Poinsettia leaves were submitted to the UMass Extension Plant Diagnostic Lab this past week. The leaves sported tan lesions with brown borders and yellow halos. Some of the lesions were slightly puckered and resembled insect galls. The lesions extended through the leaf tissue and some exuded milky sap (called latex), most often on the undersides. No bacteria, fungi, or evidence of insects were observed under the microscope, nor did the symptoms resemble those caused by common viruses. Based on these observations, the diagnosis was latex eruption- also known in the industry as “poinsettia crud.”
Latex eruption on poinsettias occurs when the environment in the greenhouse is cool and overly humid. It is a physiological condition something like edema and is believed to be caused by excessive turgor pressure in the plant. In addition to the symptoms described above, leaf distortion may also occur.
Management involves avoidance of overwatering and ventilating to reduce humidity in the greenhouse. Humid nights are especially conducive to this condition. Maintain nighttime temperatures below 75-80°F. Affected leaves may yellow and drop, but new foliage should be unaffected.
Report by Angela Madeiras