Crops
Various phytotoxicities
Among the pesticides used in agriculture, herbicides and, to a lesser extent, insecticides and fungicides, are likely to cause sometimes significant damage to tomatoes. The phytotoxicities ( pesticide injuries ) they induce are classified as non-parasitic plant diseases and are unfortunately not that rare in the field. They should therefore never be excluded from your diagnostic hypotheses.
Figures 1 to 6, illustrating some discoloration abnormalities on leaflets and tomato leaves caused by pesticides, and more particularly herbicides, should allow you to familiarize yourself with the symptoms caused by phytotoxicities. These color anomalies can be multiple: greenish or livid color of the leaflets, yellowing, bleaching, anthocyaninization, dull and / or tanned aspect of the leaf blade Yellowing is by far the most common symptom; they can have different intensity and distribution on leaflets and leaves:
- yellowing in spots, in more or less well defined areas, sometimes evolving towards tissue necrosis;
- yellowing of the veins and contiguous tissues;
- yellowing of young leaves at the apex;
- diffuse yellowing of the leaf blade between the veins;
- diffuse yellowing of the entire blade;
- yellowing and dryness between the veins evolving rapidly;
- more or less homogeneous interveinal yellowing of the limbus, sometimes progressing to tissue bleaching;
- bleaching of the leaf blade
Remember that the use of a herbicide on or near a crop is never a completely trivial operation. The risks of causing phytotoxicity are never completely ruled out.
Other pesticides, for example insecticides and fungicides, used alone or in mixture, substances such as fertilizers, can also be the cause of phytotoxicity on tomato. They sometimes cause yellowing in the same way, but also other symptoms such as:
Figures 1 to 6, illustrating some discoloration abnormalities on leaflets and tomato leaves caused by pesticides, and more particularly herbicides, should allow you to familiarize yourself with the symptoms caused by phytotoxicities. These color anomalies can be multiple: greenish or livid color of the leaflets, yellowing, bleaching, anthocyaninization, dull and / or tanned aspect of the leaf blade Yellowing is by far the most common symptom; they can have different intensity and distribution on leaflets and leaves:
- yellowing in spots, in more or less well defined areas, sometimes evolving towards tissue necrosis;
- yellowing of the veins and contiguous tissues;
- yellowing of young leaves at the apex;
- diffuse yellowing of the leaf blade between the veins;
- diffuse yellowing of the entire blade;
- yellowing and dryness between the veins evolving rapidly;
- more or less homogeneous interveinal yellowing of the limbus, sometimes progressing to tissue bleaching;
- bleaching of the leaf blade
Remember that the use of a herbicide on or near a crop is never a completely trivial operation. The risks of causing phytotoxicity are never completely ruled out.
Other pesticides, for example insecticides and fungicides, used alone or in mixture, substances such as fertilizers, can also be the cause of phytotoxicity on tomato. They sometimes cause yellowing in the same way, but also other symptoms such as:
- of leaf deformation more or less upsetting port plants, associated with a reduction or a total cessation of plant growth. FIGS. 7 to 12 make it possible to form a fair opinion of the nature and intensity of the symptoms induced by certain phytotoxic compounds. We can in particular observe: - a slower development of the youngest leaves, which can go as far as a total cessation of growth; under these conditions, the plants eventually show a stunted appearance, especially if the phytotoxicity has occurred prematurely;
- - partially or totally deformed leaflets, slightly serrated or more irregularly cut (figures 7 and 9), mottled, blistered and more or less rolled up (figure 10);
- - the more or less marked distortion and / or curling of the leaflets, which may be shorter, threadlike and present strongly thickened tissues (figure 11);
- - leaflets curved into a spoon and / or rolled up in the shape of a chistera;
- - winding of the entire limbus;
- - the corkscrew appearance, crumpled up of all the leaves (figure 12);
- - the proliferation of rigid and thick branches associated with fasciations occurring on the stem, peduncles, sepals.
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of small lesions observed on tomato leaflets. Indeed, you should know that leaf tissues, especially when they are young or from plants grown under shelters, are sometimes tender and fragile. Also, certain products (especially pesticides) can pose problems of selectivity when used under certain conditions and prove to be phytotoxic for tomatoes ( Phytotoxicities - chemical injuries) . Various necrotic changes can then appear on the leaflets, visible on both the upper and lower sides of the leaf blade (Figures 13 and 14). It is possible to confuse these alterations with some of the spots described in this chapter. If in doubt, it will be wise to have the diagnosis confirmed by a specialized laboratory.
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the wilting of drying out , and leaf necrosis . Thus, the leaflets of the affected tomato plants may present:- livid interveinal patches on the lower leaves, extending, necrotizing and gradually drying out;- necrosis and drying out of the periphery of the blade of young and old leaves;- wilting and drying out of the leaves of the apex .
Figures 15 and 16 illustrate some of the symptoms induced by herbicides, especially those which inhibit photosynthesis.
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of small dark green lesions covering more or less the most exposed parts of the fruit (17 and 18) . In fact, the sprayed product (s) must diffuse to a greater or lesser extent through the cuticle and locally affect the underlying tissues. In some cases, Microcracks may also be observed.
The origin of phytotoxicity is quite difficult to determine. Indeed, the producer very often denies the possibility of having made an error or suffered an injury causing the damage. The study of the distribution in time (date of appearance of the first symptoms and evolution) and in space (distribution of diseased plants in the plot and evolution) of the symptoms induced by this phytotoxicity allows, in the majority of cases, to confirm the cause.
What questions to ask when suspecting phytotoxicity?
- was the previous crop weeded with residual herbicides?
- have herbicide treatments been carried out near your crop?
- has the treatment equipment been rinsed well?
- is the spraying equipment well maintained (cleaning, calibration )?
- was the right product used at the right dose?
- was it not used too frequently (cumulative effect)?
- have the recommendations for use indicated on the packaging been followed?
- did the treatment take place in particular climatic conditions (too high temperatures, various stresses)?
- incompatible products, or too many products, have they been mixed?
- did the applications take place in bad conditions (strong wind, temperatures too low or too high)?
Remember that irrigation water can be polluted by a herbicide.
What to do following phytotoxicity?
While there is no quick fix in this situation, you can still take the following steps:
- clearly define the origin of phytotoxicity;
- prevent it from happening again;
- do not eliminate the plants immediately, lead them normally and observe their development, which will not be fatal in all cases. In fact, it will depend mainly on the nature, the dose and the persistence of the product (s) in question, the stage of growth of the tomato plants, the type cultivated and the variety. Some hopes are therefore permitted.
No other specific measure can be recommended.
What questions to ask when suspecting phytotoxicity?
- was the previous crop weeded with residual herbicides?
- have herbicide treatments been carried out near your crop?
- has the treatment equipment been rinsed well?
- is the spraying equipment well maintained (cleaning, calibration )?
- was the right product used at the right dose?
- was it not used too frequently (cumulative effect)?
- have the recommendations for use indicated on the packaging been followed?
- did the treatment take place in particular climatic conditions (too high temperatures, various stresses)?
- incompatible products, or too many products, have they been mixed?
- did the applications take place in bad conditions (strong wind, temperatures too low or too high)?
Remember that irrigation water can be polluted by a herbicide.
What to do following phytotoxicity?
While there is no quick fix in this situation, you can still take the following steps:
- clearly define the origin of phytotoxicity;
- prevent it from happening again;
- do not eliminate the plants immediately, lead them normally and observe their development, which will not be fatal in all cases. In fact, it will depend mainly on the nature, the dose and the persistence of the product (s) in question, the stage of growth of the tomato plants, the type cultivated and the variety. Some hopes are therefore permitted.
No other specific measure can be recommended.
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