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Net blotch may be less of a problem with sweep openers

Not the end of the world for low disturbance seeders.

November 19, 2007  By Bruce Barker

To address the lack of research on the impact of seed placement and row spacing and their interactions with fungicides on net blotch disease in barley, research scientists Kelly Turkington, George Clayton, Neil Harker and John O’Donovan with Agriculture and Agri-Food Canada (AAFC) at Lacombe/Beaverlodge, Alberta, and Randy Kutcher with AAFC Melfort, Saskatchewan, conducted a three year study looking at leaf diseases and barley performance. Surprisingly, the results were not what they expected.

“The general school of thought is that when you go to wider row spacing, there is better air circulation and less humid conditions in the crop canopy. That should mean that wider row spacing and narrow row openers would have lower disease levels than a seeding system such as a sweep that essentially has random seed placement and without distinct seedrows,” explains Turkington. “However, what we found was the exact opposite.”

The direct seeding field experiment was conducted at Lacombe and Beaverlodge, Alberta and Melfort, Saskatchewan to evaluate the effect of three seedbed utilization treatments and six foliar fungicide timing and rate treatments on disease severity and production characteristics of barley. Seedbed treatments included row spacing at nine and 12 inches (23cm or 30cm) with a knife opener, or spread bands with a 11.2 inch (28cm) sweep and a nine inch (23cm) row spacing. Fungicide treatments included full and split applications of Tilt at the two to three leaf, flag leaf and heading stages with an untreated control.


Net blotch severity was worse for narrow row openers

Contrary to what was expected, there was less net blotch with the sweep openers. Overall, the lowest levels of net blotch on the flag leaf were consistently observed for sweep, 14 perc ent leaf area diseased versus 18 percent for the nine inch and 20 percent for the 12 inch row spacing. On the penultimate leaf, net blotch severity for nine inch and 12 inch row spacing was 33 percent and 35 per cent, respectively, compared with 21 percent for the sweep system.

Turkington explains that one possible explanation for the observed differences in disease severity was the influence of seed placement methods on inter-row spaces and seedling density. The spread band placement lacked distinct rows and defined inter-row spaces, and had lower plant density compared with the distinct row placements. The uniform plant stand with the sweep may have reduced both wind speed in the crop canopy and subsequent dispersal of net blotch spores, leading to a reduction in disease severity.

In the nine inch and 12 inch row spacings, the distinct rows likely facilitated air movement among the rows within the canopy, thus increasing the potential for movement of the net blotch pathogen up from the lower canopy, leading to increased disease development. In addition, plants were closer together in the distinct row placements, which may have facilitated pathogen dispersal from diseased to healthy plants.

“We were looking to manipulate the crop canopy to assess the impact on disease severity, and we found exactly the opposite of what we expected,” says Turkington. “That’s what makes science so challenging and fun.”

Fungicide applications at late growth stages, flag leaf or heading stage reduce net blotch severity and increase grain yield and kernel quality, whereas applications earlier at the two to three leaf stage generally had a limited impact. The interaction between seed placement and fungicide application was not significant for net blotch severity, indicating that disease response to fungicide did not vary with seed placement configuration.

Yields impacted by integrated weed management issues

Overall, grain yield was affected by seed placement, with the spread band having slightly higher yield, especially when compared with the 12 inch distinct row spacing, but the response to seed placement did vary over year/location combinations and with fungicide treatment. Kernel weight, plumpness and test weight were greatest for the spread band placement, although this response varied among year/location combinations as well.

Turkington cautions that using sweeps for seeding does bring some disadvantages under certain situations. He notes that in this study, grain yields at Lacombe and Melfort in the first year were lower for sweep seeding than narrow row seeding. This was due to greater wild oats competition at Lacombe and greater volunteer wheat competition at Melfort.

Other integrated weed control studies by AAFC research scientists Neil Harker, George Clayton and John O’Donovan have highlighted the importance of weed control when using sweeps for seeding. Turkington says the research shows that soil disturbance from sweeps promotes weed germination. As a result, weed control becomes much more critical with sweep seeding. Other considerations include moisture losses due to soil disturbance and crop residue clearance while seeding.

“It comes back to manipulating one factor and not addressing the risks that come along with it. Overall, sweep seeding might be a way of reducing the risk of net blotch, but you must be cautious and look at the entire management system. There may be subtle differences in net blotch and yield, but by and large, it’s not a huge reason to change from narrow rows to sweep seeding, especially given weed management considerations.”



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