Cloudy Weather Tips
Tuesday, 15 April 2008 07:29
Root rots, foliar diseases and under-fed plants from over-watering and tall leggy growth from low light are common problems that occur during prolonged cloudy, rainy weather.
During prolonged cloudy, rainy weather, let plants run on the dry side and spot water areas as needed to prevent over-watering. Usually plants on the edges of benches or those in the path of air movement will dry first and may need to be spot watered more often than the rest of the crop. When some plants get spot watered and are irrigated more frequently than the general crop, their fertilizer program needs to be adjusted to account for the extra leaching they receive. They may need to be "spot fertilized" as well.
If media remains wet, plants are more prone to root rot. At least once a week, randomly select plants to inspect roots to monitor the health of the crop. If roots do not look healthy, conduct a soil test for soluble salts and test roots for disease, either by sending samples to a lab or by using on-site test kits.
To prevent foliar diseases like Botryis, (see message) always water in the morning to reduce the length of time the leaves stay wet after irrigating. Avoid watering late in the day or when water will sit on leaf surfaces for long periods of time. Reduce humidity by heating and venting several times in the evening and in the morning. For details, see the factsheet, Reducing Humidity in the Greenhouse. In addition to heating and venting, use circulating fans (horizontal air flow) to continuously move the air throughout the greenhouse. These fans should be shut off when exhaust or vents are being used. Horizontal air flow will mix cool and warm air, minimizing temperature differentials and cold spots where condensation can occur on plant surfaces. For more information see: Horizontal Air Flow
If pesticides are needed, read precautions for treatments during prolonged cloudy weather. Some products such as horticulture oil may cause phytotoxicity if it remains wet on the foliage and does not dry rapidly.
High temperatures and low light conditions increase stem elongation or stretch. Water soluble plant growth regulators such as B-Nine and Cycocel are best applied during cloudy weather to maximize chemical uptake. With transplants in small containers (flats & 4" pots) materials such as B-Nine and Cycocel can be sprayed at weekly intervals. Apply the first spray as soon as new growth is evident. Use a rate at the low end of the recommended range for that species. Repeat at 7-14 day intervals as needed. For more information on using plant growth regulators see articles from March and April 2007 on Plant Growth Regulators. (Articles from search are displayed in reverse chronological order.)
Tina Smith, University of Massachusetts with input from Leanne Pundt, University of Connecticut
