Dr Christopher Teh, soil biologist and senior lecturer at Universiti Putra Malaysia, answers gardening questions in Star2’s gardening column, ‘Ready, Set, Grow!’, which is brought to you by social enterprise Eats, Shoots & Roots. To send him your questions, go to the website questions.eatsshootsandroots.com.
I have a papaya tree that was doing well. We managed to eat five fruits from it. But lately the skin of the papayas appear greyish and the texture of the fruit is pulpish. Could a civet cat be the problem? – Fatimah Merican
Your papaya tree is infected with a fungal disease known as powdery mildew. This disease infects all parts of the tree, including its fruits and leaves.
Discard all infected parts – do not bury them or compost them – and avoid over-watering your papaya tree, as a humid environment encourages this disease. Also, avoid wetting the upper parts of tree when watering.
To control this disease, you can use any sulfur-based fungicide. You can also try spraying with a water and neem oil mixture.
I have a pumpkin plant in my garden that produced two to three baby pumpkins – roughly ping pong ball size – at a time but after two weeks, the pumpkins turned yellow and dropped off. This has happened a few times. Why is this happening and what can I do about it? – Tan Hon Yin
Over-watering (as well as under-watering) your trees can cause fruit drops. You should only water it when the top soil is dry. Too much water can drown the roots and cause root rot and no fruit to form.
Another possible reason is your fertilisation. Fertilise less with nitrogen and more with potassium and phosphorus. You can even include calcium in your fertilisation programme.
I have a passion fruit plant in a big pot and it produced two fruits a few months ago. Since then, there have been no sign of fruit production. I would love to know how often these plants bear fruits, and what can I do to encourage healthy growth and production. – Janis Lee
Passion fruit trees can be a challenge to grow as they require careful pruning and training to ensure they grow well and bear fruits. They are also susceptible to diseases.
Prune the tree once it reaches the desired height, then keep pruning off the top to encourage lateral growth. Remove excessive side growths.
You do not want to have entangled, messy side growths. The idea is to have a few main side growths that will have ample space to grow.
You also have to train the branches so they will grow along the netting or wire mesh you have set up.
Fertilise the tree four times a year. Give as much nitrogen as potassium but less phosphorus. Follow the instructions as recommended by the fertiliser bag and adjust accordingly with your yields.
Avoid over-watering by watering only when the top soil is dry.
I tried growing a papaya tree a few times with no success. My attempts produced a tree but before fruiting, the top core leaves will distort and turn yellow, then die off after one week. Why is this happening? – Danny Sao
It is difficult to diagnose your problem without seeing the full scale of it. Your papaya trees could be infected by a virus transmitted by whiteflies that causes leaf curling (distortion), especially near the tree top. My advice is to remove the latest infected tree and discard it by burying it very deep into the soil or chopping it then burning it up. Do not compost it.
Note that leaf curl treatment, which involves spraying with dangerous dimethoate and monocrotophos pesticides, can be costly especially just for one tree.