Diseases and Pests

Weed of the Month: Quackgrass Disease of the Month: Edema on Yew

by Heather Prince

Weed of the Month: Quackgrass

Quackgrass (Elytrigia repens) is a broad-bladed cool-season perennial grass that has been benefiting from our cold moist spring this year. It spreads via seed and by rhizome, forming patches quickly. Now is a good time to scout for it in turfgrass. Leaf blades are flat, dull green to light blue green with a pointed tip. They will be 1/8 to 1/2 inch wide and can grow 3 to 12 inches long. Leaf blade upper surfaces are smooth to rough and tend to be sparsely hairy with Quackgrass the lower surface being smooth. The sheaths can be hairy or smooth, although young plants will often have hairy sheaths. Look for the key feature of claw-like, slender auricles that clasp the stem. Quackgrass rhizomes are slender, white, and persistent, plus able to stretch several feet with new roots and shoots every few inches. Seed heads are 2 to 6 inch long spikes that occur from late May to September. Often confused with crabgrass, which is a warm-season annual, quackgrass is distinguished by the clasping auricles at the base of the leaf.

Treatment:

Quackgrass thrives in well-drained soil where there is little competition. A healthy, dense lawn will reduce quackgrass infestations. Herbicide control is challenging. You may try spot applications of glyphosate but check after a week or so to see if a second application is needed. Herbicides specific for killing grasses that may be tried such as sethoxydim or fluazifop. Read and follow all label directions very carefully. Hand-digging may be effective, but the entire plant must be removed.

Disease of the Month: Edema on Yew

Edema can be a common abiotic disease of yews (Taxus spp.) stressed by poorly drained, over-saturated soils, especially in the spring. Look for bumps or blisters on the epidermis of the undersides of needles that turn tan and corky as well as yellowing needles and dying twigs. The bumps are the result of ruptured cells, where more water is retained in the plant than can be used by it, resulting in damage to the needle tissue. When spotting yellowing needles, with edema, you will not see signs of insect chewing or fungal pathogens. Edema on yew

Treatment:

Correcting the drainage is key for this abiotic stress disease. When experiencing this disease, check irrigation systems for overwatering, use a trowel to assess soil density, and look for downspouts or sump pumps emptying in the area. Increase drainage in the area, if possible, but also consider replacing with more wet-tolerant plants if the problem persists.

Additional resources:

University of Illinois Extension Service https://web.extension.illinois.edu/state/ horticulture/index.php 217-333-0519 The Morton Arboretum http://www.mortonarb.org/Plant Clinic: http://www.mortonarb.org/trees-plants/ tree-and-plant-advice/ 630-719-2424 Chicago Botanic Garden Plant Information Service: https://www.chicagobotanic.org/ plantinfoservice 847-835-0972