By Erik Skindrud, regional editor

A worker sprays staked crape myrtle (Lagerstromia indica) with the petroleum insecticide Spray Oil 415 to repel glassy-winged sharpshooters and other insects. Similar petroleum distillates can be used to shield juvenile trees from insect pests after planting. The trees are sprayed here once every 30 days. Photo courtesy Kevin Naylor, Monrovia Growers

Nursery professionals rely on constantly-evolving tests and treatments to keep their products disease-free. Landscape contractors and others who maintain trees and shrubs can learn from their state-of-the-art practices.

Bringing nursery-grown trees to a job site involves an element of risk?EUR??,,????'??+although the risk is small. The soil clinging to a balled-and-burlapped or boxed tree is an unknown quantity that could contain pests or pathogens. Thanks, however, to increasingly rigorous inspections, almost all ready-to-plant trees and shrubs will be healthy and problem-free.

The degree of confidence that Landscape Contractors enjoy now hasn?EUR??,,????'???t always existed. In past decades, inspections were spotty or nonexistent. More recently, a series of infestations has captured the attention of nursery operators and their partners in county and state agricultural agencies.

In California, at least three nursery-plant-borne infestations have been tracked in recent years. In the early 1990s, the glassy-winged sharpshooter (Homalodisca coagulata) traveled from its native range in the southeast to Southern California?EUR??,,????'??+most likely in nursery shipments. (The insect is a large leafhopper that transmits the disease-causing bacteria Xylella fastidiosa from one plant to another.)

Buyers should inspect trees, shrubs and other plants for signs of infection, stress and damage when they?EUR??,,????'???re delivered to a job site. It also pays to check a nursery?EUR??,,????'???s track record and replacement policy before buying from new farms.

Then, in 1998, state officials discovered a relatively large infestation of Red Imported Fire Ants in Orange County, Calif. that was centered around two commercial nurseries. The ants had apparently hitchhiked to the area in soil and plant shipments from the South?EUR??,,????'??+where the South-American natives are established due to the moister climate.

Most recently, one of the country?EUR??,,????'???s largest nurseries discovered that soil on site was infected with the fungal agent that causes sudden oak death and a blight that affects camellias and other valued plant species. The discovery of the Phytophthora ramorum organism troubled horticultural experts because the same pathogen was recently found in Europe to have jumped from nursery plants to wild, forested stands.

The glassy-wing sharpshooter sucks plant fluids, but causes real damage by carrying and infecting plants with the Xylella fastidiosa bacterium. The bacteria causes oleander leaf scorch, variegated citrus chlorosis and other incurable diseases. Sharpshooter infestation can be brought under control with imidacloprid foliar sprays. Photo: USDA, www.forestryimages.org

Other pests and plant diseases?EUR??,,????'??+like the emerald ash borer, pine bark beetle and others?EUR??,,????'??+are closely monitored in other states and regions.

Industry-leader Monrovia Growers experienced the 2004 phytophthora outbreak at its Azuza, Calif. facility. The vigorous state and federal response underlines the seriousness with which experts take such events?EUR??,,????'??+which have the potential to wreak much wider havoc.

?EUR??,,????'??It?EUR??,,????'???s a huge nursery with thousands of plants that went all over the place,?EUR??,,????'?? explained U.S. Forest Service plant disease expert Susan Frankel at the time. ?EUR??,,????'??Hundreds of nurseries are now going to require inspections. Hundreds of thousands of plants will have to be destroyed. We?EUR??,,????'???re very concerned for the forests of the United States, for the nursery industry and trade.?EUR??,,????'??

A boom sprayer lets a single operator efficiently treat a crop of Wichita blue juniper (Juniperus scopulorum). The spray is a mix of the insecticide Malathion and the miticide Tetrasan, which targets spider mites. Photo courtesy Kevin Naylor, Monrovia Growers

In Dec. 2004, Monrovia moved from its Azuza location to a new, 550-acre facility near Visalia in Tulare County. There the company?EUR??,,????'???s horticulturists work with county and state inspectors to carefully inspect each plant and to follow a list of spraying and treatment procedures.

Kevin Naylor is a professional horticulturist who supervises Monrovia?EUR??,,????'???s Plant Protection Dept. He outlined the many procedures and treatments designed to insure that Monrovia delivers trouble-free products.

And while Monrovia is an industry leader, Naylor said that all growers are subject to the same requirements. It?EUR??,,????'???s always possible that a new pest or problem will crop up, but current practices help ensure that existing issues are taken care of.

?EUR??,,????'??(Phytophthora) changed everything for us,?EUR??,,????'?? Naylor said. ?EUR??,,????'??Ag inspectors are in here daily. They inspect every truck and every plant before they go through. And they?EUR??,,????'???re very thorough.?EUR??,,????'??

This eight-year-old alder (Alnus glutinosa) has been stopped in its track by a strain of phytophthora, the fungal genus that also causes sudden oak death. Providing a tree good drainage is one of the most important ways a contractor can protect a transplant from this fate. Photo: Thomas Jung, www.forestryimages.org

Dealing with the fungus is difficult because it is present in the neighboring St. John?EUR??,,????'???s River. To prevent the spores from infecting stock, the Monrovia crew uses a fungicide called Physan, which is used to disinfect the beds and soil where plants grow. On a regular basis plant samples are collected by county inspectors and sent to a state lab for testing. Monrovia also employs trained scouts who comp through the nursery?EUR??,,????'???s stocks for plants that display symptoms of leaf burn, salt or sun burn.

Workers also spray fungicide directly on root balls when they?EUR??,,????'???re exhumed for shipment. The treatment helps avoid fungal infections that can creep in when roots are cut or injured.

?EUR??,,????'??The symptoms for (sudden oak death) vary, so its important to stay on the lookout for anything that indicates the plant is less than 100 percent healthy,?EUR??,,????'?? Naylor said.

There haven?EUR??,,????'???t been any problems since the nursery moved and implemented the new procedure, but Monrovia has a policy of credit or replacement for any oak, camellia or other plants shown to be infected. Other nursery businesses have similar policies for infected or damaged plants.

Red Imported Fire Ants (seen on the pencil here) are one example of a pest that hitchhiked from one part of the country to another via the nursery plant trade. Inspectors spot most infested shipments, but buyers should always be on the lookout for signs of disease and infestation.

Buyers should always inspect trees, shrubs and other plants for signs of infection, stress and damage when they?EUR??,,????'???re delivered to a job site. Most companies offer hassle-free replacement of unhealthy plants.

In the case of sudden oak death, suspected plants should not be returned to the site of purchase. Instead, buyers should call the company for instructions and information on testing procedures.

?EUR??,,????'??Be careful with the roots. If you start damaging roots you allow secondary pathogens a chance to get in.?EUR??,,????'???EUR??,,????'???Kevin Naylor, Monrovia Growers

Back at Visalia, Naylor and his team keep an eye out for other problems that agricultural authorities want to keep under control. These include the common garden snail (Helix aspersa). The pest (which was introduced from France in the 1850s as escargot) requires its own certificate from inspectors. Naylor?EUR??,,????'???s workers use a bait pesticide sold as Deadline (containing metaldehyde) to keep snails under control.

The fading tree seen here is a tanoak in Monterey County, Calif. that was infected by the Phytophthora ramorum fungal pathogen. Ramorum has also showed up in a California and a Washington nursery where it affected camellias that were shipped across the country. Photo: Joseph O?EUR??,,????'???Brien, USDA, www.forestryimages.org

Another monitored pest is the glassy-winged sharpshooter leafhopper, which transmits a bacteria that can result in oleander leaf scorch, citrus chlorosis, plum leaf scald and other plant infections. Control of the insect vector is especially important as there is no known cure for these plant diseases. To keep tabs on the bug, inspectors have placed close to 800 sticky traps across Monrovia?EUR??,,????'???s nursery site.

Yet another problem monitored at the site is cottony cushion scale, an insect pest that infests citrus, cocculus, nandina, pittosporum and other species. Interestingly, the scale is well-controlled by a natural enemy that was introduced from Australia in the 1890s. At that time, California?EUR??,,????'???s growing citrus industry was saved from destruction by the vedalia beetle (Rodolia cardinalis), a lady beetle whose larvae chews its way into the scales?EUR??,,????'??? egg sacs.

This tree was damaged by careless treatment during transport and planting (note scrapes and breaks). The tree has been guyed and girdled to support it through transport shock. Photo: Fred Baker, Utah State University, www.forestryimages.org

Finally, it?EUR??,,????'???s important to remember that moving and replanting trees and shrubs stresses them and leaves them vulnerable to local and preexisting pathogens. Be sure to follow the tried-and-true replanting rules for best results.

Other species and strains of phytophthora (than the one responsible for sudden oak death) are opportunistic, taking advantage of plants stressed by transplanting. Creating good drainage is key to avoiding the wet soil around roots that leads to fungus growth.

?EUR??,,????'??The most important thing is planting depth,?EUR??,,????'?? Naylor explained about transplanting. ?EUR??,,????'??You don?EUR??,,????'???t want the crown level below the soil line. You want water to slope away so there?EUR??,,????'???s no standing water.

?EUR??,,????'??And be careful with the roots. If you start damaging roots you allow secondary pathogens a chance to get in.?EUR??,,????'??

A Monrovia Growers worker treats Hollywood juniper (Juniperus chinensis) with the fungicide Subdue Maxx, which targets pythium and phytophthera molds. Fungicides are sometimes applied directly to exposed roots during transplanting to prevent root rot. Photo courtesy Kevin Naylor, Monrovia Growers