Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

201
Influence of weather conditions on yellow rust in Central
Asia
M. Koishibaev and M. D. Kurmanov
Research Institute of Plant Protection, Almaty, Kazakhstan
Yellow rust epidemics have become more frequent during the last ten years in
the irrigated foothill-steppe zones of south and south-east Kazakhstan. The
increase in pathogen presence may be due to the considerable increase in area
of wheat production in Tajikistan and Uzbekistan. Analysis of weather
conditions in Gissar Valley of Tajikistan showed that the minimum
temperature in January is 3–5°C and the pathogen can hibernate on winter
wheat shoots as the uredino mycelium stage. In April and May, during wheat
heading, precipitation is 120–160 mm. Moreover, not only winter, but also
spring and facultative wheats are sown, i.e. their vegetative period is very
long. It is also possible that yellow rust infection is carried into Central Asia
from East Asia, where facultative wheat is sown predominately. Weather
conditions in the foothill and steppe zone of south and south-east Kazakhstan
and Kyrgyzstan are favourable for yellow rust development in spring and the
beginning of summer. In April, during winter wheat development, air
temperature is +10–15°C, precipitation 60–100 mm and humidity 70–75%, and
in May, during wheat heading, it is +16–19°C, with 60–90 mm precipitation
and 55–70% RH. In July and August, the daily air temperature goes up to +35–
40°C and humidity falls to 40–45%. Winter wheat is harvested in July, and is
sown in September–October. The preservation of the pathogen in natural
conditions during this period is unlikely and infection of wheat shoots in
autumn is impossible, because all vegetation is destroyed using field burning.
Weather conditions in the mountain zone of Almaty Oblast and Issyk-Kul
Valley of Kyrgyzstan is very favourable for yellow rust to hibernate as the
uredinio stage on winter wheat. Air temperature in July and August is usually
no more than 15–17°C, precipitation in summer is 150–200 mm and humidity
60–75%. Because of the cool and short summer, the harvest period of one crop
and emergence of shoots of the next occur at the same time, and rust
development in some years can reach 90–100%. Regression analysis showed
the dependence of yellow rust development on weather conditions, especially
precipitation, humidity and air temperature. High correlation was established
between the amount of precipitation and humidity in April and yellow rust
development in Kazakhstan and Uzbekistan. In 1999/00, during epiphytotics
of this disease, humidity was very high (65–75%) and precipitation was 80–
150 mm. In 2001, 2004 and 2005, when there was a low incidence of rust
problems, the humidity was low (50–60%) and precipitation was 40–50 mm.