AlfaBug: 2018 Update
By: Deborah Samac
Research Leader, USDA-ARS
Adjunct Professor, Department of Plant Pathology
What is the most important insect-pollinated crop? Not apples or squash but alfalfa. Yes, alfalfa. Alfalfa, which is the third most widely grown crop in the country is an essential food for cattle. Thus, without alfalfa we have no milk and no beef. As a perennial plant that is actively growing in early spring and late fall, alfalfa plays an important role in soil conservation by helping to prevent erosion, and its deep and extensive root system helps to prevent movement of fertilizers into surface and groundwater resources. The crop was introduced into the United States with European settlers. Native bees found the nectar produced by this plant to their liking and proceeded to pollinate it. These native pollinators were familiar with similar members in the bean family and adapted to the new arrival. Alfalfa is also a major nectar source for non-native honeybees. Besides pollinators, alfalfa provides habitat and food for an incredible number of diverse insects, some of which help to control insect and mite pests in alfalfa and other crops, and add overall to the biodiversity of the landscape. Although surveys for insects utilizing alfalfa as a habitat have been done in some locations in the Pacific West and North Atlantic states, there are no surveys from the Midwestern U.S.
The only pesticide used routinely in conventional alfalfa cultivation is to control the potato leafhopper. This small insect causes severe stunting of plants when they occur at moderate to high population levels. One potential strategy to reduce leafhoppers is to mix alfalfa and grass plants because the leafhopper does not feed on grasses. The goals of this project are to: (1) identify the major insect species in the pure alfalfa and mixed alfalfa-grass plots, (2) determine the effects of grass plants on leafhopper damage, and (3) determine the effect of grass plants on diversity and size of insect populations, particularly pollinators. This information will be useful for organic farmers to manage insect pests without pesticides and for all farmers who wish to increase local pollinators and beneficial insect populations for production of fruit and vegetable crops.
During 2018, plots for the project were prepared for planting and amended with greensand to provide additional potassium to the soil. In July, seeds of a biomass (non-lodging) alfalfa variety were planted in one plot and a mixture of alfalfa with “Hidden Valley” meadow fescue in another. Although alfalfa plants were established, there was strong competition by weeds, particularly crabgrass, and little of the meadow fescue could compete with the weeds. Plant surveys will be done in early spring 2019; however, it is likely that the plots will need to be replanted. Weeds will be controlled by application of corn gluten meal in spring as an organic pre-emergent herbicide, and by frequent shallow tillage of the plots during the summer. Replanting of alfalfa and meadow fescue seeds will be done in early August. Using these more aggressive weed prevention strategies should enable good establishment of alfalfa and grass plots so that insect surveys could begin in the spring of 2020.