease. Often, the issue occurs on one side of the tree before spreading to the entire tree.

Olive trees can be tricky to grow in tropical Singapore as they tend to require well-drained soils.

Local outdoor landscapes that feature this tree often grow it in a raised planter box.

It is not easy to detect root disease and it can be difficult to treat. You may want to carefully excavate the soil to check the health of the roots.

Withhold watering and let the root system dry out slightly before watering again may help.

Weed is likely the Hawaii Woodnettle

I have this plant growing in my pot for the last three months. I have planted various types of seedlings of fruit plants and vegetables in it, but I cannot recognise this plant. What is it?

Gary Seet

The plant is probably Hawaii Woodnettle. Its botanical name is Laportea interrupta.

It often occurs as a weed in flower pots and planted flower beds. It is reported to have medicinal properties.

Cucumber leaves infected by a fungal disease

I have several Japanese cucumber plants and ladies' finger plants that are fruiting well, but their leaves are infected, yellowing and breaking by themselves. How can I resolve the issue as the plants are dying rapidly?

Peter Lim

Your cucumber plants have been infected by a fungal disease called powdery mildew. This disease can be difficult to control.

If the disease is not widespread, you can prune infected leaves and spray a milk solution to prevent its spread.

It is best to plant a cucumber cultivar that has resistance to this disease and preventive sprays of a chemical fungicide can provide better control over the disease.

When using chemical fungicides, do observe the withholding period between fungicide application and harvesting of fruit for consumption.

• 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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