Growing poinsettias in Texas is a challenge. Our environmental conditions create a truly unique set of problems that must be overcome to produce a high quality product. Although there are a number of things that can go wrong from now until December 25, there are a few of these that seem to reoccur each year. The following is a brief discussion of six of the most common disorders on Texas poinsettias.By no means does this cover all of the poinsettia disorders that growers must deal with.
Magnesium Deficiencies – In most fertility programs for poinsettias, the only magnesium (Mg) source is dolomitic lime. After continued leaching during the growing season, the supply of Mg in the medium may be depleted. Typical Mg deficiency symptoms generally appear as an interveinal chlorosis. Supplemental Mg may be applied to the medium as epsom salts at a rate of 24 ounces/100 gallons of water.
Molybdenum Deficiencies – Molybdenum (Mo) is the most commonly deficient micronutrient in poinsettia nutrition. Typical symptoms of Mo deficiency appear as a yellowing of the leaf margin, progressing to marginal leaf burn. Supplemental Mo is generally applied to poinsettias as a component of the fertility regime. One pound of ammonium molybdate is dissolved in 5 gallons of water to make a Mo stock solution. One to 1 1/2 fluid ounces of stock solution/1000 gallons water is then added to the fertilizer solution.
Crud – This physiological disorder occurs when excessively high turgor pressure in the plant causes latex to exude from cells in the stems and petioles. After drying, these deposits may result in stunting and distortion. The latex is also anexcellent medium for sooty mold. The best way to avoid this problem is by maintaining night temperatures below 75o -80o and reduce excessive wetting of the growing medium.
Leaf Crinkle and Distortion – This problem often occurs in the early stages of a poinsettia crop. Leaves appear to have an extremely rough texture often compared to alligator skin. In severe cases, leaves become extremely misshapen. Although the cause for this disorder is still unclear, it is thought that rapid changes in humidity (i.e., when vent fans come on in early morning) causes salts to accumulate along leaf margins and veins. As cells in these areas become injured their growth is impaired and leaf growth is distorted. Most poinsettias will outgrow this condition.
Cycocel Burn – Cycocel is the most commonly used chemical growth regulator for poinsettias. When used properly, this material can effectively control stem elongation. However, applied when greenhouse temperatures are greater than 80oF can result in a foliar burn. To avoid this problem, apply Cycocel during the cool parts of the day and only when plants are well irrigated.
Color Change – When poinsettias begin to change from green to red, white, or pink, they often go through a stage of mottled chlorosis. This is a natural process and not a disorder. However, many growers “panic” and try to correct the yellowing with supplemental application of fertilizers, fungicides or other materials. Patience is the key at this stage of growth. Remember, the cure can often be worse than the ailment.