Common plant diseases

How do you deal with a plant that is sick?

Does your plant suffer from bugs or fungi? Read here how you can save your diseased plant and protect all other plants in the room against it.


Is there a white powdery substance on the leaf and does it spread quickly over the top of the leaves of your plant? Does this even affect the leaves in that they turn brown and die afterwards? Then you may have to deal with mildew. The quickest way to solve this is to ventilate the plant well and to remove the adapted parts. Is the dew on the bottom of the leaf? Then chances are this is downy mildew.

Good ventilation also helps fight botrytis – the grey mould. This mould forms a grey, fluffy haze around flowers, leaves and stems, with the result that these parts will turn black and die. Remove the diseased parts as soon as possible, so ensure good ventilation and dry leaves.

Besides mildew, there is also sooty dew. Sooty dew does not live on the plant itself, but on a sticky liquid that insects leave behind: honeydew. Soot dew does not directly damage the plant, but the black colour does block light from entering the leaves. Focus on expelling the bugs that leave the stuff and wipe the fungus off the leaves.


Let’s start with the bugs that do the most damage to your plant … the root louse. Because the root aphid is hidden under the ground, you often realize too late that your plant is (becoming) sick. Your plant grows slower than you should and you see slightly yellowed leaves. Unfortunately, it is often impossible to save the plant once root aphid has struck and there is no other option than to buy a new one.

Other types of lice are scale insects, mealybugs and aphids. All three small animals with a slightly different ‘appearance’. Scale insects carry a shield on them and, together with the mealybug (small fluff), create a wax-like crust on the leaves, stem or trunk of your plant. You can control mealybugs with Promanal-R (this also applies to spider mites and aphids and harmless to plants and bees). Aphids are usually green and can be found at the bottom of the leaf. Because the aphid sucks sap from the plants, the leaves deform, curl and discolour.

Thrips are lightning-fast and move in groups between the leaves and flowers. They leave spots and deform young leaves. You can fight thrips in a natural way by using “predatory mites” or make your own solution of water and yellow soap (20g soap per 1 litre of water). With this, you can wash away the triplets.

Do you see dot-shaped spots on the top of the sheet? Or are there even white wires in the plant? This is caused by spider mites. The spider mite is a mite, smaller than a millimetre in size and does well in dry air. Cutaway the affected areas and apply Promonal-R for a month, combined with good ventilation.

Source: Mooi wat planten doen