A Growers Guide to Producing Poinsettias:
Dr. Don C. Wilkerson, Professor of Horticulture
Texas A&M University System
College Station, Texas
Over the years poinsettia varieties and production practices have changed but many of the problems remain the same. We hope you will enjoy this reprinted article from the September, 1994 issue of the Texas Greenhouse Bulletin.
Symptom - Leaves appear to be crinkled, having the texture of alligator skin. Also, leaves drawn up at the mid vein inhibiting leaf expansion. Leaves may be unusually shaped with no apparent damage or injury to the margins.
This physiological problem typically occurs during the first 4-5 weeks of production. Although researchers are currently suggesting that calcium may have some role in the problem, there is still no clear-cut reason for why leaf distortion occurs. In most cases plants will out grow this problem and no treatment is recommended. In fact, foliar applications of calcium or other nutrients may cause secondary leaf injury.
Symptom - Leaves have a very distinctive interveinal chlorosis., typically occurring on the older leaves but new growth turns chlorotic quickly as leaves expand.
Manganese deficiencies are very common under warmer growing conditions, usually developing 6-8 weeks into the crop. Since most mixes contain limited supplies of magnesium, it is frequently leached out during the early part of the season as the result of frequent irrigation. Also, many fertility regimes do not include magnesium as a principal component. Once leaves develop the interveinal chlorosis it is impossible to green them back up. Supplemental applications of magnesium sulfate will help prevent this problem.
Symptom - Leaves develop a marginal chlorosis, usually occurring on the older leaves first and progressing to newer growth as the condition gets worse.
Poinsettias have an unusually high requirement for molybedenum and deficiencies can develop during the period of vegetative growth. Most fertility regimes designed for poinsettias include supplemental molybedenum. However, if this micronutrient is not present in sufficient quantities, the distinctive marginal chlorosis can occur.
Symptom - Leaves turn chlorotic, burn around the margins and may drop off the plant under severe conditions.
When applied incorrectly, Cycocel can cause injury to poinsettias. To avoid this problem be sure plants are thoroughly irrigated prior to application. Also, avoid applying Cycocel under high temperature conditions or when plants are under stress.
Symptom - Upper leaves or bracts appear to have a mottled green coloration.
As poinsettias begin to develop coloration in the upper leaves or bracts there is a distinctive breakdown of chlorophyll (green pigment). This natural change in color is often mistaken for some type of nutritional deficiency, phytotoxicity, or other foliar problem. Growers are cautioned against over reacting to this condition and making some type of potentially harmful chemical/fertilizer application.
Symptom - Can appear as gray colored fungal spores on leaf and bract surface. Can also causea water- soaked appearance on leaves and bracts.
Botrytis usually occurs towards the end of the crop on the soft bracts. Low light and high humidity favor the development of the disease. Any type of physical damage to bracts will typically lead to infection. Frequently, if poinsettias are fertilized heavily towards the end of the cropping cycle, a salt injury or bract burn will occur. This is perhaps the most frequent pre-disposing condition for the establishment of Botrytis in poinsettias.
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