Inspecting Incoming Plant Materials

February 10, 2014

As growers ramp up their production facilities this spring, many of them understand the importance of starting with clean production facilities. However, several growers do not exercise this same philosophy when it comes to their starting materials. How many times have growers planted suspicious starting materials only to fight with various battles and losses throughout the entire crop?

Many of the insect and disease problems growers experience can be traced back to the starting materials. This does not always imply that the source of the starter plants is not doing a good job controlling pests and diseases prior to distributing these products.  In many instances, pest and disease levels are suppressed, but not completely eradicated, leaving a small chance for them to shipped to growers. 

A great deal of potential problems can be prevented by inspecting plant materials before they are moved into the production facilities. This step is the most important method of preventing problems from developing. All new plant materials, such as unrooted cuttings, plugs, liners, and newly transplanted containers entering the production site should be free of any insects or diseases. Upon receipt and prior to transplanting, look over the entire plant to determine its general health and condition as well as observe for signs of pests and diseases.
When observing the top growth determine if the plants appear healthy. Do the leaves have a good coloration? Are new leaves expanding? If not, determine whether the symptoms resemble nutrient disorders or if a greater underlying problem such as root rot exists.

Look at several of the root systems to determine their overall health. For most plants, the roots should appear white or at the very least have white tips. The presence of brown, decayed or mushy roots may indicate root pathogens may be present or the plants have recently become injured due to stresses such as over watering, drought conditions, or high soluble salt levels. Swellings on the roots could be caused by root knot nematodes.

Examine the plants for the presence of insect pests or spider mites. Aphids and thrips are commonly found near the growing points of the plants; tapping the plant foliage over a sheet of white paper will often dislodge these pests and help to detect their presence. Observe under the leaves for the presence of spider mites or whiteflies. Stippled, speckled or mottled leaves is an indication of thrips or spider mite feeding. 

Observe the foliage for the presence of plant pathogens. Do the leaves have circular, angular, or irregularly shaped purple, tan or brown spots on them? If so, these spots could indicate the presence of fungal or bacterial infections. If there is white fluffy growth on the leaf surfaces, the fungal pathogens powdery mildew (usually on the upper leaf surfaces) or downy mildew (found on the undersides of leaves) may be present.  

Plant viruses can be difficult to identify as they often resemble other problems such as nutrient disorders, herbicide injury and fungal diseases. Virus symptoms range widely but commonly cause abnormal dark green and light green mosiac and mottling of the leaves, necrotic spots, bumps on the foliage, distortion, and stunting.

The presence of the symptoms described above or the occurrence of actual insect or mite pests on incoming plant materials could led to future production issues on these or adjacent crops. If you are unsure of whether a problem is present, submit samples to a diagnostic clinic for proper identification of the potential issue.

If there is isolated evidence of pests or diseases, these starting materials can often be kept and treated in an isolated area; hold and treat the plants in this area as needed until you are sure they are pest and disease free. Do not accept and transplant shipments with serious pest or disease issues.

Paul Pilon

Perennial Solutions Consulting

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Last Update Jun 27, 2018