Recognizing disease symptoms of greenhouse ornamentals

Successful disease management begins prior to the start of each crop. One of the most critical pieces of information needed is to know which diseases are likely to infect the crop you’re growing. As simple as that sounds, it can also be one of the most challenging tasks.

With the introduction of so many new plant materials into the ornamentals trade each year, the susceptibility of many of these plants to disease isn’t necessarily known. But by and large, these new plant materials are also susceptible to the same plant pathogens that have frustrated greenhouse growers for decades. You may not always know which diseases will infect a new plant or cultivar you’re growing for the first time.

Familiarizing yourself with the general symptoms of several common and economically damaging diseases will allow you to more quickly and accurately recognize these diseases on any crop should they occur.

However, symptom recognition and early detection are still not enough to effectively manage diseases. Prevention is paramount.

Environmental conditions
Understanding the environmental conditions that favor infection and disease development is extremely important. Most pathogens have a preferred temperature and humidity range to multiply and infect new plants. As a result, the environment can either greatly slow the spread of pathogens or contribute to an epidemic in a short period of time.

Knowing where in the production system a pathogen may be introduced will allow you to modify growing practices to help minimize your risk. For example, many of the most damaging diseases on greenhouse crops are caused by soil-borne pathogens. It is not uncommon to find some of these pathogens lurking on soil debris clinging to old pots and trays or on the top of and below benches. As a result, careful sanitation measures can go a long way to prevent the introduction of a pathogen into the next crop.

The table below was designed to help familiarize you with some of the most common disease problems of greenhouse ornamental crops, the characteristic symptoms these pathogens cause on host plants, the conditions that favor disease development and general management guidelines. While the table should not be used as a substitute for a laboratory diagnosis, it can be used to help you develop a scouting and disease management plan for your growing facility.

Click here to view the Disease Management Chart.

Colleen Warfield is corporate plant pathologist for Ball Horticultural Co., (630) 588-3290; cwarfield@ballhort.com; www.ballhort.com.