Leaves with brown spots
If your Pilea’s leaves curl, it can be quite difficult to figure out what exactly is going on, because leaf curling can have a lot of different causes. Pilea enthusiasts don’t always agree on the exact causes.
The need to take action depends on the amount of leaf loss. If the balance is off (more loss than growth, especially during the growing season), something may be going on.
Fortunately, this is not usually the case. Houseplant leaves can vary in their greenness depending on the lighting. If your Pilea is in a bright location, its leaves may be a fairly light green.
During the winter, your Pilea’s leaves may turn a darker shade of green. Again, there is no problem with this. Just make sure the plant is still getting enough light to survive and don’t forget to adjust the watering schedule. A plant that doesn’t get as much light also doesn’t need as much water.
With the above guide, hopefully you’ve been able to figure out what’s wrong with your Pilea. But what do you do when you lift the plant out of its pot and find a mess of rotting, blackened roots?
Why do the leaves of houseplants turn black?
Downy mildew and powdery mildew are fungi that are harmful to the plant and appear as a white powder on the leaves. There are numerous species of powdery mildew and downy mildew, and they are often specific to a particular crop. This is due to the fact that the diseases often evolve at the same rate as their host. One powdery mildew will affect, for example, cabbage varieties and the other only cucumber plants. These fungi can sometimes be so demanding that they even distinguish between varieties. One type of hatred, which infects cereal plants, may use either rye or wheat as host, but not both.
Figure 1: Infection of Sphaerotheca macularis on a strawberry plant. Sporangia of the fungus are found on the upper side of the leaf. This manifests as a white powder (left). In an enlargement, these organs are visible as threads (right). Source illustrations: Cal-Agri, China and University of Florida, USA.
Figure 2: Infection of Leveillula taurica on bell pepper plant. A white powder can be seen on the underside of the leaf (left) and light spots appear on the upper side of the leaf. Source of illustrations: Ministry of Agriculture and Lands, Canada.
Why do the tips of the leaves turn black?
Let’s start with the most obvious: there are many species – deciduous trees are a clear example of this – that shed their leaves with the first cold weather. The reason is very coherent and is justified as an adaptation mechanism. During the winter, the energy they would spend on maintaining their leaves would not be compensated by the energy obtained in the absorption of nutrients. So, in spite of having to replace them later, they opt to get rid of them.
On other occasions there is a previous symptomatology: the leaves languish before their fall, as if giving clues of what is happening to them. It is possible to recover the plant if you assist it in time. If it is in a pot, you can immerse it in a container of water for a few minutes. Then let it drain well. It is advisable to replace, as soon as possible, the “transport” substrate with which they come from the nursery. Peat dries out and hardens and hardly retains water.
Too much cold can cause that your magnificent plant ends up being a sad corpse. We already know how deciduous species react. But what happens when it is a tropical plant, and in principle a perennial, that “goes bald”? In many cases, plants endemic to warm places manage to live without problems in less favorable climates (as long as frosts are anecdotal, of course).
Why do plant leaves curl up?
– How to combat them: Eliminate heavily affected areas; clean with a brush in small infestations. Use a systemic insecticide every 15 days or spray with soapy water (one tablespoon of liquid soap per liter of water). Ladybugs are their natural predators.
– Symptoms: Mealybugs are visible and generally secrete a kind of honeydew that makes leaves sticky, discolored, yellow and deformed. The honeydew encourages the appearance of the black mold fungus.
– It attacks… This is a very common pest, which attacks all types of ornamental plants (from orchids, as in the photo, and coleus to chamaedoreas and arecas) and fruit trees, especially citrus and olive trees.
– How to combat: Clean the affected parts with a cotton swab dipped in methyl alcohol; cottony mealybug can be controlled by spraying with soapy water. If the infestation is massive, it is best to cut it out. Move the affected plants to a cooler place with more light. Apply an insecticide and repeat the treatment two to three times every 15 days.