Use several properly observed flotation samples and preserve specimens for identification. A negative sample does not rule out chinch bugs, and unexplained browning needs further assessment before treatment.
To test for chinch bugs, UF/IFAS describes inserting an open-ended can into the turf at the edge of a damaged patch and keeping it filled with water for five minutes. Look for insects that float to the surface and repeat at several locations. The source recommends at least four samples; one negative result does not establish that chinch bugs are absent.
Record the locations and identify what you collect before choosing treatment. A flotation sample is an inspection tool, not a diagnosis of every cause of brown grass.
Why Brown Grass Isn't Proof of Chinch Bugs
Yellow or brown spots in St. Augustinegrass don’t automatically mean chinch bugs. According to University of Florida IFAS, several other problems can look very similar:
- Dehydration
- Root rot and other diseases
- Nematodes
- Other insect pests
UF is direct about it: homeowners need a proper diagnosis to choose the right treatment. If you treat for chinch bugs when the real cause is drought stress or disease, you waste money and the lawn keeps declining.
Other lawn pests can leave brown patches too. For example, caterpillars chew the grass blades instead of feeding at the base of the plant. If caterpillars seem more likely, armyworm inspection and timing help explain that different feeding pattern.
What Chinch Bug Damage Typically Looks Like
UF describes infested areas as discolored patches that are usually circular. Damage tends to appear first in water-stressed spots, such as lawn edges or areas in full sun. Grass growing on high, dry, sandy, or shell soil is especially vulnerable.
The bugs feed in groups at the base of a plant and drain its sap. The grass fades from green to brownish-yellow and then dies. After that, the group moves to the next stolon, which is why patches spread outward over time.
What You Need for the Flotation Test
The UF flotation method needs only a few basic items:
- A metal coffee can with the bottom removed. This makes an open cylinder.
- A knife or shovel to work the edge of the can into the soil.
- A water source, such as a garden hose or a large watering can.
- Work gloves. The cut edge of a can is sharp.
- A notepad or phone to record each sample.
- A small sealable container in case you want to keep a specimen.
Handle the Can Safely
Removing the bottom of a metal can leaves a jagged edge. Wear sturdy gloves whenever you cut, carry, or press the can into the ground. Push the cut end into the soil so the smoother rim faces up. In addition, keep children and pets away from the can while you work.
Where Should You Place the Can?
Where you sample matters as much as how you sample. UF advises focusing on the perimeter of the injured spots. That means the border where damaged grass meets healthy-looking grass.
The reason comes down to feeding behavior. Chinch bugs stay together at one plant until it dies, then move to fresh grass next to it. As a result, the center of a dead patch may hold few bugs. Meanwhile, the active feeders are working along the edge.
When you choose a sampling spot:
- Pick the edge where yellowing grass touches green grass.
- Skip the middle of completely dead, brown areas.
- Check sunny, dry spots near driveways, sidewalks, and lawn borders.
- Spread your samples around the affected area instead of bunching them together.
How to Test for Chinch Bugs, Step by Step
These steps follow the flotation method described by UF IFAS:
- Prepare the can. Remove the bottom of a metal coffee can to make an open cylinder. Put your gloves on.
- Position it. Set the can on the soil at the border of the discolored grass.
- Push it into the soil. Use a knife or shovel to work the edges of the can about 3 inches down.
- Add water. Keep filling the can with water for five minutes, topping it off as it soaks in.
- Watch the surface. Any chinch bugs trapped inside will float to the top of the water.
- Record the result. Write down what you saw before you move the can.
- Repeat. Test several more spots around the damaged area.
UF notes that, inside an infested spot, chinch bugs live from the thatch down into the top organic layer of soil. That zone usually extends about 1½ inches below the surface. Pushing the can 3 inches deep encloses that whole layer, so the water can flush out hidden bugs.
How Many Samples Are Enough?
UF recommends repeating the flotation method at least four times across the discolored area. One can isn’t enough.
Chinch bugs are not spread evenly across a lawn. Instead, UF describes infested plots as scattered throughout the area. A single can might land between two groups and come up empty, even though bugs are feeding a short distance away.
Several samples around the edge of each patch give you a far more reliable picture. If you have more than one damaged area, sample each one separately.
What Do Chinch Bugs Look Like in the Water?
Chinch bugs are small, so look closely at the water surface and along the inside wall of the can. A flashlight or magnifying glass can help.
Adults
Adult southern chinch bugs are about ¼ inch (6 mm) long with a black body. Their wings are white, with a black spot on the edge of each forewing. Some adults have long wings that reach nearly to the tip of the abdomen. Others have short wings that cover only about half of it.
Nymphs
Young chinch bugs look like smaller, wingless adults. Their color changes as they grow:
- The first stage is yellow.
- Next, they turn red with a pale white band across the abdomen.
- Finally, they turn black with a similar white band.
Finding identified nymphs and adults documents multiple life stages in the sample; it does not establish that every insect developed at that exact point.
Similar-Looking Insects
Other small insects may float up too, and some of them help you. UF names the bigeyed bug as the most numerous predator of southern chinch bugs in St. Augustinegrass. If you’re unsure what you’ve found, keep a specimen and get it identified instead of guessing.
Keeping a Record of What You Find
A simple written record turns a quick check into useful information. For each can, note:
- The date and time
- The exact location, such as “north edge of the driveway patch”
- Whether the spot was at the edge or the center of the damage
- How many adults and nymphs you saw
- Any other insects that floated up
You can also scoop a few floating insects into a small sealed container. A physical specimen is often the easiest way for an extension office or professional to confirm what they are.
If you repeat the sampling, use comparable locations and the same method, and record the interval. Changing counts can guide reassessment but do not by themselves explain why a population changed.
What If the Test Comes Up Empty?
A negative result does not prove chinch bugs are absent. You may have missed them for several reasons:
- The bugs are clustered in spots your cans didn’t reach.
- You sampled the dead center instead of the active edge.
- The can wasn’t pushed deep enough or wasn’t kept full long enough.
- The population has already moved on to fresh grass.
If damage keeps spreading after a clean test, sample again. Use more cans and focus tightly on the border between yellow and green grass.
If careful, repeated testing still finds nothing, turn to the other causes UF lists. Check whether the area dries out faster than the rest of the lawn. Look for signs of disease or root problems. Also review your mowing, watering, and fertilizing habits. A turf-care assessment considers the grass cultivar, irrigation and other causes of stress before adding fertilizer or pesticides.
When to Get a Second Opinion
Some situations call for outside help:
- Your results are unclear, or you can’t identify what floated up.
- The damage keeps spreading despite negative tests.
- You suspect disease, nematodes, or root rot, which a water test can’t detect.
- Earlier treatments haven’t worked.
That last point matters. UF reports that some southern chinch bug populations have developed resistance to insecticides. That is one more reason to confirm the cause before you apply anything. Your county extension office can help identify specimens and diagnose turf problems. A licensed lawn pest professional can also inspect the site.
Source
UF/IFAS: Southern Chinch Bug, Blissus insularis provides the identification, flotation-sampling and cultural-management guidance discussed here.
Frequently Asked Questions
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What is the flotation method for chinch bugs?
It's a sampling technique described by University of Florida IFAS. You push an open-ended metal can about 3 inches into the soil and keep it filled with water for five minutes. Any chinch bugs inside float to the surface, where you can see and count them.
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Where is the best place to test for chinch bugs?
Test along the border where damaged grass meets healthy grass. UF recommends focusing on the perimeter of injured spots, because active feeders move outward into fresh grass. The center of a dead patch often has few bugs left.
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How many times should I repeat the coffee can test?
UF recommends at least four samples across the discolored area. Chinch bugs gather in scattered groups, so a single sample can easily miss them. Spread your cans around the edges of each damaged patch.
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When are chinch bugs most active in Florida?
UF describes warm-season activity and reports an early-July peak in the research summarized by its profile. Actual timing varies with local conditions. In much of Florida, they also stay active through winter near the base of the grass. Spring infestations often start where damage stopped the season before.
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Can I find chinch bugs without water?
When populations are high, UF notes that chinch bugs can sometimes be seen running over the grass blades. However, they do most of their feeding between the thatch and the soil, where they're hard to spot. The flotation method is the more reliable way to check.
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Does a negative test mean my lawn is free of chinch bugs?
No. Because chinch bugs gather in scattered groups, your cans may have missed them. Retest along the active edge of the damage. If results stay negative, consider other causes such as drought stress, disease, or nematodes.
Vincent founded On Demand Pest Control in 2017 and is a Florida Certified Operator in all four state categories. He treats pest control as a systematic problem to solve, not a symptom to spray. Read Vincent’s full bio →
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