Anyone who keeps roses knows that they are susceptible to a variety of pests and diseases, such as black spot, powdery mildew, red spider, thrips and aphids. These problems are very common in rose care, so it is important to spray regularly to control them. However, some florists find that the same medication works well for others, but doesn’t seem to work for them. Have you encountered a similar situation? Today we will analyze the common causes of this phenomenon.
If you have purchased the pesticide from the regular channel but the effect is not obvious after using it, then it may be caused by the following four reasons. You can check and troubleshoot the problems one by one.
1. Incorrect medication
Choosing the right agent is the key to managing plant pests and diseases. Although most fungicides and insecticides on the market can deal with a wide range of pests and diseases at the same time, in some cases, the right drug is still needed to achieve the best results.
For example, among diseases, fungal and bacterial diseases require different agents to treat. Most fungicides (e.g., pyrimethanil, azoxystrobin) can control both fungal and bacterial diseases. However, if the name of the chemical has the word “myclobutanil” in it, it is usually only suitable for bacterial diseases and has limited effect on fungal diseases.
Similarly, the choice of insecticide is important. Cypermethrin is a broad-spectrum insecticide that is effective against pests of all sizes, including aphids, thrips, cockroaches and even centipedes. Agents such as imidacloprid, acetamiprid and thiamethoxam, on the other hand, are better suited to deal with smaller pests such as aphids, thrips and whiteflies.
Special reminder:
Novice florists often mistakenly use chlorothalonil to kill insects. Please note that getting sick and growing bugs are completely different problems; do not use fungicides to kill bugs.
Red spider belongs to mite pests and needs to be treated with specialized agents.
2. Insufficient dose or too high concentration
Even if you choose the right agent, if the dosage is not appropriate, it may lead to poor results. Different brands of chemicals have different contents of active ingredients and different dilution ratios. Many home gardening enthusiasts tend to formulate potions by feel, which may result in insufficient or excessive concentration.
It is recommended to use a measuring tool to accurately measure the amount of medicine and dilute it strictly according to the instructions. If you find that the aphids are still not killed after one day of spraying, you can increase the concentration of the drug appropriately and spray again.
Caution:
Sometimes when severely infected with aphids, especially black aphids, their mouthparts will lodge in the plant shoots. Even if the spray kills them, the aphids may remain attached to the branch, giving the false impression that the medicine is not working. At this point, you can observe whether there are still signs of activity, if it is no longer moving, it means that it has been killed, and you can use water to rinse off the residual carcasses.
3. Incorrect timing
In addition to choosing the right agent and matching the right concentration, the time of spraying is also crucial. For example, when dealing with thrips, spraying in the evening is usually more effective than in the morning, because thrips are active during the day and frequently at night. Touch-type insecticides need to come into direct contact with the pest to be effective, so these should be sprayed in the evening.
In addition, rainy weather can also have an effect on efficacy. If it rains soon after spraying, the rain may wash away the solution and reduce its effectiveness. Generally speaking, rain 4 hours after spraying will not significantly affect the efficacy, but if it rains within 2 hours, it is almost like a waste of effort, and re-spraying is needed.
4. Persistent Pests and Diseases
Some pests and diseases are very stubborn, even if you have chosen the right agent, formulated the right concentration and mastered the timing of spraying, the effect may still not be obvious. The following are some common stubborn pests and diseases and how to deal with them:
(1) Powdery mildew
Powdery mildew bacteria are not easy to fully contact with the liquid, so often feel ineffective after spraying. It is recommended that silicone or detergent be added to the solution to enhance adhesion. Treatment of powdery mildew usually requires multiple applications and a complete cure cannot be expected in one or two applications.
For severe powdery mildew, you can try using a stone sulfur compound (600-800 times dilution). However, as lithosulphur compound is strongly alkaline and may burn the young leaves, it should be used with caution in spring when the temperature is high.
(2) Gray mold
Gray mold is very destructive, especially in rainy and humid environment, buds are most susceptible to infection. Prevention is the key, and it is recommended to spray fungicides in advance. Once infected, it is difficult to treat, especially in the case of continuous rainfall.
(3) Red Spider
Red spider is extremely easy to reproduce in poorly ventilated environments and reproduces quickly. Even after killing the adult worms, the eggs may still hatch, leading to repeated infections. When treating red spider, it is necessary to firstly strengthen the ventilation of the environment, then wash the leaves thoroughly with water, dry them and then spray special agents comprehensively. After three days, the leaves should be inspected again, and the cleaning and spraying should be repeated if necessary.
(4) Thrips
Thrips is actually very easy to manage, usually spraying once will have obvious results. However, many florists pursue the goal of “complete eradication”, hoping that not a single insect will be left, which is almost impossible to achieve in an open environment. Even if the local thrips are eliminated, thrips from other places may still fly over.
Spring is a high season for rose pests and diseases, especially in the midst of continuous rainy weather. To ensure healthy growth of roses, it is advisable to take precautions against pests and diseases, spray regularly and keep a close eye on the condition of the plants. By choosing the right chemicals, mastering the correct dosage and timing of spraying, and patiently treating stubborn pests and diseases, you can effectively protect your roses from infestation.