What to do with the leaf miners on your cannabis plant?

  • If small tunnels or channels appear on the leaves of your cannabis plant, be careful. There is a strong possibility that you have a plague of leaf miners before you.  Leaf miners are extremely small flies that can cause serious damage to your plant unless you take the right measures.

There are several species that fall under the category of leaf miners, but the most dangerous ones for cannabis plants are those known as Liriomyza trifolii, Liriomyza cannabis and Liriomyza strigata. What makes plants so attractive to these small flies are their leaves, where they find a plentiful source of food. However, the appearance or non-appearance of these pests does not merely depend on the species itself but also on the cannabis variety being grown, as some varieties are more appealing for miners than others.

These peculiar flies lay their eggs inside the leaves. One or two weeks later, the larvae start to build their tunnels in the leaf, this being definitive visual proof that the plant is at risk of pest infestation.

Their appearance is a source of worry for growers as larvae cause damage when creating their mines and even get to destroy the plant’s photosynthetic organs. In addition to this, the females, once in their adult age, make small perforations on the leaves in order to obtain food.

The measures to be taken to prevent a pest or solve it if it has already appeared differ according to whether we are dealing with indoor or outdoor growing.

When it comes to indoor crops, the mere existence of appropriate equipment interferes with the appearance of a plague, as this acts as a strong entry barrier. If we find just one or two channels on a leaf, we can use our bare hands to find the larva at the end of the tunnel and remove it, thus leaving the rest of the leaf in a healthy state. If the plant is seriously affected, it is advisable to remove it with care.

As regards outdoor crops, prevention becomes a slightly more complex task. Environmental conditions are uncontrollable: if they happen to be favourable to the reproduction of miners, they can lead to pests and a resulting damage to the plants’ health. Insect screens are effective as barriers for preventing flies from entering the area where one is growing plants. Neem oil or garlic extract can also serve as excellent allies.

Spinosad is quite an effective insecticide for fighting plagues of this type. Although it is regarded as a safe product (albeit not permitted everywhere), it is necessary to proceed carefully if one chooses it and not use it in areas where bees are present. 


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