Powdery Mildew

• Powdery mildew is a white or grayish powdery fungus that grows on grass leaves. Powdery mildew grows in warm, dry and humid climates. The fungus eventually causes grass blades to yellow and dry out, reducing the wheatgrass yield in a planting. Gardeners can get rid of most of the disease by removing infected parts of the wheatgrass. Fungicides also help get rid of powdery mildew, but the National Gardening Association recommends using milk as a more natural alternative to chemical fungicides.
  
  

Slimy Molds

• Slimy molds grow on grasses in very wet and humid conditions. If a wheatgrass houseplant gets white or gray slimy mold growing on it, the plant is probably being overwatered. Experts at North Dakota State University recommend brushing slime mold off of plants with a broom or a rake. Slime molds do not damage grass right away, but they can eventually cause grass blades to yellow and become weak.
  
  

Rust Fungi

• If wheatgrass gets a reddish or orange fungi on its leaves, it probably has rust. Rust shows up during hot times, and when grass is not growing normally due to a lack of care. Rust eventually causes grass blades to wither and die. Prevent rust by making sure to water and fertilize wheatgrass often enough for it to grow at a normal rate. Fungicides can help get rid of existing rust infections. However, rust should not infest well-maintained wheatgrass, and fungicides can contain toxic chemicals that make wheatgrass less safe to eat.
  
  

Fungus Prevention

• Many fungi like wet or humid conditions, so do not overwater wheatgrass. The University of California Davis recommends watering in the morning instead of in the afternoon or evening. Evening waterings lead to wheatgrass sitting in water overnight, which creates a wet and humid environment for fungi to thrive in. Morning waterings, on the other hand, give grass blades a chance to dry out in warm daytime temperatures and sunlight.