Prevention and treatandcure of landscape plant phytotoxicity
According to different symptoms, landscape plant phytotoxicity can be divided into dominant phytotoxcity and recessive phytotoxcity. According to the speed of deleterious effect, it can be divided into direct phytotoxicity and indirect phytotoxicity. However, no matter what kinds of phytotoxicity, once they occur, they will have irreversibility, which can only be avoided or alleviated by taking targeted prevention measures.
Symptoms of landscape plant phytotoxicity
Spot will occur
The common spots mainly include yellow spot, brown spot, reticulate spot, scorched spot and so on, which often generate in leaf segment and also can be found in limb and flowers sometimes. For example, when using copper sulfate of Bordeaux mixture on oriental cherry and apricot branches, they will be easy to have brown reticulate spot. Besides, blade will have necrotic spots and will even wither; by using butachlor, zoysia japonica and early-maturing grass-blade will have irregular brown spots. Spot is the most common drug symptom, which will rapidly generate once the pesticide is sprayed and will irregularly distribute on plant, besides, the size and form will change a lot.
The common etiolation symptoms include blade yellowing, limb yellowing and whole plant yellowing, which is generally occurred in branchlet and leaf segment as well as stem sometimes. For example, by using diuron (the effective constituent of herbicide), many shrub blade will have chlorisis, besides, it can also cause yellowing of many herbal blades. By using simazine, the whole gramineae grass plant will yellowing. Etiolation that caused by phytotoxicity usually generate fast and will be easy to cause wither, which can be related with drug delivery position and concentration.
It will lead to malformation
The common malformation symptoms mainly include leaf roll, clump, plasmodiophora brassicae and so on, which often can be found in stem, leaf and root and is mainly caused by herbicide. For example, trifluralin can cause swollen root and caudex cracking of crucifer, 2,4-D can cause hollow fruit and fruit shrink of nightshade, nitrofen can cause the growing point atrophy of some plants, lime (one of compositions of Bordeaux mixture) can thicken cucurbitaceae and vitaceae blade. The abnormal symptoms will widely distribute, but it will often distribute partially in plant.
It will lead to withering
Phytotoxicity also will cause withering, in which the whole plant will be in dehydration state. For example, glyphosate will cause dry yellow and atrophy of gramineae grass, dimethoate will cause petal curling and leaf drop of coral flower and justicia brandegeana. Phytotoxicity will also cause leaf drop, flower drop and fruit drop. For example, if copper agent is misused, it will cause leaf drop of peaches, plums and grapevine; if methamidophos is used in the flower season of pear and apple, it will cause flower drop; besides, if ethephon is used improperly on hawthorn and malus spectabilis, it will cause fruit drop.
Preventive measures of landscape plant phytotoxicity
Try to use chemical pesticide as little as possible in garden plant protection, continuously strengthen biological control, solve the contradiction between chemical control and biological control, coordinate the relationship between them, make full use of the control effect of natural enemy organism as well as introduce natural enemy species that can be used in commercial production, thus it can not only sustainably prevent garden pest, but also can effectively eradicate or reduce phytotoxicity.
Correctly select pesticide category
Choose pesticide that has low toxicity, can resolve fast, has little residual and will cause little pollution as many as possible, such as mineral pesticide and botanical pesticide. Choose appropriate pesticide according to different prevention objects, for example, stomach poison (such as abamectin insecticide) can be used in preventing chewing mouthparts pests, while systematic poison can be used in preventing sucking mouthparts pests; sulfur preparation can be used in preventing powdery mildew, while copper agent can be used in preventing downy mildew.
Correctly choose dosage form
Generally speaking, hydrosolvent will have better effects than powder no matter on killing pests or reducing phytotoxicity. Among them, oil emulsion will have best effect when it is sprayed on the crown. If we can correctly choose dosage form and improve drug delivery method, the pesticide effect will be better. By choosing granules, controlled release formulation, colloidal suspension agent and ultra low volume agent as well as spraying pesticide in the early period of pests, alternatively using various pesticides and using various formulations interactively, it can reduce phytotoxicity.
Use appropriate dosage
When spraying the pesticide, the dosage should be controlled strictly. If the pesticide is used too much, it will be easy to cause phytotoxicity, while if the dosage of pesticide is too small, it may not have good control effect. Therefore, when preparing the pesticide, we should calculate exactly and measure strictly according to the instructions. The drug should be prepared and used at the same time and should not be stored for too long, otherwise, it will generate sediment or will go bad. Besides, we should also pay attention to the drug application frequency, which will depend on the hazard situation of pest and pesticide lasting period. If the pesticide is used too often, it will be easy to cause phytotoxicity. Therefore, it should be used within the endurance of plant.
Use pesticide according to the plant condition
Different kinds of plants will have different tolerance to various pesticides. For example, some gramineous plants will be sensitive to DDVP, some cucurbitaceous plant will be sensitive to phoxim, some pulse will be sensitive to phenoxyacetic herbicide and copper agent will easily cause phytotoxicity on peach and plum trees. This should be paid much attention to when spraying the pesticide. Besides, the resistance to pesticide will also differ a lot in different developmental stage of plant. For example, as plant will be sensitive to pesticide in the germination stage, seedling stage, flowering period and booting stage, we should properly reduce drug delivery frequency or reduce pesticide concentration so as to prevent phytotoxicity.
Use drug according to the climate conditions
When the pesticide is sprayed under high temperature, high humidity, strong light, strong wind and other bad weather conditions, it will be easy to cause phytotoxicity. For example, if copper hydroxide and other copper agents are sprayed when the dew has not been completely dried, or in a short time after raining, continuous cloudy days and dense fog, it will cause phytotoxicity as the copper content that has been dissolved by leaf water has exceeded the tolerance of plant. If the pesticide is sprayed under continuous low temperature condition, it will also cause phytotoxicity. Therefore, pesticide should be used under mild weather conditions. For example, fungicide will have good effect when it is sprayed in the morning or afternoon in sunny days, while closed herbicide will have good effect when it is sprayed before raining or in the rain.
Treatandcure measures of landscape plant phytotoxicity
Increase nutrition and fertilizer
Regarding the spot, scorch, etiolation and other phytotoxicity that caused by contact insecticide, fertilizer can be used so as to improve the regeneration and compensation ability of plant and reduce the occurrence degree of phytotoxicity. For example, if chlortoluron causes phytotoxicity on gramineae seedling, by spraying night soil, cake fertilizer and other organic fertilizers or spraying urea, monopotassium phosphate and other chemical fertilizers on the blade surface, it can promote plant growth and alleviate phytotoxicity symptoms. Besides, by watering immediately, it can satisfy the water requirement of root system, increase cell moisture, reduce plant drug content, improve the resistance to phytotoxicity and alleviate phytotoxicity.
Watering, flushing and soaking
Regarding the phytotoxicity that caused by overdosage or improper dosage, watering and soaking as well as repeatedly flushing methods can be used so as to dilute the drug concentration, reduce the drug residual in the soil and alleviate the phytotoxicity of pesticide on plant root. Regarding the phytotoxicity that caused by excessive foliar spraying, large amount of clean water can be sprayed on the plant leaves when the drug has not been completely permeated or absorbed. Besides, it should be repeatedly sprayed and flushed 3 to 4 times so as to scour the drug that has existed on the leaves as many as possible as well as eliminate or reduce the pesticide residual in plant leaves.
Spray growth hormone
Regarding some phytotoxicity that caused by plant growth regulator and conduction type herbicide, gibberellin and other growth hormones can be used. For example, regarding the phytotoxicity that caused by the misusing of chipton on lagenaria siceraria seedling, diluted gibberellin can be sprayed so as to reduce drug hazard; gibberellin can also be used in alleviating the phytotoxicity that caused by excessive use of MET. Regarding the phytotoxicity that caused by using ethephon on clover, diluted brassinolide liquid can be used.
Use antidote or absorbent
Some phytotoxicity can be neutralized and alleviated by the drugs that have opposite nature, or it also can be remedied by using antidote or absorbent, such as spraying whitewash, plant ash, activated carbon and MET. By coating the seedling with NA and R-25788 antidote, the mixed sowing lawn will not be poisoned by thiocarbamate herbicide; by using ferrous sulfate on ryegrass, it can reduce the phytotoxicity caused by gramoxone; by using calcium polysulfides, it will eliminate the activity of residual simazine in the soil; by spraying 0.5 percent of calcium oxide liquid, it can alleviate the phytotoxicity caused by excessive using of copper sulfate.
Select or breed resistant variety
Regarding some protected cultivation landscape plant that has been sprayed with certain kinds of chemical pesticides, we can select or breeze some plants that have strong resistance or are insensitive to these kinds of pesticides. These kinds of plants can effectively reduce phytotoxicity frequency or reduce the damage degree of plant.
Remove damaged tissues
Remove the damaged flowers, fruits, branches and leaves of plant in time, thus it can prevent the continuous conduction and permeation of drug in plant body.