Heavy Rains Causing Growers Grief (June 2010)

Submitted by Dr. M. Mirza

Heavy rain in many parts of Alberta has filled up the dugouts and ponds which many greenhouses use for irrigation of crops. The water runoff takes place from a large catchment area. Herbicides can leach out of soil and end up in the dugout. A grower made the observation that top growth of his tomato crop showed curled leaves and all plants were showing such symptoms. Look at the pictures below:

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The tomatoes above show the symptoms of leaf curling, distortion, shoe stringing and below is mini-cucumbers showing the leaf curling symptoms.

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The symptoms were first noticed on tomatoes and later on mini-cucumbers with some slight evidence of peppers. This sequence of symptoms shows that tomatoes are more sensitive to herbicides that cucumbers and peppers. The grower made the connection to the presence of herbicides in water right away based on the information which we have been providing at the workshops and conferences. Charcoal filtration system was available in this greenhouse and immediately water supply was passing through this system. It is interesting to note that charcoal system was in place but was not being used for the past few years. There were many questions needing answer in making decisions to install these charcoal filters and saving the crop.Is the herbicide coming with water or could it have been a spray drift? Since all the plants were showing the symptoms so it is due to the presence of herbicides in water.

  • What type of herbicide may be involved? The symptoms appear to that of a category of herbicides called "phenoxy" type. It could be 2,4-D, dicamba or picloram. When I looked at the plants, my diagnosis was that symptoms are more typical of picloram. This herbicide is long lasting, meaning that it could stay in water for several years and can settle in the soil. So if water is pumped close to the bottom then the concentration of herbicide may be higher.
  • How do I confirm the presence of this herbicide? The water sample can be sent to a laboratory for analysis. I always suggest that ask for clean bottles from the lab. And then write instructions to condense 4L of water to 1L and then analyze for herbicides. That is what a plant does, that is it evaporates water from leaves and retains the chemical in its cells until it reaches a level to trigger symptoms. My guess is that the level of picloram is around 0.1-0.05 parts per billion (ppb)
  • How do I know when to change the charcoal in filters? The best approach is to set up a bioassay using lentils, faba beans or tomatoes. Simply grow lentils in perlite, rockwool of another growing medium with and without contaminated water. Check out other Grower Alerts on www.agga.ca from previous years. You will find more detailed information on setting up bioassays.

I think in this case grower was alert and used his knowledge of make quick decisions and I am sure the crop should recover. Further information contact This email address is being protected from spambots. You need JavaScript enabled to view it.