The unseasonably long and unrelenting cold weather this past year has turned into a cool, wet spring for many parts of the country. As a result, the horticulture industry is experiencing a delay in insect and disease pressure by approximately three to four weeks.
In some cases, swings between freezing and warm temperatures during the early spring helped reduce insect populations –- as the warm weather may have caused eggs to hatch, the freezing cycle reduced those populations.
The excessive moisture in April and May that some regions of the United States received helped spread the spores that cause many disease problems. As such, once we settle into more normal weather patterns, superintendents and their technical partners will need to be diligent in guarding their properties’ perennial landscape plantings against a potential myriad of problems.
Common problems due to a cool, wet spring
Scales (various species)
Regardless of region, late spring to early summer is the time to watch for scale insects, specifically immature stages and young scale crawlers that are actively searching for new places to feed and establish new populations.
Most scales overwinter as eggs or as adult females. In the spring, young scale crawlers emerge and are dispersed by wind to new plants or migrate with their small legs to new tender areas on the plants, where they insert their mouthparts, begin feeding on the plant juices and no longer move. As the scale insects mature, they become more difficult to control. If left undetected and untreated, populations can quickly build, causing a noticeable decline in the landscape plantings.
There are many different types of armored and soft scale insects that cause problems in our landscape plantings. The body of an armored scale is protected by a hard, waxy covering made from wax that is secreted by the insect and cast skins of previous growth stages.
Depending on the species, scale covers can vary in size and shape from circular to elongate, sometimes resembling an oyster shell. Male and female covers will also vary in shape and size, with male coverings being more elongate and slightly smaller than the females.
A needle or probe can be used to remove the cover off the scale revealing a pink, orange or yellow bodied insect. Most females produce eggs under their covers, which are protected from predators and from topical sprays.
Depending upon the species, both the armored scale and soft scale females can lay eggs or give birth to live young. Some examples of armored scale include Euonymus Scale, Magnolia White Scale, Pit Scale, Lobate Lac
Scale and White Peach Scale
| OTHER INSECTS & DISEASES TO LOOK FOR IN 2009 |
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Following is a brief list of other predominant insect and disease pressures for landscape ornamentals, as well as detection methods. Detailed recommendations for detection and treatment of numerous insects and diseases are available in the Syngenta Guide to Protecting Woody Ornamentals. Superintendents can get a free copy by calling 800-395-8873 or at www.greencastonline.com/woodyshrubguide.pdf. Azalea Lace Bug and Southern Red Mite (insects) Aphids (insect) Leaf-feeding Beetle (insect) Powdery Mildew (disease) Downy Mildew (disease) |
Soft scales differ from armored scales in that they do not secret a thick, waxy covering that is separate from the insect body. Most soft scales produce a thin, glassy wax layer that adheres tightly to the insect’s body and cannot be separated from it. Depending upon the species, the size and shape of the body can also vary from round to oval, with a hemispherical or convex profile.
Another notable difference between the two types of scale insects is that unlike armored scales, soft scales produce honey-dew. This sugary, sticky substance is secreted by the soft scale and sticks to the leaves and stems of the plants, leaving a shiny residue. It is also a good substrate for the sooty mold fungus, which over time, will grow over the top leaving the plant with a dark and dirty appearance.
Some examples of soft scale that can be problematic in the landscape include Wax Scale, Tessellated Scale, Cottony Cushion Scale and Hemispherical Scale.
While many scale insects feed on leaves, young stems and branches, there are some, such as the White Peach Scale, that will infest trunks and large branches of trees such as Maple, Lilac and Privet. Severe infestations can cause plants to lose vigor and some branches.
Scale feeding damage on foliage will appear as small, yellow spots directly under the area of the insect. As the population builds, entire leaves may turn chlorotic and defoliate. Small stems and branches may become so heavily encrusted with scale that the entire branch may die.
Plants on golf properties to scout closely for scale include Azalea, Crotons, Holly, Ixora, Gardenia, Euonymus, Eleagnus, Camellia, Pachysandra, Oleander, Peony, Pittosporum and Magnolia.
Early detection of scale insects can be difficult due to their small size, coloring and outer covering, which sometimes enables them to blend in well with the plant parts. Often, it is not until the visible signs of feeding damage are evident that we realize we have a problem. Since many scale species have two to three generations per year, and each female scale is capable of producing 50+ offspring, populations can develop to high levels.
Scales are more difficult to control as they mature and develop their protective waxy cover, so early detection is key. Apply topical applications of an approved insecticide or horticultural oil in the spring and early summer to target early nymphal stages. Follow up with a systemic insecticide as a foliar spray or as a soil drench or granular treatment to the root zone for longer residual control.
Fire Blight (Erwina amylovora)
On the disease front, those regions that experienced a wet spring may see more cases of fire blight in the landscape. Superintendents will normally see activity of this destructive disease once daytime temperatures are consistently in the upper 60s or warmer.
Caused by the bacterial agent Erwinia amylovova, wind-driven rain can cause this bacteria to infect susceptible flowering and fruit-bearing shrubs and trees such as Photinia, Indian Hawthorn/Hawthorn, Crabapple, Lilac, Pyracantha, Cotoneaster and Spirea; causing affected flowers to appear water-soaked and darkened.
Tender new growth is also susceptible to infection and may appear scorched, shrunken and curl downward. This tell-tale sign of infection is often referred to as a “shepherd’s crook”. Infections can also cause cankers on young twigs and branches, which enables the bacteria to overwinter to the next growing season.
Fire blight is best treated by pruning out infected plant stems and branches, cutting back into clean wood. When doing this make sure to disinfect pruning tools between uses as this disease is easily spread by the sap and “ooze” from infected cankers.
Fire blight can only be managed preventively. Apply a protective spray of a copper-based product like copper sulfate or a bactericide containing streptomycin before bud break or when environmental conditions are conducive to infection. Juniper Canker (Botryophaeria & Seiridium spp.) and Juniper Tip Blight (Phomopsis juniperivora and Kabatina juniperi)
Though a popular landscaping option due to their low maintenance and high drought tolerance, junipers are prone to several different diseases, particularly during wet and humid weather. Considering the somewhat unseasonable spring weather thus far in 2009, it’s possible that canker and tip blights will be the primary problems superintendents may notice on their courses or surrounding properties.
Juniper cankers form on twigs, branches and main stems. The lens-shaped cankers become sunken and sometimes cracked, with healthy tissue surrounding it. Scattered black pustules can develop at the infection site, which contain spores that will initiate new infections.
A sticky resin may exude from active lesions. The tell-tale sign is dead foliage, though a severe infection can kill an entire plant. Cutting into the stem and removing the outer bark will reveal dark brown decayed tissue.
Cankers tend to be associated with stress due to winter damage, drought and other environmental factors. The disease can easily be dispersed to other junipers by splashing water. Though we can’t control the weather, excessive rainfall will hasten the disease and new infections. Remove any dead and infected plant parts with sterilized pruning tools (and re-sterilize after use) and make sure to cut into clean wood. There are no chemical control measures for canker.
Kabatina tip blight is the first problem to show up in early spring on the previous year’s growth. The terminal ends of infected branches turn dull green, then reddish brown and become desiccated. Small black fruiting bodies can be seen at the base of the infected and discolored branch tissue. In comparison, Phomopsis tip blight affects new growth as the young shoots are more susceptible to infection.
In the spring, infection occurs from conidia (fungus spores) released from fruiting bodies on shoots or twigs killed the previous year. Late-season infections are caused from conidia formed in the spring on infected tissue.
Once infected, new shoots will turn a light green-yellow then fade to a reddish-brown. A gray-colored band develops at the base of the infected shoot, which marks the infection site. Dead shoots will remain on the plant for several months, eventually turning gray. Tip blight can sometimes grow into stems and cause cankers.
Like canker, tip blight is best controlled by avoiding overhead irrigation or water splashing from irrigation systems. Remove infected and dying branch tips with clean tools and make sure to cut into clean wood. Application of certain fungicides in the spring and early summer will help provide protection against these tip blighting pathogens. Consult the fungicide product label for specific instructions regarding control of various diseases.
Leaf Spotting Diseases (Anthracnose, Cercospora, Alternaria)
Spring and early summer is the time when leaf-spotting pathogens become active. Overwintering on fallen leaf debris and lesions on persistent leaves and stems, wind-splashed rain and irrigation help move viable spores to tender new tissue. Once the weather becomes warmer and more humid, leaf-spotting diseases can explode, detracting from the plant’s attractive appearance. This is the best time to review which hosts are susceptible and have a management plan in place.
Two popular plants in the landscape that are prone to various leaf-spotting diseases are Hydrangea and Holly. On Hydrangea, infections by Colletotrichum (Anthracnose), Alternaria sp. and Cercospora sp. generally start to appear in late spring/early summer and can be troublesome. Severe infections can cause spots to coalesce and leaves may drop prematurely.
Other landscape plants to watch closely for leaf-spotting diseases include: Azalea, Euonymus, Nandina (Anthracnose), Hawthorn, Indian Hawthorn, Photinia (Entomosporium), Itea (Phyllosticta), Ligustrum (Cercospora), Rose (Diplocarpon- Blackspot) and Pittosporum (Alternaria,Cercospora).
To help avoid problems from leaf-spotting diseases, remove fallen leaf debris around the base of the plants, avoid wetting the foliage with irrigation water, use drip irrigation if possible and protect new growth by making periodic applications of an approved fungicide. Applications in the late spring and early summer can help protect plants and avoid severe disease problems from developing later in the summer.
Rust (Puccinia)
Rust diseases are common fungal infections that affect a wide range of landscape ornamental plants. Rust fungi are opportunistic parasites, dependent upon a live host for growth and development that reduce plant health and vigor, flower production and aesthetic value in the landscape.
The good news is that rust rarely kills plants. The bad news is that the excessive moisture this spring means that it may be a problem superintendents will see this summer.
Rust often first appears as small, pale yellow spots on the upper surfaces of leaves. All rust fungi produce powdery masses of spores in pustules, typically on the undersides of leaves that are yellow, orange, purple, black or brown. Some rust fungi produce pustules on upper leaf surfaces as well.
Spores are easily spread via air or with splashing water. Lesions may form together, resulting in large areas of dead tissue; leaf distortion and defoliation often follows. Landscape plants susceptible to rust include Hawthorns, Rose, Elaeagnus, Poplar and many perennials such as Asters, Canna, Dianthus, Daylily, Hollyhock, Hypericum and Iris.
Prevention and control methods for rust include spacing plants appropriately to allow for good air circulation and rapid drying of the foliage. During installation of landscape ornamentals, avoid planting the same species in locations where rust has been a problem. Contact and systemic fungicides may help to reduce or prevent rust on those susceptible plant species.
Looking toward summer, it’s a safe bet that superintendents will be busy scouting and tending to disease and insect problems that develop in landscapes.
Nancy Rechcigl is technical manager for Syngenta Professional Products.
