Category Archives: Pests & Diseases

Basil Troubles

Posted on February 26, 2010 | 2 Comments

Basil is probably the most common Western culinary herbs grown by most gardeners at home. Several cultivars of basil are grown by Singaporeans at home. Sweet basil appears to be quite common for those who cook Western food and are also fans of pesto. Those of us who are into Thai and Vietnamese cuisines would grow the Thai basil. Our Hindu friends would grow a pot of the green or purple sacred basil.

One of the most common pest problems faced by gardeners when growing basil is the infestation of the young and emerging new leaves at the growing point by sucking insects such as aphids or mealy bugs. The symptom of a prevailing infestation is quite obvious – the affected new leaves become crumpled and distorted. In some of the more severe cases that I have across, leaves can fuse into a tight mass.

Aphids and mealy bugs that cause this disfiguring symptom can only be found on the underside of the affected leaves. These small sucking insects hide amongst the folds formed in the distorted leaves and this makes the spraying of infested plants with contact pesticides rather ineffective in the eradication of these pests as it is difficult to ensure that the delivery of the chemical to all surfaces of the plant. Note that affected leaves do not recover even when the pests have been eradicated.

What I often resort to is to prune away all affected parts of the plant – cut away affected growth points down to the next healthy and uninfested node. It is essential to note that the node is still green and capable of producing new growth. Older basil plants tend to become woody near the bottom portion of the plant. Cutting such plants down to the woodier portion can prove to be rather risky as new growth may not regenerate as a result.

By pruning away infested parts of a basil plant, we are in fact reducing the number of pests that need to be eradicated. After cutting away affected portions of a plant, you may want to apply a contact pesticide to kill any remaining sucking pests and over the next few days, monitor the population of these pests. There may be a need to spray plants again after a few days to ensure the progeny of these pests have all been wiped out. Because basil is grown for food uses, I often opt to use either neem oil or white summer oil, which are more environmentally-friendly and non-toxic compared to conventional synthetic pesticides.

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Posted in Herbs, High-rise Gardening, Pests & Diseases

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Now I know why my Edible Bananas are dying!!!

Posted on November 8, 2008 | 2 Comments

The dwarf banana plants have been my pride and joy in my Ginger Garden. Recently, out of a sudden, I noticed two of my plants started to yellow and the pup that was growing beside one of these plants started to die back. This is not the first time that this happened. It occurred to another larger banana plant and a Bird-of-Paradise plant that were grown in the same garden.

An apparently healthy banana plant that started to turn yellow and die away.

When I uprooted the affected that banana plant, the pseudostem gave way very easily and what I saw was a black coloured, rotten mess inside the stump. It looks like rot and there were numerous tunnels that ran through the mushy remains of the pseudostem.  

The base of the pseudostem of the affected banana gave way very easily and the soft, musy tissue seemed to say that the plant was affected by rot.

This symptom was also seen in my White Bird-of-Paradise (Strelitzia nicolai) that was planted in the same Ginger Garden. The plant showed the same signs and died in the same way some time ago. The growth of my Bird-of-Paradise plant first slowed down and then, its leaves started to turn yellow. One day, the entire plant just collapsed at its base. When examined, the base of the plant exhibited the same rotten mess and presence of numerous tunnels. Some areas exuded a gummy substance.

Notice the three holes inside the pseudostem? They are the tunnels that have been made along its length.

As I was trying to uproot the stump of the dead banana plant, a small, white but fat grub started to crawl out from one of the holes. It was then that I knew what was the culprit that made the numerous tunnels that probably caused the death of my Bird-of-Paradise and banana plants!

I took a photograph of the evil grub and did a search on the Internet and found that it could either be the larva of the Banana Stem Weevil (Odoiporus longicollis) or Banana Weevil (Cosmopolites sordidus). From the pictures that were available online, I cannot really distinguish the two. The reported symptoms of affected plants are also relatively similar.

As described earlier, the base of all my plants that were affected by the Banana Stem Weevil/Banana Weevil were rotten. From published literature, that could be due to secondary infection caused by fungi or bacteria present in the soil or surroudings. Moisture in the soil during the rainy season could have accelerated the advancement of the disease.

The culprit – larva of either Odoiporus longicollis or Cosmopolites sordidus.

Very detailed discussions are given in the articles that were published by Banana Bioveristy International. Click on the links below to learn more about the Banana Stem Weevil (Odoiporus longicollis) or Banana Weevil (Cosmopolites sordidus):

Banana Stem Weevil (Odoiporus longicollis)
http://bananas.bioversityinternational.org/files/files/pdf/publications/pest5.pdf

Banana Weevil (Cosmopolites sordidus)
http://bananas.bioversityinternational.org/files/files/pdf/publications/pest4.pdf

Stated in the e-pamphlet below, Confidor is an insecticide that is indicated for use to control weevil damage. It is commercially available here but is an extremely toxic systemic pesticide. Confidor can also be quite expensive to use large-scale:


http://apepuganda.org/downloads/Publication%206%20THE%20BANANA%20WEEVIL.pdf
 

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Posted in Fruits, Pests & Diseases

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My Milkweed got eaten up!

Posted on May 30, 2008 | 2 Comments

I have recently planted some milkweed plants (Asclepias curassavica) in my community garden after seeing how nice they were at HortPark. It is a marginal water plant which produces eye-catching scarlet umbels of flowers. It is a water-loving plant, which is why I have chosen to grow it in its current location as the soil there can get quite wet during the rainy season. Not many woody flowering shrubs will survive in seasonal waterlogged conditions!

Just this evening, I decided to go take a look at the community garden after work while there was still a wee bit of daylight. As I was strolling through the garden, I was horrified to find my milkweed being defoliated!

At first, I was feeling little angered as I thought it was due to some pranksters who went around to damage my plants. But it did not take too long for me to realise that the damage could be brought about by caterpillars as I recalled that the milkweed is a butterfly food plant. My mood quickly simmered down and I went about to find for the culprits.

Armed with the knowledge that caterpillars are the ones that ate up the foliage, I bent down and then tilted my head upwards to look for the creepy crawlies that may be hiding on the undersides of my milkweed leaves. I was surprised with the two things I saw.

First, it was the large number of caterpillars that were feasting on the plants’ foliage (there are about 15 of them, could have been more as I have lost count). Second, the caterpillars present on the plants were so beautiful. They had white, black and yellow bands on their bodies and there were six black appendages which were thin and floppy on the back of each caterpillar.

With the help from one of my GCS forum members, Mr Gan, whose username on the forum is Green Baron, he identified the beautiful, banded caterpillars as the larvae of the Plain Tiger butterfly (Danaus chrysippus), which is a close relative of the Monarch (Danaus plexippus) butterfly. Mr Gan is also a member of the Butterfly Interest Group of the Nature Society (Singapore). I will be handing over to him the entire lot of caterpillars, which I have caught and temporarily housed inside a disposable food container.

OK, wait! Doesn’t it sound kind of weird to hand over caterpillars to someone?

This practice of handing over caterpillars from one’s garden over to people like Mr Gan is something that some members from the GCS forum have been doing for quite a while. It is like passing over what is considered as pests by gardeners to butterfly enthusiasts who regard them as gems as they want to do their part to conserve our natural biodiversity and heritage.

Besides Mr Gan, Ms Rosalind Tan from Alexandra Hospital who was featured in the papers recently, is one other kind soul whom I know that re-homes unwanted caterpillars that would most probably be killed by most gardeners. These butterfly enthusiasts actually feed these caterpillars until they undergo metamorphsis and then release them back to Nature when they emerge from their pupae.

Take a look at the picture below of the Plain Tiger butterfly, courtesy of Mr Gan. Don’t you think it is a beautiful butterfly?

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Posted in Pests & Diseases, Tropical ornamentals

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Attack of the Mites!

Posted on April 1, 2008 | 3 Comments

Even though it has been documented in books, spider mites are pests that rarely visit bromeliads. I told my friends who grow bromeliads about it and they were quite astonished to know. In fact, this misfortune have become quite a ‘laughable’ matter to them. They were wondering how on earth did my bromeliads get infested?

As far as I can trace, I suspect it was a costus cutting that I brought back home from the garden to nurse under my light garden that is located in my bedroom. It was seemingly clean but as we all know, spider mites and their eggs are not easily visible to the human eye and I won’t be surprised that some were hiding somewhere. Prior to that, my bromeliads have been growing happily indoors under the fluorescent light lit garden for more than a year.

Lesson learnt – please quarantine your plants. Pests and disease can be introduced into a healthy collection of plants very easily.

It all started with me having noticed that my bromeliads showed wierd spots of discoloration on their leaves. These weren’t too visible when the leaves were dry. Because I either periodically mist the leaves of my plants or bring them under the shower to wash the dust off and to flush their tanks, those ugly spots became obvious when the leaves became wet.

At that time, I couldn’t quite figure out what happened. Nothing could be seen because the plants then had just been washed relatively clean. It wasn’t long when I saw web-like substances appearing on my bromeliads. Those fine silks straight-away raised an alarm – spider mites. I examined those threads and I saw small little cream-coloured creatures crawling on them!

Upon closer inspection of all my plants, I noticed colonies of mites having a good time on the undersides of my plants’ leaves.  I also later realised that the spot where these idiotic pests gathered, the colouration of the leaves at that particular location will be permanently destroyed.

Some plants were so badly affected that almost all their leaves became damaged as shown in the photograph below. There is no way to salvage those damaged leaves. I just had to wait for the new ones to appear to replace those that have been damaged and if the entire crown dies, the only next best thing to do is to wait patiently for a new pup to appear.

As I have mentioned earlier, washing away with water did not work too well for this bout of spider mite attack. The eggs that were laid earlier probably did not get washed away and were allowed to hatch.

Next, I tried something that was not that toxic to start with. I used a very diluted summer oil spray to treat my plants on every alternate day. Bromeliads have been reported to be somewhat sensitive to oil-based sprays. That failed to work. The mites came back.

I then frantically went through my chest of garden chemicals and found something that I have bought quite long ago but never used it. The bottle read “Abamectin”. I checked with my fellow gardening friend who grows African violets. He told me that abamectin is very effective against mites but it is very smelly to apply.

Yes – the odour from the spray was quite difficult to bear. Had to hold my breath when I sprayed my plants, leaf undersides and all. Wore gloves as a safety precaution too. I did not bring my plants back into the room for several days. I washed them with water before bringing them back to the light garden – just to play safe.

Abamectin in miticide preparations consist of a mixture of  avermectin B1a and less  avermectin B1b . These two components are derived from the soil bacterium Streptomyces avermitilis and have some systemic activity. It also has a long residue life – up to 30 days but is highly toxic to aquatic life.

So far, abamectin has kept the mites away from my bromeliads for about a week already. Will continue to monitor. Hope the mites will never come back again.

P/S – At present, I am still not very comfortable of using abamectin on edible plants until I am really sure of its safety.

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Posted in Pests & Diseases, Tropical ornamentals

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