Weeds- are unsightly and undesirable plants that grow where they are not needed. Weeds often grow faster than the desired turf grass, compete with lawn for nutrients, water, and light. If weeds are left uncontrolled it will result in the deterioration of the athletic field over time. Weeds tend to infest turfs that are sparse and poorly established and maintained.
There are two approaches to have a turf area with little or no weeds, using pre-emergence and post-emergence. Pre-emergence herbicides kill the weeds before they emerge from the soil while post-emergence herbicides kill weeds after they have been established. The pre-emergence approach is the best method. Please note that pre-emergence herbicides do not prevent germination but rather kill weeds shortly after they germinate.
Cultural Practices– It is very important for a field manager to first consider Integrated Pest Management (IPM) prior to using any pesticides. Cultural weed control is very important; for example the field manager should routinely scout the field to identify weeds and to note new species that are present. Early detection is critical to prevent the spread of problem weeds. It is proven that weed populations are influenced by irrigation; how much water per application, and the frequency, can help determine the level of weed infestation. In 2006, Busey and Johnston from the University of Florida established that daily irrigation influenced the occurrence of dollar weed in St. Augustinegrass. In addition, wet soil makes the turf conducive for sedges, such as purple nutsedge and kyllinga. Cultural practices cannot be overemphasized because one should not only depend on herbicide to prevent or fix weed problems
Applying Pre-emergence– In order to effectively prevent the target weeds from emerging, the turf manager must acquire the basic knowledge and understanding of the temperature requirement for the target weed to germinate. Knowledge of whether the weed is a winter/summer annual is vital. For example, crabgrass which is a summer annual will germinate when there is temperature range of 55-70 degree F for several consecutive days. In Central Florida, there is a narrow window of time to apply pre-emergence herbicide. If application is not done within that window, the herbicide will have little or no effect because the weeds already started growing. Application must be done prior to weed emergence so predicting the weed life cycle is absolutely vital in applying pre-emergence at the right time. Monitoring the soil temperature in the upper half inch of the soil is an excellent way to determine when the right time to apply pre-emergence.
It is also important to note that there are winter annuals and summer annuals. Most winter annual weeds start germination in fall and growth continues until late spring to early summer. In Central Florida, to have proper control of winter annual weeds, it is best to apply pre-emergence in mid-October into the middle of November. After applying pre-emergence, a ¼ inch of rainfall is required within 7 days of application for the pre-emergence to be activated. If rainfall is not available the herbicide should be thoroughly watered in with a sprinkler. Irrigation/rainfall moves herbicide into the root zone of the soil.
Rotate Herbicides-Rotating your pre-emergence is just as important as rotating other pesticides; this will prevent weeds from building of resistance to a particular herbicide. In order to effectively rotate a pesticide, the manager has to have the basic knowledge of the pre-emergence mode of action and the class which each chemical falls under. Rotating a name does not necessary mean that you are using a different chemistry of chemical. For example, benefin (balan), pendimethalin (pendulum), and prodiamine (barricade) are from the same class which means substituting any of the above for the other would not be an effective rotation.
Over-seeding– Never over-seed and apply pre-emergence in the same time period. Pre-emergence herbicides will both prevent target weeds and the desired turf from emerging. Always read the pesticide label. .
.For more information on commercial landscaping and other related horticulture topics, contact Grantly Ricketts with UF/IFAS Extension in Osceola County at 321-697-3000 or email firstname.lastname@example.org.