*2.2.4.1 Defoliation*

Arresting the growth of the cotton plant followed by the defoliation of leaves at the physiological maturity stage of the plant would facilitate in harvesting the fully opened bolls through mechanical instruments. As we know that killing and fixation of specimen are required for having cytological observations by employing a mix of acid and alcohol, the two events namely growth arrest and defoliation have to occur for effecting the harvest of bolls in cotton. Thus, cotton defoliation requires the application of certain chemicals to help prepare a cotton crop for harvest. Benefits of proper cotton defoliation include: reduction of the main sources of stain and trash (leaves), increased harvest efficiency, quicker drying of dew, potential for increased boll opening and a reduction of boll rots. As a cotton plant matures, a physiological process takes place which separates the living tissue near the leaf petiole called the abscission zone. A regulated enzyme activity under the influence of plant hormones making the leaf to fall through the creation of abscission zone is the need.

Two types of defoliants, by and large are available. A herbicidal defoliant can be used to cause injury to the leaf, upset the hormone balance resulting in the abscission process and finally the leaf drop. The other one is the application of a hormonal defoliant which increases ethylene synthesis in a plant causing the leaves to fall off. Correct application rates are important, especially with herbicidal defoliants, as over application can cause the leaf to die before the abscission process, resulting in "stuck" leaves. Conversely, when too little defoliant is applied, the abscission process may not begin, resulting in no leaf defoliation.

#### *2.2.4.2 Factors affecting defoliation*

When applying a defoliant or desiccant or boll opener, many factors must be taken into consideration for successful application. Best results from an application occur when the factors like the type of cotton being grown, its duration, weather/ climatic conditions, soil conditions, availability of inorganic fertilizers to the plant, bursting of bolls, water availability to the plants, spacing between the rows and plants, etc. are taken into consideration.

**Figure 4.** *Application of Mepiquat chloride and defoliant in CO 17.*

Studies taken up at TNAU utilizing the application of MC and Defoliant indicated that the combination of application of MC 50 g ai/ha at 45 and 65 DAS and Dropp ultra (Thidiazuron and Diuron) @ 200 ml/ha at maturity resulted in 90 per cent defoliation in CO 17 and prepared the crop for harvest by 135 days. This is in the preliminary stage of testing and would be tested in the years to come to arrive at a comprehensive package (**Figure 4**).

## **2.3 Pests management**
