Spring dead spot

Overview

The problem

Spring dead spot (SDS) is an important root disease of common couchgrass [known in the US as bermudagrass (Cynodon dactylon) and hybrid bermudagrass (C. dactylon x transvaalensis)]. SDS is most damaging on couchgrass that experiences winter dormancy, especially in areas where freezing injury occurs. Typically, SDS is most problematic in the transition zone but it also can occur in regions where prolonged cool winters create slow couchgrass growth over extended periods. The disease has also been occasionally reported on zoysiagrass and buffalograss. SDS is caused by any one of three closely-related, ectotrophic, root-infecting fungi: Ophiosphorella herpotrichaO. korrae and O. narmari. The species causing SDS may vary by region, and differences in how they cause disease are not yet fully understood. Generally, these fungi infect roots from late summer until early autumn and damage roots, stolons and crowns. The SDS damage exacerbates root death caused by cold temperature winter injury. Typically, affected areas do not emerge from dormancy or grow slowly in the spring, and are prone to invasion by weeds.

What to look for

Signs of spring dead spot infection initially appear as small brown flecks on roots, stolons and rhizomes. Eventually, SDS progresses and couchgrass roots become rotted and discoloured, with black sunken lesions. In spring, as couchgrass breaks dormancy, above-ground symptoms appear as circular or arc-shaped patches of straw-coloured leaves. Green leaves on the periphery of SDS patches appear to die back from the leaf tip downwards. On golf courses, severe SDS symptoms (circular, well-defined and sunken patches) can develop on hybrid couchgrass fairways and are often associated with areas of high traffic/soil compaction.

Spring dead spot is a perennial disease and once established, symptoms can reoccur at the same location. Following disease initiation, the radius of each patch will generally increase in size each year. Over time, patches can coalesce and result in very large areas of dead couchgrass. SDS is most common on established couchgrass that is at least three years old but can develop on sites of all ages.

The solution

Cultural practices can reduce spring dead spot and are the first step to enable SDS control:

  • Variety. Couchgrass can have good resistance to SDS; associated with low-temperature tolerance.
  • Drainage. Optimise root zone with good drainage to maximise root growth potential.
  • Cultivation. Practice vertical mowing and core aerification twice per season (summer only).

Dedicate™ is labelled for control of spring dead spot and is effective when applied at 2 litres per hectare. Dedicate combines a DMI and a strobilurin solution for SDS that has provided control equal to current standards. Dedicate gives improved turf health without the negative growth regulation effects that can be attributed to other fungicides.

Important application strategies are necessary to target SDS with Dedicate: time the first autumn application when the average soil temperature at a 50 mm depth falls below 24°C. A second autumn application is recommended 28 days later; the average soil temperature at a 50 mm depth should be above 15°C. Water in each fungicide application to move the product into the root zone.

Technical Information

Spring dead spot

SOLUTION RATE (per 1000 sq ft) APPLICATION INTERVAL2
Dedicate 2L Autumn, 2 applications, 28 days apart

1. See fungicide labels for complete details. Always read and carefully follow label instructions. 2. Time the first autumn application when the average soil temperature at a 50 mm depth falls below 24°C. Lightly water-in applications (6 mm) to move fungicide into root zone.

Three closely related fungi are responsible for spring dead spot of couchgrass. Isolated from roots and plated on agar media, they include Ophiosphorella korrae (top row), O. narmari (centre row) and O. herpotrica (bottom row).
Photo: Fanny Iriarte, University of Florida.

Spring dead spot patches can be 25–300 mm and more in diameter. High traffic areas with soil compaction, such as a couchgrass golf green approach, are most susceptible to SDS damage.
Photo: Derek Settle, Bayer CropScience.
Close-up of a severe spring dead spot patch symptom in a couchgrass fairway. This patch is approximately 450 mm in diameter.
Photo: Derek Settle, Bayer CropScience.

Numerous small spring dead spot patches in a single, untreated strip have coalesced to cause extensive damage in a couchgrass fairway maintained for research during spring, 2014.
Photo: Derek Settle, Bayer CropScience.