CROP MONITOR

Winter wheat 2005: The year of the rust?

Results from the Defra CropMonitor project in 2005 showed that despite widespread prevalence of both yellow rust and brown rust throughout the late spring and early summer, overall disease levels in the national crop at GS75 were low. The first reports of yellow rust in commercial crops were issued in early April and the disease became relatively widespread in susceptible cultivars such as Robigus and Savannah during the late spring. However, high temperatures during the middle of June virtually stopped development of this disease. These warmer conditions were optimal for brown rust, which then developed rapidly in some crops, particularly Claire, Consort and Solstice. Timely alerts about the risk from brown rust were issued and spray programmes applied at ear emergence were effective in controlling the disease. In contrast however, brown rust caused substantial loss of green leaf area in untreated varuety trials.

Septoria tritici, which has been the most damaging foliar disease of wheat over the past two decades, continued to be a significant focus for monitoring and risk assessment in 2005. Weekly monitoring of crops at 15 reference sites across England showed that the severity (proportion of leaf area with symptoms) of S. tritici on leaf 2 at GS73-75 reached an average of 10% in untreated crops; very similar to the amounts recorded in 2004. Nationally however, septoria levels in commercial crops were lower than the 10-year average, and the second lowest since 1997. Septoria nodorum and mildew were found at very low incidence, similar to levels in 2002 and 2003. The incidence of moderate or severe symptoms of eyespot increased compared to 2004, but levels were below the 10-year average. Tan spot was recorded at trace levels, though there were reports of a small number of crops with particularly high levels of this disease.

CropMonitor used 15 locations across England to monitor disease levels in treated and untreated plots of four commonly grown cultivars (Consort, Malacca, Claire and Robigus), which were selected to represent the range of disease resistance available to growers. Disease levels throughout the season clearly illustrated the benefits from cultivar resistance. For example, in untreated plots, S. tritici levels at GS 73-75 on the susceptible cultivar Consort were more than double those on the more resistant Robigus. Crop managers could exploit these differences to provide savings in the amount of fungicide necessary to control disease. However, cultivars did not perform in accordance with their ratings for some diseases. Levels of mildew on Robigus and levels of brown rust on Claire were higher than might have been anticipated based on the ratings alone. These results demonstrate the importance of crop monitoring in order to quantify seasonal and regional disease pressures and their impact on cultivar performance.

National foliar and stem base disease levels (GS 73-75)

Disease	10-year mean (1995-2004)	2003	2004	2005 *
Mildew	0.2	0.2	0.2	0.2
Septoria tritici	4.6	3.8	4.6	3.7
Septoria nodorum	0.1	trace	trace	trace
Brown rust	0.1	trace	trace	0.1
Yellow rust	trace	0	trace	trace
Eyespot	11.0	7.3	6.5	8.6

Foliar diseases - percentage are of leaf 2 affected
Stem base diseases - percentage stems with moderate or sever symptoms
trace = < 0.05% area affected
* - provisional

	RAPID ACCESS TO THE LATEST REGIONAL CROP PEST AND DISEASE LEVELS