A pest-free nursery should be the resolve of every grower in the New Year. Start the New Year with a clean nursery and keep pests from being introduced. It is more important than ever now because there is increasing risk that serious invasive pests and diseases can be moved through the nursery trade. Phytophthora ramorum (the cause of Sudden Oak Death) and light brown apple moth (LBAM) are current notable examples that could cause ecological or economic damage and trigger regulatory oversight.
Keeping a nursery clean and preventing introductions of new pests and diseases is often difficult in the complex and fast-paced nursery industry. But here's a short list of things that you could do:
Know the source of propagative material you plant, and insure that the propagator is doing everything possible to provide healthy seed or plants to you. Inspect seed, transplants, or other plants when they are delivered to your nursery or greenhouse. Make sure no diseases or pests are evident. Use your hand lens (See link below).
Pull transplants or other plants out of their containers and look for healthy root tips. Insects such as aphids, thrips or mealybugs hide in young folded leaves or tightly angled stems. There are field test kits to detect Phytophthora and common viruses such as tomato spotted wilt, impatiens necrotic spot and cucumber mosaic. If a pathogen or insect infestation is detected, controlling the problem before you plant in the field is much easier than after the problem is established in the field. “Controlling the problem” sometimes means destroying the plants before they are planted or introduced into a nursery or greenhouse.
Start clean and stay clean in the New Year, and have a Happy New Year!
The first factor in the disease triangle to evaluate is the host plant. Know what a healthy plant looks like-- both its aboveground portions and roots-- so that abnormalities can be recognized. Identify the plant species or cultivars that the unknown disease is occurring on. Look for patterns where abnormalities are occurring. Are there certain species or many species? Are there patterns that could suggest abnormalities caused by abiotic factors such as excesses in temperature, light, fertilizer, or pesticide application?
The second factor is the pathogen. Identifying biotic diseases is sometimes facilitated if the pathogen is visible. Particularly with some fungi, distinctive mycelium and spores can be visible on diseased tissue. Sometimes the pathogen can be seen with the naked eye but sometimes a hand lens can aid in seeing them. Gray mold (Botrytis), powdery mildews, and rusts are good examples of diseases that have distinctive spores and mycelium that are usually quite visible. Often, however, diseased tissue must be cultured in the laboratory to get the pathogen to produce mycelium, spores, or spore-producing structures that could aid identification. A light microscope can help the plant pathologist see and identify the specific pathogen in the laboratory. With viruses or other similar microscopic pathogens an electron microscope is needed to see and identify the pathogen. Sometimes evidence of a secondary fungus, bacteria or insect is visible and not directly related to the primary cause of disease.
The third factor is the environment. The diagnostician can collect information on the environmental conditions associated with the disease. Does irrigation frequency, dew, greenhouse condensation support disease occurrence? Do temperatures support the pathogen? Have temperatures been excessively high or low for plant growth? Have there been excesses applied of fertilizer, soil amendments, or pesticides that have been associated with the occurrence of disease?
References that aid in the diagnostic process are often organized so that they use and describe these three factors. To use these references, you need to first identify the host plant. After host identification, you can often go to a section where the host plant's common diseases are listed. The disease symptoms are described along with a description of the pathogen's mycelium, spores, or spore producing structures. There usually is a description of the specific disease's life cycle and any environmental conditions that support infection and development of a disease. Together, the information helps to focus the diagnostic process and formulate a likely diagnosis of an unknown plant disease.
Next: Suggested references that aid in identifying diseases and pests of ornamental plants.
For a more comprehensive look at the diagnostic process see attachment below:
As you walk quickly down the nursery walkway on the way to the sales team meeting, you glance over at the 1- gallon stock that's almost ready to sell. Then you stop; something is wrong with the Chamaecyparis lawsoniana. Yikes, the older portions of the branches are browning on many plants. So you take a closer look.
Left, what you might see quickly walking by. Looks pretty good!
Left, a closer look, without a hand lens. Something is wrong!
If you are like me, I've got my field hand lenses ready to pull out to take a closer look. I have got a 10 X and a 20 X (magnification) lens. The 10X is the most common magnification used in the field, and sufficient to help see and generally identify most of the common adult insect pests such as aphids, whiteflies, scales, mealybugs, fungus gnats and two-spotted spider mites.
When I see symptoms that appear to be caused by much smaller pests, such as eriophyid or broad mites, I'll pull out my 20X lens and take even a closer look. Sometimes I might see them. The 20 X lens has a very limited field of view, short depth of field, and is crazy hard to hold still. For these pests, and many other tiny immature insect life stages, it is best to take a sample back to the office or lab and use a stereo-microscope (binocular microscope), which works well at higher magnifications (20 X to 40X). But for me the 20X gives me a first look in the field, and may help pinpoint an infested sample to take back for the "scope".
You get the best view with a hand lens by holding it close to the eye. Use whatever hand and eye combination that seems comfortable. (Often right-handers use the right eye). You can keep glasses on if it works for you. Brace your lens holding hand on your cheek to stabilize it. Now with the other hand, move the specimen-- leaf, branch, stem-- to your lens until it is focused. With a 10X lens this will be about 1 inch away from the lens; with a 20X lens, about 1/2 inch away. With the subject in focus, position your body so that ambient light can illuminate the specimen. No hunching over the specimen like it is some big secret or something; let the light in.
Field hand lenses come in various forms and quality. "Hastings triplet" lenses have the best clarity, least distortion, and larger field of views than lower quality lenses. These high quality lenses are only about $35.
And back to the Chamaecyparis lawsoniana. What did the grower see associated with the necrotic branches when viewed with a field hand lens? Surprise, greenhouse thrips. Adults are black with pale wings. This slow-moving species lives in groups, unlike the solitary, fast-moving blackish predatory thrips. Larvae are white or yellow. At the tip of their abdomen they often carry a droplet of dark excrement. (Below. Adult circled in red on left image. Light colored larva and one adult on right image).
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