What Is Killing Your Pasture?

By NTFR Staff

A brown patch in a pasture may look simple from the pickup. The grass is dry, the cattle have grazed it too closely or it needs a good rain. Sometimes one of those explanations is correct. Other times, the damaged area may be the first visible sign of insects, disease, poor soil fertility, compaction or a grazing problem that has been developing for years.

Many pasture problems look alike from a distance. Drought-stressed grass can turn yellow or brown, but so can grass damaged by armyworms. A nutrient deficiency may cause weak, pale growth that resembles disease. Overgrazing can thin the stand and let weeds move in, while compacted soil can keep rainfall from reaching plant roots.

Treating the wrong problem wastes money and lets the real cause get worse. Fertilizer will not stop an insect infestation, and insecticide will not correct a soil deficiency. Before applying anything, slow down, walk the pasture and figure out what the grass is telling you.

Start With the Pattern

The shape and location of the damage provide the first clues. A problem that appears evenly across the entire pasture may point toward drought, poor fertility or a widespread management issue. Damage that begins in patches, follows a fence line or moves across a field may point more toward insects, disease, drainage problems or soil differences.

Begin by comparing the affected area with healthy grass nearby. Look at the color, height and density of the forage. Check whether the damage is limited to one forage species or affects nearly every plant in the area. Notice whether weeds stay green while the desired grass struggles.

Drought stress commonly shows up first on shallow soils, exposed slopes and other places that hold less moisture. Grass may fold or roll its leaves to conserve water before it turns gray-green, yellow or brown. In severe conditions, the plant may stop growing above ground and live on stored energy.

A pasture does not always recover as fast as it greens up. Rain may bring new leaves, but plants weakened by prolonged drought still need time to rebuild their root systems and energy reserves. Turning livestock onto new growth too soon can strip away the leaf area the plants need to recover.

Overgrazing can produce similar symptoms, especially when livestock keep returning to their preferred plants. Overgrazing has more to do with timing than with how short the grass gets. It occurs when livestock graze a plant again before it has recovered from the previous grazing.

When leaves are removed, the plant uses stored carbohydrates to begin regrowth. If livestock eat that new growth almost immediately, the plant must draw from its reserves again. Repeated grazing without recovery eventually weakens the roots, reduces forage production and may kill desirable plants.

Signs include closely cropped grass, bare soil, increasing weed pressure and an uneven pasture where livestock graze some plants repeatedly while less desirable species stay tall. Areas around water, shade, mineral feeders and gates often get especially heavy use, and soil in those spots may also become compacted.

Compaction reduces the pore space that lets air and water move through the soil. Rainfall may run off instead of soaking in, and plant roots may stay shallow or struggle to penetrate the soil. You can compare suspected areas by pushing a soil probe or sturdy rod into the ground when soil moisture is similar. A shovel can also reveal shallow roots, dense soil layers or standing water below the surface.

Poor fertility is another common cause of weak or discolored grass, but plant color alone can’t diagnose a nutrient deficiency. Nitrogen deficiency often produces pale green or yellow growth and reduced production. Other nutrient problems may affect older or younger leaves differently, depending on how the nutrient moves within the plant.

Soil testing is the only dependable way to find out what the soil needs. A representative sample should combine soil collected from several locations with similar soil type, management and production history. Sample unusual areas, such as feeding sites, wet spots or visibly damaged patches, separately instead of mixing them with the rest of the pasture.

Soil pH deserves particular attention because it affects nutrient availability and plant growth. Fertilizer applied without correcting an unsuitable pH may produce disappointing results. At the same time, adding lime or nutrients the soil doesn’t need raises costs and may create new problems.

Look More Closely

When damage seems to appear overnight, put insects high on the list of suspects. Fall armyworms can remove large amounts of forage in a short time, particularly when producers discover them late in their development.

Young fall armyworm larvae scrape the green tissue from grass blades, leaving a thin, pale membrane sometimes described as a windowpane. Larger larvae chew through the leaves and can leave a pasture looking frosted or burned. Birds feeding heavily in one part of a field can also be a clue that caterpillars are present.

Scouting works best early in the morning or late in the afternoon, when larvae are more active. A sweep net can collect small caterpillars that are hard to see. You can also bend a wire coat hanger into a hoop, place it on the ground and carefully count the larvae inside it. Check several locations, including field margins and the interior of the pasture.

Base treatment decisions on the number and size of the larvae, the amount and value of forage at risk and the cost of control. As a general guideline, Extension specialists often recommend considering treatment when about three to four larvae per square foot are present. Small larvae are easier to control than large ones, so early detection matters.

Any pesticide used on pasture must be labeled for that site and pest. The label also lists grazing, haying and harvest restrictions that can differ among products. Grass disappearing is not reason enough to spray an insecticide. The caterpillars must still be present and actively feeding for treatment to accomplish anything.

Plant diseases are less common than drought, fertility and grazing problems in many pastures, but don’t dismiss them. Several fungal diseases can affect bermudagrass, including some that damage roots or produce irregular patches of dead grass. Disease may become more noticeable when plants are already stressed by heat, drought, poor drainage, improper fertility or other unfavorable conditions.

Pull several plants from the edge of a damaged patch instead of from the completely dead center. Examine the roots, crowns, stems and leaves. Healthy roots are generally firm and well developed. Dark, shortened or rotting roots may indicate disease or prolonged soil saturation. Leaf spots, lesions and discolored stems can provide additional evidence.

Because pasture diseases can closely resemble other problems, applying a fungicide without a diagnosis is seldom a good first step. You may need to submit samples to a plant diagnostic laboratory. The best samples usually include plants showing a range of symptoms, along with healthy plants for comparison. Photographs of the entire affected area can help diagnosticians understand the pattern in the field.

Weeds may be part of the cause, the result of the problem or both. As desirable forage thins, sunlight reaches the soil surface and gives weed seeds a chance to germinate. Weeds then compete with the remaining forage for water, nutrients and space.

Spraying the weeds may improve the look of the field, but it will not necessarily fix the condition that let them move in. Unless grazing pressure, fertility, soil condition or forage density improves, another weed may take their place.

Consider simpler possibilities, too. Herbicide drift can produce distorted, twisted or discolored growth. Fertilizer or chemical application errors may leave straight lines, overlaps or skipped strips. Standing water can kill plants in low areas, while damaged water lines may create isolated wet spots. Salt, manure and concentrated livestock traffic can also affect grass near feeders, troughs and corrals.

Good records make these problems easier to solve. Rainfall, fertilizer applications, grazing dates, stocking rates, herbicide use and previous insect outbreaks can help explain what is happening. Photographs taken from the same locations throughout the year may reveal gradual changes that are hard to recognize during daily ranch work.

Most pasture failures build as several smaller problems overlap. Dry weather weakens the grass, and livestock keep grazing the remaining plants. Bare ground expands, weeds appear and runoff increases. Then an insect outbreak or another dry spell pushes the pasture past the point where it can recover quickly.

When you spot the first brown patch, inspect it closely before you buy fertilizer or chemicals. Walk past the edge of the damage, look at the whole plant and consider what has happened in that pasture over the previous weeks and months. Identifying the cause before choosing a treatment is usually the least expensive place to start.