Impacts on Crop Protection - Climate Resilient Agriculture for Ensuring Food Security - page 108

Table 6.2 Seriou s crop pest epidemics critically infl uenced by climate change
Event effects Pest damage to crops

Floods and
heavy rains

Increased moisture benefi ts epidemics and prevalence of fungal leaf pathogens
Rice leaf blight caused great famine in Bengal (1942), two million people died
Wheat stripe rust outbreak in major production regions of China contributed to the 1960s
famine
Fungal epidemics in corn, soybean, alfalfa, and wheat in the US Midwest (1993)
Mycotoxin produced by wheat scab ( Fusarium spp.) reached a record high in the US Great
Plains (1993)
Humid summers drive epidemics of gray leaf spot of maize in Iowa and Illinois (1996)
Water-induced soil transport increases dissemination of soilborne pathogens to noninfected areas
Outbreaks of soybean sudden death syndrome in the north central US states (1993)
Continuous soil saturation causes long-term problems related to rot development and increase
damage by diseases

Crazy top and common smut in maize

Drought Water stress diminishes plant vigor and alters carbon-to-nitrogen ratios, lowering plant resistance

to nematodes and insects. Attack by fungal pathogens of stems and roots is favored by weakened
plant conditions. Drought promotes insect outbreaks
Outbreak of soybean cyst nematode correlated to drought conditions in the north central US
states (1990)
Summer locust outbreak correlated to drought in Mexico (1999)
Dry and warm conditions promote growth of insect vector populations, increasing viral epidemics

Storms and
air currents

Air currents provide large-scale transportation for disease agents (e.g., spores of fungi) or insects
from overwintering areas to attacking areas

The spread of the stem rust fungus that overwinters in Mexico and Texas is always favored by
moist southern air currents

The southern leaf blight of corn spread from Mississippi to the Midwest by air currents of a
tropical storm in the Gulf of Mexico during 1970

Warm winters Warm winters increase overwintering populations of all pests

Data reported for the European corn borer, wheat scab, and wheat rust
Increase overwintering populations of insect vectors

Increase population of aphids that carry the soybean mosaic virus

In addition, increased atmospheric carbon
dioxide is expected to alter the nutritional makeup
of crops, thereby affecting the severity of attack
from insects and disease organisms (Coviella and
Trumble 1999 ).
In general, however, most pest species are
favored with warm and humid conditions. Pest
infestations often coincide with changes in cli-
matic conditions, such as early or late rains,
drought, or increases in humidity, which, in
themselves, can reduce yields (Table 6.2 ).

crop production due to weeds have been valued at
approximately US$ 12 billion, amounting to
some 10 % of potential production. Large efforts
are made to limit these damages through a variety
of weed control measures.
Around the world, more human labor is
expended in hand weeding than in any other agri-
cultural task, and most cultivation and tillage
practices are designed to aid in weed control. The
chemical industry manufactures herbicides,
which, next to fertilizers, account for the largest
volume of chemicals applied to crops. Over US$
9 billion are spent on weed control every year in
the USA (USDA 1999 ).
Weeds, which are better adapted to arid condi-
tions than crops, will provide increased competition
for moisture, nutrients, and light. Herbicidal con-

6.1 Weeds

Worldwide, weeds have been estimated to cause
annual crop production losses of about 12 %