Weather A cold first few 10 days of April transitioned warm for a few days and then crashed right back down. April temperatures are 7-10 degrees below normal throughout the region, which is in stark contrast to any spring temperatures in the last seven years. April 2007-08 and 2013 were 2-3 degrees below normal (~55 F average temperature), but at 7 degrees below average for this month we are bordering on the all-time lows of 1904, 1907, 1920, 1926, and 1983. A warm-up into late April and early May is forecasted, and the flower blooms stymied by April should bust into season over the next two weeks. The April showers to spawn those May flowers, however, were greatly dependent on your region of the state. Towards St. Louis, southeastern MO and northern AR copious amounts of rain have fallen, two three inches above normal in some areas. From middle and northern Missouri, southern IA, and much of Kansas, a lack of rainfall has landed the region into a moderate to severe drought situation with 2-3 inch deficits over the past 30 days. Some rain is forecasted in early May, but most of this week looks particularly dry. Good for the farmers in the Bootheel region to dry out and plant their fields, and perhaps an opportunity for mowing, weed control, and perhaps even disease prevention later this week or early next.
Quick Hits Several zoysia lawns in St. Louis have declined considerably over the past year, and I visited several last week and received calls about several more. In all of these cases, the cause is very difficult to discern and no pattern has been found among the cases. Several of the residents indicate the decline started the previous June and July, which indicates potential insect damage from chinch bugs or billbugs. For controlling either of these pests, remember that bifenthrin or other pyrethroid may not be the sole answer. Billbugs cause significant damage in their below ground larval stage and only adults may be impacted by a pyrethroid application. Chinch
bugs, with their huge populations, have been reported to acquire resistance to the pyrethroid class of chemistry in other states. These instances of decline may also be related to winter dessication, particularly in late fall/early winter when rainfall was scarce and the temperature plummeted abruptly. The good news is that zoysia has just started to emerge from its slumber to refill and compete with weeds and cool season turfgrasses. The bad news is that some of these gray areas are gone and will have to be resodded, plugged (slow), sprigged (slower) or seeded with a cultivar like Zenith (slowest). Lawn care operators should be mindful of preemergent applications on these injured lawns if zoysia is to be reestablished. Oxadiazon (Ronstar) should be used according to label instructions to allow for zoysia recovery. Our first early spring application for preventive large patch control was applied according to the five-day two-inch soil temperature average of 50 F last Tuesday. This application, which is part of a USGA sponsored control study investigating postapplication irrigation and spring timing, has worked well in the two previous years. The only difference is that in 2016 and 2017, the applications were made on March 6 and March 8, over a month prior to these! As we near 25% greenup now in mid MO, and with warmer temperatures certain to spark more green, consider a preventive application on areas with a history of the disease at the end of this week in southern regions of MO and northern AR, and next week in mid Missouri.
On the Outside Corner As the late Tom Petty sang the waiting is the hardest part, and this mild spring has rung these chords true. The chance for another killing frost is low, however, so the fight against summer annuals should begin. Mowing of cool season grasses should therefore be at least 3.5 4 or in some cases as high as the mower deck will go, to shade and outcompete weed seedlings. According to the growing degree day tracker (www.gddtracker.net) current soil temperature data, the forecast and the Frost-Freeze Probabilities Guide, at least the first preemergent application should be down on cool-season lawns if this route is chosen. Like a frustrated pitcher, the soil temperatures for soilborne disease control on golf putting greens are still nibbling on the outside corner. The strike zone is when five-day two-inch soil temperature averages stay in the 55-60 F range, and the warmup into early May will most
likely get us there. This threshold is the target for the first of two watered-in fungicide applications aimed at prevention of fairy rings on golf putting greens. A second application is targeted for 28 days after the first, however, in this odd year sliding the second application back to 21 days is advised to reduce the chance of DMI regulation in the heat. A few important notes about this preventive strategy are outlined below. Low rates of the demethylation inhibiting (DMI) fungicides have worked well in this management strategy. Triadimefon (Bayleton), triticonazole (Triton, Trinity), metconazole (Tourney), and tebuconazole (Torque) have been demonstrated as effective. Combination products with these fungicides should also be effective. Preventive fungicides must be watered-in with at least 1/8 and preferably 1/4 of post-application irrigation. Preferably, irrigation should occur immediately afterwards, but our research indicated no loss in fairy ring control if irrigation occurred 10 hours after application. Wetting agents should not be tank-mixed with these preventive applications, but should be made on their regular schedule 14 days after/before the fungicide application. In a curative situation with fairy ring symptoms present, a wetting agent should always be tank-mixed with the fungicide. Side effects with DMI fungicide use should be minimized due to utilization of lower rates and a spring application window with minimal heat stress. Caution should be exercised when using plant growth regulators such as paclobutrazol (Trimmit, TGR) since they are related to DMI fungicides. For those with ultradwarf bermudagrass greens with possible winter damage (outside the MO viewing area), I suggest waiting until after full bermudagrass green-up (and damage can be assessed) before making a DMI application. As a side benefit, we have also noted substantial reductions in dollar spot activity on creeping bentgrass greens through August in treated plots. The longest residual dollar spot control was observed in triadimefon and tebuconazole treated plots. Since the treatment window is similar, other root diseases such as take-all patch and summer patch may also be controlled with these spring applications.