SFF Project Summary
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| Latest update | |
| Dry Rot Field Day Handouts [213K PDF] | |
| Updated: | 03 October 2008 |
Problem/Opportunity that the Project is Addressing
Southland and Otago farmers grow approximately 50,000 ha of swedes each year to transfer summer feed surplus to winter grazing. There is a widespread incidence of the fungus dry rot (Leptosphaeria Maculans) in a significant number of crops. Up to 80% loss of yield/utilisation can occur. This has serious consequences for the farmers concerned and creates a spore source for infecting next year’s crops. The resistant swede varieties have succumbed to new strains of dry rot. It is thought management opportunities exist to mitigate dry rot but monitoring is required to confirm this and an extension programme is required to ensure uptake of any best practices. It may also be possible to develop a spore counting service to advise farmers of the best sowing date.
As well it is likely the increasing area of summer brassicas being grown is contributing to the problem. The percentage of seriously infected crops appears to have risen in recent years to be as high as 40% in some localities.
Controlling the problem is important because of the reliance of swedes for winter feed and the high cost of crop failure which usually isn’t detected until late in the season.
Also knowing and using best practices will be crucial if a bio fuel industry based on soil seed rape is to be developed in the future, especially with the increasing amount of summer brassica being grown.
Proposed Work Plan
- A survey has been initiated to determine if there are any trends that can be identified from the pattern of disease in 2004-2005 winter crops.
- Overseas and New Zealand literature is being reviewed to determine if there are any obvious management techniques that can be applied to mitigate the disease in New Zealand.
- Formal replicated trials are to be established by Crop & Food staff at Gore. Treatment will include sowing date, cultivar and fungicides.
- Paddock trials on farm will be conducted also comparing sowing date and fungicide.
- The fungicide treatments will also compare early and later application.
- It is planned to set up two spore traps to monitor the wind borne spore phase of the disease. If trends are recorded then spore trapping may be a useful predictive management tool in the future.
Extension
- It is proposed to have meetings in the autumn of 2006, 2007 and a final field day in spring 2007 to explain the work programme and results as they are recorded.
Latest update
The project aimed at further testing of fungicides to control dry rot and assessment and development of management techniques to mitigate the disease. For the 2006/07 year trials were set up in first and second crop paddocks. Three Swede varieties and three chemicals were trialed in the first crop paddock. Two varieties and three chemicals were trialled in the second crop.
The incidence of disease was relatively low in the first crop, approximately 10% of plants in the susceptible variety which is typical across the province.
The application of chemicals was able to give significant control of the disease.
In the second crop paddock, varieties that didn’t have a high level of disease tolerance were overcome by the disease. Fungicides gave some control but the disease pressure was overwhelming. A highly tolerant variety was successful in producing a crop but growing tolerant Swedes under these conditions is not recommended because of the increased risk of the selection pressure causing the disease to overcome the plant tolerance.
March 2007
Trials were carried out during the 2005-2006 growing season on swedes to monitor the incidence and effect of dry rot and what treatments might have a mitigating action.
Key Points
- Cultivar, sowing date and fungicide trials were established on a paddock that had been in swedes the previous year and had an incidence of dry rot.
- Time of sowing, cultivar and fungicide treatments all showed initial positive effects.
- Extreme disease pressure by late season masked the effects likely to be observed in a farm situation.
- Sowing into infected residue from a previous crop led to extreme disease pressure, more than what was wanted for this trial work!
- Closely observing the disease regularly during the season provided a lot of information about its development and spread.
The disease source for the current season primarily comes from diseased crop residue from the previous season. This is demonstrated by the incidence of dry rot in second year swede crops.
Survey Results
A survey of disease incidence was carried out on the 2005-06 crop.
Farmers provided information on 57 first crops and 13 second crops, all swedes, both first crop and second crop varieties. 84% of the first crops had dry rot infection, on average 18% of bulbs were infected. 92% of the second crops were infected, on average 56% of bulbs were infected.
Trial Work 2006-2007
A total of 26 treatments with 4 replicates per treatment is planned.
In a first crop paddock 18 treatments involving a seed treatment, 2 fungicides with 1 or 2 applications and 3 swede cultivars is planned.
In a second crop paddock a seed treatment, 2 fungicides and 2 cultivars will be evaluated. The fungicides will each be applied early and late.
To date the disease incidence in the first crop treatments is very low so no scoring of plots has been done as there are no differences between treatments. In the second crop there are early indications of treatment differences which will be quantified when a harvest yield is completed.
Quarterly Update: October 2006
Survey
A survey of swede crops for dry rot incidence was conducted with the following results. The survey area was Southland and West Otago.
There were 41 farms and 70 crops in the survey.
There were 57 first crops, only 9 didn’t have any dry rot infection. Both first and second crop varieties were involved. The average infection rate was 18% of bulbs.
There were 13 second crops and 12 recorded dry rot infection. The average incidence of infection was 56% of bulbs. Varieties were generally the most tolerant available, Winton and Aparima Gold.
It is worth noting the severity of infection was a lot lower even though there was a higher incidence.
Trials
Trials will be established by Crop & Food Research at Gore again this year. Treatments will include variety, seed coatings and fungicides. Also trials will be established in a first crop and a second crop situation.
Trial results for the 2005-06 year showed that although Winton and Aparima Gold are not fully resistant they do have a much higher tolerance for dry rot.
Fungicides do have some activity and further testing will provide more information this season. Extreme disease pressure from early sowings last year affected later sowings and some of the other treatments were difficult to interpret due to the presence of other diseases.
However close observation of the disease as it progressed during the season gave some valuable information about its ingress and spread. Windblown spores were infecting emerging seedlings in November 2005 and by August 2006 windblown spores were being released from 2005 crop residue.
June 2006
Monitoring of trial plots and farmer’s crops this season has provided the information to make the following recommendations.
The risk of dry rot infecting a swede crop can be reduced by using good husbandry practices.
Dry rot is a fungus disease which lives on crop material, both dead or alive. Next seasons infection comes from the fungus releasing airborne spores which land and grow on new crop leaves.
Plough any swede crop residue under as soon as it is practical to do so. Even paddocks that are going to be sown out and not sown into a second crop should be ploughed as the spores can travel hundreds of metres and affect crops some distance away.
Once diseased material is buried it cannot release spores. If it is ploughed before the new season’s crop is sown the risk of a significant number of spores being released to infect the new crop is greatly reduced.
Avoid growing swedes after swedes. It is highly likely there will have been some disease in the first crop. Spores can travel long distances and extremely few first crops have no infection whatsoever.
Chou has greater resistance to dry rot than swedes and would be a safe choice if a second crop was to be grown.
Aparima Gold and Winton are the most dry rot tolerant varieties available. Trial work in 2005 confirmed a lower disease level than other varieties. If you consider your property to be in a high risk area for dry rot these are the best varieties available.
A later sowing date may result in a lower disease incidence. As the season progresses and diseased crop residue decays the quantity of spores being released diminishes. However a later sowing will probably also reduce the yield potential.
For agronomic reasons sowing should occur after 20 November to avoid plants bolting. An earlier sowing date may be appropriate on light summer dry soils or where it is planned to feed the crop off early.
March 2006
Spore traps were set up at Gore and Wairio. While they were successful in trapping a whole range of spores there was no detectable pattern of dry rot spore capture. This technique is used overseas so it is proposed to find out what differences, if any, there are in methodology.
At the Gore trial site the level of disease pressure was extremely high. Yield measurements will be taken at the end of May. Initial results indicate some fungicide activity but it is unknown yet how successful the result will be under such high disease challenge. Similarly swede variety differences in tolerance have been observed and yield data will confirm the magnitude of the effect.
The Wairio and Fortrose sites had surprisingly low levels of disease, not enough to allow the collection of meaningful treatment results.
A meeting was held on 27 April to update Southland and Otago merchants and farm consultants on progress to date.
December 2005
The 2004-2005 survey result returns were collected and analysed with the help of Wrightson Seeds database. There were a moderate number of returns but no conclusive trends appeared from the data. This in part may be due to the unusual weather pattern during December and January. It is planned this year to mount a campaign and achieve more surveyed crops and perhaps change the format of the survey form slightly with the information we will have to date.
With the help of BASF, Wrightson Seed and Crop and Food four trial sites have been set up at Hindon, Fortrose, Gore and Wairio. At these sites four or more fungicides are being evaluated and all sites have several swede cultivars. At the Gore site current commercial and future cultivars under trial are being grown. Also at Gore there are three sowing dates treatments as well. At two sites a seed treatment is also being evaluated that in Australia gives up to eight weeks seedling protection in canola.
Two spore traps have been set up and run from mid November, one at Wairio in Western Southland in the middle of 200 ha of Brassica. The other at Crop & Food Gore in the trial paddock. From this data we hope to get an indication of timing and intensity of spore release. These tapes are being analysed by Ian Harvey at Lincoln.
In January all trial sites were assessed for the incidence of dry rot and other diseases. The results from this are currently being analysed.
The Gore trial site has a good level of disease which should show which treatments are having an effect.
