Foliar and root diseases can affect both warm- and cool-season grasses. Disease-causing fungi are almost always present in the soil, waiting for a time when conditions are right to attack. The most common times are when the host (turfgrass) is under stress.
Examples of environmental stress are excessively wet or dry weather and exceptionally hot or unseasonably cool temperatures.
In addition to being a reaction to environmental changes, lawn diseases can also be signals of soil problems. Any part of a lawn can be affected. Slopes, depressions, high traffic and shady areas are vulnerable.
Improper mowing or watering habits, too much or too little fertilizer, thatch and compacted soil all increase the chances of disease.
Diseases often start as yellow, tan or brown areas of varying sizes in the lawn. But before you assume you have a lawn disease, make sure it isn't something else. Injury, stress or deficiencies can produce similar symptoms and also set the stage for infection. These are often things that you can control, so it's wise to recognize and remedy these situations. Dormancy in the grass is a natural occurrence and is another factor that can cause discoloration.
To help identify whether the problem is injury, stress or a deficiency, here are some examples and solutions:
Injury to Grass
Pesticide, fertilizer or gasoline spills
Spills can cause lawn damage quickly, resulting in yellow or brown spots. Refill spreaders, sprayers and outdoor power equipment carefully. Use a funnel or a "no-spill" container. You can rake up dry products and collect them for use later. Flood the area with water to dilute. You need to remove liquid spills with an absorbent product and dispose of the liquid and absorbent properly. Repair and reseed the area as needed.
These spots show up as a dead area with a green ring around it. Flush the area with water as soon as possible after the occurrence (within the hour is best). Work with your dog to use a less conspicuous area.
Aerate to relieve soil compaction and reseed. Redirect the traffic. If that proves impossible, install a walkway.
Mowing Too Close
Raise the mower blade to the proper cutting height for your variety of turfgrass. Fix high spots in the lawn.
Dull mower blade
A mower blade that is not properly sharp can produce a ragged cut and discoloration. Replace or sharpen the blade according to the manufacturer's instructions to prevent ongoing damage.
Aerate to relieve soil compaction. Add organic matter and reseed.
Too much or too little water
If the lawn is not getting enough water, the turfgrass begins to resemble straw. Walking on the lawn leaves footprints in the turf. Water only when needed to prevent overwatering. Do it as early in the day as possible to allow evaporation from grass blades. Be sure to follow any watering ordinances or restrictions for your area.
Too much or too little fertilizer
Too much fertilizer causes excessive growth. Too little does not provide enough nutrition to promote the strong roots, crowns and leaves needed to withstand disease. Follow the proper feeding schedule for your turfgrass.
Excessive pesticide use
Applying too much insecticide or herbicide can "burn" turfgrass and lead to yellow or brown grass. Follow the manufacturer's specifications on amount and frequency of application.
Hot and cold temperature extremes
Wait for a change in the weather. Keep your eyes open for early signals of lawn problems.
Nutrient Deficiencies in Grass
Lawns that are not getting enough nitrogen (the key component of lawn fertilizer) will begin to change to light green and then yellow. The color change usually begins to show first in the lower leaves. Reduced growth is also a sign of nitrogen deficiency. Normally the entire lawn is affected. Adding nitrogen will help restore the green color if you fertilize properly. Applying too much at the wrong time can do more harm than good. Follow the package instructions carefully. Grass cycling - leaving grass clippings on your lawn after mowing - adds nitrogen naturally to the lawn.
Another reason for discoloration could be lack of iron in your soil. Some of the more common areas of the yard that you might find turning yellow from iron deficiency are those adjacent to things made of concrete. Driveways, sidewalks and concrete planters can be the culprits. The high alkaline content in concrete tends to absorb the iron found in soil, reducing the amount of iron your lawn or garden receives.
Iron deficiency appears in patches. Blades may yellow but the veins retain their green color. Iron deficiency may not affect growth. Alkaline soils (such as those in the midwestern and western states) are especially susceptible to iron deficiencies. You can add iron as a soil supplement to neutralize alkalinity and help replenish the iron that occurs naturally in the soil. Apply as directed on the package. Remove the product from masonry or concrete surfaces before watering to avoid staining.
When using lawn treatments or lawn care products, always follow package directions regarding proper clothing, protective equipment, application procedures and safety precautions.
Other Lawn Conditions
In addition to injury, stress and deficiencies, there are other things that may be making your lawn look less than picture perfect.
Damping off is a fungal infection that is usually limited to newly seeded areas. When seeds are sown too densely and then receive too much fertilizer and water, the crowded young seedlings collapse and die. You'll need to rake and reseed the area.
Dormancy is a natural occurrence. Cool-season grasses will turn brown when the weather gets hot and/or dry. Warm-season grasses go dormant when cooler temperatures arrive. They will return to normal conditions when the weather changes. If dormancy occurs late in the growing season, they will remain dormant until the next growing season arrives. Before taking any type of action to solve discoloration, make sure your lawn is not turning yellow or brown because it's going dormant. Dormancy is a resting period – do not fertilize during dormancy.
Insects are another possibility. Signals are holes in the leaves and chewed-off spots. If the turf can be pulled up easily, grubs are the likely culprit (diseased grass remains firmly rooted). Other lawn-harming insects include billbugs, chinch bugs, nematodes, mole crickets, mites, leafhoppers and various larvae. Upon close examination you can see many of these bugs.