Chemical injuries
 

Some overdosed pesticides sprayed in bad conditions or introduced inadvertently may cause chemical injuries including changes in plant habit and leaf shape. The following symptoms may be observed:

- plant growth either stops completely or development is very slow, plants have stunted appearance (figure 1). The internodes are often shorter (ethofumesate, glyphosate ...);
- more or less marked distortion and/or curling of younger leaves which are sometimes shorter and thicker and showing veins in relief (pendimethalin carbetamide ...) (figure 2);
- slender young leaves, yellowing and necrosing on some parts of lamina, causing deformation (figure 3);
- leaf curling (spoon-shape);
- entire lamina curling (figure 4);
- stem thickening and curling, and sometimes swelling (figure 5)
- lamina margins may be slightly serrated (figure 6), curled-up or irregular, which is either due to pesticide absorption, or foliar lesions in leaf areas where the pesticide tends to accumulate (figure 7). Altered leaf tissues are much less elastic, resulting in distorted development of the leaves. These may curl up or present an abnormally cut lamina.

Herbicides most likely to produce these symptoms are hormones such as 2,4-D, dicamba, picloram...
 

• The following questions should be asked:

- Have you treated with a herbicide near your tobacco field?
- Have you rinsed your treatment equipment thoroughly?
 
Beware that irrigation water may be polluted by a herbicide, residues may have persisted in the soil.
 

• What to do after the chemical injury? 

 
 
Although there is no quick remedy to this situation, the following procedures should be adopted:
 
- determine the origin of phytotoxicity precisely;
- prevent it happening again;
- do not remove the plants immediately, grow them normally and observe their evolution. The latter depends mainly on the dose and persistence of the used product