Spring 2015: Three unusual diagnoses
Regional Report San Diego and Riverside Counties by James A. Bethke
I’m sure you’ve heard of the “bad things always come in threes” rule. Seems like every time a famous actor or actress dies, everyone starts looking for two other celebrity deaths to keep this superstition alive. If you search the Internet, you will find lots of information related to this popular belief and the general subject of things that occur in threes, such as the blog “45 wonderful things that come in threes,” written in honor of the publishing date (12/12/12) with the same number repeated thrice. In this short article, I want to provide you with my own version of occurrences in threes with three recent stories about plant damage diagnoses that emphasize the need and the importance for good observation skills, good diagnostic tools and good resources.
First, my favorite story begins with my son. We live in a rural area with a large backyard where he likes to shoot his airsoft rifle at paper targets and cans. Watching my son has taught me a lot about airsoft, and I obviously have had to clean up thousands of pellets from our patio and landscape. Keep this in mind as a preface to this ornamental plant production problem that I diagnosed in San Diego County.
I received a call from a bird-of-paradise cut flower grower who lives in a rural area, and he grows many of his plants along his lengthy driveway. He called about what he thought were “big insect eggs” embedded in the plant stalks and leaf petioles. I asked if he would send me a digital photo because I can usually identify things like that relatively easily. Sure enough, I saw what indeed looked like white eggs laid in rows up the plant from the base to the top of the petioles in the photo he sent me. However, my experience with my son taught me better. The objects that looked like eggs shoved into the tissues were actually airsoft pellets, which had penetrated the stringy, vertical plant tissues and spread them open side to side. After discussing this with the grower, he confirmed that the pests in question were Homo sapiens Linnaeus, the neighborhood children, not big insects.
The second story is about a grower who was concerned that he had a disease on his young queen palms. Many of the palm leaves were bent in half, near the middle of the leaf, and did not fully unfold. He thought it was a disease because he couldn’t see a living organism there, even with a hand lens. No matter what he did to change the environmental conditions or what he sprayed, he couldn’t solve the problem. I made a visit to his facility and collected leaves which I viewed with one of our microscopes under high magnification (in my experience, all growers would benefit from owning a dissecting microscope). And voilà, there they were: eriophyid mites deep in the folds of the leaf tissue.
Lastly, I visited a grower with an annual problem on agave that was previously diagnosed as edema (editors’ note: see "Science to the Grower"). The agave plants were abnormal looking and had spots on the foliage that were relatively small (about 1/8-inch pits in the leaf tissues), but this aesthetic damage would still reduce the value of the crop. The spots would turn necrotic, and the damaged tissue was not uniform, as you would expect if caused by an insect or disease. The size of necrotic tissue was variable, with some plants having long, thin stretches of old scar-like tissue.
My first question was, “How long were the plants in this area of the nursery?” The answer was the plants had been there a couple of months because they were moved from the greenhouse to outdoors to acclimatize them before going to market. That was the first clue. My second clue was determining that the nursery was located at one of the higher elevations in the area, and a couple of months ago had experienced an afternoon of snow and hail. The grower thought nothing of it because the inclement weather only lasted a short time, and apparently this happens almost annually at this elevation. My diagnosis was that cold, snow or hail killed small areas of epidermal cells, which eventually turned necrotic or scarred over time. Similar snow and cold damage can be observed on schefflera in fig.1. Keeping the agave in the greenhouses longer and not exposing them to the cold conditions would solve the problem.
Fig. 1. Snow and cold damage to schefflera that appeared well after the weather event. Photo: J. Bethke.
To summarize, the first problem described above was physical damage caused by humans, the second was caused by microscopic organisms, and the third had an abiotic cause. Each incident indicates that good investigation, experience and proper tools are needed in the diagnosis of plant problems. Additional training through the use of visual aids or by hands-on trainings and workshops will make diagnosing plant damage much easier and less stressful. Take advantage of the latest technologies, such as new apps for your smart phone or other digital devices. This is especially helpful if you are in the field and observe an organism that you might be able to immediately confirm through Internet images. Additionally, take a digital photo and send it to your local Cooperative Extension advisor who might be able to help identify a problem immediately and save a lot of time.
To diagnose a problem in ornamental plant production, the diagnostician must have very good observation skills and also be a good detective. Several important steps are necessary in the diagnosis process. First, know what is normal or recognize when plants appear healthy. Second, identify characteristic symptoms and determine if they have a distinct pattern or are erratic and without pattern. Next, review the cultural practices and growing environment, looking for abiotic causal agents (water, light, temperature) or recent environmental changes. Finally, it is really important to document individual events for future use and experience.
James A. Bethke
Farm Advisor, Nurseries and Floriculture
UC Cooperative Extension San Diego, North County Office
151 E. Carmel St., San Marcos, CA 92078
(760) 752-4715 phone; (760) 752-4725 fax