Plant Disease Clinic -- Highlights

Leaf Spot - turf

Leaf spot has been a common problem on turf this spring and summer. Leaf lesions are initially reddish-brown to dark brown. As they enlarge they take on an oblong shape and develop a lighter center with a dark border. Heavily infected blades may turn yellow, wither, and die. The pathogen may also move to the crown and cause plant death. This is referred to as melting out. At the melting out stage, the lawn appears to thin out; this damage is sometimes mistaken for drought injury (not in 1993!). There are a number of cultural management practices that aid in controlling this disease:

  • Provide good surface and subsurface drainage; fill in low spots where water may stand.
  • Use disease resistant grass blends; in shaded areas, grow shade-tolerant cultivars.
  • Fertilize according to local recommendations and soil tests.
  • Mow frequently at recommended height (remove no more than one-third of the leaf height at one cutting); keep mower blades sharp.
  • Water thoroughly during droughts; avoid frequent light sprinklings.
  • Increase light penetration and air movement to the turfgrass area and speed drying of grass by selective pruning of trees and shrubs.

Fungicides can also be used, but a full-season spray program is needed. Spraying every 10 to 14 days is impractical in most situations. Cultural controls are generally the most practical.

Tomato Blights

Wet spring and early summer conditions have favored the development of fungal blights of tomato. Two common foliage diseases of tomato are early blight, caused by Alternaria solani, and Septoria blight, caused by Septoria lycopersici.

Lower leaves are usually attacked first. Early blight causes brown spots (up to more than 1/2" in diameter) that contain concentric rings of darker brown. Septoria causes smaller brown spots that eventually turn light tan or gray in the center with a dark border. Both diseases cause foliage to eventually turn brown and die.

Cultural practices can help reduce disease outbreaks. Just after transplanting, apply a 2-4" layer of mulch (leaves, grass clippings, straw, etc.). This acts as a barrier against the introduction of fungal spores from the soil. Space plants adequately to allow good air circulation. Since these fungi can overwinter on infected leaves, it is also important to remove plant debris at the end of the season. Rotate away from tomatoes and potatoes for several years.

Fungicide sprays, such as Daconil 2787, may be needed. Sprays should be applied every 7 to 10 days from fruit set through harvest.

This article originally appeared in the July 14, 1993 issue, p. 115.


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 14, 1993. The information contained within may not be the most current and accurate depending on when it is accessed.