Light and temperature extremes this time of year can stress plants in greenhouses and retail yards. Tender new growth and plants under water stress are particularly prone.
Faded, dull upper surfaces of most recently expanded leaves are often the beginning signs of sunscald. Sunscald -paper thin brown spots can occur on tender new growth and when cloudy weather is followed by bright sun and high temperatures. In greenhouses, shade cloth may be needed for some crops.
Anthracnose (Colletotrichum sp) was recently diagnosed on mandevilla. Anthracnose is common on many ornamental plants. The primary symptoms are leaf spots, leaf blights and dieback. Infected leaves develop tan to brown spots or lesions that are typically associated with leaf veins. In severe cases leaf drop may occur. Because anthracnose symptoms take on different forms and appearances it can be mistaken with other fungal diseases. Submit suspicious plants to a diagnostic laboratory for proper identification.
Here are some management tips especially important for periods of cloudy, rainy weather:
Clean Plants: Keep plants in retail areas clean. Remove dead and injured plants and spent flowers a couple times a day even during the busy season. Botrytis and high ethylene concentrations from decaying plant tissue will cause premature loss of foliage and flowers.
It is not unusual to discover outbreaks of pests such as spider mites, thrips, whiteflies and aphids in greenhouses full of flowering bedding plants scheduled to be sold within a week or two. If you discover an insect or mite problem within a couple of weeks of sale, we suggest using a safe, effective contact spray that will knock down the infestation to provide good protection for a couple weeks. If infestations are localized, spot treating may be best. Once plants are planted outdoors in a garden, aphids, mites, whiteflies and thrips are not usually a problem.
It has been a challenging year to harden-off transplants with cold temperatures, rain, then sunshine. The transition from the greenhouse to home gardens involves changes in light, temperature and wind. Vegetable transplants benefit by a gradual "hardening" off period before they are transplanted into the customer’s garden. Gradual exposure to outdoor growing conditions and reduced watering at the end of the growing period with some protection from wind and temperature but full exposure to light can increase the survival rate of planted transplants.