This year has been a bit more ‘normal’ compared to last year. The timely rains have kept many from having to run their irrigation systems and saved many lawns from going dormant. The question that is stumping many people this season is “What’s with all the yellow turf?”
Yellow colored Kentucky bluegrass has been spotted all around the region. While we don’t know the exact cause of the yellow lawns, there are several factors that are known. The symptoms appear to only be affecting some cultivars of Kentucky bluegrass. It has not been seen in tall fescue or perennial ryegrass. The symptoms mainly appear only on the upper, young leaves. This discriminating coloration means that it probably isn’t a deficiency of nitrogen. Nutrients like nitrogen are mobile in the plant; if one leaf is affected, they will all be affected. Other nutrients like iron might be to blame as it isn’t as mobile in the plant, which can lead to spotty symptoms. On the turf that has been examined, there isn’t a notable lesion or spot on the leaf, which rules out many diseases and fungal infections.
The weather we have had this season might be playing a role in the yellow streak. The symptoms are most often seen in lawns that are mostly irrigated. They also happen when the soil temperatures are at their seasonal highs during wet summers. There can be some similar yellowing symptoms in the spring, but they are attributed to denitrification, or loss of nitrogen, in the soil.
What can a person do? You will be happy to know that this sickly color only affects the visual appeal of the Kentucky bluegrass. It doesn’t seem to have any long term impacts on the overall health of the plant. No need to apply a fungicide, insecticide, or fertilizers with less than 0.5 pounds of nitrogen per 1,000 sq ft. Reducing irrigation for the short term should help with this coloration issue. If you wanted to try to green up your turf, you could try a low rate application of iron. This could give you back your green color, without the use of nitrogen fertilizer, which isn’t recommended in August. Mowing could also remove a majority of the discolored younger foliage which is higher up in the canopy.
Some longer term solutions might need to be considered if this turns out to be an annual occurrence. The main goal is going to include increasing drainage and reducing compaction. Core aeration is one way to increase drainage to lawns that are compacted, on heavy clay, or have heavy traffic. Another longer term option could include overseeding with a different cultivar of Kentucky bluegrass or possibly changing turfgrasses altogether. To get the best of both worlds, you can try both aeration and overseeding. Take advantage of the holes caused by core aeration and overseed at the same time. The rule of thumb is that for each week grasses are seeded before Labor Day, development is speeded by two weeks. The optimal window to seed cool-season turfgrasses is August 15 to September 15. Thin stands of Kentucky bluegrass should be overseeded with improved cultivars at .75 to 1 pound of seed per 1,000 square foot. If you are overseeding a tall fescue lawn, use a blend of improved turf-type tall fescue cultivars at a rate of 4 to 6 pounds of seed per 1,000 square feet. Ensure the seed has good seed to soil contact and irrigate frequently to for the best germination.
If your lawn has a yellow streak, don’t worry. A little time and a lot of patience will yield a greener appearing lawn.
For more information contact Elizabeth Killinger at firstname.lastname@example.org, 308-385-5088, on Facebook, Twitter, her blog at https://huskerhort.wordpress.com/, or visit the University of Nebraska-Lincoln Extension website: hall.unl.edu.