Causes of and Solutions for Black Rot on Rose Stems in Summer
Roses are known as the queen of flowers, with their many varieties, diverse colors and long blooming period, so in recent years more and more people have taken up growing roses. But summer is the season when roses are most prone to illness, and a moment of carelessness during cultivation can lead to problems such as black rot on the stems. If they are not rescued in time, the black rot will quickly spread through the entire plant and eventually cause it to wither and die. Here I share a few tips and treatments about black rot on rose stems, hoping they will be of help to everyone.
Black rot from the bottom up. In most cases this happens because the root system has rotted, and potted roses are the most prone to this phenomenon. Because the space inside the pot is limited, overwatering and poor ventilation, combined with the high summer temperatures, raise the temperature inside the pot and cause the roots to rot. Over-fertilizing roses in summer can also cause root burn, because the high temperatures make the fertilizer volatilize heavily.
When this phenomenon appears, the plant should be removed from the pot promptly. If the roots are found to have rotted completely, it means the plant can no longer be saved. If only part of the roots have rotted, cut off the rotten parts, rinse the roots clean, soak them in a carbendazim solution to disinfect, let them dry, then replant them in sterilized potting soil. The soil must be loose and breathable to prevent poor drainage later on from causing the roots to rot again. At first, place the plant in a cool, ventilated spot and do not expose it to sunlight; after a week, gradually give it light. During this period, do not rush to fertilize; wait until the plant has truly recovered before returning to normal care.
Black rot from the top down. There are two reasons for this phenomenon: 1. Pathogen infection. Roses are famously heavy feeders of pesticides, and improper care easily leads to various diseases. Especially in the rainy season in summer, when temperatures are high and humidity is great, pathogens easily breed in the potting soil and black stems appear. After some growers prune their roses, the wounds are exposed to the air, and rain or warm, humid air can easily cause the wounds to rot and then blacken from the top down.
2. Overwatering or watering in the sun. Fellow growers all know that roses like plenty of light. Some growers water their roses at noon in midsummer, and under the strong sun this easily causes the temperature inside the pot to rise sharply, obstructing root respiration and preventing nutrients from being transported normally to the stems and leaves, which leads to black rot on the stems.
If you find black rot spreading from the top down on a rose stem, promptly cut off the blackened stem. The cut can be made a few centimeters below the blackened part into healthy stem tissue, and after cutting, immediately apply carbendazim to the wound or seal it with wax to prevent re-infection. Also promptly check the condition of the potting soil. If the soil is too wet, you can loosen it without damaging the roots and improve ventilation, to prevent the stems from blackening again due to overly wet soil.