Expect production areas with black fiber cloth to get hot, again this weekend. Garden mums, flowering cabbage and kale may exhibit signs of wilting during extended periods of 90 plus degree temperatures. Plants wilt when the soil is dry, but wilting will also occur in hot weather which may cause plants to be stressed, or if the roots are damage from a root disease such as Pythium, even if the soil is saturated with water. When the roots stop functioning the plants will show signs of stress by wilting.
Feeding injury caused by Four-lined plant bug is showing up on Shasta daisies, Gentiana and other perennials. Retail customers may confuse the damage with disease. Feeding damage appears as spotting on the upper leaf surface. The adult is greenish yellow with 4 black lines running down the back and about 1/4 in long. The immature stage is bright red or orange with black spots on the segment behind the head. As they mature, a yellow stripe appears on each side of the wing pads. They feed for about 6 weeks and plants often outgrow the damage.
There are a variety of ways to produce garden mums using different pinching and planting strategies. Traditional garden mum production schedules involve planting the end of May or early June and pinching plants two times. The first pinch is given within two weeks of transplanting when roots of the cutting reach the bottom and sides of the container and the tops show 1.5-to 2.0 inches of new growth. The second pinch is given when the axillary shoots from the first pinch are 3 to 4 inches long, usually three weeks later in late June or early July, but prior to July 20th.
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.