Seed safener

To facilitate premixes in sorghum, Ciba-Geigy developed a seed safener to ensure greater tolerance to the chloro-acetanilide mixing partners. The development of the safener had a significant impact on use of atrazine and propazine... 

Direct-seeded rice does not tolerate pretilachlor in doses required for adequate weed control. The Ciba Geigy AG has discovered and developed a new safening agent, 4,6-dichloro-2-phenyl-pyrimidine (CGA123 407,23), which protects the rice seedling from damage and does not interfere with the herbicidal activity of pretilachlor. 

In the 1970s compounds were developed which eliminated these harmful effects on the growth of crop plants. They can be applied for the treatment of the seeds or admixed with EPTC in a quantity of 5-10%. These antidotes or safener substances presumably exert their action by stimulating the functioning of the EPTC-detoxicating enzyme of crop plants, of glutathione-S-transferase. This theory is supported by the observation that sensitive and tolerant plants absorb and translocate EPTC to essentially the same extent, but in tolerant plants the active substance is rapidly metabolised oxidatively to sulfoxide, then to biologically inactive sulfon derivatives, while in sensitive plants this process is slower and the plant meanwhile dies. 

The tolerance of maize to chlorsulfuron can be greatly increased by seed dressing with 1,8-naphthalic anhydride (NA) at 0.5%. Seed dressing with R 25788 (N,N-diallyl-2,2-dichloroacetamide) is less effective. NA has a safening effect on sorghum, rice at 5 g chlorsulfuron/ha. Wheat and barley are also well protected by NA to doses in excess of 100 g/ha active ingredient. 

Herbicide safeners (also referred to as herbicide antidotes or protectants) fulfill an important role in crop protection. Safeners are chemicals that protect crop plants from unacceptable injury caused by herbicides. Either by placement on the crop seed or by way of a physiological selectivity mechanism, safeners in commercial use do not negatively impact the weed control of the herbicide. Although many herbicides have been developed for use without a safener, some of the strongest and most broad-spectrum herbicides tend towards border-line crop selectivity, which may completely preclude use in a particular crop or at least limit maximum use rates or the crop varieties that can be safely treated. It is for such situations that safeners have been developed. Several books and reviews of safeners have been written over the past 20 years [1-3]. It is not the intention of this chapter to cover in detail older safeners, but rather to focus on more recently developed commercial safeners as well as some of the older compounds still in wide commercial usage. 

A fundamental problem for safener discovery and development is to find safeners that do not also antagonize weed control. The fruits of Gulf Oil Company research (reported by Hoffmann in 1969) was 1,8-naphthalic anhydride (NA), which works best as a seed treatment, whereby antagonism of weed control is not an issue. To the authors knowledge just over a dozen further safeners have been commercialized in the years since NA was introduced, although several of the early safeners have since been superseded and/or withdrawn. This subse-... 

These chemically diverse safeners all need to be applied to the crop (maize, sorghum) by seed dressing to obtain the selective safener effect. The oldest and best... 

NA had also a stimulatory effect on the oxidative metabolism of the herbicide bentazone. Microsomal preparations of etiolated shoots from maize, which had received a seed treatment with NA, showed activity of a bentazone hydroxylase, which was not detectable in extracts from controls without safener pre-treatment [35]. Also, the improved tolerance of maize to the imidazolinone AC263222 after NA seed treatment could be related to enhanced AC 263222 hydroxylation by stimulation of a cytochrome P450 monooxygenase [31]. 

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