A smattering of brown needles in your own Norfolk Island pine (Araucaria heterophylla) should not cause worry; it happens naturally as these stately trees mature. However, when Norfolk’s distinctive foliage turns brown on a broader scale, then your tree is in distress. Don’t delay taking action; distressed Norfolk Island pines may drop entire branches that never grow back. Prompt investigation and corrections start with basic culture and proceed through diseases and insects.
Temperature and Timing
Norfolk Island pines withstand winter outside in U.S. Department of Agricultural plant hardiness zones 10 and 11. In such zones and all others, they serve as valued houseplants too. From statuesque landscape specimens to container-grown trees, Norfolks are frost-sensitive. Foliage damage begins when temperatures dip below 40 degrees Fahrenheit. At 30 to 32 F, the tree’s hints stop growing and die. Temperatures below 25 F hurt the tree irreparably. High temperatures over 95 F can also bring about tip damage. If your tree began browning after exposure, consider a more appropriate, protected setting. Move potted Norfolks inside whenever the temperature falls near 50 F.
Light and Relocations
Norfolk Island pines prefer full sun, but they tolerate partial shade. Foliage turns dark green when lighting levels remain too low, but left long enough, needles turn brown. Droopy branches also signal when Norfolk pines need more lighting. Move potted trees to sunnier places, and change the environment of scenery trees to permit more sun in. Sudden relocation also causes brown needles, and entire branches may fall. Gradually acclimate Norfolks to new settings and lighting levels whenever feasible. Supply indoor Norfolks with trendy, bright places away from drafts and heating or air-conditioning vents.
Soil and Moisture
True to their native South Pacific shores, Norfolk Island pines prefer consistent moisture, fast-draining soil and high humidity. They also tolerate soil salts and adapt readily to highly acidic to slightly alkaline soils of all sorts. Overwatering causes foliage to yellow and then brown, but acute dryness can brown trees fast. Examine the soil by hand, several inches down, for clues to browning difficulties. Soil should be moist and cool — neither wet nor fully dry. Water Norfolks until the entire root area is moist. Then allow the soil to dry to a finger’s length deep before watering again. Let water run through drainage holes to potted trees, and vacant surplus water in saucers. Don’t fertilize stressed Norfolks; nutrient deficiencies turn leaves yellow, not brown.
Norfolk Needle Blight
Anthracnose caused by the fungal pathogen Colletotrichum derridis browns Norfolk needles. Known as Collectrichum needle blight, the disease starts with small spots, and then entire needles brown and die. Large branch sections turn brown and needles drop. Close inspection reveals small, black, specklike fungi. Foliage kept too wet for too long is that the offender. To solve the problem, start by eliminating overhead irrigation and keeping foliage dry. Treating huge trees is impractical, but fungicide helps small plants. Sizes all leaf surfaces using ready-to-use copper soap fungicide, inside or outside. Duplicate at seven- to 10-day intervals, as required. Wear gloves and safety goggles, and steer clear of chemical contact with exposed skin. Do exterior spraying on a calm, cloudy day. Wash thoroughly with soap and water after handling.
Needle-Browning Pests
Several insects influence Norfolk Island pines, but mites cause brown Norfolk leaves. They hide well until needles start puckering or turning brown. Shake a Norfolk division on a white piece of paper to see if mites fall. Raising relative humidity to Norfolk’s favored 50 percent variety frequently relieves mite problems inside. Insecticidal soap also heals the insects. Spray all plant surfaces thoroughly using ready-to-use insecticidal soap, including undersides of leaves. The spray must speak to the insects. Repeat weekly or biweekly, as required, to remove needle-browning mites. Wear gloves and protective clothes, following label security precautions. Don’t spray outside during peak sun hours.