Scouting for turf weeds

Scouting and monitoring are important components of an effective integrated management program for turf weeds. Monitoring should be done every time a turf manager is on a particular site, in addition to an all-inclusive, in-depth scouting event carried out in late summer or early fall.

The turf manager should use a back and forth or zig-zag pattern when scouting for weeds, being sure to cover all distinctly different and/or known problem areas. Special attention should be given to areas of thin turf and possible causes, as well as newly introduced weeds and historically problematic weeds that are not controlled with the current management program. All weed species present and their respective life cycles should be recorded. Observations can be recorded on a site map or listed on a sheet with location identified. Regular scouting and accurate weed identification enables a turf manager to plan and implement an appropriate management approach and to evaluate the long-term effectiveness of control strategies.

Indicator weeds

There is an old adage that states “Weeds are the result of a poor turf, not the cause of a poor turf”. Weed infestation often suggests that there are one or more underlying factors contributing to poor turf health and vigor. A comprehensive list of all weeds should be developed as a turf manager scouts a specific turf site; however there are certain weed species that should be scrutinized more carefully. These weed species, often referred to as “indicator weeds” or “diagnostic weeds”, are particularly competitive when environmental conditions are not optimal for turfgrass growth. The occurrence of indicator weeds can be used as a starting point in identifying those factors that may contribute to poor turf. Identifying and correcting those factors can tip the competitive balance in favor of the turfgrass while minimizing, and in some cases eliminating, many weed infestations.

Red sorrel and bluets are common inhabitants of acid soils, whereas broadleaf plantain may be more abundant at high soil pH. Crabgrass and many other annual weeds require light for germination and thrive in turf areas that are thin as a result of low fertility. White clover and birdsfoot trefoil are also common in low fertility situations and may indicate the need for fertilization. Prostrate knotweed, goosegrass, pineappleweed and path rush commonly occur where the soil has become compacted. Excessive irrigation and/or poorly drained soils may result in an increase in the occurrence of algae, moss, annual bluegrass, creeping bentgrass and yellow nutsedge. Some weeds such as ground ivy, common speedwell and moss are able to thrive in shaded conditions.

Turf managers should not assume that just because these weeds are present that a specific problem exists. For example, red sorrel can grow at high pH and ground ivy may persist in turf areas that receive full sun. While the use of “indicator weeds” is not a fool proof method, it can be a valuable tool in the assessment of potential problems at a turf site.