Plant disease in interiorscapes: What to look for and what to do about it
By Phil Harmon

While shoppers rush around malls, interiorscapes of bromeliads, ficus and other plants make spirits bright. Instal-lation and care of these interiorscapes happens behind the scenes as if by elves, but we know it’s due to the hard work and diligence of horticultural and pest management professionals. Maintaining the health of an interiorscape is not entirely different from maintaining the health of plants outdoors with a few key exceptions.

PREVENTION
Pesticide options for interiorscapes are very limited, placing even more importance on disease prevention. Prevention efforts start by excluding pathogens. You can do this by selecting healthy plants free of disease. Look for a nice white root system and foliage unmarred by disease or pests. Purchase your plants from reputable distributors and take the time to learn the symptoms and signs of the most common ailments for each species you commonly work with. Be aware that some plant diseases result in chronic and not-always-obvious symptoms such as stunting, yellowing, reduced vigor etc.

Plant pathogens don’t just come in on the plants though. They can be introduced into an interiorscape in growing media and on dirty containers as well. If native soil is to be used, consider pasteurization or sterilization as a way to eliminate pathogens and pests. Use clean, new growing media and containers to get your plants off to a good start. Several options are available to sanitize growing containers, including soaks in dilute bleach solutions, heat treatment, and various commercially available products. The length of time needed to kill pathogens is proportional to the amount of organic matter left on the containers, so a good rinse to remove excess media is a good start.

CULTURAL REQUIREMENTS
Pathogens tend to end-up “finding” our plants from time to time despite our best efforts. When a plant is challenged with a pathogen, the overall health and vigor of the plant can greatly influence whether or not the pathogen will successfully infect and to what extent disease will develop. This is why it’s important to know the cultural requirements of your plant investments. Plants with low light requirements and a reputation for being pest and disease-free are a good place to start when selecting for an interiorscape. Carefully consider the environment and choose plants as best suited to that environment as possible. This makes horticultural management decisions easier and more likely to result in healthy vigorous plants.
Fertilization and irrigation schedules are two important factors. Salt build-up due to over-fertilization can predispose plants to root rot pathogens. Slow-release fertilizers suited for your planting can encourage root development and reduce the need for frequent applications. Irrigation schedules need to provide adequate moisture without prolonging root zone saturation. Containers should have drainage and catchment mechanisms to draw away and hold excess water so the roots will not be in saturated soil for long periods of time, as these conditions favor some common root rotting pathogens. Repotting plants in larger containers with new growing media from time to time will help maintain a healthy soil environment and will give roots room to grow.

MONITORING
Prevention may be the key, but from time to time, disease happens. Monitoring for problems can help us identify diseases early and allow us to take action before excessive losses occur. Symptoms of disease often are identical to symptoms caused by abiotic disorders not due to path-ogens. For example, wilting is a common symptom that can be caused by root disease, drought stress, and excessive soil salinity. The majority of problems in interiorscapes turn out to be abiotic disorders. Rule these potential causes out first by checking and adjusting horticultural practices. If disease is still suspected, send plant samples to a diagnostic clinic for confirmation. Once a root rotting pathogen is established in an interiorscape, options are limited. Removal of affected plants and media may be necessary. Check and correct any irrigation and drainage issues and replace symptomatic plants, using new media and clean containers. For high-value specimens, you may want to remove the plant to a greenhouse where some fungicide treatments can be applied.

Foliar diseases can largely be managed by avoiding prolonged periods while leaves are wet and relative humidity is high. For some diseases, foliar symptoms may be pruned out and discarded. Sanitizing pruning shears between plants and cuts will help ensure you don’t unintentionally spread the pathogen. Treatment options are limited in the interiorscape, so high value plants may need to be removed to a greenhouse for fungicide treatment.

It is important to remember that ornamentals in interiorscapes are distinguished from other ornamental plantings on fungicide labels. In order to use a product indoors, interiorscapes must be listed as an acceptable use on the label. For example, see the product labels for Compass by Bayer (labeled for various foliar fungal diseases), Fungo Flo by Scotts (labeled for Rhizoctonia and Thielaviopsis diseases), or Subdue Maxx by Syngenta (labeled for Pythium and Phytophthora root rot diseases) as examples of fungicide products labeled for use in interiorscapes. Always read and follow all
label instructions.