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Fall Diseases in Southern Lawns

 

As fall begins, new challenges arise in the slowly changing environment. The days grow shorter and the weather starts to cool down. These changes affect circadian rhythms for thousands of organisms, including us, triggering new behaviors. 

As each season progresses, many insects will reproduce as older generations die off. After heavy rains and changing weather patterns, swarming insects like ants and termites, fly out of old colonies to form new ones. 

Cooling weather mean shorter days and falling leaves. November 1, we will set our clocks back an hour to save daylight. Resetting our internal clocks is not as easy. It can take up to a week for us to adjust to daylight savings time. The difference of only an hour affects us very much like jet lag does when flying from one time zone to another.

Insects are also affected by circadian rhythms, though not as drastically as humans are. Biological clocks are an essential part of adapting to cyclical changes in the environment. All living things have this internal clock. 

Scientific studies have revealed that biological clocks play many roles in an organism’s survival. An insect’s internal clock is measured by 24 hours in the day just as ours is. Behavioral and physiological changes are intertwined with light and temperature in almost every living complex organism.

Scientists discovered a puzzling trait in European honey bees who use the sun to navigate. The worker bees pass along information to each other such as distance to a food source by performing a specialized dance. This strange behavioral trait is called a “waggle dance.”  The honey bees navigate by using the angle of the sun, orienting their location with a “solar compass” or “sun compass.”

The monarch butterfly uses a similar method to migrate long distances. They and other animals and bugs use the earth’s magnetic field along with the moon and stars in a mechanism called “Celestial navigation.” These navigation techniques would not be possible without an internal biological clock. 

Circadian clocks are believed to originate in the central nervous system deep in an organism’s brain, located in the optic lobes. When part of this brain tissue was removed from invertebrates like crickets, they displayed abnormal behaviors and were not able to survive. This mechanism to measure daylight is thought to have formed very early in the evolution of all organisms on earth. 

Bed Bugs need the same integrated circuitry to know when to feed. They can detect the carbon dioxide emitted from our breath. Their internal mechanism is adapted to feed on human blood when, statistically, we are in our deepest part of sleep between two a.m. and five a.m.  Feeding too early or too late, will increase the bed bug’s chances of being seen and immediately killed. This is most certainly an adapted behavioral trait, as opposed to a predetermined amount of time the bed bugs require for feeding.

A suspended period of development in insects or other mammals is called diapause. Diapause is believed to be triggered by changes in daylight, temperature, and other environmental conditions. Similar to hibernation, which is exclusively characterized by very low body temperature, diapause is characterized by metabolic changes in insects. 

Dormant Bugs

Dormancy is another form of hibernation. Paper wasps, yellow jackets, and mosquitoes all go dormant when temperatures get too cold. They remain in a dormant state until temperatures warm up. 

Fleas and bedbugs can also remain dormant until conditions are favorable for feeding. An adult bed bug can survive a year without feeding. Bed bug nymphs can survive up to 3 months without a blood meal. 

Understanding the organisms that suspend their metabolic activity to survive long periods of time may one day help humans to survive for the decades of time needed for space travel outside our galaxy. 

Grass in Fall and Winter

In the northern states, Kentucky bluegrass, ryegrass, and fescue are the most common grass types found in suburban areas. All these grass types go dormant in the winter. Green urban landscapes turn into a frozen pale brown color, dotted with red, orange, and yellow leaves. Soon snow and ice may cover the lawn, and all biological mechanisms stop. Without growth, grass is in a suspended state between living and dying. Grass does not get nutrients from sunlight or nutrients from the ground, nor does it need them.

Come Spring, after months without warmth and sunlight, and being buried in snow and ice, the warming rays of the sun bring lawns back to life. What was brown dead grass, becomes green and growing. 

At Dave’s Pest Control, our highly trained lawn technicians know a lot about diseases in turf grasses. During fall weather in Volusia and Flagler Counties, while temperatures remain humid during the day, cooling temperatures during the night can bring fungus problems to southern grasses like St. Augustine and Zoysia grass. Applying fungicides is necessary for control of diseases. Which fungicide should be used depends on what kind of disease the lawn has. 

Large Patch Disease 

One serious disease brought on by cooler temperatures that affects warm season turf grasses is large patch disease. This fungus most often attacks St. Augustine grass, centipede grass, seashore paspalum, and zoysia grass. Grass blades with large patch disease are dark brown at the bottom and are easy to pull out by the roots.

As the name suggests, Large Patch disease affects very large areas of turf grasses. It spreads quickly and can be difficult to manage, especially when it is mistaken for chinch bug damage. 

Root Rot

Root rot is a disease in which the roots of a plant decay and rot. Since this disease is deep down in the soil, the symptoms are often not seen until the fungus has spread considerably. This disease is mostly caused by poor drainage of the soil or over watering. Some insects and arthropods help spread the fungus spores by their natural movement in the soil. The roots affected by root rot in warm season grasses will look dark brown to black as they begin to die. The grass leaf blades will turn yellow and die off in irregular patterns. Other diseases have more defined or circular patterns in grass that dies off.

Dollar Spot

Dollar spot is another turf disease caused by a fungus living in the soil. This disease is most common when the soil is dry and the air humid. Wet leaves from dew, rain or irrigation can bring about dollar spot disease. 

Small to medium distinct circular patches, about the size of a silver dollar, form in grasses with dollar spot disease. Visible yellowing develops on the leaves of the grass. The crown and roots of the grass plant can completely die in a lawn severely infected with dollar spot fungus. 

Fairy Ring

Fairy Ring disease is a common problem with many different symptoms. Some lawns have a dead spot shaped like a ring. This is referred to as type 1 Fairy Ring. Type 2 Fairy Ring is characterized as a circular patch of stimulated growth. Mushrooms may or may not be present in turf grass infected with Fairy rings. Sometimes mushrooms will grow in an open arc formation. 

How Fungi Spread

A fungus needs three elements to grow: food, water, and oxygen. Without all three, spore reproduction will not be successful. This is called the disease triangle. When trying to eliminate a fungus, we try to remove one of the three elements, most commonly, the water. 

Fungicides work by disrupting the cell membranes in fungus spores. Controlling fungi that damage turf grasses like rusts, mildews, and blights can be a difficult task. Expert knowledge of the many factors, in addition to grass type, include the weather, surrounding trees, and how the turf is mowed. 

Disease spores can be spread from one lawn to another by uninformed mowing service personnel. The clippings containing fungi spores can be spread over many lawns in one day’s work. Mowing service personnel should clean and wash their lawn mowers and other tools frequently. 

Recognizing the Signs of Turf Diseases 

Knowing which disease you are treating is essential; each different disease requires a specific chemical. 

Fungicides are classified by their mode of action. Mode of action refers to how fungicides target specific areas in the fungi genome. 

Presently, more than 85% of American crops are treated with a fungicide every growing season. The benefits are deemed to outweigh the risks of using fungicides on American produce crops. Without fungicides, billions of dollars would be lost to crop diseases.

Fungi feed on the turf grass’ thatch layer. A lawn’s thatch layer is composed of dead and decaying grass clippings, leaves, stems, and shoots. Thatch grows if this organic matter cannot be broken down more quickly than it is deposited. 

Many diseases thrive in a lawn’s thatch layer by feeding on decaying organic matter. Managing a lawn’s thatch layer involves periodic soil aeration to allow more oxygen to penetrate the soil. This will help the organic matter in the thatch to break down more easily. Specialized dethatching rakes sold in hardware stores help, but this method is extremely labor intensive and backbreaking.

To help reduce the chances of getting a fungus disease in your turf grass, water the lawn in the morning. This allows the grass to dry out before evening, and will help reduce the availability of water, essential for fungi to develop.

Cool nights and warm days are perfect for fungi to grow into damaging diseases affecting large areas of lawn. Fertilize often to encourage healthy turf grass growth. A healthy lawn will resist fungi spores more readily than an unhealthy, slow growing lawn. 

If you suspect diseases in your lawn this fall, call us at Dave’s Pest Control.

Dan Coffey

Dcoffey@davespestcontrol.com

 

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