May 2020 Articles

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Investigating purple Bermudagrass – it’s a cold case

Investigating purple Bermudagrass – it’s a cold case Source: U of A Animal Science jjennings@uaex.edu Producers have recently noticed bermudagrass turning purple and are trying to root out the cause. The evidence indicates that many cases involve well-managed hay fields. Many of these fields were treated for winter weeds and fertilized to support early bermudagrass growth. No obvious insect problems have been reported, soil fertility is variable among cases, so from there the evidence goes cold. Let’s examine the physiology of the victim – the bermudagrass itself. This is a warm-season grass. It grows best at temperatures above 85 degrees. Green leaf tips always show up in March especially when there is no overburden of winter weeds to block sunlight. But it takes a series of consecutive warm nights above 60 degrees to get the internal machinery of the grass working efficiently. Early on, the bermudagrass will start to grow on warm days, then gets shut down when temperatures drop back. Night temps in the 40’s shut down growth for several days. It’s a bit like trying to start a cold engine - it hits, sputters, hits, then finally starts sluggishly. Now think back to a few weeks ago in late March and into early April. Temperatures hit 80+ degrees in late March. The warmup prompted a lot of producers to fertilize fields to push the bermudagrass out of dormancy for early growth. Then temperatures took a dive for several days and warmed back up just before Easter. It was as if Spring had finally sprung, then Blackberry Winter hit right about Easter. Temperatures dropped and frost even occurred in northern areas. Blackberry winter is an old-timer saying referring to the often-annual event when spring temperatures suddenly drop just about the time the blackberry briers start blooming. The tender growth of the bermudagrass, fueled by sunlight and fertilizer suddenly sputtered and stalled. Purpling is often due to accumulation of anthocyanin pigments due to stress. It is frequently associated with cold-weather induced phosphorus deficiency. Plants normally grow out of it when warmer weathers arrives. Some key points here: 1. Controlling winter weeds is a good practice to allow more sunlight to reach the grass and to warm the soil; 2. Temperatures frequently turn cold sometime during late March and early April which can stress the plants being pushed out of dormancy early; 3. Don’t apply N fertilizer too early in spring to warm-season grasses – wait for a week of night temperatures of 60 degrees For more information, ask your County Extension Agent. Find them at UAEX.edu