Fall Cutting of Alfalfa in the North Central USA

The North Central (NC) and Northeast (NE) states produce almost two-thirds of the alfalfa (Medicago sativa L.) in the USA. Three cuttings by early September is the most popular management system. A third cutting in mid-September to early October has been considered deleterious to subsequent yield and persistence compared with cutting in late August or early September. Our objective was to determine the effects of the final cutting date on subsequent yields and persistence of fertilized and unfertilized hardy and moderately hardy cultivars in a three-cut system in southern Michigan. Hardy (‘Vernal’ and ‘Cayuga’) and moderately hardy (‘DuPuits’, ‘Saranac’, and ‘Honeoye’) alfalfa cultivars were used in four separate experiments on well-drained Conover loam (fine-loamy, mixed mesic Udollic Ochraqualfs). Third cuttings made on 15 September or 1 or 15 October for three consecutive years did not reduce the subsequent year's yield or persistence compared with the control cutting date of 1 September if the cultivar was resistant to bacterial wilt [Corynebacterium insidiosum (McCull) H.L. Jens] and fertilized with K. Yields were reduced if the cultivar was wilt-susceptible and was cut on 15 September. Levels of total available carbohydrates (TAG) followed similar bi-monthly trends between 6 September and 13 December for both cultivars. Average TAC content of the two cultivars increased to 304 g kg⁻¹ on 1 November and then decreased to 271 g kg⁻¹ on 13 December when alfalfa was dormant. On 13 December, levels of TAC were the same within cultivars for all fall cutting treatments and lower for DuPuits than for Vernal. Yields and persistence were not reduced by variable dates of fall cutting after a second cutting in mid-July if the cultivar was wilt-resistant, hardy or moderately hardy, and the soil had been well fertilized with K. The present recommendation of not cutting in September and early October or 4 to 6 weeks before the first killing frost in the NC and NE states should be reevaluated.