One of the primary problems with annual bluegrass (Poa annua, A.K.A "Poa") is the flush of seedheads in spring that disrupt turfgrass uniformity and lead to more annual bluegrass. The standard method of suppressing Poa seedheads is through application of the chemical seedhead suppressors ethephon (Proxy) and mefluidide (Embark). Both products may discolor Poa and possibly creeping bentgrass but ethephon is the safer of the two and enjoys more market share. To improve turfgrass uniformity and mask injury symptoms, ethephon is typically tank mixed with trinexapac ethyl (Primo) and mefluidide is typically applied in sequence with foliar iron. Both products are best applied when growing degree days (GDD) at base 50 F reaches 50 units. Start measuring GDD on Feb 15 and spray when you reach 50 units. Repeat full-rate treatments on a 3-4 week interval or apply the products weekly or biweekly at a cut rate. Discontinue treatments as the Poa seedhead season is ending or as turfgrass growth slows due to rising temperatures (typically late April to early May in Richmond and eastern Virginia and mid to late May in mountains and northern Virginia). It should be noted that the seedhead suppression season has been unusually early in the last two to three years. When applied at the perfect time of year and at the perfect rate, these products will "usually" control Poa seedheads better than 70% for the entire season. The problem is that both products can lead to inconsistent Poa seedhead suppression, especially in the early part of the season. The following discussion will cover the high points of using each product and introduce a new treatment program that improves efficacy based on Virginia Tech research.

Mefluidide (Embark)

Mefluidide can be more consistent at controlling Poa seedheads than ethephon but only at higher rates that cause transient turf injury. For example, some superintendents will apply Embark T & O to putting greens at 40 fl oz/acre per month while others will not exceed 20 fl oz/A per month. At 40 oz/month, seedhead suppression will typically be great but severe discoloration of the putting green may occur for about two weeks. To avoid discoloration, most mefluidide users will apply 10 oz/A initially, wait a week, and assess the response of bentgrass and Poa. If no response is noted, an additional 30 fl oz/A may be applied. If a noticeable response is observed, the mefluidide is "spoon fed" at around 10 fl oz/A per week. It is best to apply foliar iron 3 days before or after a mefluidide treatment. When the two are tank mixed, the iron will cause mefluidide to precipitate out in the tank and reduce efficacy. If you are inclined to tank mix the iron and mefluidide, spray the mixture as quickly as possible. In some years, it seems that Poa and creeping bentgrass respond to mefluidide more than in other years. The "spoon feed" method, along with foliar iron, can help maximize seedhead suppression will keeping turf injury in check. A monthly target of 40 fl oz/A is a good "aggressive" target but will not be needed in all years.

Ethephon (Proxy)

Ethephon when applied with trinexapac ethyl (Primo) will maintain or improve putting green aesthetics and uniformity but may exhibit serious swings in seedhead suppression from one year to the next. The standard recommendation is to apply Proxy at 5 fl oz/1000 sq ft mixed with Primo at 0.125 fl oz/1000 sq ft. This tank mixture is applied initially at 50 GDD50 and repeated 3 to 4 weeks later. Alternatively, one may apply half rates of each product every 2 weeks. New research is evaluating the addition of Signature with the Proxy Primo program for added putting green uniformity and color. Although ethephon may discolor Poa, it is much easier to manage turf response to ethephon compared to mefluidide. Potential problems with ethephon may occur when the product is applied later in the season during hot weather or on thatchy putting greens. In these situations, ethephon can cause "crown rising" that results in scalping injury. On properly managed putting greens and baring unseasonably hot weather, scalping should not be an issue if ethephon is used with trinexapac ethyl and at the correct rates and timings.

New Methods

Both mefluidide and ethephon tend to exhibit erratic seedhead suppression in the first four weeks of the seedhead suppression season. While exploring the reasons for this phenomenon, I hypothesized that Poa seedheads were initiating at various times in late fall and winter due to periodic warming spells. I believed this because I can find a random Poa seedhead at any time of year on putting greens. If more Poa initiates seedheads in winter one year compared to another, that may explain the differences in seedhead suppression between years. Since ethephon and mefluidide only work to prevent seedhead initiation and will not arrest seedhead development, they will have no effect on seedheads that were already started earlier in winter but are not yet visible. For the past 5 years, several research trials have shown that applying ethephon at least one month before the normally expected seedhead season can mean the difference between 20% seedhead suppression from the normal ethephon program and 95% seedhead suppression with the early application. During a warm (non frozen) day on January or February, apply 5 fl oz/1000 sq ft of only ethephon to putting greens. Follow this application with a normal GDD-timed ethephon plus trinexapac ethyl program later in the spring. The result should be some of the best seedhead suppression you have ever achieved with ethephon.