Large and smooth crabgrass: As we move from full bloom to past full bloom of Forsythia, we should be looking at the very end of the preemergence herbicide application window. At some locations in New England seedling crabgrass has been seen, especially in very thin turf and/or south or southwest facing slopes. If you are seeing crabgrass seedlings and have not completed your preemergence herbicide applications there are two options at this point:
- Option one: the herbicide dithiopyr (active ingredient in DimensionTM) has very early postemergence activity on crabgrass (prior to tillering or about less that 5-leaf stage of growth). The use of a sprayable formulation of dithiopyr will control early emergence crabgrass and also provide preemergence control for future crabgrass growth.
- Option two: Tank-mix a sprayable preemergence crabgrass herbicide with fenoxaprop-ethyl (Acclaim ExtraTM). In situations in which overseeding is needed, application of mesotrione (TenacityTM) or quinclorac (DriveTM) will provide early postemergence control of crabgrass and allow for overseeding of cool-season turfgrasses.
Broadleaf weed control: Dandelions are in full flower and should be targeted now. Many winter annual weeds are in flower as well. Any of the postemergence combination products will provide good control at this time of the year. Ground ivy and wild violet are difficult to manage this time of the year and application should be delayed until September if possible.
Japanese knotweed, Polygonum cuspidatum or Fallopia japonica, has begun to emerge from rhizomes. Do not attempt to control this weed at this time as herbicide applications are not effective. Repeat cutting or mowing can be used as a non-chemical strategy, and if that is the control strategy selected then cutting and mowing should begin now. Repeat cutting or mowing should be done as regrowth reaches 4 to 6 inches.
Submitted by: Randall Prostak