It isn't easy to give overly general advice about lawn diseases because they tend to be geographically based. A problem in a wet coastal region is not going to have the same impact a few miles farther inland, and away from the constant humidity. A problem of high clay and damp soils will seldom be a problem on sandier soils. Trickier still, different grass species are predisposed to certain diseases while others are immune. It's very much like a horse race. You just have to go with the odds.
That's the long way of saying there are no hard-and-fast rules for identifying which diseases are going to be problems for all gardeners. It really depends on your area and your garden management. The following descriptions, however, should get you started on figuring out how to identify and treat these major lawn diseases.
These are the major lawn diseases that a homeowner might face. Keep in mind, of course, that there are many more lawn diseases than the ones we list here. Some diseases are so specialized that it takes a laboratory to differentiate between them and the ones listed here. Realize, however, that the following is a thorough overview of what you'll need to know. The vast majority of lawn diseases will never grace your yard. Most of them are found on golf courses where the grass plants are forced to grow and are stressed more than your lawns will ever be.
So read about these diseases, but relax. If you grow your lawn properly, you'll never get to meet them.
KNOW YOUR SIGNS AND SYMPTOMS
A symptom is a visible expression of disease on a grass plant. For example, yellowing grass plants are symptoms.
A sign of a disease is the visible expression of the pathogen. For example, visible mycelium masses are signs and not symptoms.
Looking at it another way, symptoms are the visible results of the effects of the signs. Sometimes you can't see the signs, but you can see the symptoms.
You'll get the best results in diagnosing a problem when you have both symptoms and signs. Unfortunately, in the real world this is hard to obtain. See the instructions on pages 137–138 and try to obtain both signs and symptoms. Your choice of treatment will depend on proper identification.
This fungus overwinters in the plant debris and sheaths of grass plants. When the temperatures rise above 78°F and the relative humidity is high, spores germinate and infect grass leaves. If this problem is going to happen, it will happen after a period of high temperatures and high humidity. Anthracnose discolors the grass (yellowing) in patches that range from an inch or two to several yards. You can recognize anthracnose by the marks on individual grass leaves. Small yellow lesions will have black centers. As the disease progresses, the grass will yellow and then bronze. As it dies, it becomes a lovely shade of khaki tan. In advanced stages, the fruiting body of the fungus, a small black moldlike circle, grows out through the grass cuticle. These fruiting bodies are about the size of a pinhead but are clearly visible with a 10x lens.
REMINDER: ENJOY YOUR LAWN!
The advice about relaxing when it comes to problems with your lawn is probably the best advice in the entire book. If you are growing a lawn that is kid-friendly, use lots of compost and few chemicals. If you don't spray chemicals but rely on corn products and eco-friendly techniques, you'll rarely see a problem. And, when you do see a problem, you'll find that there's usually a relaxed technique to deal with it.
Also, get a bench. Put it in your garden. Use the bench. By using the bench, you'll relax in your garden. You'll spend time there that satisfies your soul without needing to solve problems. The only time that most people walk over their lawns and spend time in the gardens is if they mean to work—to mow, to rake, to pull weeds. Spend time on your bench. Love your lawn. It'll love you back.
Annual bluegrass is the most severely affected; it can be killed in a single season. Anthracnose targets Kentucky bluegrass and red fescue, but not as severely. Other grasses may get the problem but will not die from it.
If the lawn is prone to this problem, syringe the lawn mid-morning and mid-afternoon with your sprinkler system. This cools the turf area and prevents the spores from developing. Note this is not watering to get the soil damp, but just a light misting to reduce the temperature around the grass leaves. Ensure adequate fertility, aerate the soil, and raise the mower height. Do not water during the evening to minimize water staying on the leaves. In general, reduce the stress on the lawn as much as feasible.
Bermuda Grass Decline
Up until recently, this problem was thought to be one of those complex multi-disease problems specific to Bermuda grass. None of the labs had been able to identify a specific species of fungus causing the grass to thin out and have yellowing patches 12 to 24 inches in diameter. The roots go brown and die because the feeder roots rot off. As with many fungal diseases, most of the badly infected lawns were also under stress from other causes. Removing the stress sometimes helped the lawn to recover and slowly regain its health. It is interesting to note that the number-one stress agent was too low a mowing height.
Now, researchers have found that a specific fungus is responsible for this problem. Although its name is too long for any tongue to get around, it is related to the take-all patch problem (page 160). and while its name is too long for any tongue to get around, it is related to the take-all patch problem.
Get the management right and this fungus is not going to be a problem on most home lawns. If you have a severe case, there are fungicides registered for this problem. Apply them in the fall. Most of the fungicides have to be used at the beginning of the problem. Once this fungus is established, control is normally less-than-satisfactory with fungicides. See the tables on pages 164–165 for general fungicide recommendations.
This is a fungus that survives on thatch and one that the average homeowner will never see. It is primarily a disease of low-cut grass (low as in golf green low). Brown patch creates a ring of quite distinctively purple grass. This ring appears first thing in the morning and disappears by noon in most cases. On home lawns, there may be a round circle of brown grass and some healthy grass will still be growing within these small circles. The circles can expand to 1 yard in width and may appear dead or simply as thinned-out, weak-growing grass.
Brown patch attacks all turfgrasses, particularly the bent grasses used on golf greens. Annual bluegrass and perennial ryegrass are also particularly susceptible.
Generally speaking, a topdressing is used to repair damaged areas of lawn. I've found using three things in combination works quite well. The first is good-quality grass seed. Sprinkle it onto damaged areas so that the seeds almost touch each other. You don't want them piling up on top of each other, but neither do you want much space between them on the ground. It takes a small bit of practice but it's not rocket science, you'll get it pretty quickly.
The second is cornmeal. Sprinkle it on any damaged area to help the fungus predators destroy fungus spores. If you control the fungus where it breeds, you'll have less of a problem.
The third is good compost. I always recommend sprinkling a quarter inch of compost over the damaged area on top of the seed and then watering the area until it is well soaked. The compost feeds the soil and knocks back fungus. The seed will have no problem germinating and growing through the compost. You'll have to keep the seed damp until it germinates, so a daily soaking is part of the routine.
In terms of cultural controls, avoid excessive nitrogen and water. Eliminate the overwintering protection of thatch. Do not water during the evening to minimize water staying on the leaves. If this is a constant problem, increasing the soil pH to 7.0 will provide some relief. Spray fungicide when day temperatures reach approximately 65°F.
With this disease, circular dead areas appear in the spring and continue to enlarge all summer long. The grass at the edges of the dead areas continues to yellow and die, particularly if the grass is under stress. This is strictly a problem on centipede grass.
With this southern turf, maintain the soil pH between 5.0 and 5.5 (quite acidic) and do not fertilize excessively. Do follow the 1 pound per 1,000 square feet of nitrogen feeding rule for southern lawn grasses. Avoid drought stress and do not mow too low. Chelated iron sprays help green up the foliage. Treat for nematodes. If the problem persists, choose another grass variety.
Abiotic plant disease:
Caused by unfavorable growing conditions.
Biotic plant disease:
Caused by plant pathogens.
So, most of our lawn problems are abiotic, even though this particular section is discussing biotic problems.
Cercospora Leaf Spot
This fungus causes a small brown spot on the leaves of St. Augustine grass; sometimes the spots are brown ranging to purplish brown. As the spots get older, the center of the spot may turn a tan brown. Where the fungus is well established, the entire grass leaf may get the problem and then the leaf simply turns yellow, withers away, and dies. This dying causes what appears to be a “melting” of irregular spots on the lawn as more and more individual plants are infected.
While St. Augustine grass is most susceptible to the problem, the common or yellow green-leafed forms are more likely to be infected than the newer bluer hybrids and selections. Warm, humid weather favors the incidence of this disease.
Proper feeding with nitrogen lowers the outbreaks; stressed lawns are more likely to see this problem. Try to keep the grass blades as dry as possible; irrigation should be deep and infrequent. Fungicides that control leaf spot diseases will control this problem.
Crown and Root Rot
This fungus affects the crowns and roots of the plant leading to plant death. Initial symptoms are a leaf spotting with purplish brown lesions, and then the turf takes on a purplish tinge. The turfgrass starts to thin out and then finally the crowns and roots are infected and the grass begins to die. The experience of many turf experts is that this disease can infect a lawn and is often not recognized until the grass starts to die off in irregularly shaped patches on the lawn.
RESISTANCE TO FUNGICIDES
Just as insect pests develop resistance to chemicals used to kill them, infectious fungi are equally capable of developing resistance to fungicides. This happens most often when a product is used repeatedly instead of alternating its use with another unrelated chemical. The problem of resistance is made worse when lawnowners rely on chemicals to control problems rather than fixing the underlying causes. Without the environmental pressures to reduce their growth, the fungi grow and mutate quite quickly to develop chemical resistance. There are now many fungicides, particularly the systemic fungicides, that are useless for disease control.
There are two strategies that homeowners should adopt to reduce the risk of fungicide resistance building up in your area. First, don't rely on fungicides alone when faced with a problem. Fix the underlying cause so the fungus is not given a free ride. By fixing the underlying causes, fungus propagation will be reduced. Second, use different fungicides if repeat sprays have to be done. Do not spray with the same chemical product time and time again. The best system is to use at least two sprays on alternate application dates. Another recommended practice is to tank-mix (use two products in the same spray tank) two different products. Be sure the two products are registered as being compatible. Read the label for this information. If you tank-mix incompatible sprays, you run the risk of harming not only your lawn but also yourself.
This problem can attack a wide range of plants; no species is particularly vulnerable. You can control crown and root rot by following good cultural practices, in particular, ensuring that nitrogen and potassium levels are adequate for good growth. The problem is more developed on compacted soils, so aeration is indicated if the problem exists. Do not use a herbicide. It will weaken the grass further. Mowing at the proper height is also important in the management of this problem. Fungicides will help; however, without improving cultural practices, the problem will return. If the problem is particularly bad, it may be worth considering a preventative spray program as well as a remedial one.
THE MANY FORMS OF PESTICIDES
Plant scientists now refer to all chemical sprays as pesticides. Anything you don't want on your lawn is a pest. So we have:
Insecticides: Pesticides used to kill insects.
Herbicides: Pesticides used to kill weed pests.
Fungicides: Pesticides used to control fungi.
Bactericides: Pesticides used to kill bacteria.
Bacteriostats: Pesticides used to stop bacterial growth and reproduction. I thought I'd throw this one in even though it isn't a “cide.” These sprays don't kill bacteria, they simply stop them in their tracks. You won't often see them on the garden center shelves.
Irregular patches and streaking are the first sign of this fungus disease. Then the leaves yellow and brown from the leaf tips down to the sheath. The fungus invades the grass through the cut tips of the leaves.
Bent grasses, annual bluegrass, and fescues are the most susceptible, particularly during the high heat of the summer when poor cultural conditions weaken the plants.
Control is mainly to improve the growing conditions by avoiding overwatering and to ensure moderate growth through proper fertilizer application. If this is a problem on your lawn, increase the mower height immediately and reduce the thatch layer by raking. You can use fungicides, but the damage is rarely so bad as to warrant the expense.
This fungus produces small spots (2 to 6 inches in diameter) in lawns. It usually occurs later in the spring, so you know it is not a winter-caused injury. The spots on the leaves are shaped like an hourglass and extend across the blade. They have a lighter center with darker border and the border appears to be a shade of brown, purple, or black. Early in the morning before the sun hits the grass you'll often be able to see a cottony fungus growth on the infected blades, but it disappears with the hot sunshine.
Centipede grass, Bermuda grass, zoysia grass, bluegrass, ryegrass, and fine fescues are hosts. This occurs especially on poorly nourished lawns.
The easiest control for this problem is to feed your lawn adequately. Reduce any water stress by irrigation. The grass plants are very rarely killed. They are simply knocked back, but they will regrow new leaves with feeding and care.
Adequate fertilizer will help the turf overcome this disease. Irrigate turf as needed to avoid drought stress. Do not mow too low and avoid excessive leaf wetness.
Fairy ring occurs in three different stages: a killing ring, a stimulated ring, and a ring of mushrooms. The killing ring starts as a ring of wilted, purple-tinged turf. This ring then dies off leaving brown dead grass in a circular form. The circles can be anywhere from one yard across to several yards. The area in the middle of the ring appears normal. The stimulated ring is slightly more common in northern areas. It is a circle of dark green, fast-growing grass that is darker and taller than the surrounding lawn. These circles are usually smaller, with the largest only reaching several yards across. The last ring—a ring of mushrooms—is exactly that, a ring of mushrooms in the lawn. Gardeners will normally see only one of these conditions when the problem strikes.
This mushroom fungus grows throughout the soil, forming a white network of mycelium up to 12 inches deep. Untreated, the circles will get larger every year as the fungus grows.
The most drastic option is to remove the infected soil and replace it with good soil. Otherwise, ensure good nutrition because the disease more often strikes soil with low fertility. Adding iron in a spray formula will often mask the damage. Adding compost will increase the soil micro-organisms that fight fairy ring fungus. Drenching with an organosilicone wetting agent may alleviate symptoms. The problem will eventually go away on its own regardless of gardener activity.
Rakes are one of the lawn managers’ most useful tools. Weed rakes, leaf rakes, and small-tined rakes all have their place in the management of the lawn. Invest in good rakes because you will use them more than any other tool on the lawn. Ergonomically designed rakes are a good investment and a good idea. Although a little more expensive than common discount-store tools, they'll help your back and make it easier to do the job.
Once thought to be a separate disease, Fusarium blight is now recognized as a complex mix of several similar diseases: necrotic ring spot, yellow patch, and summer patch. Treat it as you would those problems.
Fusarium Patch or Pink Snow Mold
The pink snow mold fungus grows over the summer. In the fall, spores germinate to grow and attack grass blades over the winter. Although it prefers snow cover, this mold lives and grows without it. The typical reddish brown patch when the snow melts is the prime symptom; if you look closely the pink mycelium are visible on the edges of the dead spot for a few days immediately after the snow melts. If the fungus continues to live in a cool, damp spring, it can create secondary symptoms known as Fusarium patch, which are small dead areas with the typical reddish brown color. Sometimes, you can see both at the same time—the new growth of reddish brown Fusarium patch growing on the edges of the dead turf killed by pink snow mold.
The primary management technique is to reduce thatch because this is where the fungus lives during the summer. Prevent succulent growth that is a good food source late in the fall by regular mowing right up until the grass stops growing. If you don't give the succulent food, it doesn't grow well. Do not apply any nitrogen within six weeks of dormancy. Good potassium levels will help the grass fight off this problem, so make sure that your potassium feeding is adequate. In the fall, rake the lawn to remove leaves and dead and decaying grass (this stops spores from hiding and germinating in the debris), and do not topdress. If the problem is severe and consistent, apply fungicides in the fall.
Gray Leaf Spot
This fungus causes small brown spots to grow on the grass leaves. These spots then enlarge into oval or elongated oval spots on the leaves, sheaths, and stems. The color is a dark ash-brown with purplish margins. During wet or humid conditions, the spots are covered with a gray velvety fungus mycelium. Severely infected leaves wither and die, lending a scorched look to the lawn. Note that the dead grass is brownish in color, not yellowish.
COMPOST, THE WONDER DRUG
Cornell University has done research into the disease-suppressing components of compost. In general, they found that many different disease organisms are suppressed by compost. The current recommendation is for two applications of 50 pounds of compost per 1,000 square foot of home lawn. Apply compost first thing in the spring and again late in the fall.
The most effective composts are those that are at least two years old and are composted on a natural soil base or under trees. Compost works on the lawn in several ways.
It produces chemical compounds that actually kill bacteria and fungi. So, by applying compost, you are actively killing the bad fungi that attack your lawn.
It acts as a food source for those micro-organisms that eat fungi. If you feed the good guys, they'll eat the bad guys for you.
In the process of breaking down into humic acids (to feed your plants), compost uses the same food sources as the bad fungi. So, it competes with them for food.
By applying compost, you are actively killing some fungi, feeding the good guys that eat fungi, and competing with the survivors for the remaining food. Oh yes—and you're feeding your plants at the same time.
Compost is the closest thing to a wonder drug that Mother Nature has produced for gardeners.
Bahia grass, Bermuda grass, centipede grass, ryegrass and St. Augustinegrass are the worst hit, particularly the St. Augustine grass blue cultivars.
As with most fungal problems, warm humid summer months are the optimal time for this problem to become firmly established. Prolonged wet spells or extended periods of wet leaves through improper irrigation techniques also help establish this problem. Excessive nitrogen feeding has been implicated as well in creating conditions right for gray leaf spot establishment.
It only makes sense then that the initial control methods would include proper watering and fertilizing. Also look for disease-resistant cultivars as a primary line of defense.
Leaf blotch is not quite a blotch at first, it appears as tiny purplish to reddish spots on the leaf blades and sheaths. It is mostly a disease of seedlings. The infected seedlings normally wither away and die, turning brown in the process. In fact, there will be so much seedling death that patches, ranging in size from 2 inches to 3 feet in diameter, are developed. Interestingly enough, older grass plants develop an immunity to this problem.
It is a disease of Bermuda grass and as older plants are not bothered, it is normally only recommended that thatch be removed, adequate nitrogen be applied, and good cultural practices be used. No sprays are indicated.
If you are reading the fine print in many of these diseases, you'll often see that excessive nitrogen is implicated in many of the problems. Excessive nitrogen creates lush growth that is tender and has thin cell walls. The thin cell walls are more easily damaged by physical injury and invaded and colonized by fungus. Overfeeding is something you can control. And you should if you want to avoid the problems discussed in this chapter.
Leaf spot is one of the more easily recognized grass problems. Occurring mostly in warm weather, the leaves develop small brown to tan spots with purplish red (sometimes fading to purplish brown) borders. The spots may be as wide as the grass leaf and are almost always longer than they are wide. The tips of the grass leaf often die, giving a brown look to the lawn. If the leaf sheath is infected, the plant will often die, leaving a thinned-out section of turf. This fungus is very similar to the melting out fungus, and sometimes leaf spot can create similar large patches of “melted” grass. The grass appears withered, slimy, and dead—rather like it has been melted under a hot sun.
It is very important to avoid the excessive use of nitrogen fertilizers with leaf spot fungus problems. Lush growth is particularly sensitive to leaf spotting. Remove excessive thatch; this is where the fungus overwinters. Never water in the evening; it is important to keep the leaves as dry as possible and keep the fungus dry. If you use fungicides, apply them as soon as the problem is seen at the “spot” stage. If you delay treatment until patches start to brown, the results of spraying will be less than satisfactory. Topdress to repair any damage.
Melting out is very similar to leaf spot. The melting out spots start as purple to brown with a lighter center. They grow by moving down the leaf sheath to the crown to eventually kill the plant. When this fungus disease gets to an advanced stage, irregularly shaped patches (from a few inches to several yards across) are created. As in leaf spot, the dead grass appears to be wilted and “melted.” It's not a pretty sight. Although many different grasses are susceptible, Kentucky bluegrass and Bermuda grass are the most susceptible.
LEAF SPOTTING DISEASE
The older Kentucky bluegrass varieties are more prone to leaf spotting than the newer ones. Check with your garden center to obtain new varieties if you are having a problem. Bermuda grass is also prone to leaf spot diseases.
The control for melting out is the same as for leaf spot.
Necrotic Ring Spot
The initial symptoms of this fungal problem are dead patches 6 to 24 inches in diameter. Surrounding the patch is a mix of normal, yellow straw-colored, and sometimes reddish blades. It is said to resemble a “frog's eye” pattern where a circle of dead grass surrounds green growing turf. Black strands of the fungus cover the roots and crowns of individual plants. Sometimes, existing thatch will decompose quickly in these patches, and the patch will appear sunken or lower than the rest of the lawn. This problem normally appears in spring or fall, but in warm weather, the red blades are seldom seen. The infected plants (either infected in spring or fall) are very susceptible to summer heat and drought stress. In fact, under summer stress, weakened plants are quite likely to die.
Once necrotic ring spot is established, it is difficult to control and damage may remain or reappear yearly for two to four years. Fine fescues and bluegrass are affected; it can be a serious disease of Kentucky bluegrass in some areas.
To control this problem, avoid high nitrogen feeding and drought stress. Topdress with a grass/compost mix, using a tall fescue or ryegrass varieties that are resistant to the problem. Adequate control requires a combination of practices including: thatch control, adjustment of fertilizer practices, relieving soil compaction, changing watering practices, and possibly using a fungicide. Keep the thatch to as low a level as possible to reduce the overwintering home of the fungus. Avoid excessive nitrogen feeding, particularly in the spring when the grass doesn't need it. Rent a core-aerator machine (one that takes little cores out of the grass) to improve aeration and compaction. Mow a bit higher to reduce the stress on the grass plant and irrigate a bit more often than normal. More frequent waterings reduce any water stress by keeping the top inch or two of soil moist most of the time. This reduces both water and heat stress on the plants.
You'll need to adopt all of these management practices, and you'll find a fungicide a useful tool here. Remember that the fungicide alone will not solve the problem, you'll need to change your management practices to keep the grass healthy and the fungus from reappearing.
TO STOP OR REDUCE SNOW MOLD PROBLEMS
Fertilize cool season grasses in late fall (after the last mowing) with a slow-release nitrogen carrier. This feeds the roots and enables them to store lots of carbohydrates. This food storage means they'll survive the winter in good shape and start growing strongly in the spring.
Keep mowing in the fall until all leaf growth stops. Do not leave long grass to overwinter. It will decay over the winter and become a food source for fungi.
Reduce thatch with aeration, vertical mowing, power raking, or a combination of these practices. Again, thatch decomposes and provides a ready food source for these snow molds.
Prevent large drifts of snow on important turf areas by proper placement of snow fences or landscape plantings. Deep snow provides exactly the right conditions of temperature and humidity that these particular fungi enjoy.
Prevent snow compaction by restricting walking, snowmobiling, skiing, or sledding on important turfs. This is not as much of a problem on the home lawn as it is on golf course greens. The intensively managed turf on golf courses is more easily damaged than a healthy home lawn. So, don't worry about the kids playing on the lawn and making snow forts. As a father of four, I would suggest the snow forts are more important than a bit of snow mold anyway.
Repair snow mold damage by raking the affected patches in early spring to disrupt the encrusted mat and by lightly fertilizing to encourage new growth.
Use a preventative fungicide program on high-value turf and on areas where snow molds cause injury year after year. Make the initial fungicide application in early- to mid-November and repeat applications during midwinter thaws, as needed.
This fungus girdles the stolons of St. Augustine grass, and the girdling prevents the stolon from getting water and nutrients. The leaves and stolons are under severe moisture stress and dry out turning a yellowy brown color. The problem is particularly bad during a dry spring followed by a dry, hot summer. In many ways, the symptoms appear to be exactly like chinch bugs-patches of yellowing grass. The key difference is the brown lesions on the stolons.
The good news is that this fungus is a particularly weak one and only picks on weak plants. Grow your lawn properly and you'll never see it. If you do, immediately improve your management practices and spray with a fungicide to stop the problem in its tracks. Grass will recover nicely with improved management without the need for fungicides.
Pink patch and red thread are quite similar problems with nearly identical symptoms—irregularly shaped patches of dying grass, and from a distance the grass appears to be ever so slightly pink tinged. The fungus usually restricts itself to the leaves, sheaths, and stems; but in severe cases, it will kill the plant. Both pink patch and red thread develop well when the temperatures are 65° to 75°F. The major difference is an obvious one. The fungus on pink patch tends to create pinkish fungal growth, while red thread has reddish fungal growth. Prolonged humid or rainy weather is also blamed for high incidences of this fungus.
In general, if pink patch is a problem, increasing the level of nitrogen to the lawn will help the grass plants outgrow the problem. Focus on reducing the stress by increasing the level of management to get a good control. For the most part, this disease is not severe enough to warrant using a fungicide. Sometimes a pure stand of ryegrass or fine fescue may be severely hit, which may warrant fungicide use.
Powdery mildew is a relatively minor fungus problem of turfgrass. The primary symptom is a whitish or grayish powdery covering on the grass leaves. It looks as if the leaves have been dusted with white flour. Badly infected leaves may yellow and die. In very severe cases, the plant may die. Powdery mildew is normally found only in shady sections of the lawn under conditions of high humidity and temperatures of 60° to 72°F.
It is a problem on almost all lawn grasses, bluegrass may be marginally more susceptible to it than other species.
To control powdery mildew, avoid high nitrogen feeding and low mowing. Both activities stress grass more in shady situations than in the full sunlight. If powdery mildew is a problem on shady bluegrass, replace it with a shade-tolerant grass species. Fungicides can treat the primary symptoms, but once established, it will return unless the underlying causes are corrected.
The early signs of this fungus are small spots (about 2 inches across) that are dark and slimy looking. They will continue to increase in size. In the early dew-soaked morning or other wet period, the water-soaked leaves collapse and mat together. The white mycelium of the fungus will be visible at these times. As the weather dries, the mycelium disappears and the grass turns a dead shade of brown. The shape of the dead patches often streaks along the direction of the lawn mowing because the mower will spread the fungus spores. This fungus does kill the plant crown, so the grass won't recover and you'll need topdressing.
The fungi grow most rapidly in hot, humid weather and are not a problem in cooler temperatures. Creeping bent grass, annual bluegrass, and perennial ryegrass are the most susceptible to Pythium blight.
This is a difficult problem to control once established because it explodes so quickly. Use infrequent and deep watering with good drainage to keep the humidity levels around the grass crowns low. No nighttime waterings. If Pythium is a problem on your lawn, avoid mowing and watering the lawn when the temperatures go above 82°F, if at all possible. Fungicides are recommended—follow label directions.
This fungus overwinters as a dormant mycelium in diseased or dead tissue. In the spring, while the turfgrasses are still growing slowly, it invades the leaves. High summer temperatures slow its growth. In the fall, when the temperature drops and normal moist conditions prevail, it can explode into growth just as the turf is going dormant.
The primary symptom is a reddish brown irregular patch on the lawn. While initial symptoms look like dollar spot, later symptoms are like those of melting out—oval spots on the leaves that eventually girdle and kill the leaf. The grass appears to wilt, turn a yellow straw color, and, if the crowns rot with severe cases—disappear. Under advanced infections, a pinkish red gelatinous mass grows from the cut ends of the grass leaves.
This fungus infects nearly all northern lawn grasses. Perennial ryegrass and fine-leaf fescues are the most commonly infected.
This disease is most commonly found on poorly fertilized lawns where the grass cannot outgrow the initial infection. As with most fungus problems, try to minimize evening waterings to keep the grass leaves as dry as possible. The good news is that most of the time, damage from this problem is insignificant unless you have perennial ryegrass. Fungicides will knock it back if the problem persists.
Rust-infected grass blades start with a small yellow-orange pinhead-size fleck on individual grass blades. These flecks enlarge and develop into brick red pustules. If you rub the pustule, the spores will easily come away on your finger. Severely infested rust grass starts to look reddish brown or yellow as it dies. Severe infestations can thin out the grass stand but rarely kill the lawn area. A severe rust infestation may weaken the lawn, making it more likely to be thinned out and killed by other stress or winter's cold. The development of rust is greater with night temperatures of 70° to 75°F, day temperatures of 85° to 95°F, and wetness from dew lasting many hours after sunrise. Homeowners who water lightly and frequently have more rust problems than those who water deeply and less often.
Although any grass plant can get rust (even zoysia), perennial ryegrass and bluegrasses are the most susceptible. Bluegrass varieties Merion and Touchdown are more susceptible than other varieties.
To stop rust from becoming a major problem, avoid low nitrogen conditions and leaf wetness. Plant resistant cultivars available from good garden centers. There are fungicides registered for rust, but most are not all that effective. Sulfur-based fungicides are your best bet in severe infestations. Minor infestations are not worth spraying; feed to help your grass outgrow the problem. Be prepared to topdress thinned out areas. Rust is easily controlled on the home lawn by maintaining good lawn growth with adequate fertilization and adequate watering.
St. Augustine Decline
A nonfungus problem, St. Augustine decline (SAD) is a virus that causes a yellowing and stippling on the grass leaves. As the disease progresses, the leaves turn mostly yellow. The grass becomes weak and the stands thin, enabling other weeds or grasses to invade. This is particularly true with grass growing in the shade. An important diagnostic tool is that infected grass is slower than healthy grass to recover in the spring. So, if your St. Augustine lawn is still brown when your neighbor's is greening up, get suspicious. The virus is widespread in Texas and has been reported in Louisiana and Arkansas. It can also infect centipede grass.
The decline can be slowed by the proper use of fertilizer, and an extra application of iron in the summer will help the grass maintain its green color. Do not confuse SAD with iron deficiency, however. Iron-deficient leaves are uniformly yellow, or their veins are still green, particularly on new and younger leaves. SAD, on the other hand, produces the mottling in both young and old leaves, and it is a mottling, not a consistent yellow color. Iron deficiency is also easily and quickly corrected with a single iron spray—SAD is not.
WHERE DO THE FUNGI COME FROM?
Most fungi start from spores-tiny reproductive cells. Spores commonly are blown around by the force of wind. If they land where conditions are right, they start to thrive and reproduce.
Because SAD is a virus, there is no use spraying anything on the lawn. Fungicides do not work on viral problems. Instead obtain some SAD-resistant cultivars of the grass and plug them into the lawn at 2- to 3-foot centers across the lawn. They will spread in the weakened lawn. Within a few years the problem will be eliminated as the strong grass crowds out the weaker.
Sclerotium Blight (or Southern Blight)
This fungus kills rather large patches of grass plants in circles up to 3 yards in diameter. The grass turns a reddish brown as it dies and the odd plant will survive within the dying fungal circle. In advanced cases, the mycelium mass is quite visible as a whitish growth on the lawn. Look for tiny mustard seed-size bits of fungus resting bodies (resting bodies are called sclerotia and function like seeds) at the base of grass stems.
Bent grass, bluegrass, fescues, and ryegrasses (along with many different nongrass plants) are susceptible to this problem. The disease is spread by the sclerotia and infected plant parts. As with many fungal problems, warm to hot weather, high moisture, and heavy thatch layers all contribute to this blight.
To control the problem with cultural methods, reduce the thatch and fertilize regularly. Fungicides are extremely useful at the first sign of the disease.
Slime mold is one of those opportunistic fungus problems that can hit any grass if the conditions are right. The mold looks like a white or grayish powdery covering that affects the grass leaves in a 6- to 12-inch circle. It normally develops during warm, wet, or humid weather, and the fungus will leave by its own accord during hot dry weather. You can remove these white fungus bodies by washing, mowing, or brushing the leaves. This does not require a fungicide treatment.
Spring Dead Spot
This fungus primarily attacks the well-managed Bermuda grass and zoysia grass lawn and is rarely seen on low-maintenance lawns. As the grass starts to green up in the spring, circular dead patches of 3 to 4 feet across appear. The problem usually appears in the same area year after year and the grass can take upward of two to three months to regrow into this area.
To control this problem, keep nitrogen levels at a moderate level throughout the growing season to keep the grass growing steadily. Annual dethatching is important to remove the overwintering site for the fungus. Potash applications seem to help, so a fall application of a fertilizer should focus on potash (potassium) and not nitrogen. This is one problem where fall fertilizing with nitrogen is not recommended. Control with a fungicide in the fall.
Stripe Smut and Flag Smut
This fungus problem is a cool weather disease that sometimes shows up when there is a long period of cool weather either in the early spring or fall. Temperatures of 50° to 60°F are favorable for its development. It disappears in the heat of the summer. Leaves of infected plants have long yellow-green streaks that turn gray and then black. When the streaks turn black, they break open to release fungus spores. Because of this rupturing, the leaves look tattered and split into ribbons. The tips of the leaves curl downward, and then the leaves turn brown and die. Infected plants can die, resulting in a thin patch of lawn. The fungus hits irregularly across the lawn so the lawn is uneven, generally thin, and in poor health.
Stripe smut attacks some varieties of bluegrass, as well as creeping bent grass. Damage is seldom severe with stripe smut, so control is not usually required. If the damage is severe, apply nitrogen and water deeply early in the day. Topdress to fill the lawn holes. Avoid watering late in the day or with light applications. If disease is severe, there are fungicides registered for this problem. Apply them either in early spring or in late fall.
Flag smut has almost exactly the same symptoms and controls. It attacks bluegrass as well and is best controlled by sowing resistant varieties.
This fungus attacks the roots and crown of grass plants, especially during the high summer when the temperatures rise and drought is likely. So when it is hot and dry, look for spots about 6 to 12 inches in diameter. The grass in the spots starts turning light green and then it fades quite quickly to a straw brown color because the tips of the grass leaves are all bronzed and straw colored. The dead patches may have tufts of sickly grass or weeds may colonize those areas. Summer patch kills bluegrass and fine fescues.
When choosing fungicides to treat your lawn or garden, be sure to choose one that presents the fewest health risks to you and your family. You also want a fungicide that will be friendly to the enviornment.
To prevent the lawn from losing patches to this problem, avoid high nitrogen feeding, overly wet soils, compaction, and the stress caused by low mowing. If the problem occurs, replant with a tall fescue or resistant cultivar of bluegrass.
This fungus attacks the roots of grass plants, rotting them and creating dark strands of mycelium (quite visible) on the roots. The dying grass creates circular or ring-shaped dead areas ranging from a few inches to 3 or more feet in diameter.
Bent grasses are the most susceptible to the problem, although fescues and ryegrass are also susceptible.
The fungus overwinters in grass debris. Conditions that encourage take-all patch include a sandy soil, low organic matter in the soil, low or unbalanced fertility, high pH, and high moisture conditions.
Reverse these conditions to reduce the problem; improve the soil and organic matter through the use of compost applications, improve drainage, lower the soil pH using sulfur if it is above 7.0. Replant with grass varieties that are resistant to this problem. Apply fungicides in the fall.
Take-All Root Rot
This fungus is responsible for Bermuda grass decline, yet take-all root rot is mostly a disease of St. Augustine grass. Centipede grass is also known to be affected. Generally, all cultivars of St. Augustine grass are susceptible, particularly if they are grown under stress.
The initial symptom is a patchy yellowing of the grass and as the roots decay, the turf thins out. As the fungus stops the plant from transporting water from the roots, the plant dies. If you dig up the plants, you'll find that the roots are rotted.
The susceptible times for this fungus are the summer and fall seasons when temperatures and moisture levels are both high. Poor management practices such as low mowing (scalping) or insect injury such as nematodes will stress the plant making it susceptible.
The solution to this problem is deceptively simple. Avoid stressing the plant by providing good cultural conditions. If a problem strikes, mow St. Augustine grass at 4 inches in height to further reduce plant stress.
Typhula Blight (Gray Snow Mold) Typhula Species
Also known as snow scald and winter scald, this fungus attacks all cool season turfgrass varieties; creeping bent grass, annual bluegrass, and perennial ryegrass. (Note that the first two grasses mentioned are weed species in home lawns.) Kentucky bluegrass, red fescue, and tall fescues are less susceptible.
Visible in the spring immediately after snowmelt, Typhula blight appears as an overall blighting rather than as distinct dead patches. The turf appears to be bleached in irregular patches. These patches can range from a few inches in size upward as patches overlap to contain large areas.
The fungus is active over the winter. It takes snow cover of at least three months to create conditions for the survival of this fungus.
To control this fungus, minimize thatch. Prevent succulent growth in the late fall by stopping or reducing summer feeding. In other words, no nitrogen within six weeks of the last frost date in your area. Mow the grass right up until growth stops, so there are no long, succulent grass leaves for infection. In the spring, the infected areas can be raked and cleared of debris to encourage drying out, which reduces the fungus spread. Lightly fertilize the damaged areas to encourage new top growth and apply light topdressing to severely damaged areas. To be effective in stopping the overwinter life of the fungus, apply any fungicide before the first snowfall.
This is an interesting disease of grass plants planted in recently wooded areas. The symptom is a circular white patch between 6 inches and 1 foot in diameter. Sometimes small tan colored mushrooms will ring the circles.
Fescues seem to be more susceptible to this than other grass plants, but usually enough plants survive to start filling in the lawn again.
RAISE THE MOWER DECK
You'll see this advice in other parts of the book, but it bears repeating here. Raise the mower deck as a first line of fungus prevention. For every eighth of an inch that you raise your deck, you increase the remaining working surface of the grass leaf by approximately 30 percent. Research at the University of Maryland showed that rhizome development increased just over 10 times when the mowing height was raised from 2¾ inches to 3½ inches.
There is also evidence that mowing high in the spring reduces the incidence of weeds later in the summer. For example, if the grass is mown higher, crabgrass is less likely to receive enough light to germinate.
Mowing at taller heights is the most effective form of weed control we have.
Ensuring proper soil pH and nutrient levels (particularly phosphorus) will eliminate or reduce white patch on new lawns. The problem rarely requires fungicides.
The early symptoms of this fungus are small patches (2 to 3 inches) of light green to a sick yellow-green grass color. These small areas turn a light brown and grow in size up to 2 feet across. A “frog's eye” pattern is common; this is where a circle of dead grass surrounds green growing turf. These patches may appear sunken because of the decomposition of the thatch layer. The leaves near the margin of the brown patch may have a reddish tinge, which starts at the tip and progresses down the leaf. There may also be some midbrown darker spots on the leaves below the red discolorations.
If you decide to spray your lawn with a chemical (organic or otherwise), then the most important thing you have to do is ensure that nobody walks on that lawn while the spray is still wet on the grass. With chemical fungicides that have a residual effect (residual effect means they “reside” or last for longer than a few hours), it is very important that children and pets be kept off the lawn as long as the chemical is effective. Safety data is measured on adult bodies and not calculated for the reduced mass of children's bodies. Better safe than sorry. Read the product label for data on how long the chemical is active
The difficulty in identifying yellow patch is compounded by its overlap with necrotic ring spot. The key difference is that the roots and crowns of yellow patch-infected grass do not have the black fungus strands on them that characterize necrotic ring spot.
This fungus is a particular problem on Kentucky bluegrass lawns, although others can be infected. New sod lawns laid on clay soils are quite susceptible because of the constant moisture needed to establish the sod.
Control is the same as for necrotic ring spot (see page 152). Emphasize reducing the wet conditions for the lawn and aerate the lawn if it is on clay soils. There are no effective fungicide sprays for this problem.
Zonate Leaf Spot
This fungal problem tends to attack Bermuda grass and St. Augustine grass particularly during hot, humid temperatures when the thermometer climbs over 85°F. Two types of symptoms are displayed when grass starts to succumb to this problem. One is a large irregular area of chlorotic (yellowing) turf. The grass just starts turning yellow. The second is necrotic (dying) rings of grass, full circles as well as half and quarter circles that enlarge quite rapidly. The fungus causes the individual grass leaves to be spotted and die.
Make sure the turf has a balanced fertilizer program, perhaps by using slow-release fertilizers instead of the more normal fertilizers. This avoids excessive applications of root-ready nitrogen that seems to promote the disease. Irrigate only to keep the plants alive—do not overwater. Apply the water early in the morning when dew is already present. Do not wet leaves more than necessary. To reduce the spread of the fungus, limit the movement of people and objects across the grass.