Use of glyphosate salts in seed dressing herbicidal compositions

Details Use of glyphosate salts in seed dressing herbicidal compositions Use of glyphosate salts in seed dressing herbicidal compositions

1998-12-07

2000-08-01

Clardy, S. Mark

Plant protecting and regulating compositions

Seed coated with agricultural chemicals other than fertilizers

504206, A01N 5702

Patent

active

060966866

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to means and methods for control of parasitic weeds in glyphosate-resistant crop plants, and in particular to the use of glyphosate in seed dressing herbicidal compositions for this purpose.


BACKGROUND OF THE INVENTION

Glyphosate (International Standards Organization common name for the anionic form of N-phosphonomethylglycine) is widely used as a postemergence foliarly applied herbicide.
Until recently glyphosate could only be used to control weeds in a non-selective manner, i.e. if applied to foliage of a standing crop it would kill the crop as well as the weeds. Very low rates of postemergence foliar application of glyphosate have been shown to allow the control of parasitic weeds on standing crops (Foy et al., 1989), but the rate dependence was so crucial and hard to adjust that this use has not been widespread. This use though was predicated on the well known fact that glyphosate is systemic once applied to plant foliage. The ability of glyphosate to act solely through foliage is well accepted in agriculture, as it is well known that it is rapidly degraded in all natural soils, i.e. soils that have not been sterilized (Rueppel et al., 1977). It thus cannot be used as a soil-applied "preemergence" herbicide to control weeds underground, unlike so many commonly used herbicides in agriculture.
As noted above, glyphosate has been used as a non-selective herbicide until recently. That has been changed with the advent of glyphosate-resistant crops. This change has been achieved by engineering a gene coding for enolphosphate shikimate phosphate synthase also known as 5-enolpyruvyl-3-phosphoshikimate (EPSP) synthase, an enzyme that is found in, and is vital to, all plants, and is inhibited by glyphosate. The transgenic plants either contain multiple copies of the natural gene (Rogers et al., 1983) or a modified gene coding for an enzyme that still has a modicum of natural enzyme capacity but is severely reduced in its capacity to bind glyphosate and thus be inhibited (Comai et al., 1985). The gene must code for a modified form of the EPSP synthase, whereby this enzyme is less inhibited by glyphosate than the naturally-occurring enzyme, or for elevated expression of the enzyme, or both.
Such engineered glyphosate-resistant plants often contain subsidiary genetic elements that target the modified gene product to the chloroplasts, and control the level and tissue-localization of the gene (Shah et al., 1986; Kishore, et al., 1988). Examples of such transformed plants are described in U.S. Pat. No. 5,145,783, EP 550633, U.S. Pat. No. 5,310,667 and U.S. Pat. No. 4,971,908, all of them incorporated herein in their entirety by reference. In addition, glyphosate resistance can also be achieved when a plant is able to amplify the gene (Suh et al., 1993) or to enhance the expression of the gene (Hollander-Czytko et al., 1992) coding for EPSP synthase.
Parasitic weeds can either be holoparasites, i.e. plants totally lacking the capacity to produce nutrients for themselves, e.g. Orobanche spp. (common name: broomrapes), or hemiparasites, i.e. they can perform photosynthesis for parts of their life cycles (e.g. Cuscuta spp. (dodders), Striga spp. (witchweeds) and Alectra spp.), but derive much of their organic nutrition, water and minerals from the host plants. The Cuscuta spp. attach to stems and grow above ground, the others attach to roots and spend much of their life cycle below ground until a flower stalk emerges from the soil. One of the major modes of dissemination of parasitic weeds is by contamination of crop seed. Half of the seedlots sampled in local African markets by Bemer et al., 1994 were contaminated with Striga seeds. Orobanche seeds stick to crop seeds and arduous procedures are required to remove them so as not to infest uninfested fields. Thus, a good general topical disinfectant is needed for inactivating parasitic weed seeds in contaminated seedlots prior to sowing. Additionally, there is also a general need for ridding crop seed of other contam

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