by Tim Baker, Northwest Region Horticulture Specialist, University of Missouri Extension
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In late February 2009, a commercial greenhouse grower in Harrison County contacted our MU Extension office in Bethany about a problem he was starting to see in his greenhouse. The grower was beginning to lose many plants, and wanted help in finding the cause of the problem and a solution.
Our regional agronomist based in Harrison County, Heather Benedict, visited his farm and took some photos of the problem. She then brought the photos of the plants to a vegetable workshop in Jamesport where several Horticulture Specialists were present.
We looked at the photos and discussed possible causes. The photos looked like the greenhouse had gotten too hot at some point, with many species affected. Excessive heat can cause problems like this, but other causes can produce similar results.
In March, I was visiting Harrison County, and stopped by the grower’s greenhouse. Many species were affected with the disorder, and by this time, plant losses were becoming substantial. When we look at possible causes of a problem like this, one key factor is how many species are affected. As a general rule, if there are many species affected, it is usually not a pathogen, since fungi, viruses and bacteria are typically limited to single plant families. If many species are involved, we look for a non-pathogenic cause, such as chemical injury or excessive cold or heat damage.
The grower indicated that at one point, the greenhouse had indeed been too hot, but he also indicated that there had been no overheating since the plants were first seen by Heather, and yet the losses continued. After taking close-up photos, I sent them to Dr. David Trinklein, MU Greenhouse Specialist in Columbia.
Several possible explanations were discussed, including media problems, fertilizer problems, and water quality. Heather was able to obtain the analysis of a water sample and fax it to Tim and Dr. Trinklein. She also was able to take some plant samples to Columbia for Dr. Trinklein to look at.
The final verdict was that water quality was causing the plant mortality.
Before I go further, let me say that our rural water districts do a great job of providing safe, clean water for us to drink. The problem is that water that is safe for human consumption can occasionally have problems that can be bad for plants.
The grower had indicated that the rural water district where he obtains his greenhouse irrigation water had changed some of the chemistry used to treat the water since he had last used it in his greenhouse in 2008, with good results.
In my next column, I will continue this story, and tell you the happy ending.