Cotton Defoliation – Defoliation Products

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Defoliants can be categorized as having either herbicidal or hormonal activity. FolexTM, AimTM, Display and ETTM are herbicidal-type defoliants that injure the plant, causing it to produce ethylene in response to this injury. The ethylene promotes abscission and leaf drop. If these defoliants are applied at rates too high for the temperature, they kill the leaf too quickly before ethylene can be produced. This results in desiccation or “leaf stick” instead of the desired defoliation (leaf drop). FreeFallTM, FinishTM, First PickTM and PrepTM are hormonal defoliants that result in increased ethylene synthesis by the plant. Prep (ethephon) releases ethylene, which stimulates further ethylene synthesis in the plant, resulting in abscission zone formation in the boll walls and leaf petioles. Dropp is a type of hormone called a cytokinin. Although cytokinins promote leaf health in most plant species, in cotton and related species such as velvetleaf, cytokinins promote ethylene synthesis and act as a defoliant. Because these hormonal-type defoliants bypass herbicidal injury, they are not as likely to cause desiccation (leaf stick) as herbicidal defoliants.

Herbicidal Defoliants

Folex :  A phosphate material has been the standard defoliant in Tennessee for several years. Performance is effective over a broad range of environment conditions. Minimum temperature for optimum performance is 55-60 degrees F. Floex does not inhibit re-growth or appreciably improve boll opening. Activity improves with increased maturity of the crop. Leaf removal usually rapid and addition of surfactants offers benefit only under adverse conditions.

GinstarTM:  Ginstar is an emulsifiable concentrate formulation of thidiazuron (active ingredient in FreeFall) and diuron (Karmex, Direx). It is applied to mature cotton at least five days before harvest, but defoliation may take longer under cool conditions. Addition of adjuvants or excess rates can cause desiccation or “stuck leaves” under warm conditions. The Ginstar label does not discuss tank mixtures, but tank mixtures with ethephon have enhanced boll-opening activity.

Paraquat (Gramoxone InteonTM):  Paraquat can aid in opening of mature bolls when 2.1 to 3.3 oz./A are mixed with Folex, Freefall or Ethephon. Development of immature bolls will be inhibited by paraquat application. Paraquat acts as a dessicant to dry out leaf tissue rapidly which can result in ‘stuck leaves’ if use rates are too high.

Aim:  Aim has excellent activity in desiccation of juvenile growth, but does not inhibit re-growth. In mature cotton, and/or cool conditions, Aim activity has been shown to be similar to Folex and ET. In warm conditions, however, less-than-desirable defoliation and excessive desiccation have been shown with Aim rates above 0.75 oz/ac. In situations in which two applications are necessary, Aim has performed very well as the second application. Aim has shown excellent activity in desiccating morningglories. In situations with thick vines, Aim alone or in combination with other defoliants will desiccate morningglories very well. Aim can be tankmixed with  other defoliants, and the addition of 0.25% non-ionic surfactant is need to best results.

ET: ET has excellent activity in desiccation of juvenile growth, but does not inhibit re-growth. In mature cotton, and/or cool conditions, ET activity has been shown to be similar to Folex and Aim. In warm conditions, however, less-than-desirable defoliation and excessive desiccation have been shown with ET. In situations in which two applications are necessary, ET has performed very well as the second application. ET can be tankmixed with  other defoliants, and the addition of 0.5-1.0% v/v crop oil is needed for best results.

Glyphosate (many formulations):  Glyphosate provides excellent re-growth inhibition of conventional (non-Roundup Ready) cotton when applied in conjunction with defoliants or ethephon and results in excellent johnsongrass control. Glyphosate should be used as complementary re-growth control product in conjunction with other products for leaf removal and boll opening. Check specific product labels for registrations as a harvest aid. Labeled Rates:  13–51 oz per acre for weed and re-growth control in non-Roundup Ready Flex cotton.

Hormonal Defoliants

Freefall (SC or 50 WP): Thidiazuron products require a 24-hour rainfree period and are also sensitive to cool weather. DFreefall should not be applied when the average 24-hour temperature is predicted to be below 60 degrees F for two to three days after application. Freefall is slower in leaf removal than Def or Folex and may leave some bottom leaves, Freefall effectively removes younger leaves at the shoot tips. Freefall does not improve boll opening. However, it will strongly inhibit re-growth when applied under favorable weather conditions. If  used under less-than-favorable conditions, the addition of crop oil concentrate (1 pt./A) may enhance the activity of this material. It is important to follow suggested cleanout procedures with or FreeFall.

Finish 6 Pro:  Finish contains ethephon and the synergist cyclanilide that aids in defoliation. Finish is an excellent boll opener and can be a stand-alone product in cooler temperatures and well-cutout situations. Finish also exhibits a limited level of re-growth control. Finish is generally a faster boll opener than ethephon and can be tankmixed with thidiazuron, phosphate materials and Ginstar.

FirstPick:  FirstPick also contains the boll opener ethephon and a synergist, urea sulfide. It is an excellent boll opener. Acceptable defoliation with FirstPick alone requires mature cotton with mature leaves. In cases of rank growth, or the potential for re-growth, the addition of Freefall or Folex is recommended.

Display: Is a combination of the active ingredient in Aim plus fluthiacet-methyl, the active ingredient in Cadet hernicide. This combination of two PPO inhibitors and provides excellent activity on vine weeds that need dessication prior to harvest. Display requires the addition of 0.25% v/v non-ionic surfactant. Use adequate spray volume and spra tips that promote through coverage of cotton foliage for best results.