Small Grains

 

Black Point (Black Tip Fungus or Kernel Smudge)

Ned Tisserat, Kansas State University, Plant Patholgy
Mary Burrow, and Ronda Koski

Cause:  Several genera and species of fungi, including:  Alternaria sp.,  Alternaria infectoria, Aspergillus sp., Bipolaris sorokiniana, Chaetomium sp., Cladosporium sp., Cochliobolus sativus, Curvularia sp., Fusarium sp.,, Gloeosporium sp., Helminthosporium sp., Myrothecium sp., Nigrospora sp., Penicillium sp., Plenodomus sp., Rhizopus sp., and Stemphylium sp.

 

Occurrence:  Black point develops on ripening heads of wheat during warm and moist periods. According to the Official Grain Grading Guide (Canadian Grain Commission 2001), the discoloration is considered “smudge” if more than one half of the kernel is discolored, or if the discoloration extends into the crease. If the discoloration penetrates and extends throughout the endosperm, it is referred to as “penetrated smudge”.

 

Key Symptoms: 

·        Infected seeds appear weathered with dark discoloration of the pericarp at the embryo end.

·         Reduced germination of discolored wheat seeds.

·         Reduced growth of roots of seeds infected with the black-pointed fungi

 

Favorable Conditions:

·         Humidity greater than 90% RH and/or rainfall from anthesis to soft dough stage of kernel development. 

·         High nitrogen fertility.

·         Excessive late season irrigation.

·         Lodging of ripening wheat plants.

·         Expanding green kernels are most susceptible

·         Premature seed senescence also promotes black point.

 

Diagnosis:

 

Problem:   

·         Infected, discolored kernels will reduce the quality and the value of the grain at the market. 

·         Dark discoloration of the embryo end of the kernel may result in a discount if the grain is graded as damaged.

·         The germination rate of the affected grain may be reduced.

·         Reduces the commercial grade of wheat, causing economic losses to producers.

·         Blackened kernels are considered “damaged”, by U.S. wheat standards (only 2% are permitted in the U.S. No.1, and 4% in U.S. No.2).

·         Most problematic on durum wheat because black specks can appear in the semolina, making it undesirable for further processing.

 

Management Approaches:

·         Reduce irrigation frequency after heading.

·         Infected grain should be stored in areas where relative humidity is less than 90% and grain moisture content is less than 20%.

·         Infected grain should be stored for the least amount of time as is possible.

·         Plant wheat cultivars less prone to damage. Current cultivars differ in the level of resistance or tolerance to the disease, although there are no completely resistant cultivars available.

·         It is impossible to exclude these fungi from maturing wheat kernels in the field. 

·         Many fungicides are toxic to these fungi, but application of fungicides to maturing heads is rarely economical, and is generally off-label.   

Categories: Small grains, Diseases, Black Point

 Date: 07/06/07