Symptoms of phytotoxicity and main compounds

Common phytotoxicity symptoms

1. Plant withering: The phytotoxicity is more serious, manifested as the leaves are dry, the plants are wither and eventually die;

2. Leaf yellowing: This kind of phytotoxicity is generally mild, and the main symptom is leaf yellowing, which is caused by pesticides hindering the photosynthesis of chlorophyll. According to the severity of the phytotoxicity, there are yellowing of leaves and yellowing of the whole plant. There are two types of yellow leaves, yellow heart leaves and yellow old leaves;

3. Spot: This kind of phytotoxicity is mainly manifested on leaves and fruit peels. Common symptoms are brown spot, yellow spot, net spot and so on;

4. Deformity: Most of this kind of phytotoxicity is caused by hormonal pesticides. The stems, leaves, fruits and roots of crops will be deformed. Common symptoms include leaf curling, clustering, root swelling, deformed ears, and deformed fruits;

5. Growth stagnation: Most of this kind of phytotoxicity is caused by triazole pesticides or hormone/inhibiting pesticides, which inhibits the normal growth of crops and slows plant growth;

6. Infertility: This kind of phytotoxicity is caused by improper use of pesticides during the reproductive growth period of crops, which leads to male plants sterility or inability to pollinate, thus failing to bear fruit (seed) and reducing yield;

7. Falling off: This kind of phytotoxicity is mostly manifested in fruit trees and some dicotyledonous plants, causing a large number of fallen leaves, flowers and fruits;

Remedial measure

1. Water spraying: A large amount of water can be sprayed repeatedly for 2~3 times to wash away the pesticides on the plant surface as much as possible. Since most pesticides are easily decomposed when encountering alkaline substances, so baking soda 0.2% or lime water 0.5% can be added to water to accelerate the decomposition of active ingredients;

2. Watering: Watering should be sufficient when overdose causes phytotoxicity to increase root water absorption and cell water content, and reduce the relative content of the pesticides in the crop;

3. Spraying plant growth regulators: when plant growth is inhibited due to phytotoxicity, gibberellin, brassinolide and other plant hormones can be sprayed to promote crop recovery;

4. Spraying plant growth regulators: when phytotoxicity inhibits plant growth, spray gibberellin, brassinolide and other plant hormones to promote crop recovery;

5. Removing: When fruit trees, vegetables, grains, cotton, etc. suffer from phytotoxicity, the affected fruits, branches and leaves should be removed in time to prevent the spread of phytotoxicity;

6. Detoxification: Neutralize excessive pesticides with pesticides of the opposite nature. For example, when copper sulfate causes phytotoxicity, quicklime water 0.5% can be sprayed; when excessive paclobutrazol causes phytotoxicity, gibberellin can be sprayed to promote crop growth;

7. Application of quick-acting fertilizer: When the above-ground part of the crop has mild phytotoxicity and the root system has no symptoms, quickly topdressing quick-acting fertilizers such as urea can increase nutrients to enhance the growth vitality of crops and enhance the recovery ability of crops. This has obvious effects on melons and solanaceous fruit crops with mild phytotoxicity before and after fruiting;

Common fungicides that easily cause phytotoxicity include triazoles, sulfur-containing and copper-containing preparations, strobilurin.

Triazoles

1. Category:

1.1 Strong inhibition: triadimefon, triadimenol, tebuconazole, hexaconazole, diniconazole, propiconazole, flusilazole, epoxiconazole, paclobutrazol;

1.2 Weak inhibition: difenoconazole, fenbuconazole, myclobutanil.

2. Crops:

2.1 Sensitive: All kinds of fruit trees in the Rosaceae, vegetables such as tomatoes, eggplants, pepper potatoes, cruciferous vegetables, and umbelliferae vegetables, melons such as watermelon, bitter gourd, and cucumber are more sensitive, while melons, pumpkins, and winter squash are relatively better. Generally speaking, melons is more sensitive;

2.2 Not sensitive: Gramineae such as wheat, corn, rice, legumes such as beans, soybeans, and peanuts.

3. Usage:

3.1 They have a great influence on young parts such as fruits, flowers, leaves and fast-growing parts, so pesticides with weak inhibitory properties should be used as appropriate;

3.2 Do not use pesticides with strong inhibitory properties in seedlings, young fruits, flowering periods, and shoot budding periods.

4. Disease:

Control powdery mildew, rust, anthracnose, scab, fungal leaf spot, early blight, white rot, etc. caused by higher fungi.

Sulfur preparations

1. Category:

1.1 Inorganic sulfur: lime sulfur mixture, sulfur powder, sulfur suspension concentrate, sulfur evaporator, sulfur fumigator;

1.2 Organic Sulfur: ethylicin.

2. Usage:

Lime sulfur mixture: It can kill bacteria, insects and eggs. When cleaning up the orchard, use 3-5 Baume-degree of lime sulfur mixture to spray the ground, tree trunks, and branches. While the roots, shoots and fruits should be sprayed with 0.3-0.5 Baume-degree of lime sulfur mixture. Do not spray at temperatures above 30℃.

Copper preparations

1. Category:

1.1 Inorganic copper: bordeaux mixture (quicklime + copper sulfate), copper dihydroxosulphate, copper hydroxide, copper oxychloride, cuprous oxide； 

  1.2 Organic copper: copper quinolate, thiediazole copper, thiosen copper, copper rosinate, copper amino acid, copper succinate, copper acetate.

2. Sterilization principle:

Copper ion destroys the protein structure of pathogen and causes its death.

3. Disease:

Fungal diseases such as downy mildew, bacterial diseases such as bacterial wilt, leaf spot, angular leaf spot, ulcer disease, and viruses, plasmodiophoromycetes and slime mold. Only suitable for surface diseases, no systemic sterilization. Long-term exposure to high humidity or too much dew is prone to phytotoxicity.

4. Usage:

4.1 Do not adjust the concentration at will, do not use them when the temperature is too high；

4.2 Inorganic copper fungicides are recommended to be used alone, and organic copper fungicides should be used in time after mixing；

4.3 Inorganic sulfur and copper-containing fungicides should be used separately, and the interval is greater than 15 days.

Strobilurin

1. Category:

Azoxystrobin, Kresoxim-methyl, Pyraclostrobin, Trifloxystrobin, Enoxystrobin and Picoxystrobin.

2. Usage:

2.1 Alternate use with other types of fungicides;

2.2 Reduce the concentration when used in seedlings and young parts;

2.3 Due to the strong permeability of strobilurin, do not mix them with silicone adjuvants or emulsifiable concentrates.

Amides

1.  Category:

Succinate dehydrogenase inhibitors: carboxin, thifluzamide, fluopyram, fluxapyroxad, etc.

2. Usage:

2.1 It is easy to cause phytotoxicity when used on vegetables and fruit trees;

2.2 Do not mix with silicone adjuvants or emulsifiable concentrates;

2.3 Do not use at high temperature;

2.4 Do not mix with compounds containing metal ions, manganese, zinc, and calcium;

   2.5 It is recommended to use alone or after testing.