July 12, 2006
We recently received a pumpkin sample showing marginal chlorosis (yellowing) of the leaves. The combination of symptoms and the presence of the bacteria in the sample were indicative of a bacterial disease. Angular leaf spot is a common bacterial disease of pumpkins and other cucurbits that causes chlorosis and necrosis (death) of leaf tissue.
Samples with the following problems have been seen in the Plant Disease Clinic recently:
Anthracnose on oak and maple
Ash flower gall
Bitterness in cucumbers is caused by the compounds cucurbitacin B and cucurbitacin C. The cucurbitacins are normally found in the leaves, stems and roots of the cucumber plant. The cucurbitacins spread from the vegetative parts of the plant into the cucumber fruit when the plants are under stress. Hot, dry conditions are usually responsible for bitterness in cucumbers in Iowa.
When selecting shrubs for the home landscape, gardeners should carefully examine growing conditions at the planting site. Most shrubs perform best when grown in areas that receive partial to full sun. However, there are shrubs that can be successfully grown in partial shade. (Sites in partial shade receive 2 to 4 hours of direct light.) A list of deciduous shrubs that can be grown in partial shade is provided below.