E-Letter 3

Ecke Ranch Tech Help Email Message: October 2002

October is here and crops should be actively growing. There have not been reports of major problems with the crop, so the focus now is to start toning the plants as they develop and begin to show color. Also, October is the month to anticipate crop needs and prevent nutritional problems, internode stretch, pests and diseases or other issues that risk damage to plants.

Monitor the nutritional status of crops through soil and tissue analysis, paying close attention to the balance and availability of all major and minor elements. During October we anticipate minor element deficiencies if the pH is allowed to rise above 6.5 or if adequate supply of the nutrients is not provided. Symptoms of minor element deficiency are observed in the youngest leaves and bracts and usually include lack of normal expansion as well as interveinal and marginal chlorosis (yellowing) of affected leaves. It has become common practice to apply STEM or other similar trace element mixes on a monthly basis to supplement the standard fertilizer regime.

Shoots should be growing with normal internode space. The first line of defense for stretch is the use of cultural practices (spacing, drying of soil, drop of morning temperature, etc.) to control height of poinsettias. The window to use Cycocel is fast approaching the cut off date, so take a good look at the crop now to assess how much growth can be tolerated. Do not treat once color becomes evident! It is still too early to be using Bonzi, A-Rest or Sumagic as a drench, these PGR’s should not be applied until after November 1st, and then only at recommended rates.

Continue to monitor crops closely for signs of insect pests (whitefly, fungus gnat larvae, mites, etc.) and treat populations identified before plants begin to show bract color. In the past few years growers have experienced some problems with mites, most likely related to current practices targeted at controlling whitefly. As effective as Marathon has been on whitefly, it does not control mites. This pest does not move aggressively in the crop so populations are usually localized. Start by cleaning out any infected plant parts (leaves, etc.) and treating the area where the problem is found. Mites can be moved by workers (on their clothing) or equipment; inspect plants along aisles and near vents/fans where physical dispersal is most likely to happen. As with any chemical applications, monitor the plants in the weeks after treatment to determine if additional follow up is required. Chemical residue or burn becomes more significant to the end value of the crop, so avoid having to treat later on by cleaning things up now.

A common response to whitefly buildup on poinsettias will be a distinct bleaching out of the color in the stem, petioles and leaves. Watch for these symptoms in the crop as any plants that were missed during an application of Marathon will become a major host for the whitefly. Usually if isolated plants like this are found it is best to remove them from the greenhouse in a sealed plastic bag rather than risk having a population in close proximity to other clean plants.

Lower temperatures, shorter days and higher humidity all favor foliar diseases, such as botrytis and powdery mildew. As October progresses, more attention is needed to airflow in greenhouses and efforts to keep foliage dry at all times. For growers who have experienced mildew in past seasons, it is important to begin a preventive spray program now before the disease can become active in the cool, humid climate. We believe that at least one preventive spray should be made regardless of past history with mildew, and in higher risk areas of central to north regions of the US and Canada.