Potato leafhoppers in alfalfa: effects of alfalfa–grass mixtures, cultivar resistance status, and insecticides on forage yields

Alfalfa ( Medicago sativa L.) is increasingly affected by high potato leafhopper (PLH, Empoasca fabae (Harris)) populations in some regions of Quebec. A study was conducted in three environments to contrast the use of different strategies to mitigate the effects of PLH on alfalfa including the addition of grasses in mixture with alfalfa, the use of a PLH-resistant cultivar, and insecticide applications. Foliar insecticide applications in the seeding year temporarily reduced PLH populations, but only increased alfalfa yield of a PLH-susceptible cultivar in one out of three environments. Insecticides also had an indirect residual effect in the first post-seeding year in low PLH conditions in the same environment increasing alfalfa yield of the PLH-susceptible cultivar at the first two harvests, compared to plots not treated with insecticide. The use of a PLH-resistant cultivar overall provided limited benefits across years and environments, it actually yielded less than a susceptible cultivar in some environments with low PLH populations. The addition of small percentages of grasses to alfalfa overall had minimal effect in high PLH conditions. Of the three strategies investigated, the use of insecticide had the greatest effect on alfalfa response to PLH, it is although important to note that harvesting was also effective in reducing PLH populations. Results need to be further validated across a wider range of environments as PLH populations we observed were low in most post-seeding years.