G.D. Alexander was a prominent farmer in Natal and was elected chairman of the first annual congress of the Intercolonial Agricultural Union of South Africa, founded in 1904. In July 1903 he wrote a critical analysis of the first two interim reports issued by Robert Koch* on his investigation of East Coast fever in Southern Rhodesia (now Zimbabwe). Koch had studied the disease in East Africa in 1898 and at that time concluded that it was a form of Texas fever or Redwater, but in his reports from Zimbabwe stated (on much the same evidence) that it was a distinct disease. Alexander pointed out this and other inconsistencies between Koch's reports of 1898 and 1903. He concluded that Koch had misled the scientific fraternity and criticised Koch's expensive appointment. His report was published in the Natal Witness of 17 July 1903, and in the Veterinary Record a few months later.
Alexander's comments on agricultural matters often appeared in the Natal Witness and in Natal's Agricultural Journal. During the latter part of World War I (1914-1918) he wrote a pamphlet on "Development of inventions and industries in South Africa", which was published in Pietermaritzburg. In 1915 a revised edition of his report on "The rearing of calves as practised on the Nel's Rust Estate, Natal" was published by William Cooper and Nephews, manufacturers of veterinary products in East London.