Forage yield and nutritive value of potato leafhopper-resistant and susceptible alfalfa cultivars grown in Quebec

The potato leafhopper (PLH; Empoasca fabae (Harris)), a pest affecting several crops including alfalfa ( Medicago sativa L.), is a recurrent problem in several regions in the province of Quebec. A field experiment was conducted at three sites over three growing seasons to evaluate the impact of foliar insecticide applications and the use of PLH-resistant cultivars on forage yield and PLH population dynamics. In the seeding year, insecticide applications effectively reduced PLH populations but did not lead to significant yield increases compared to untreated controls. However, at one site, three insecticide applications in the seeding year resulted in increased first-cut yields in the post-seeding year of some cultivars compared to untreated controls. Yield differences between PLH-resistant and PLH-susceptible cultivars were minimal and variable in the seeding and post-seeding years regardless of the PLH population levels. Insecticide applications increased crude protein concentration of PLH-susceptible and some PLH-resistant cultivars in the seeding year. With high PLH populations in the seeding year without insecticide applications at one site, two PLH-resistant cultivars had higher crude protein concentrations compared to susceptible ones. Under relatively low PLH populations, the overall benefit of currently available PLH-resistant cultivars may be limited. However, further research is needed to confirm these results, as PLH populations remained relatively low in all post-seeding year environments.