Rotting geraniums

Rotting geraniums

Question: geraniums rot

good morning and thanks in advance for your reply.

I have carefully read the vs. answers already published on the topic of geranium rot but I have not found an analogy with my problem and therefore I ask for further clarification:

my geraniums so called "francesini", present some areas of rot but not at the collar of the branches or at the roots but at the tips of the branches themselves.

For a few years, after spring pruning, they develop very generously both as vegetation and as flowering and all this remains perfect, let's say until the end of June, mid-July. Then the decay begins although I continue to water every 8/10 days with a special liquid fertilizer. Part of the leaves dry up and the stem of the tips rots becoming black and "watery" when cut. At the same time, new shoots develop at the collar of the leaves underlying the rot. The plants are in boxes, facing east. During the winter I take them to a south terrace where I don't need to repair them because I put them close to the wall of the house and they have sun all day (when there is). Then in spring: abundant pruning, change of surface soil with the addition of manure and, after about 20 days, I start watering with specific fertilizer. I repeat, until the end of June they are a show and then the drama begins. All this has been repeated systematically for at least 2/3 years. What am I doing wrong ?

Thank you so much for what you will be able to tell me and for the advice you will want to give me.


Answer: geraniums rot

Dear Pina,

often when the plants have blackened and limp areas these symptoms are attributed to fungal diseases, such as root rot; in fact, however, root rot tends to develop mainly when the soil remains moist and fresh for a long time, which is quite probable in a geranium pot exposed to the June sun. Therefore, the simple symptom of branch rot is not sufficient to diagnose the presence of a fungal parasite. In addition to this, unfortunately the parasites that affect plants change and increase from year to year, due to the fact that more and more often fruits, plants, vegetables and plants of all kinds travel around the entire globe, and the climate tends to change. Precisely for the reasons mentioned above, namely the transport of plant material and the European climate which is becoming increasingly dry and hot, in recent years some tiny butterflies have emigrated, from Africa to the northern Mediterranean areas; such parasites were not known until a few years ago, because they could not survive in Italy, it is only since 2011 that their presence has been reported practically throughout Italy. These are small butterflies, which in spring lay their eggs near the flowers or in the buds of geranium; the larvae that emerge from the eggs feed exclusively on geraniums, preferring the fleshy pulp found inside the twigs; as the larvae are born near the flowers, the branches that are first hit are the apical ones, where there are buds; as the larvae feed on the inside of the twig, you will notice the entrance hole of the caterpillar, the exit hole, and between the two holes the branch that blackens and dries up, with the mushy interior, consisting mainly of the larva's excrements . These larvae are very voracious, and in addition to the twigs, they also feed on the leaves, where it happens to see some. Generally the caterpillars on geraniums are difficult to notice, because they are the same color as the foliage and stems, more than anything else you can see their droppings, scattered here and there on the leaves, in the form of small black spherules. These caterpillars have their peak development between May and June, but the hatching of the eggs and their production can continue until September or October, depending on the climate. In winter, the butterflies pupate and overwinter among the leaves, or inside the dark stems, to be ready to awaken when spring arrives. So if your geraniums survive from year to year, you are continuing to breed the little caterpillars. To eradicate them it is important to remove the dark and mushy parts of the branches, checking the branches which have tiny holes; all pruned parts must be burned immediately, because otherwise the caterpillars will move from them to other plants. In spring, as soon as the climate becomes mild, immediately do a treatment with a systemic insecticide, that is, one that enters the plant, so that future larvae die as soon as they try to feed on your plants. The best method is to use insecticides in tablets, to be inserted into the soil of the pot, which dissolve every time you water, to have a long insecticide cover. Also because, even if you manage to eradicate all the larvae from your plants, consider that there are always the neighbors' geraniums, from which harmless-looking butterflies can arrive.


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