Newberrians have enjoyed a bountiful growing season and many outdoor activities. It is time now to turn our attention to our lawns and how to control two of those particularly pesky weeds in our turfgrass.
One of the best ways to control weeds is to maintain a healthy lawn. By using proper fertilization, irrigation, and mowing techniques, the turfgrass will be dense enough to prevent some weeds from emerging.
Many weeds are unsightly but do not harm anything other than our visual notice of their presence. Weed control programs will not completely eradicate all weeds but allow us to manage the weeds to a level that we may tolerate.
Spurweed is a particularly burdensome plant that resembles parsley. For those who enjoy barefoot days, encountering this weed is painful. The razor sharp spines that surround the bloom of this weed inflict intense pain on humans and pets. It is one turfgrass weed that must be managed properly because it is so painful to encounter.
Spurweed is a broadleaf, winter annual that flowers in mid to late spring. Once the spines are formed, there is little that may be done to it. One must wait until fall to treat with a pre-emergent herbicide in late August through the first week in September. The pre-emergent will prevent this problem weed from emerging from seed.
Certain pre-emergent herbicides are more effective in controlling spurweed. Therefore, make certain that the pre-emergent herbicide you use is one that will specifically prevent this troublesome weed. Read and follow all label directions when applying any herbicide.
Annual bluegrass, poa annua, is a winter annual grass. It has smooth leaves and boat shaped tip. It is a lighter green color with a coarser texture than most turfgrasses. It is noticeable by its abundant seed heads.
Annual bluegrass seeds germinate in late summer or early fall as the soil temperature drops to less than 70 degrees. The resulting seedlings grow and mature and ultimately produce more seed in the spring. Each plant may produce hundreds of viable seed. The seed may remain dormant in the soil for years before it germinates making control difficult.
It thrives in short day lengths and cool conditions and has the capacity to out-compete turf in late fall and early spring. It often dies during the summer when other turf is stressed unless it is irrigated. It is seen more often in lawns that are closely mowed, frequently irrigated, and fertilized with a high nitrogen fertilizer. It prefers shady or high traffic areas with compacted soil.
Certain cultural practices help control annual bluegrass in turf. Irrigation should be deep and infrequent to promote turf root development as well as prevent ideal conditions for annual bluegrass growth.
Measures to prevent soil compaction should be employed. Aerations should be done during periods of active turfgrass growth to prevent prolonged periods of open soil. Fall aerations of cool-season turf should be timed so the turf recovers prior to annual bluegrass germination. Warm-season turf should also recover from summer aerations prior to annual bluegrass germination.
Avoid high nitrogen fertilizer applications during peak annual bluegrass germination periods. Do not fertilize turf during dormant periods as this encourages annual bluegrass growth.
Follow recommended turf specific mowing heights. Competition from turf will reduce weed infestations. Avoid any mowing practices that stress turfgrass. Clippings left on the turf returns the nutrients to the soil but clipping removal when seedheads are present may reduce the spread of viable seeds.
Cultural practices may not be sufficient to reduce the population to tolerable levels. Chemical controls are also available in the form of pre-emergence and post emergence herbicides. Application timing of pre-emergence herbicides is critical to control. They should not be applied if reseeding or re-sodding will occur within a few months of application. Also, make sure that the turf type is suitable for the herbicide being applied. As always, read and follow all label instructions!