No. 5/June 29, 2023
Modified Growing Degree Days
Insect development is temperature dependent. We can use degree days to help predict insect emergence and activity. Home, Yard, and Garden readers can use the links below with the degree day accumulations above to determine what insect pests could be active in their area.
Dutch Elm Disease
Dutch elm disease (DED) is a destructive wilt disease caused two closely related fungi, Ophiostoma ulmi and Ophiostoma novo-ulmi. Since its introduction to the United States in the 1930s (Illinois 1950s) DED has killed millions of native elm trees. American elm (Ulmus americana) and red elm (Ulmus rubra) are very susceptible. Asiatic elms, Lacebark elm (Ulmus parvifolia) and Siberian elm (Ulmus pumila), are the most resistant species.
A Few More Weeds That Do Well in Drought
This warm-season annual broadleaf reproduces by seeds and spreads by rooting stem pieces. Common purslane germinates late in the season and forms a long taproot with fibrous lateral roots. The stems are succulent, smooth, fleshy, usually purple–red, and may root at lower nodes. The stems are many-branched, reach up to 24 inches long, and grow in a prostrate fashion to form mats. The leaves are alternate to nearly opposite, wedge-shaped (rounded at the tip and narrowed at the base), up to 1-1/4 inches long, thick, fleshy, and smooth and are often clustered near the ends of branches. The yellow flowers are borne individually in the leaf axils or clustered at the ends of branches. There are five petals. The fruit is a globular capsule. Flowering occurs from July through September. Common purslane thrives in sunny, fertile, sandy soils and can be troublesome in late-summer seedings. It tolerates poor, compacted soils and once established, drought.
University of Illinois Extension Horticulture Resources - Summer 2023
Looking for more horticulture and gardening information? The University of Illinois Extension has two resources with summer content that may interest you.