Marching Up and Down
The crazy swings of spring that we all know and love are in full force in this early season. After record breaking warmth in January and February, an early spike in March temperatures sent trees a bloom and many turf managers scurrying. As warned in the previous update, if history was our guide another hard frost was in the cards for March, which is exactly what happened on March 14-15 with 14 – 20 F lows in the region. At MU South Farms, the 13.4 degree low on March 15 was the coldest since January 8. Forsythia and particularly Bradford Pear tree flowers shocked to a special shade of orangish – brown, and the budding spring season came to a grinding halt. The Missouri Frost/Freeze Probabilities Guide is a valuable resource that provides a historical perspective of both spring and fall in the state. Kudos to our state climatologist Dr. Pat Guinan for creating this tool.
Much needed rain graced the region, with 1 – 2.5” around the state in the last 7 days. Since January, the region has been devoid of snow cover or rainfall, with deficits ranging from 0.5-1” in northern AR/Springfield to over 3” in the St. Louis area. Good rainfall chances will continue through this week and into early April. Warm weather is also slated to return in April, which will presumably vault soilborne disease prevention onto the to do list.
8-14 Day Outlook: Warmth returns, rain persists
Cool Season Brown Patch & Dollar Spot - First Arrivals
Cool season brown patch – The recent blast of cool weather shut down bentgrass greens and let cool season brown patch or yellow (caused by Rhizoctonia cerealis) in the door. A report of the disease came in from Springfield, and on the same day we observed the disease on a few bentgrass collars at the turf farm. The disease causes very little, other than cosmetic, damage and the grass recovers quickly when warm temperatures resume. For this reason, unless the disease is extremely prevalent, curative controls (azoxystrobin, flutolanil, fludioxonil or propiconazole) are not advised.
Dollar spot – Dollar spot arrived on the extremely infested disease green at the MU turfgrass farm late last week. While noteworthy, and indicative that a preventive application is near necessary, the observation should also be taken with a grain of salt. The green is located in a low spot at the farm and each year this green is inoculated with a heavy load of the dollar spot pathogen. Still, the observation should perk the ears that the time for preventive disease control on greens and zoysiagrass fairways is very nearly upon us.
Large Patch: The first few green leaves of zoysiagrass are peaking through prominently now in mid Missouri and according to our recent research the time is ripe for large patch prevention. Last year, we initiated a large trial investigating the impact of spring application timing, post-application irrigation, and fungicide choice on large patch control. Neither post-application irrigation or fungicide made a statistically significant impact on large patch severity, but timing surely did. Applications made at a threshold of 50 F 5-day average 2” soil had significantly less large patch than plots sprayed later at the 60 F threshold. Fungicides were applied to very dormant zoysia in the earlier timing, and near the second mowing during the later timing. These results indicate the best timing for prevention is likely now during this rainy period and when the zoysia is slowly greening up.
Nipping the 5-day Soil Temperature Threshold
If forecasted temperatures hold, 2” soil temperatures should stabilize in the 55 F to 60 F threshold area for much of the region near the end of this week and at least by early April. In the figure above, average daily 2” soil temperatures (the blue line) peaked in the threshold region a few times in mid-February, early March, and few days ago, but the steady climb of the more important 5-day average (the red line) should reach and maintain in the zone over the next week. For those aiming to prevent fairy ring and patch diseases like summer patch and take-all patch in the region, the first of two (28 d interval) watered-in applications of a low rate DMI fungicide is advised in the next week. A few important notes about this preventive strategy are outlined below.
Follow on Twitter! @muturfpath
Like on Facebook! Mizzou Turfgrass
Extension Turfgrass Pathologist
University of Missouri