Diseases Which Challenge Global Wheat Production—Powdery Mildew and Leaf and Head Blights - Wheat Science and Trade - page 148

Chapter 7
Diseases Which Challenge Global Wheat
Production—Powdery Mildew and Leaf
and Head Blights

David Marshall

SUMMARY

pathogens to complete their life cycle,
thereby increasing variability in the patho-
gen populations.
(3) Crop diversity and host-plant resistance
when used together are the two primary
methods of managing residue-borne dis-
eases of wheat. Emphasis must be placed
on methods of identifying and incorporat-
ing durable host-plant resistance that does
not encourage resistance-breaking vari-
ability in the pathogen populations.

(1) Conservation tillage practices have pro-
vided wheat producers with many crop
production benefi ts but have exacerbated
the effects of residue-borne pathogens.

(2) Not only does wheat residue increase the

quantity of primary inoculum available
to infect subsequent wheat crops, it also
serves as the primary means for powdery
mildew, leaf blight, and head blight

INTRODUCTION

tillage has replaced plowing and disking as the
standard method of cropland management in
many areas.
At the heart of conservation tillage is the man-
agement of crop residue. Following harvest of the
primary economic yield (typically grain or lint),
what remains in the fi eld is the crop residue. For
simplicity, crop residue is equated here with
stover and postharvest aboveground biomass.
Conservation tillage or no-till results in crop
residue left on the soil surface not incorporated
into the soil or removed for other purposes such
as energy production. When crop residue remains
on the soil surface, it is degraded much more
slowly than if incorporated into the soil where
microorganisms can use it as a food source. As a
result, pathogens that can colonize the crop
residue are provided a safe harbor between actively
growing crops. Subsequently, if crop diversity is
minimized, or if a pathogen can attack multiple

Perhaps the most underrated phenomenon in
agriculture is the introduction or intensifi cation
of new, unsuspected, or underappreciated prob-
lems associated with changes in agricultural prac-
tices (Hunter and Leake 1933). Taking root in the
1950s, conservation tillage had become a common
and widespread practice by the mid-1980s in
many parts of the world, particularly in wheat
( Triticum spp.), maize ( Zea mays L.), soybean
[ Glycine max (L.) Merr.], and cotton ( Gossypium
hirsutum L.). First used for its control of soil
erosion, conservation tillage was also found to
improve soil structure, conserve soil moisture,
insulate the soil to temperature fl uctuation, store
soil carbon, and reduce farming costs due to
reduced tractor use (Minoshima et al., 2007).
Combined with the advent of highly effective her-
bicides and better fi eld equipment, conservation