3 minute read
Diseases and Pests
Disease of the Month: Septoria Leaf Spot on Dogwood Weed of the Month: Fall Armyworm in Turfgrass
by Heather Prince
Septoria leaf spot is a common disease in our area, especially on redtwig or yellowtwig dogwood shrubs. It appears as circular, angular, or irregular shaped spots with olive-gray to brown centers surrounded by dark purple or reddish borders on the leaves. They are similar to but larger than anthracnose on flowering dogwood trees. Symptoms usually appear at the end of summer to the beginning of fall and are more common in wet or humid conditions. Heavily infected leaves will turn yellow and prematurely drop from the plant.
Treatment:
Fortunately, Septoria leaf spot is mainly aesthetic and will not typically kill the shrub. This fungal disease overwinters on leaf litter, with spores splashing to susceptible tissue each spring. Rake and dispose of fallen leaves to reduce the population. It may be treated preventatively with chlorothalonil, chlorothalonil + propiconazole, myclobutanil, or thiophanate-methyl. Begin sprays at bud break and two to three more applications may be needed at 14-day intervals if conditions are favorable for disease development.
Pest of the Month: Fall Armyworm in Turfgrass
Fall armyworms (Spodoptera frugiperda) feed on a wide variety of crops in addition to several turfgrasses. In Illinois, they will have one to two generations in late summer to early fall. Identifying which armyworm you have is key, as there are several similar species. Fall armyworm grow up to 1 1/3 inch long. They vary in coloration with some being dark green, tan or brown. They can be distinguished from other caterpillars by the Y-shaped marking that runs from the top of its head down between its eyes and the orange stripe that runs along each side. The adult male moths have brown forewings with tan and gray markings and a white triangular shape near the tip of the wing. The forewings of females are brown with less distinct markings than males. Both males and females have silvery-white hind wings. Fall armyworm egg masses can be found on grass, leaves, and structures. The egg masses may contain up to 400 eggs laid in three to four layers and are covered in fuzzy-looking silk. Eggs hatch in 5 to 7 days. When young larvae feed on the surface of grass blades, but large caterpillars can chew the grass blades off. The larvae complete growth in 3 to 4 weeks. Treatment:
Larvae typically do not feed on the crowns. Watering and fertilizing turf can allow plants to re-grow after the fall armyworms have been controlled. Effective biological treatments include Bt products or Spinosad. Chemical controls for fall armyworm include: carbaryl, chlorantroniliprole, and clothianidin, as well as pyrethroids like bifenthrin, deltamethrin, lambda-cyhalothrin, or trichlorfon. There have been reports that some fall armyworm populations have not responded well to pyrethroids, so you may want to try alternatives first.
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
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