What is phytotoxicity in flowers and ornamental plants? An analysis of pesticide poisoning causes

Using chemical pesticides is an effective way to control pests and diseases in flowers and ornamental plants. However, if pesticides are used improperly, phytotoxicity often results. The main symptoms are uniform spots on the leaf surface, curled and scorched leaf edges, slow plant growth, and in severe cases even death. People usually assume that the main cause of phytotoxicity is mixing the pesticide at too high a concentration, but that is only one cause. Sometimes the pesticide concentration is not high, yet phytotoxicity still occurs. The main reasons are as follows:

1. Unreasonable mixing of pesticides

When flower diseases and insect pests occur at the same time, people usually mix insecticides and fungicides, using two or three agents, and some even add foliar fertilizer. If the several pesticides have the same properties and similar pH values, no chemical reaction will occur and there will be little effect on pesticide efficacy; otherwise, it will affect the performance of the pesticide and also cause phytotoxicity. For example, Bordeaux mixture is a suspension made from copper sulfate, quicklime and water. It can control many fungal diseases, and its liquid is alkaline, so it cannot be mixed with commonly used pesticides, nor with lime sulfur mixture or rosin agents, otherwise it will reduce efficacy and cause phytotoxicity. Therefore, when mixing pesticides, you must first understand their pharmacological characteristics; mix those that can be mixed, and those that cannot be mixed must be used separately.

2. Spraying intervals that are too short

At different stages of pest and disease occurrence, the length of the pesticide spraying interval varies. Generally, it is once every half month in the initial stage and once a week at the peak. In reality, many pests are difficult to kill and pathogens are difficult to eradicate, so some flower growers use pesticides frequently, some once every 3 days, and some even once a day. As a result, the pests are not killed and the disease is not eradicated, but the flower seedlings show phytotoxicity. In this situation, you must strictly control the spraying interval, otherwise phytotoxicity is harder to treat than the pests and diseases themselves. When controlling them, pay attention to alternating pesticides to prevent pests and pathogens from developing resistance, which leads to frequent application and ultimately causes phytotoxicity.

3. Improper spraying methods

Uneven spraying can also cause phytotoxicity in flowers and ornamental plants. When some flower growers spray pesticides, they do not spray the pesticide onto the key parts, and sometimes they linger too long on a certain part, causing a large amount of pesticide solution to remain on the leaf surface and resulting in phytotoxicity. This phenomenon is especially obvious on old leaves and large leaves.

4. Non-standard pesticide preparation procedures

Chemical agents come in many formulations, including wettable powders, emulsions, tablets, granules, solutions, and so on. Some of these formulations can dissolve directly, while others cannot dissolve completely. Undissolved particles suspended in the solution can easily clog the nozzle during spraying. Even if smaller particles are sprayed out of the nozzle, they remain on the leaf surface, causing localized phytotoxicity in the plant. Therefore, when preparing pesticides, pay attention to strictly following the procedures: first dissolve pesticides of different formulations in a small container, then transfer them to a large container, and after they are completely dissolved or evenly melted, transfer them to the sprayer.

5. Residuals of other pesticides in the sprayer

Strictly speaking, different types of pesticides should use different sprayers, but in actual practice, flower growers often use certain sprayers as general-purpose equipment. Sometimes after using one type of pesticide, they fill it with another type without cleaning it, and as a result the original pesticide residue causes phytotoxicity in the flowers and ornamental plants, especially residues such as herbicides, which are even more harmful to flowers and ornamental plants.

6. Allergic reactions of flowers and ornamental plants to pesticides

Practice has shown that some flowers and ornamental plants are allergic to certain specific pesticides. For example, cockscomb (Celosia argentea) and Chinese rose (Rosa chinensis) are quite sensitive to dichlorvos, and chrysanthemum is sensitive to dimethoate emulsifiable concentrate at dilutions of 1500 times or less, and phytotoxicity still occurs even when the pesticide concentration is not high and the operation is fully standard. There are currently no rules to follow for allergic reactions of flowers and ornamental plants to pesticides; they can only be explored through practice. This requires that when applying pesticides you are not very familiar with, you first conduct a phytotoxicity test, so as to reduce the occurrence of phytotoxicity.

In short, phytotoxicity is not caused simply by too high a pesticide concentration. The causes must be analyzed and identified from multiple aspects so as to avoid this kind of man-made damage.