Golfdom, January 2013

Super Science Continued from page 51 it works the traditional application timing of mid spring still usually trends higher for crabgrass control than very early spring or late fall application Therefore higher PRE rates must be used for late fall and very early spring to maximize control Sequential applications After working with PREs for 25 years I am convinced that it is best to maximize crabgrass and goosegrass control with sequential applications Depending on your location two applications at one half plus one half the high use rate will usually sufce and will almost always improve crabgrass and goosegrass control over a single application at the high use rate Te second application is usually made 4 6 weeks afer the first expected crabgrass germination but the frst application can be made at the traditional timing late fall or very early spring Up until the last few years we recommended using the same active ingredient for the initial and sequential applications However our recent research shows that when using one half the high use rate for the initial and sequential application it does not matter which Weed control in dormant or spring seedings is critical to limit crabgrass pressure in spring and summer Most PREs cannot be used prior to seeding and their use is delayed afterward active ingredient is used for the initial or sequential applications Figure 1 we tested only dithiopyr pendimethalin and prodiamine Tis increases fexibility in product selection allows use of remaining product from previous years applications and could increase postemergent herbicide POST control of breakthrough crabgrass if dithiopyr is used for the sequential application s Watering in Tough the label on all PREs especially the sprayable formulations clearly state that they should be watered in within 24 to 48 hours afer application this recommendation is ofen ignored However watering in PREs immediately after application with 01 to 02 inches of water resulted in up to 50 percent improved crabgrass control in one of our studies on fairway height Kentucky bluegrass in 2011 Figure 2 Watering in the PREs moves the active ingredient to the soil where it can be effective and reduces loss through volatilization and UV degradation USe in neW SeedinGS Hot dry summers like 2012 s followed by a dry fall mandate either dormant seeding this winter or seeding next spring Weed control in dormant or spring seedings is critical to limit crabgrass pressure in spring and summer Most PREs cannot be used prior to seeding and their use is delayed following seeding to limit damage to seedlings Dithiopyr has the most fexible label and can be applied after the second mowing of the seedlings Tenacity mesotrione is especially useful over new seedlings of many cool season turfgrass species other than creeping bentgrass because it provides excellent PRE control of crabgrass annual bluegrass and many broadleaf weeds when applied immediately prior to seeding on bare soils However Tenacity is not an efective PRE on turfed soils Our research indicates aggressive use of herbicides after seeding may cause some shortterm injury to the desired turf but is more than compensated in decreased weed pressure over the long term AnnUAl blUeGrASS control POST and growth regulators for annual bluegrass control have improved with new strategies and products but annual bluegrass is best controlled with a multi pronged approach This is at least partly due to variability in annual bluegrass biotypes where one biotype may be susceptible to a specifc FiGUre 2 Dimension 2EW 025 lb ai A 100 90 80 70 60 50 40 30 20 10 0 Crabgrass control July 15 2011 Dimension 2EW 05 lb ai A No water Watered in LSD 15 Check 15 cover Prodiamine 4FL 038 lb ai A Prodiamine 4FL 075 lb ai A Pendimethalin 33 15 lb ai A Pendimethalin 33 3 lb ai A Effect of watering in vs not watering in the pre emergent herbicide on crabgrass control in low mowed Kentucky bluegrass Applications were watered in immediately with 025 inches of water or left un irrigated for three days Watering in pre emergent herbicides will help improve control and consistency in control of crabgrass 52 Golfdom January 2013 Golfdom com