Enhancing yield of long season wheat varieties at Eneabba 2014 trial report

Background

A higher yielding, longer maturing wheat variety is a desirable component of a cropping system to fully utilise an early start to a season and to reduce the risk of frost damage. Disease is a risk in the high rainfall and how will wheat variety choice and your management influence profitability on your paddocks.

Early sowing can increase the leaf disease (yellow spot/septoria) pressure on varieties. The trial will examine the yield response of varieties under natural disease levels or without any disease though the use of fungicide. In addition, root diseases are an increasing risk in continuous cropping rotations and a new in-furrow fertiliser dressing may provide control for both foliar and root disease.

Aim

Determine how management with foliar fungicide and an in-furrow fungicide may influence the profitability of long season wheat varieties with an early sowing opportunity at Eneabba.

Trial details

In this trial, 18 wheat varieties were sown at Eneabba and four disease management treatments were applied to each variety. There were three replicates of each treatment.

Comments

This trial was sown early in May, however despite this relatively early sowing date the longer maturing varieties did not perform significantly better than mid maturing varieties. This is most likely due to the environment (warm winter and low rainfall) not favouring the later maturity types or their susceptibility to leaf disease. The trial was sown into wheat stubble and disease pressure was high (a mixture of yellow spot and septoria nodorum blotch) early in the season (tillering – stem extension). Late rains in September may have supported late disease development (not measured) and this may have influenced yield penalties of susceptible varieties.

The trial was sown into moist soil with a high stubble load. Across all treatments, plant establishment averaged 145plants/m².  A high level of leaf disease was evident at early growth stages (a mixture of yellow spot and septoria (stagonospora) nodorum blotch) but dry conditions limited the spread of disease up the canopy between stem extension and heading. Disease was assessed at three times – 14 July (Z31), 29 July (Z39) and 27 August (Z69) and involved assessing the diseased area on the top 4 leaves on 10 tillers per plot.

At first node stage (Z31), about 10 weeks after sowing, and prior to foliar fungicide treatment, the in-furrow fungicide was significantly reducing disease on the fourth leaf and varieties varied significantly in levels of disease (Table 3). There was no evidence of rhizoctonia at the site so the benefit of the in-furrow fertiliser dressing is most likely from early suppression of leaf disease.

Following the foliar fungicide application in July (Z31), significant differences in disease severity were evident between varieties and fungicide was  significantly reducing disease on the fourth leaf. Average percentage leaf area diseased for fourth leaves was 65% in nil treatment but only around 50% in both in-furrow and foliar fungicide treatments. Due to low rainfall disease levels did not progress much during this period, consequently fungicide effects which we would have expected on leaves higher in the canopy were not observed. By the end of crop flowering there were no fungicide effects in terms of percentage disease observed on any of the leaves assessed but there were significant variety differences. The percentage average leaf area diseased of Cobra and Magenta were significantly less than Harper, Mace and Yitpi. Significant rain events occurred in early spring after the final disease assessment in late August. At the time of the field day, major differences between varieties were evident, with complete death of flag leaves in some untreated susceptible varieties and residual fungicide impacts evident on retention of green leaf area on flag leaves.

Despite a relatively dry spring (decile 2-3) the average yield response to two applications of foliar fungicide was still nearly 0.8t/ha. There was also an interaction between the fungicide treatments and variety, with varieties such as Mace and Zen achieving  high yields with the absence of fungicide and not responding as clearly to foliar fungicide. Meanwhile Trojan, Magenta, Yitpi and Cobra had a significant yield response with the application of foliar fungicide (Table 4).

Fungicide applications had the biggest impact on grain quality of the disease susceptible mid-long maturing varieties. Yitpi’s screenings reduced from 6.39% with nil fungicide to 4.62% with the application of foliar fungicide (Table 5). Similar responses were observed for Trojan and Harper (Table 5). In contrast, screenings of the mid-short maturing varieties Cobra, Mace and Wyalkatchem and more resistant mid-long maturing varieties Zen and Magenta were less than 5% for each fungicide treatment (Table 5). This site had high potential disease pressure, it was sown in early May into wheat stubble, resulting in extended exposure to inoculum of stubble borne diseases. Favourable weather for disease development in early growth stages resulted in significant disease development, particularly in susceptible varieties. Despite dry conditions in the mid-season limiting disease severity for a period, significant yield responses to fungicide were seen in most varieties, this is likely a response to disease development in early and later growth stages of the crop. No benefit from longer maturing varieties was evident.