Weeds and Chemical Defense in Our Vineyard

We began weeding our vineyard rows on Friday, the first nice day after the rains. We found a plethora of these weeds with yellow flowers on the north side of the vineyard and began hoeing them out. A search on the Internet revealed that these weeds are from the mustard family and are called Barbarea vulgaria or yellow rocket. Knowing the weeds in the vineyard can be a clue to the type of soils. In the book Weeds of the Northeast, written by Richard H. Uva, Joseph C. Neal and Joseph M. DiTomaso, they mention that the yellow rocket is most common on nutrient rich sandy and loamy soils. Precisely the type of soil that we have. On very close inspection of the yellow rocket, we found some very tiny beetles and were able to identify the beetles as well. The beetles are Phyllotreta nemorum, a flea beetle that likes to feed on the yellow rocket making little shot holes in the leaves.

There is an interesting interatcion between the yellow rocket and the flea beetle reported in the research paper Identification of Defense Compounds in Barbarea vulgaris against the Herbivore Phyllotreta nemorum by an Ecometabolomic Approach written by Vera Kuzina, Claus Thorn Ekstrøm, Sven Bode Andersen, Jens Kvist Nielsen, Carl Erik Olsen and Søren Bak and available on line:¹
The Barbarea vulgaria the yellow rocket, a member of the mustard family, has developed chemical defense against the Phyllotreta nemorum flea beetle in the form of saponins, which are triterpenoid glycosides. These saponins are constituents of many plant drugs and folk medicines and possess a wide range of biological activities, including antifungal, antibacterial, molluscicidal, and insecticidal activities. The toxicity of saponins to fungi and insects is thought to be a result of their ability to form complexes with sterols in the plasma membrane, thus destroying the cellular semipermeability and leading to cell death. Although saponins are toxic to cold-blooded animals, their oral toxicity to mammals is low. I found the chemical structures of these saponins in another online article:²

The yellow rocket exists as two genotypes, the P and the G. The pubescent P-type is susceptible to all known flea beetle genotypes, whereas the glabrous G-type is resistant to most common genotypes of the insect. We must have the susceptible P-type genotype growing in our vineyard!
References:
1. Vera Kuzina, Claus Thorn Ekstrøm, Sven Bode Andersen, Jens Kvist Nielsen, Carl Erik Olsen and Søren Bak, Identification of Defense Compounds in Barbarea vulgaris against the Herbivore Phyllotreta nemorum by an Ecometabolomic Approach, Plant Physiology, December 2009, vol. 151 no. 4 1977-1990.
2. Jörg M. Augustin, Sylvia Drok, Tetsuro Shinoda, Kazutsuka Sanmiya, Jens Kvist Nielsen, Bekzod Khakimov, Carl Erik Olsen, Esben Halkjær Hansen, Vera Kuzina, Claus Thorn Ekstrøm, Thure Hauser and Søren Bak, UDP-Glycosyltransferases from the UGT73C Subfamily in Barbarea vulgaris Catalyze Sapogenin 3-O-Glucosylation in Saponin-Mediated Insect Resistance, Plant Physiology December 2012, vol. 160 no. 4 1881-1895.