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Closeup of the center and partial petals of a deep yellow sunflower.

Why Is My Lawn Yellow, Red and Even Black?

The wet, cool weather in Vermont and New Hampshire has meant many lawns have essentially “used up” their reserves to support healthy leaf growth, including depleting any fertilizer application that may have been applied in the early spring. In addition, fungal diseases such as red thread and leaf spot are also becoming more widespread with the humidity/moisture levels. As is true for many lawn stressors, the healthier the lawn the more likely the lawn is able to withstand and outgrow these afflictions.

What Does This Wet Weather Mean For My Lawn?
Lawns may take on a yellow or light green color compared to a healthier darker green. Red thread and leaf spot can add to the rainbow of unappreciated colors ranging from reds, pinks, browns, oranges, and black tints.

Yellow or Light Green Lawn
These undesirable colors are simply due to a lack of nutrients, especially with lawns that have sandy soils and those that don’t have the organic reserves to maintain color in extended wet/cold periods. Many lawns simply used up the fertilizers applied earlier in the spring and exhausted what would normally be sufficient nutrition between treatments.

Red Thread
The fungal disease red thread is usually visible as small red or pink patches, especially with the morning dew or under wet conditions. As the grass dries, the affected leaf blades turn to a tan or bleached straw color. Red thread is known for its fist-sized red to pink patches in an affected lawn.

Leaf Spot
Leaf spot disease gives your lawn an undesirable hew or tint where the grass blades themselves take on a combination of colors ranging from yellow, orange, to black lesions. Wet and humid weather along with susceptible grass varieties will make this disease more likely in the spring and or fall.

What To Do?
Hope for drier weather! But beyond that, applying a fertilizer will help rejuvenate lawns and allow the grass to simply outgrow the issue. In most cases, neither red thread nor leaf spot are considered serious damaging diseases; they are mostly aesthetic concerns. These too are likely to ‘grow out’. Mowing while the lawn is dry helps too. And with leaf spot, mowing at the recommended 3” height helps by keeping the disease from reaching the crown as can occur with shorter cuts. If the disease issues persist, a fungicide spray may be warranted just to clean up the situation much like using an antibiotic or fungal cream for athlete’s foot.