Wednesday, August 5, 2015

High Humidity Encourages Turf Diseases

A composite photo of turfgrass with brown dead areas caused by the fungus, Bipolaris. The photo on the left shows small brown areas when the disease was in the early stages and the photo on the right shows the same turfgrass area 10 days later with a very large brown area.
Turfgrass infected by Bipolaris sp. - these photos are the same turfgrass
area photographed 10 days apart (Photos: NMSU - PDC)
Summer rain is a welcome occurrence in the desert, however it can also create a favorable environment for diseases. Recently, conditions have been especially favorable for a few common turfgrass diseases. Leaf spot, melting out and brown patch, have been identified in a number of samples submitted to the plant clinic over the past several weeks. These diseases are caused by common soil-borne fungi that are favored by wet, humid conditions. They can be especially severe when heavy rains follow periods of drought or dry conditions. Leaf spot and melting-out diseases are caused by a group of pathogens that used to be grouped together in the fungal genus Helminthosporium. Two fungi in this group, Bipolaris sp. and Curvularia sp., have been isolated from turfgrass samples in New Mexico. Brown patch is caused by Rhizoctonia solani. Similar environmental conditions favor these diseases and it is not uncommon to find more than one of these pathogens in the same sample. When
environmental conditions are highly favorable for disease development, these diseases can spread rapidly resulting in large areas of blighted turf.

A composite microscope photograph of spores of the Curvularia fungus
Curvularia spores
(Photo: NMSU - PDC)
A blade of turfgrass with small dark brown spots with a tan center
Leaf spots
caused by
(Photo: NMSU-PDC)
A composite microscope photograph of spores of the Bipolaris fungus
Bipolaris spores
(Photo: NMSU - PDC)

Turfgrass with a large patch of brown (dead) grass
Brown patch caused by Rhizoctonia solani
(Photo: NMSU - PDC)
A microscope photo showing the characteristic hyphae (fungal strands) with right angle branching of Rhizoctonia solani
Characteristic hyphae of Rhizoctonia
(note the right angle branching)
(Photo: NMSU - PDC)

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