Diseases Of Holly Bushes: Pests And Diseases Damaging Holly Bushes

While holly bushes are common additions to the landscape and generally quite hardy, these attractive shrubs occasionally suffer from their share of holly bush diseases, pests and other problems.

Common Pests and Diseases Damaging Holly Bushes

For the most part hollies are extremely hardy, suffering from few pests or diseases. In fact, most problems that do occur are usually associated with other factors, such as environmental conditions. However, pests and diseases damaging holly bushes can happen so it’s important to become familiar with the most common ones for help in prevention as well as treatment.

Holly Tree Pests

Holly tree pests such as scale, mites, and holly leaf miner are the most commonly seen affecting hollies.

  • Scale – While light infestations of scale can usually be controlled by hand, scale control for heavier infestations generally requires the use of horticultural oil. This is usually applied prior to new growth to kill both adults and their eggs.
  • Mites – Spider mites are common causes of discoloration and speckling of holly foliage. While introducing natural predators,such as ladybugs into the landscape can help minimize their numbers, a nice healthy dose of soapy water or insecticidal soap sprayed regularly on plants can also help keep these pests at bay.
  • Leaf Miner – The holly leaf miner can cause unsightly yellow to brown trails throughout the center of leaves. Infested foliage should be destroyed and treatment with a foliar insecticide is often required for leaf miner control.

Holly Tree Disease

Most diseases of holly can be attributed to fungus. The two most prevalent fungal holly tree diseases are tar spot and cankers.

  • Tar Spot – Tar spot usually occurs with moist, cool springtime temperatures. This disease begins as small yellow spots on the leaves, which eventually become reddish brown to black in color and drop out, leaving holes in the foliage. Always remove and destroy infected foliage.
  • Canker – Cankers, another holly tree disease, produce sunken areas on the stems, which eventually die out. Pruning out infected branches is usually necessary in order to save the plant.

Improving air circulation and keeping debris picked up is good for prevention in both cases.

Environmental Diseases of Holly

Sometimes a holly bush disease is due to environmental factors. Such is the case for problems like purple blotch, spine spot, holly scorch, and chlorosis.

  • Purple Blotch – With purple blotch, leaves of holly become splotched with purple-looking spots, which are usually brought on by drought, plant injury, or nutritional deficiencies.
  • Spine Spot – Spine spot is similar with gray spots edged with purple. This is most often caused by leaf punctures from other leaves.
  • Scorch – Sometimes rapid temperature fluctuations in late winter can lead to browning of the leaves, or holly scorch. It is often helpful to provide shade to plants most susceptible.
  • Chlorosis – Iron deficiency can lead to the holly bush disease, chlorosis. Symptoms include pale green to yellow leaves with dark green veins. Reducing pH levels in the soil or treating with supplemental iron-fortified fertilizer can usually alleviate the issue.

Holly Diseases & Insect Pests

Diseases

Damaged Japanese holly (Ilex crenata) roots infected with black root rot.
Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, www.forestryimages.org

Black Root Rot: Black root rot is caused by the fungus Thielaviopsis basicola. This fungus primarily affects the root system and reduces plant vigor. Aboveground symptoms may include stunting of terminal growth, shortening of internodes, and interveinal chlorosis. Infected roots are dark brown to black, usually starting at the root tips. Plants with extensive root rot damage will usually decline and die during dry periods.

Prevention & Treatment: The fungus has the ability to persist in the soil for many years, even in the absence of susceptible plants. High soil moisture and low soil temperatures favor development of black root rot. Fungicide drenches are not generally recommended for landscape use since infected plants cannot be cured. Remove infected plants and replace with other shrubs or resistant holly species, such as Chinese holly (Ilex cornuta). Yaupon holly (I. vomitoria) and American holly (I. opaca) are moderately resistant, while Japanese hollies (I. crenata) are very susceptible to black root rot. Use raised beds in landscape plantings to provide good drainage.

Phytophthora Root Rot: The water mold fungus, Phytophthora cinnamomi, causes root rot on hollies growing in very poorly drained sites or wet areas. Planting too deeply and over-mulching may also contribute to disease development. The symptoms of this disease and black root rot are similar. Typically, yellowing of the leaves (particularly at the shoot tips), early leaf drop, slowed plant growth, and twig dieback are seen at early stages of the disease. Later, one or more limbs may wilt and die back to the main trunk, and a brown to black streak of dead tissue may extend from one area of rotted roots to the damaged limb. Often, the root system will continue to disintegrate until the plant dies.

Prevention & Treatment: Hollies grown under stress are much more sensitive to root rot disease than are well-maintained, vigorous plants. Always select hollies that are adapted to the local climate and soil conditions. Root rot pathogens are often introduced into the landscape on diseased container plants. To avoid introducing these pathogens, purchase hollies with healthy roots and good foliage color. Good cultural practices, such as proper fertilization, control of soil moisture, and providing good drainage (raised beds) will reduce the disease. Japanese hollies (I. cenata) are very intolerant of poorly drained soils and are especially prone to root rot.

The fungus thrives in areas with poor drainage and warm soils. Always choose locations that have good drainage for planting. The drainage of existing areas can be improved by using raised beds. Fungicides can be effective on a preventative basis only, and repeat applications are required. Fungicides containing mefenoxam can be applied in the home landscape, but will not cure an infected plant. See Table 1 for examples of products containing the active ingredient. Due to product cost and for accurate application, homeowners may want to hire a licensed landscaper to apply products containing these fungicides. Apply all chemicals according to directions on the label.

Tar Spot: This disease is caused by the fungus Phacidium curtisii. Yellow spots appear on the leaves of American and English hollies in May. These turn reddish-brown and finally black by fall. In years of heavy rainfall, berries as well as leaves are spotted.

Prevention & Treatment: Remove and destroy badly spotted leaves, prune to improve air circulation and overcrowding, and clean up and destroy fallen leaves.

Nematodes: Root-knot (Meloidogyne), ring (Criconemoides), stunt (Tylenchorhynchus), sting (Belonolaimus), and spiral (Helicotylenchus) nematodes are seldom seen due to their microscopic size. They live in organic matter in the soil or on roots and other parts of living plants. Most parasitic nematodes feed by a stylet, sucking juices from plant cells. They injure plants by direct feeding or wounding tissue, making an entrance for other disease organisms. Plant decline is often the only symptom, followed by gradual stunting, chlorosis, and leaf drop.

Prevention & Treatment: Presently there are no effective chemicals registered for control of nematodes in existing landscape plants. Remove infected plant material and surrounding soil. Plant resistant varieties into nematode-free soils. Chinese holly cultivar ‘Burford’ and Yaupon holly cultivar ‘Nana’ are tolerant to root-knot, stunt, and ring nematodes.

Insects & Mites

Adults, eggs, and cast skins (white) of southern red mite (Oligonychus ilicis).
John A. Weidhass, Virginia Polytechnic Institute and State University, www.forestryimages.org

Southern Red Mite: Southern red mite (Oligonychus ilicis) is an important pest of hollies, especially I. crenata ‘Convexa’, a Japanese holly. Mites are not insects, but are more closely related to spiders. Southern red mite adults are reddish brown and less than 1/50-inch long. Using sucking mouthparts, they feed on the undersides of leaves, where their fine webbing is often seen. Symptoms of feeding include light yellow speckling on leaves. Leaves may turn a bronze color and then drop. With severe infestations, webs may cover both leaf surfaces and branch tips. Populations of southern red mites usually peak in spring and fall. They are almost inactive during the heat of midsummer. Check for mites by looking at the undersurface of leaves in early spring or by shaking a branch over white paper.

Control: Naturally occurring predators of mites include various predatory mites, ladybird beetles, and other insects. Mites can be removed with a strong spray of water, if applied on a regular basis. Insecticidal soap sprays can provide control when applied before population numbers get too high. The following pesticides are labeled for use by homeowners against southern red mite: horticultural oil, bifenthrin, and acephate. See Table 1 for examples of products containing these active ingredients. These products should be applied when mites are present and again in seven to 10 days. A 2% solution of horticulture oil may be sprayed when temperatures are between 45 and 90 °F. Good spray coverage of the lower leaf surfaces is important, as most mites will feed there. As with all pesticides, read and follow all label instructions and precautions.

Leafminer damage on American holly (Ilex opaca).
Daniel Herms, The Ohio State University, www.forestryimages.org

Leafminers: Leafminers (Phytomyza species) are common pests of hollies. In South Carolina, the native holly leafminer (Phytomyza ilicicola) is the most common. Leafminers are the larvae (immature forms) of small (about ⅛-inch in length) black and gray flies. The larvae are about 1/16-inch long. The adult female inserts eggs into young leaves through puncture wounds made by her ovipositor. The presence of many punctures can result in deformed leaves. The eggs hatch in about four days. The larvae then tunnel through the leaf between the upper and lower surfaces. The paths they follow turn yellowish brown and typically broaden into a blotch. Their presence inside the leaf protects them from many insecticides. Parasitic wasps and birds are natural predators of these pests. American holly (I. opaca) cultivars are particularly susceptible to leafminer damage.

Control: With a light infestation, homeowners can handpick and destroy infested leaves. Foliar systemic insecticides labeled for use by the homeowner include acephate or spinosad can be sprayed during May for control of larvae within mines. As an alternative, a soil application of dinotefuran or imidacloprid is effective in controlling the larvae within the leaves. Treat shrubs with dinotefuran or imidacloprid in the early spring for season-long protection. Dinotefuran may move into shrubs more quickly than imidacloprid for faster pest control. Read and follow all label instructions and precautions.

Florida wax scale (Ceroplastes floridensis) on Chinese holly (Ilex cornuta).
United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, www.forestryimages.org

Scale: Many scale species are pests of holly, especially Chinese holly cultivars (I. cornuta). Scales are unusual insects in appearance. They are small and immobile, with no visible legs. Scales vary in appearance depending on age, sex, and species. They feed on sap by piercing the leaf or stem with their mouthparts and sucking. They are typically found on the undersurfaces of leaves and look like small brownish or grayish bumps. Some species may be found on the branches as well. Adults are relatively protected from insecticides by their waxy covering. However, their immature forms, called crawlers, are susceptible.

Greedy scale (Hemiberlesia rapax) is an armored scale that has been reported on ‘East Palatka’ holly. Indian wax scale (Ceroplases ceriferus) is a soft scale that may infest Chinese and Yaupon hollies. Holly pit scale (Asterolecanium puteanum) is a pest on American, ‘Burford’, Japanese, and Yaupon hollies.

Plants may appear water-stressed, and there may be a yellowing of foliage followed by leaf drop. On extensively infested hosts, there is a general decline in plant health, with limb or branch death, and possibly plant death. Check other nearby woody plants for infestations.

Control: Light infestations of scale can be scraped off by hand or infested branches pruned out. Promptly dispose of prunings. For heavier infestations, spray with a horticultural oil in the early spring to kill adults. An oil spray should be applied before new growth begins to kill both over-wintering adults and eggs. Horticultural oil sprays kill by suffocation and can provide excellent control of all scales. More than one spray may be required.

Monitor the crawler emergence with sticky cards, double-faced tape wrapped around a branch, or by putting an infested shoot or leaf into a baggie and watching for crawler movement. Crawler activity often coincides with the flush of new plant growth in the spring. However, some scale species may have overlapping generations with an extended crawler emergence period, such as along the coast. Spray with horticultural oil in the spring after the plants have begun growing and the danger of cold weather has passed. Repeat this application after 10 days to better control the crawlers, adults, and eggs by smothering them. Horticulture oil may be sprayed when temperatures are between 45 and 90 degrees and no rainfall is predicted within 24 hours.

Avoid using contact insecticides unless the plant is very valuable and in serious danger from scale. Insecticides will often kill the naturally occurring predators of scale. If insecticides are going to be used, spray when crawlers are observed. Insecticides labeled for homeowner use against scale crawlers include acephate, malathion, cyfluthrin, lambda- cyhalothrin, permethrin, and bifenthrin. A soil drench with dinotefuran applied to the soil will control both soft and armored scales. See Table 1 for examples of products containing these active ingredients. As with all pesticides, read and follow all label instructions and precautions.

Two-lined Spittlebug: Two-lined Spittlebug (Prosapia bicincta) is primarily an insect pest of Southern turfgrasses, especially centipedegrass and St. Augustinegrass, but also of certain trees and shrubs. ‘Savannah’, ‘East Palatka’, and ‘Foster’ hollies may be significantly damaged by adult spittlebug feeding in the late summer and early fall. The adult is about a ⅓-inch long and brown with two orangish-red stripes on the wings. The nymph (immature stage) is white or yellowish and without wings. Nymphs create the white, frothy spittlemass, which helps keep them moist and protects them from predators and parasites.

There are two generations of two-lined spittlebugs in South Carolina, and this insect over-winters as eggs (generally laid in turfgrass). The eggs hatch in late-March or April and the nymphs suck leaf sap from turfgrass. After approximately a month, the nymphs become winged adults, which also feed upon turfgrass sap. A second generation of eggs is laid, again in turfgrass, where the nymphs will feed. However, it is the resulting second generation of adults that cause the most damage, both in lawns, but also in nearby ornamentals, such as on certain types of hollies. Holly leaf damage from adult feeding can be leaf distortion, wilting, discoloration of younger leaves, blotches on older leaves, and leaf-drop.

Control: In late summer or early fall when damage occurs, apply an insecticidal spray to control the adult feeding. Sprays will last about 10 – 14 days. An insecticidal spray containing one of the following active ingredients will reduce damage by adult spittlebugs: acephate, bifenthrin, cyfluthrin, lambda-cyhalothrin, or permethrin.

In anticipation of adult spittlebug damage the next year, another means of control is to use a soil-applied insecticide in the spring as new growth appears on the shrubs. These products contain imidacloprid, which will move up and throughout the shrub and protect the holly from most insect damage for a year. These products are either granules or liquids that are applied around the base of the hollies. Follow the product label for rate and application directions. See Table 1 for examples of products containing these active ingredients.

Disorders

Purple Leaf Scorch: The most common leaf discoloration is a purplish blotch due to the environment rather than a fungus. This leaf scorching is caused by the presence of water or ice on the leaves at the time the sun is shining brightly. This causes a scalding, followed by invasion of secondary organisms and finally by scorching.

Spine Spot: Small, gray spots with purple halos are caused by the puncturing of the leaves by the spines of adjacent holly leaves. This “spine spot” is often confused with the slits made by the holly leafminer. Leafminer damage has neither a gray center nor a purple halo.

Winter Damage: Symptoms of winter damage may be browning of leaves, marginal leaf scorch, defoliation, twig and limb death, and death of entire plants.

Drought Damage: Holly leaves often turn yellow or brown during a sudden drought period. Japanese hollies, particularly ‘Helleri’, are not very tolerant to low soil moisture, particularly for the first several years after planting. Keep plants watered during periods of drought.

Table 1. Fungicides, Insecticides & Miticides to Control Diseases & Pests of Hollies.

Active Ingredient Examples of Brands and Products
Acephate Bonide Systemic Insect Control Concentrate
Bifenthrin Ortho Bug-B-Gon Insect Killer for Lawns & Gardens Concentrate; & RTS1
Hi-Yield Bug Blaster Bifenthrin 2.4 Concentrate; & RTS1
Ferti-lome Broad Spectrum Insecticide Concentrate
Upstar Gold Insecticide Concentrate
Bifen I/T Concentrate
Talstar P Concentrate
Cyfluthrin Bayer BioAdvanced Vegetable & Garden Insect Spray Concentrate; & RTS1
Cyhalothrin, lambda or gamma Spectracide Triazicide Insect Killer for Lawns & Landscapes Concentrate; & RTS1
Martin’s Cyonara Lawn & Garden Concentrate; & RTS1
Dinotefuran Valent Brand Safari 2G Insecticide (2%, granules)
Valent Brand Safari 20SG Insecticide (20%, drench2)
Gordon’s Zylam Liquid Systemic Insecticide Concentrate (10%, drench2)
Gordon’s Zylam 20SG Systemic Turf Insecticide (20%, drench2)
Ortho Tree & Shrub Insect Control Ready to Use Granules (2%)
Horticultural oil3 Ferti-lome Horticultural Oil Spray Concentrate
Bonide All Seasons Spray Oil Concentrate
Southern Ag ParaFine Horticultural Oil Concentrate
Espoma Earth-tone Horticultural Oil Concentrate; & RTS1
Monterey Horticultural Oil Concentrate
Summit Year Round Spray Oil Concentrate
Imidacloprid Bayer BioAdvanced Garden 12 Month Tree & Shrub Insect Control Concentrate, Landscape Formula (2.94%, drench2)
Bonide Annual Tree & Shrub Insect Control w/ Systemaxx Concentrate (1.47%, drench2)
Ferti-lome Tree & Shrub Systemic Insect Drench2 (1.47%)
Monterey Once A Year Insect Control II Concentrate (1.47%, drench2)
Bonide Systemic Insect Control Granules (0.22%; 8 weeks control)
Hi-Yield Systemic Insect Granules (0.22%; 8 weeks control)
Martin’s Dominion Tree & Shrub Insecticide (1.47%, drench2)
Merit 2 Granular (2%)
Malathion Spectracide Malathion Insect Spray Concentrate
Southern Ag Malathion 50% EC
Hi-Yield 55% Malathion Insect Spray Concentrate
Tiger Brand 50% Malathion Concentrate
Gordon’s Malathion 50% Spray Concentrate
Bonide Malathion Insect Control 50% Concentrate
Martin’s Malathion 50% Concentrate
Ortho MAX Malathion Insect Spray Concentrate
Mefenoxam Subdue GR
Permethrin Bonide Eight Insect Control Vegetable, Fruit & Flower Concentrate
Bonide Total Pest Control Outdoor Concentrate
Hi-Yield Indoor/Outdoor Broad Use Insecticide Concentrate
Bonide Eight Yard & Garden RTS1
Tiger Brand Super 10 Concentrate
Spinosad Southern Ag Conserve Naturalyte Insect Control Concentrate
Bonide Colorado Potato Beetle Beater Concentrate
Bonide Captain Jack’s Deadbug Brew Concentrate; & RTS1
Ferti-lome Borer, Bagworm & Leafminer Spray Concentrate
Monterey Garden Insect Spray Concentrate
Natural Guard Spinosad Landscape & Garden Insecticide RTS1
Dow Conserve SC Turf & Ornamental Concentrate
Ortho Insect Killer Tree & Shrub Concentrate
  1. RTS = Ready to Spray (hose-end applicator)
  2. Drench = Add to water and pour around base of plant.
  3. Do not apply horticultural oil sprays when the temperature is above 90 °F or to drought-stressed plants. Spray late in the day and when no rainfall is expected within 24 hours.
    With all pesticides, read and follow all label instructions and precautions.

Caution: Pollinating insects, such as honey bees and bumblebees, can be adversely affected by the use of pesticides. Avoid the use of spray pesticides (both insecticides and fungicides), as well as soil-applied, systemic insecticides unless absolutely necessary. If spraying is required, always spray late in the evening to reduce the direct impact on pollinating insects. Always try less toxic alternative sprays first for the control of insect pests and diseases. For example, sprays with insecticidal soap, horticultural oil, neem oil extract, spinosad, Bacillus thuringiensis (B.t.), or botanical oils can help control many small insect pests and mites that affect garden and landscape plants. Neem oil extract or botanical oil sprays may also reduce plant damage by repelling many insect pests. Practice cultural techniques to prevent or reduce the incidence of plant diseases, including pre-plant soil improvement, proper plant spacing, crop rotation, applying mulch, applying lime and fertilizer based on soil test results, and avoiding over-head irrigation and frequent watering of established plants. Additionally, there are less toxic spray fungicides that contain sulfur or copper soap, and biological control sprays for plant diseases that contain Bacillus subtilis. However, it is very important to always read and follow the label directions on each product. For more information, contact the Clemson Extension Home & Garden Information Center.

Two holly trees, self-seeded about 30 years ago, are growing a few feet apart in our garden. One is healthy, the other, having had several of its lower branches removed last year, has gradually lost nearly all of its leaves, although it is covered in berries. Is it dying or can we save it?

Geoff Peasland – via email

There are several things that point towards your tree’s eventual demise.

First, although holly can drop an alarming amount of yellowed old foliage in spring, yours has continued to do so. Secondly, trees that are about to die often put an enormous effort, just before they go, to reproduce themselves by flowering/berrying heavily.

Lastly, I should say that this does look like a case of “natural selection”. Your two self-seeded trees are growing unnaturally close together. If you look at a wild woodland (as opposed to a plantation), you will see that trees space themselves out to suit their needs for water, light etc, with weaker ones eventually falling by the wayside as the stronger ones grow.

The healthier of your two hollies is multi-stemmed, indicating that it was once stooled (cut down to a point just above the ground). It has since grown back vigorously to become a thick, wide tree which enabled it even more to overshadow the one that you say was quite severely pruned last year.

Credit: Alamy Credit: Alamy Credit: Martin Pope

Holly Leaf Spot

The fungi Coniothyrium ilicinum and Phacidium species are two of several that regularly cause leaf spots on holly (Ilex) in this area. Other fungi cause leaf spots on holly but they are rarely found in New England. In addition, feeding damage by the holly leaf miner and winter desiccation cause spotting symptoms.

Host Plants

Several Ilex species are susceptible to Phacidium species or holly tar spot, while Coniothyrium ilicinum normally causes leaf spots on leaves of American holly (I. opaca).

Description

Small to large irregularly shaped yellow-brown spots appear during the winter and spring on old American holly leaves infected with Coniothyrium ilicinum. Heavily infected leaves drop prematurely from the trees in the spring. Phacidium species initially causes yellow spots on the leaves of American and English holly by late spring. During the summer the spots turn red-brown then develop the characteristic black tar spot by early fall.

Disease Cycle

Leaf spot diseases are more common on American holly, but usually appear during the winter and spring on old leaves. As a practical matter these fungi have not been studied enough to understand their biology and life cycle. In fact, there is some dispute about whether Coniothyrium ilicinum is a primary leaf spot disease or a secondary invader of senescing foliage. On the other hand, Phacidium species is considered a tar spot disease but its biology has not been studied in detail.

Management Strategies

Holly leaf spots seldom cause significant damage to the health of infected plants. Maintain plant vitality with proper fertilization, irrigation during dry periods, mulching, and attention to soil pH levels is the best way to minimize these diseases. Prune plants to promote, sunlight penetration, air circulation and rapid drying of foliage. Also, minimize leaf wetness by irrigating before midday so the leaves dry rapidly in the afternoon. Removal of infected fallen leaves reduces the amount of the inoculum present for new infections. Holly leaf spot diseases are usually more severe after wet springs, but they rarely warrant fungicide controls. Fungicide sprays protect the new green shoots and leaves. Begin sprays as the buds swell and reapply 2-3 more times at label intervals to maintain protection during vulnerable periods.

Written by: Dan Gillman
Revised: 09/2011

Photo: Gail Ruhl, Plant and Pest Digital Library, Purdue University

George Weigel Sometimes apparently dead and bare holly branches will push out new shoots from dormant buds in spring.

Q:

I planted a new holly in the fall, and I just noticed that the leaves are turning black and curling. Some leaves have dropped off. A few weeks ago some of the leaves looked dry, so I watered them very well (when we got that 45-degree weather in November). What shall I do????

A: Not much for the time being, other than to check during winter thaws and add water if the soil is dry.

Fungal leaf blight can turn holly leaves black, but I’d suspect it’s more related to watering or the planting depth.

Excess or standing water that leads to rotting roots is more likely to cause the color you’re seeing rather than lack of water, which results in more of a browning. Either one of these isn’t good, though. If enough roots have died, your plant may be on an irreversible death spiral. You’ll know for sure come spring when new shoots should appear. Sometimes plants will bounce back surprisingly well from an early setback.

Check on the planting depth and make sure the rootball wasn’t placed below grade. Also be sure mulch isn’t packed up on the trunk. You shouldn’t have any more than 2 or 3 inches of mulch around the plant, and it should be a couple of inches back off the trunk.

No need to spray or fertilize. That won’t help and may even hurt. It’s highly unlikely you’ve got bugs, unless you can see little white specks all over (those would be holly scale, and the black would be scale waste that can be wiped off the leaves).

The best scenario is that the plant was too dry and starting to die before you rescued it with your November watering. Even if you lose a lot of the holly leaves over winter, it’s possible that the plant will push out new leaves from the dormant buds in spring. Two tests you can do now: 1.) bend a few branches… dead wood will snap rather than bend, and 2.) scratch off some bark… dead wood will be brown underneath instead of green. The for-sure test is whether it leaves out in spring.

If the plant doesn’t bounce back, check your guarantee and see if you can get a replacement. Many garden centers have a 1-year guarantee. Whenever you plant, those first 6 weeks afterward are the key time to keep consistent water around the roots. Consistent dampness is good. Soggy is bad.


Hollies can usually recover from leaf spot.

The leaves of my newly-planted ‘Carissa’ hollies are covered in black spots. What should I do? Will this do long-term damage to my hollies? – Nikki

It sounds like your holly plants have been infected with a fungal disease known as holly leaf spot, sometimes called holly tar spot. It can be caused by several different fungi, but the symptoms are similar: the leaves develop black, brown, or yellow spots. Eventually, the infected leaves fall off the plant, leaving your holly bare and spindly. Leaf spot usually develops during wet spring weather, and the leaves begin dropping throughout the summer and fall.

The good news is, holly leaf spot is rarely fatal, and your bushes will likely recover if you take steps to keep the problem from getting worse. The plant damage comes from the stress of losing leaves, so treatment and prevention focus on protecting new holly leaves so that the plant can recover. Here’s how to go about it.

Treatment and Prevention of Holly Leaf Spot

Follow these steps to treat and prevent fungal leaf spot on holly:

  • Pruning: If your holly is really dense, prune and thin out some branches to increase air circulation and to allow sunlight to penetrate the plant.

  • ‘Carissa’ holly

  • Watering: Water your hollies before noon, so that the leaves have a chance to dry off during the day.
  • Keep Plant Healthy: A strong plant can easily recover from leaf spot. See our article on How To Grow Hollies for tips on keeping your plants happy.
  • Remove Diseased Leaves: Gently shake your holly, or lightly sweep with a rake, to encourage as many diseased leaves to fall off as you can. Then bag up the leaves and throw them away. You can probably put them in a really hot compost pile, but it’s generally recommended to throw diseased plant debris either into the trash or in an out-of-the-way composting area.
  • Apply Fungicide: Fungicides may help reverse the earliest stages of leaf spot but are mostly used as a preventative on unaffected leaves. They are really only necessary if the other measures above have failed.

Further Information

Tree Diseases: Holly Leaf Spot

Introduction

Holly leaf spot, also referred to as holly tar spot, is a fungal disease that affects holly plants. Holly tar spot induces the formation of black spots on the leaves of holly. Severe infections often result in extensive defoliation of the host plant.

Hosts

Leaf spot diseases are most common on American holly, and holly bush. They may also be observed on other species of Ilex.

Disease Cycle

Holly leaf spot is likely caused by several fungi, including Phacidium curtisii, Rhytisma curtisii, Coniothyrium ilicinum, Marcpderma curtisii, and Phytophthora ilicis. Infections occur on older leaves during winter and spring. When infected, leaves will appear abnormally spotted. Infection spots are irregularly shaped, and vary in size, ranging from large to small. As the infection progresses, the spots deepen in color, eventually turning black. As the black spots develop, a cushion-shaped stroma forms beneath the leaf epidermis. The orange-red apotheical discs mature the following spring, and release ascospores, which are disseminated by air currents or rain to other host plants, where they initiate new cycles of leaf infection.

Symptoms

Symptoms of holly leaf spot are easily distinguished. Most species of holly will develop tiny yellow spots on the leaves in spring. During summer, the spots gradually enlarge, turning reddish-brown. They develop into the characteristic black tar spot by early fall. Severely infected leaves drop prematurely. Defoliation generally occurs from the bottom of the plant, progressing upwards.

Management

  • Plan holly bushes in conditions suitable for the holly type.
  • Maintain plant vigor through sound cultural practices. Ensure that holly plants are sufficiently watered, especially during extended periods of drought. Apply a layer of organic mulch around the base of holly plants to improve soil quality, moderate soil temperature, and retain soil moisture.
  • Routinely prune holly plants to promote sunlight penetration, and air circulation.
  • Avoid watering holly bushes in the morning, or at night. Minimize leaf exposure to irrigation before midday. This will enable the leaves to dry rapidly during the afternoon.
  • Fungicide applications on the shoots and leaves of holly plants will mitigate the effects of holly leaf spot. Initial applications should be performed in spring, just as the buds begin to swell. Two or three subsequent applications should be made during summer.
  • Once the leaves fall, the disease cannot be treated. While this will temporarily reduce the ornamental value of the plant, the damage seldom lingers. In most instances, the host will survive, and produce a healthy flush of growth.
  • Rake and dispose of any infected leaves. This will reduce the amount of inoculum available to initiate new infections. Avoid composting infected leaves; while composting will destroy most fungi, some may survive.
  • Prune and dispose of infected leaves from holly plants. Disinfect pruning tools between each cut using a solution comprised of one part bleach and nine parts water.

If you have any questions about holly leaf spot, or you are interested in one of our tree services, contact us at 978-468-6688, or [email protected] We are available 24/7, and can accommodate any schedule. All estimates are free of charge. We look forward to hearing from you.

Photo courtesy of Gail Ruhl.

Holly Insects & Diseases

Holly leaf miner larvae mines out the leaf middle leaving yellow or brown trails. Use Diazinon or Orthene
when the mines are first noticed.
Scales of various types may infest holly. Crawlers can be controlled with Orthene, Diazinon, or malathion. Two to three sprays may be needed at 7 to 10 day intervals when Orthene is used. The other two chemicals are used when ever the crawlers are present.
Spider mitescause discoloration and speckling of holly foliage. Use sprays of Orthene.

Diseases

Tar spot may occasionally cause small yellow spots on the leaves in summer. Eventually the spots turn reddish brown with narrow yellow borders. Leaves may not drop prematurely but the infected areas drop out leaving holes in the leaves. Gather up and destroy badly infected leaves.
Many different fungi cause leaf spots on holly. Reduce the injury caused by leaf spots by keeping trees healthy. Should a leaf spot become serious, identify the causal fungus before spraying. Dispose of diseased leaves.
Cankers caused by several different fungi lead to sunken areas on stems and plant dieback. Keep trees healthy and prune out infected branches.
Spine spot is small gray spots with purple margins and is caused by spines of one leaf puncturing an adjacent leaf.
Chlorosis symptoms are light green or yellowish leaves with darker green veins. This problem is due to a high pH leading to iron deficiency. Use acidifying fertilizers and chemicals to bring down the pH. Sprays of iron chelate will green up plants until the pH can be lowered.
Hollies scorch during the late winter due to rapid and wide temperature fluctuations. Shade plants during the winter to prevent the problem.
Purple blotches on the leaves are caused by some environmental factor such as nutrient deficiencies, drought, and winter injury.

How can I help my holly bush with brown leaves and dead branches on it?

The browned leaves and dead branches are the result of winter injury, likely sustained during the very cold temperatures we had back in January. Broad-leaved evergreens, such as hollies or rhododendrons, are particularly susceptible to damage. Yet, cold temperatures aren’t the only factor. Warm spells in late winter can also injure plants. In fact, rapid temperature fluctuations are usually more damaging than sustained periods of extreme cold. Sunlight and warmth trigger the leaves to start photosynthesis, which causes them to lose water. If the ground is still is frozen, the plants’ roots can’t absorb the water needed to replenish the supply in plant tissues. As a result, the leaves or needles turn yellow and then brown, a condition often called “winter burn” or “winter kill.”

Dead Leaves May Not Mean The Branch Is Dead

However, don’t rush to prune out branches because they may not really be dead. Plants may exhibit discolored leaves but still have live buds. Once the ground thaws and the shrub can absorb water through its roots, it may recover. One way to tell whether a branch is alive is to gently scratch a small nick in the bark with your thumbnail. If you see a green layer beneath the outer bark, the branch still is alive. Although it may drop its damaged leaves, it will flush new ones in the spring.

If you do have sections of dead branches, you should prune them out. Hollies are very tolerant of being pruned and will often re-sprout even if they are cut to the ground. Many people do not prune their hollies as they like the symmetrical shape they naturally assume. However, they tolerate pruning very well. Wait to prune your holly until it begins to show new growth in the spring. At this point, you can prune out the dead tissue above the new, emerging leaves.

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