OFA Bulletin May/June 2012 : Page 2

OFA Mission Statement To support and advance professional horticulture. OFA – The Association of Horticulture Professionals Grower Plant Nutrition: Sherlock Holmes Style By Brian A. Krug and Claire Collie 2130 Stella Court Columbus, Ohio 43215-1033 USA 614-487-1117 Fax: 614-487-1216 ofa@ofa.org www.ofa.org OFA Bulletin May/June 2012 NUMBER 933 U Editorial Staff Stephen A. Carver, Ph.D. Scott Leyshon Laura Kunkle Editor nderstanding plant nutrition, including identifying nutrient deficiencies on the fly, can be a bit of a mystery to many growers. Identifying the nutrient deficiency is really only a fraction of the mystery; if we can’t identify why our plants have the deficiency, we are bound to experience it again and again. To unravel this mystery we need to put on our plant detective hats and go to work. And I do mean work. It is unrealistic to think that you can just look at a plant sitting on the bench and tell what is going on with it. To become the resident Sherlock Holmes in your greenhouse you need to learn the process of diagnosing the problem. Deficiency Symptoms Contributors Joe Baer Dr. Raymond Cloyd Claire Collie Paul Fisher Lynn P. Griffith, Jr. Charlie Hall Alan Hodges Pablo Jourdan Brian A. Krug Ingram McCall Carol Reese Denise Ryan Bill Swanekamp Angela Treadwell-Palmer Brian Whipker Carrie Wiles Knowing nutrient deficiency symptoms is essential, yet can be one of the largest stumbling blocks. The key is to use the process of elimination rather than recognition. The first step is to look at where the symptoms are first appearing; knowing this can eliminate more than half of your options. If the symptoms appear first on the lower leaves than you are looking at a deficiency of nitrogen (N), phosphorus (P), potassium (K), or magnesium (Mg), otherwise known as the mobile elements. Symptoms first appearing in the middle or the entire plant are caused by the partially mobile elements, sulfur (S), or molybdenum (Mo). Finally, the symptoms you see on the newest growth are caused by calcium (Ca), boron (B), iron (Fe), manganese (Mn), zinc (Zn), or copper (Cu). When breaking it down this way there are still a lot of similarities, so focus on the key difference between the deficiency symptoms. Mastering this concept will help clear up any confusion when it comes to nutrient deficiencies that appear too similar. Keep the big picture in mind because many symptoms associated with nutrient deficiencies can also be caused by a number of other factors. To determine if the problem is caused by a biotic (pest or disease) or an abiotic (nutritional or environmental) pressure look at the pattern of the symptoms. Biotic pressures usually result in symptoms that do not follow a pattern, but have a point of origin. They spread from that point but are not necessarily symmetrical. For example, an infestation of aphids will begin in one location and move outward from there overtaking one plant at a time. Abiotic pressures, on the other hand, do typically follow patterns affecting an entire crop or section of a greenhouse evenly. You can use this concept for crop or the individual plant. Imagine folding a leaf in half – do the symptoms line up on both sides of the leaf? Iron chlorosis will usually be evenly distributed across the leaf, but a lesion from a botrytis infection won’t. Symptoms caused by the lack of nitrogen will show up evenly everywhere a particular injector is delivering (or not delivering) fertilizer. Over-watering can predispose roots to disease and lead to root damage. When the roots become damaged they can no longer take up nutrients, even if the nutrients are present and available in the substrate. Under-watering has obvious results but can have residual effects as well. Water stress affects plant metabolism and can result in the reduction of nutrient uptake, even days after the stress event occurred. In the controlled greenhouse environment in which we work nutrient application is required. Fertilizers can be potentially basic, potentially acidic, or neutral, therefore OFA Bulletin Knowing the Causes of Symptoms Pests & Diseases Published Bimonthly Copyright © OFA 2012. Permission is hereby given to reprint articles appearing in this OFA Bulletin provided the following reference statement appears with the reprinted article: “Reprinted from the OFA Bulletin, (phone: 614-487-1117) May/June 2012, Number 933.” No endorsement is intended for products mentioned in this OFA Bulletin, nor is criticism meant for products not mentioned. The authors and OFA assume no liability resulting from the use of practices printed in this OFA Bulletin. Water Fertilizer 2

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