How to use this page. Each section is written with suppression of grass diseases in mind. Using the sound cultural techniques listed on this page can help you reduce the use of fungicides, lower disease pressure, and develop a healthier lawn, so you spend less work repairing damaged areas. That leaves more time to enjoy your beautiful lawn.
There is a lot of information on this page, so please take time to look it over carefully. It will allow you to go greener with a much healthier lawn.
Diseases Must Have Three Things:
These three things must be present for a disease to occur.
If just one of these three things are missing, a disease will not develop.
Below are some of the cultural practices that can help you in maintaining a healthy lawn.
New Technological Advances That Reduce Grass Diseases
Since the original publication of this page, many advances in biostimulants have occurred. Agri-Gro Biostimulants have almost eliminated fungicides in some instances. Diseases instances have fallen sharply. I have not used any fungicides since using Agri-Gro Biostimulants.
We have also reduced the amount of fertilizer by 30% or more. By incorporating these high tech all natural biostimulants you produce healthier lawns with far less chemicals. You owe it to yourself to try it. See our product pages for Agri-Gro Biostimulants.
Climate Zones and Grass Selection
Healthy grass can resist grass diseases much better than unhealthy grass. Like other living things, weak or unhealthy grass is more susceptible to diseases, insects, heat, cold, or drought pressure.
The first step is to make sure your lawn grass is suited for your geographical location. A little research is a worthwhile investment. Lawn grass growing outside of its preferred climate zone may be under stress much of the time. Choosing the right grass for your needs and climate zone starts you off on the right foot.
Consider where the grass will be growing and how it will be maintained. For example:
How you answer these questions will narrow the field of choices considerably. You should also consider the needs and growth habits of different grass types. For example:
For cool season grasses:
For warm season grasses:
There is no perfect grass, but a little planning may save you some headaches down the road.
Please review the Grass Types section on this site for additional information on selected grasses.
A Note About Disease resistant varieties
Planting a disease resistant variety is at times the only way to stop certain diseases. Planting a disease resistant variety can save you a lot of time and money.
St. Augustinegrass and centipedegrass suffer from a virus called panicum mosaic virus commonly referred to as St. Augustine Decline or SAD. Since there is no cure for SAD, planting a resistant variety is the best way to avoid grass diseases.
Information on Where to Find Quality Seed
The newest and best seed varieties are not always sold directly to the public. They are distributed to wholesale companies that sell to the landscape and turf industry. However, some "wholesale" outlets will sell to the public at an increased price.
In case you didn’t know, "wholesale price" is a relative term. It ranges from above the retail price to considerably lower. It usually depends on the volume you buy, if you are a business owner, and other factors. If the wholesaler allows, negotiate for the best price.
You can also purchase seed in small quantities from online seed companies, but often at an inflated price. Check with your local landscaping or turf company to see if they have what you need. They often buy seed in 50lb bags, so that may be the amount you will have to buy. You may find it to be the best price.
Important Note on the Word "Resistant"
In the plant world, the word resistant does not necessary mean what it implies. The word "resistant" has a variety of meanings. At times it may mean a grass is completely resistant to a particular disease. At other times it simply means that the variety has been made more resistant than what it used to be. The degree of resistance varies, but generally the increase in resistance is often quite significant over previous varieties.
All grasses have a lowest optimum mowing height. That height will vary with grass type and even cultivars within a specific grass type. All grass types need a certain amount of blade length to conduct photosynthesis. Photosynthesis produces the food grasses consume for survival. If you consistently mow below the optimum height, it hinders photosynthesis and weakens the grass. The grass must use stored energy to replace the leaf blade until it reaches the level where it can continue optimum photosynthesis.
There is also a connection between mowing heights and root depth. Grass that is maintained at low mowing heights will have shallower root depths, while grass maintained at taller mowing heights will have deeper roots. This is true even for grasses that are designed specifically for low mowing. For lawns, always raise the blade to the tallest recommended height for your grass type. Deeper roots withstand drought and heat stress better. Taller grass blades shade the soil better and retain more moisture. All this works to the benefit of the grass to fight off grass diseases.
Importance of Blade Sharpness
Every time the mower blades clip the grass, it creates an injury that grass must heal. Sharp blades make a clean cut that heals quickly. Dull blades make a jagged or shredded cut that takes longer to heal. Until the cut heals, it leaves an opening through which disease pathogens can enter. Many grass diseases begin this way. Be sure to sharpen your blades as often as it needs it.
You should be aware that mowers can spread grass diseases. If your lawn has a disease, always mow that section last. Always rinse the underside of the mower after use to keep from further spreading a disease.
If You Have A Mowing Service
If you have a mowing service, be aware that they can easily spread grass diseases. They perform a valuable service, especially for those who are not able to mow the lawn themselves. However, most have little knowledge of grass diseases and don’t realize how they spread. If they just came from a lawn with a disease, it could possibly spread to yours.
However, if he mowed several healthy lawns between the diseased lawn and yours, then you will probably be okay. You shouldn’t stay up at night worrying about such things. Just do what you can to keep your grass strong and healthy.
If you have a disease, it has been suggested that a mulching mower or a mower with closed openings could help keep the disease contained to a degree. Some mowers have a flap that drops down to close the opening. If you are allowed to bag the grass for disposal, then that can help some. However, these are just band-aids and will only keep the disease from spreading faster. Diseased grass can be placed in compost piles if it is composted properly. The heat will destroy all the pathogens.
How Soil Fertility Influence Grass Diseases
Proper soil fertility strengthens plants and their ability to endure stress, including resisting and recover from disease. However, over-fertilization, especially nitrogen, promotes tissue succulence and excessive growth. Excessive growth also depletes stored carbohydrates and thins the cell walls making it easier for disease penetration.
Take some time to learn how grass diseases can infect your grass and what environmental conditions are needed for them to become active. When it is time to fertilize, if you have had trouble with grass diseases before, always apply fertilizer on the leaner side. You can always add more nitrogen later on if you need to, but you can’t easily remove it once it is applied.
Grass Diseases That Love Nitrogen Rich Grass
(Photo shows "Helminthosporium Leaf Spot Disease", courtesy of ForestImages.org)
If you have an active disease and you find it necessary to fertilize, be sure to use a slow release fertilizer. Organic fertilizers made from animal waste or water treatment sludge products work well when soil temperatures are above 60. There is evidence that they can suppress pathogenic fungi.
Grass Diseases of Low Nitrogen Turf
Some grass diseases attack turf that are low in nutrients, especially nitrogen. These diseases are usually not as severe and can be signs of nitrogen deficiency. These grass diseases include:
If these diseases are present, this is where an application of nitrogen fertilizer can help. The purpose is to add just enough nitrogen to stimulate grass growth, so it will grow out of the disease. However, be careful not to over-fertilize or you could create other problems.
Soil and Thatch Problems and Grass Diseases
Healthy soil that meets the grass’ needs is necessary for healthy turf. If the soil pH is too high or too low, it will block the uptake of certain nutrients. Check the soil pH and make any corrections if needed. For help understanding soil pH review the page on "Understanding the Soil Analysis Report".
Remember that sandy soils do not retain nutrients as well as loamy soils. Heavy clay soils tend to compact easily leaving less air and water available to the roots.
Poorly drained soils weaken the grass that can lead to problems with pythium or other water related diseases. All these conditions will affect the health of the grass and offer less resistance if disease problems do arise.
Not all grass types produce thatch. Warm season grasses and bluegrass can be thatch producers. Zoysia accounts for some of the most severe cases.
Thatch is an accumulation of grass roots, stems, decomposing grass blades, etc. A small amount of thatch is fine, but excessive thatch is not. Since thatch is organic, it can harbor huge amounts of micro-organisms and soil insects. Dormant pathogens find safe haven in thatch while waiting for the right conditions to become active.
Excessive thatch can hinder the downward movement of water, trap fertilizer, insecticides and fungicides. Thatch is also acidic and can be an indicator of pH problems.
Heavy applications of organic fertilizer during the warmer months or organic top dressing with compost, combined with core aeration, has been observed to help keep thatch in check.
Lawn grass is about 70% water and is necessary for all plant functions. Therefore, lawn irrigation is very important for grass health, especially during dry periods.
The time of day you irrigate is just as important as how much water is applied. Most grass diseases require a considerable amount of moisture or very high humidity before an infection can start. For this reason, it is important to water correctly to avoid creating an environment favorable for disease.
There are several common irrigation mistakes people make that can influence disease development. They are:
What seems the most logical is not often the correct method when it come to lawn care. Watering in the evening or at night would seem like a good choice because the water doesn’t evaporate as quickly. However, prolonged moisture is an enemy to turfgrass, not an ally. The goal is to deeply irrigate the lawn, while keeping the period of time that the grass and soil will be wet down to a minimum. This is very important in hindering grass disease development.
The single best time to irrigate is in the pre-dawn or early morning hours when dew is still present on the grass. Irrigating at this time means that the soil will dry out by late morning or early afternoon. Irrigation also washes off the sugary guttation fluid (fungi love this sweet fluid) that accumulates on the grass surface.
If you irrigate in the late morning hours after the dew has already dried, it only serves to extend the wet soil period. This is extremely important during high humidity periods when grass diseases are most likely to start.
During the high heat of summer, if necessary, you can irrigate a second time in the late afternoon, but not as heavy as in the morning. The goal is to cool and water the grass, but to make sure the grass and soil surface is dry before dark.
In-Ground Sprinkler Systems
If you have an in-ground sprinkler, do not set it to come on each day. Instead, irrigate whenever the grass needs it.
To irrigate properly, you want to adequately moisten the soil three or four inches deep. Deep irrigation promotes deeper rooting. It also means you will need to irrigate less frequently. As the surface dries, it will still have plenty of moisture around the deeper roots. Shallow irrigation promotes shallow rooting. During periods of drought, it won’t have root depth and will become easily stressed.
How often you will need to irrigate will depend on the soil structure, grass type, heat and humidity and how much rain you are getting.
How to Tell When the Grass Needs Water
Cool Weather Lawn Diseases
Profiles of common spring and fall diseases. Learn what they are, recognize disease symptoms, how to prevent them, treatment options and more.
Hot Weather (Summer) Lawn Diseases
Profiles of common summer lawn diseases. Learn how to identify them, recognize disease symptoms, cultural practices that hinder disease growth, treatment options and more.
Understanding Lawn Fungicides
Never used a fungicide? While cultural practices are the best way to prevent diseases, you may someday find it necessary to use a fungicide. Knowing what they are and how they work is important for successful disease control.
Using Chemicals Safely
Safety for yourself, your family and the environment should be your main concern. This page contains valuable information about safe use, storage, personal protective equipment (PPE) and more.
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