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.