Focus paddocks - Disease

Disease was measured using the SARDI Predicta-B service, in soil sampled pre-sowing (generally late March – early April, May in 2006) from a balance of row and inter-row. Plant roots were also inspected at GS65 but symptoms were seldom found.

Crown rot

Crown rot, mainly Fusarium pseudograminearum, was present in at least half of the paddocks each year, and consistently present in both Donald paddocks and the Culgoa Till paddock (Figure 27). Only the Patchewollock Till paddock recorded no crown rot at all.

Crown rot symptoms were visible on the Donald crops (both wheat) in 2006, more severe on the No-Till crop and consistent with F. pseudograminearum levels, but not F. culmorum. The following autumn, levels were similar for both paddocks, and for both Fusarium species. In 2008, after a barley crop on the No-Till paddock, and Tilled fallow on the Till paddock, levels were even higher, although F. culmorum levels had fallen on the No-Till paddock. Relatively low crown rot levels were observed in the Till wheat crop in 2008 (the No-Till paddock had a vetch hay paddock).

Higher crown rot DNA levels tended to be reported in Till paddocks; Sea Lake in 2006 (before a cereal) and 2007 (after a cereal), Culgoa in 2007 (after a cereal), Yaapeet in 2008 (after a cereal). At the time of testing, these paddocks had not necessarily been Tilled (Sea Lake in 2007 had been chemical fallowed). Perhaps because crowns are less evenly spread at the wider row spacing typical of No-Till systems, sampling of infected material is less likely.

Figure 27a
Figure 27b
Figure 27c

Figure 27. SARDI Predicta-B measurements of crown rot (Fusarium pseudograminearum and Fusarium culmorum) DNA in soil sampled from the focus paddocks in March, 2006-2008.

Nematodes

Cereal cyst nematode eggs were mainly detected in the Till paddock at Minyip (Figure 28), and in 2007 in the No-Till paddock at Patchewollock. Pratylenchus eggs, mainly P. neglectus, were consistently present at Culgoa, Minyip and Yaapeet, and were at higher levels in 2007 than in other years. After the dry spring of 2007, there were few nematodes in 2008. Apart from the cereal cyst nematode in the Minyip Till paddock, there was no particular pattern of higher egg numbers in either Till or No-Till paddocks.

Figure 28a
Figure 28b
Figure 28c

Figure 28. SARDI Predicta-B measurements of cereal cyst nematode (Heterodera avenae), Pratylenchus neglectus and P. thorneii eggs in soil sampled from the focus paddocks in March, 2006-2008.

Root disease

The fungal root disease take-all (Gaeumannomyces graminis var. tritici) was only detected at low levels, mainly in the Patchewollock and Yaapeet Till paddocks in 2007/8, and in each of the Donald paddocks (Figure 29).

Rhizoctonia (Rhizoctonia solani) was consistently detected at medium (40-80) to high (80+) risk levels in the Culgoa no Till paddock, and the Yaapeet Till paddock. In both cases symptom levels were low on plants in spring. Rhizoctonia levels appeared higher in 2007, when Till paddocks at Sea Lake and Yaapeet had higher levels detected than No-Till paddocks.

Common root rot (Bipolaris sorokiniana) was detected in most paddocks, but it was difficult to see any pattern between paddocks, establishment method or previous crop.

Overall, the Minyip paddocks were least affected by fungal root diseases, possibly a characteristic of the soil (vertisol). 

Figure 29a
Figure 29b
Figure 29c

Figure 29. SARDI Predicta-B measurements of take-all (Gaeumannomyces graminis var. tritici). rhizoctonia (Rhizoctonia solani), and common root rot (Bipolaris sorokiniana) DNA in soil sampled from focus paddocks in March 2006-2008. Note that the take-all and rhizoctonia measurements are presented as a standardised ‘risk rating’. 

Blackspot, Phoma and Pythium

The levels of Blackspot and Pythium detected tended to be consistent from year to year (Figure 30). In the Donald, Minyip and Patchewollock pairs there were relatively high Blackspot levels in Till paddocks. Blackspot was virtually absent at Sea Lake, and detected at low levels in the Culgoa No-Till paddock and both Yaapeet paddocks.

Pythium DNA was detected at high levels at Donald and Patchewollock (not measured by SARDI in other paddocks in 2006), and in following years in all paddocks. Pythium levels were higher in the No-Till paddocks at Yaapeet and Culgoa, and higher in the Till paddock at Patchewollock. In the remaining paddocks levels were similar or changed from year to year between paddocks.

Figure 30a
Figure 30b
Figure 30c

Figure 30. SARDI Predicta-B measurements of blackspot (Mycosphaerella pinodes), Phoma X (several species?) and Pythium (several species) DNA in soil sampled from focus paddocks in March 2006-2008. Note that the blackspot measurements are presented as a standardised ‘risk rating’, and Pythium was only measured at Donald and Patchewollock in 2006.