Juniper, a type of coniferous evergreen plant, has attractive needle-like foliage that ranges in colour from a lovely silvery-blue to a deep, intense green. This versatile, drought-tolerant plant enhances landscapes and gardens as a stately tree, a medium-sized filler shrub and even as a creeping, low-lying ground cover. With the right care and planting techniques, you can prevent your juniper bushes from turning brown and unsightly; with some vigilance and prompt action, you may be able to stop any browning that has begun.
Plant your juniper bushes in a site where there is good soil drainage. Soggy roots and excessive moisture make these plants susceptible to fungal diseases which can cause browning of foliage.
Space your juniper bushes far enough apart to prevent overcrowding and the increased risk of fungal disease that comes with it. A good rule of thumb is to plant them so that their distance from each other equals the width you expect them to become when mature.
Check your juniper bushes for bagworms, which can not only cause browning, but can kill the junipers as well. Look for whitish bags, about 2 inches long, hanging from the tips of branches--these contain the caterpillars. Pick the bags off and burn them. When you see caterpillars emerging, usually in the late spring and early summer, spray with bacillus thuringiensis, a natural bacterial insecticide. Repeat spraying every 10 days until midsummer.
Examine your juniper bushes at the beginning of July for webworms--small brown worms with red-brown stripes running lengthwise--as well as their webby-looking nests, which encase juniper leaves and cause browning and even death. Pick off the webs and worms and destroy them, and spray juniper foliage with bacillus thuringiensis weekly for three weeks in a row.
Look for bright orange swellings on branches that indicate cedar apple rust fungus, which is an issue only if apple trees are growing nearby. The tips of your juniper will turn brown and die, but the bush itself usually survives. Prune out the orange galls. To avoid risk of cedar apple rust fungus, plant the columnar, Chinese, or Andorra cultivars, which are resistant to the disease.
Check for blisters at needle bases and brown leaf tips that indicate the presence of the juniper midge, a small insect that can prey on your juniper. Spray bushes with insecticidal soap to kill the midges, and spray with light horticultural oil in early spring to kill the eggs.
Spray foliage with pet repellent to discourage dogs from urinating on your juniper. Dog urine not only discolours foliage, it can kill branches. Low-growing juniper is particularly at risk.
Wrap the stem bases of your junipers with guards of 1/4-inch hardware cloth to discourage mice, which gnaw the bark off and cause increased risk of infection and disease.
Cut into the heartwood of a branch that is turning brown in order to see if your junipers have tip blight--also called juniper twig blight or phomopsis--a serious fungal disease that kills juniper branches and sometimes the whole bush. If the heartwood is black instead of a healthy red, prune and burn affected twigs and branches. If you have to pull your junipers up, replace them with spiny Greek or hill juniper cultivars, which are resistant to this disease.
Use an anti-desiccant spray, such as Wilt-Pruf, to create a barrier on needles to help slow water loss and resultant browning. Spray foliage after the first autumn frost, when temperatures are no lower than the mid-40s. Apply again in late winter or early spring during a thaw day.
Take a sample of affected foliage to your local state or county extension office for diagnosis if your juniper bushes are turning brown and you can't determine the reason.