For certain weeds, such as crabgrass, foxtail or spotted spurge, application of herbicides are most successful in the spring.
Pre-emergence application, used for crabgrass prevention, is put onto turf before weeds grow. Post-emergence application is put down after weeds have already started growing. Pre-emergence application is preferred because it prevents weeds from visibly detracting from the lawn’s appearance and competing for water and nutrients.
The best prevention for weeds is having a healthy and aggressively growing lawn. In Nebraska, stressful growing conditions for turf can allow weeds to take advantage of poor conditions. Any unwanted plant can be a struggle to get rid of, and if the lawn isn’t managed properly, weed invasion is bound to happen.
Proper mowing height will help to strengthen grass and weaken weeds. Cool-season grasses such as tall fescue and Kentucky bluegrass should be no lower than two and a half inches. If a lawn is mowed too short, the plant tries to compensate for the lost top growth by growing the top growth back, resulting in a loss of rooting. Rooting is the foundation of a healthy plant, and without it, weeds will be more likely to grow in turf.
The right amount of water and fertilizer also are essential in keeping turf healthy and weed-free. During spring under Nebraska’s weather conditions, only supplemental irrigation is needed. Over-watering will harm the lawn. In spring, grasses need one inch to one and half inches of water per week. That can be gained just from rainfall. Later during the summer, more frequent watering is necessary. The right amount of fertilizer is necessary as well. Depending on the level of color desired, bluegrass lawns need about four pounds of fertilizer per year. Tall fescue needs closer to three pounds a year. Optimally, pre-emergent fertilizer combinations should be put down the first week of May, with more being put down five to seven weeks following that.
Limiting traffic from pets and people also helps in keeping a healthy, thick-grown turf. If cultural practices such as mowing, watering and fertilization are done correctly, the lawn is in better condition to compete against invasive weeds.
SOURCE: Roch Gaussoin, UNL
