Edition September 2018

Transcription

1 Edition September 2018 This Crop Action contains information on: 1. Ryegrass closing dates and grazing 2. Managing extra feed if short on grazing mouths 3. Slugs 4. Disease control in barley 5. Aphid suction trap data 1. Ryegrass closing dates and grazing Closing date Closing date refers to final defoliation. Determining closing date is important in ryegrass seed crops to reduce the risk of lodging, while maintaining reproductive tiller numbers. This is achieved by reducing the biomass of the crop through grazing, ensiling or topping. Optimum closing date is related to cultivar heading date. The optimum closing date for Grasslands Nui sown at Lincoln and Chertsey is in the first week of October. Areas with cooler climates, such as the upper plains, can delay the closing date for up to five days for irrigated ryegrass crops. To estimate closing date for other cultivars, adjust by the relative heading date of Grasslands Nui. Crops that have been lightly grazed will have higher growing points and will need to be closed earlier. In contrast, crops that have been grazed by set stocking can be grazed for a few days longer than the optimum closing date. Closing too early can promote early lodging and seed shattering at harvest. Closing too late, will ultimately reduce seed head numbers. To maximise seed yield, the crop should have a seed head density of at least 1800 heads/m² for forage types and 2,400 head/m² for turf types. This seed head density can be achieved through nitrogen application and closing date. Defoliation will help initiate tiller emergence and increase the number of tillers/m². For Italian/annual ryegrass cultivars the optimum closing date is between the 20 th and 30th of October. To find out more read Cropping Strategies: Closing date in Perennial ryegrass and Closing date in Italian ryegrass. 2. Managing extra feed if short on grazing mouths Having limited stock on farm may require the use of alternative methods to manage excess feed and to close the crop. Increasing PGR rate will help reduce the risk of lodging. Mechanical topping or ensiling the crop are good methods to mimic grazing. For silage, the cutting date should be about two weeks earlier than the grazed closing date. For topping, it is better to consider topping twice if the crop is bulky, rather than once and leaving a large amount of leaf to decay.

2 3. Slugs There seem to be plenty of slugs around at present, so monitor for them if you are sowing crops, particularly when direct drilling as surface trash provides an ideal habitat. Crops are most vulnerable during establishment because slugs attack and hollow out seeds and bite young seedling plants off at ground level. Monitoring for slugs should continue until the crop is well established (6-8 weeks). The best way to establish if you have a slug problem is to put out wet sacks or tiles. Slugs require moisture for reproduction, survival and activity, resulting in greatest crop damage during wet weather. Burning and cultivation reduce slug pressure, however this does not prevent ingress from paddock edges. There are several types of baits available although they all kill slugs they differ in cost, ease of application, longevity and impacts on non-target organisms. Secondary poisoning of generalist beetle predators occurs when the beetles which eat a slug that has ingested methiocarb baits, so if you wish to protect these beneficial insects it is not advisable to use methiocarb based baits. Timing of bait application is critical and applying baits for peace of mind when slugs are not active is a waste of money. In the right conditions slug populations will recover rapidly from baiting, cultivation, or declines due to a period of dry weather. Slugs are most active in spring and autumn, so this is when slug baits should be applied. Baiting in the previous crop may need to be considered if monitoring shows high numbers and a slug sensitive crop is being planned. Work in Oregon has found that baiting under the following conditions increases efficacy: Applying the bait at dusk Not applying the bait if windy or too cold (below 8 O C) Not applying the bait if it is raining or too wet. Another thing to consider is the trade-off between how rain-fast the baits are and the concentration of baiting points. The more rain-fast baits have the active embedded (i.e. Metarex ) but if there are very high slug numbers then the number of baiting points may be a more important consideration.

3 4. Disease control in barley What has changed in barley disease management? Ramularia has been the main disease present in recent FAR autumn sown barley trials. Ramularia together with leaf rust have been the main diseases present in recent FAR spring sown trials. Ramularia is resistant to the strobilurins and has recently become less sensitive to the SDHI fungicides. The new multisite fungicide Phoenix has shown good control of Ramularia when used in a mix with Proline, but currently does not have a registration for control of this disease. Ramularia resistance to the SDHIs Leaves infected with Ramularia were collected from barley crops throughout New Zealand in Laboratory tests carried out by Plant & Food Research in spring 2017 identified Ramularia isolates sampled from Canterbury, Southland and Otago with reduced sensitivity to the SDHI fungicides. The presence of three mutations which impact the performance of SDHI fungicides were confirmed. Isolates with two of the mutations required more than 0.5 ppm bixafen to inhibit growth by 50%, compared with less than ppm bixafen to control the wild-type isolates. This means that the isolates were 100 x less sensitive to the fungicide than the wild type i.e. they had a resistance factor of 100. A similar result would be expected with other SDHI fungicides as they are cross resistant. As this publication goes to print, microplate assays of Ramularia isolates collected from crops in Canterbury, Manawatu and Southland in is nearly complete. Interim results indicate that there has been a further shift with more than 80% of isolates collected insensitive to SDHI fungicides. Another mutation, C-N87S, was also found, and is associated with a low-to-moderate reduction in sensitivity to SDHIs. Autumn sown barley field trial data The following table shows the disease severity, mean yield and margin over fungicide cost from 11 fungicide treatments tested from a dryland trial of cultivar Cassia at Geraldine and an irrigated trial of cultivar 776 at Southbridge in The main disease at both sites was Ramularia. The 2017 season was hot and dry from late spring. The average yield response to fungicide was low, at 15% for both trials with low margins over fungicide cost. There was no significant yield gain from increasing the fungicide input above two sprays of Proline 0.4 L/ha. This result was similar to four trials run in 2014 to 2016 where the main disease was also Ramularia. In comparison, the average yield response from fungicide in the three trials from 2010 to 2012 was 30% (Cropping Strategies Cereal disease management). In these trials, there was a further 1 t/ha yield increase from the best triazole and SDHI mixes over Proline alone. This raises the question; are the SDHI fungicides still effective against Ramularia, particularly since Ramularia strains with reduced sensitivity to SDHIs have been identified. Seguris Flexi alone did provide significant control of Ramularia in the Southbridge trial, however, in comparison to previous seasons, Ramularia control with SDHI plus triazole mixes has become less effective. Disease control

4 when assessed 40 days after the second application of Aviator 0.7 L/ha decreased from 97 and 98% in 2011 and 2012 to 56% in In 2017 trials, adding Phoenix (Phoenix is a multisite protectant fungicide, Ramularia is not on the Phoenix label) to Proline in a two spray programme gave significantly better control of Ramularia than mixes of triazole with SDHI and the highest yield. The Proline plus Phoenix mix also gave the highest margin over fungicide cost in both trials. Phoenix will be further assessed in trials. What role if any do SDHI fungicides now have in autumn sown barley disease management programmes? Although not common in FAR autumn sown barley trials, leaf rust is a disease that Proline + Phoenix mixes are less effective against that SDHI fungicides can strengthen, especially with cultivars without good rust resistance. Table 8. Influence of fungicide on leaf area affected (LAA) by Ramularia (%), yield (t/ha) and margin over fungicide cost relative to the untreated (MOFC, $/ha, grain price $380/t) in autumn sown barley dryland trial at Geraldine and irrigated at Southbridge in Trt GS31 GS Geraldine Trial (cv Cassia) Southbridge trial (cv 776) %LAA (L2 & 3) Yield (t/ha) MOFC ($/ha) %LAA (L2 & 3) Yield (t/ha) 1 nil nil Proline 0.4 Proline * Seguris flexi 0.6 Seguris flexi Aviator 1.0 Aviator Aviator 0.7 Aviator Adexar 1.25 Adexar MOFC ($/ha) 7 Adexar 1.0 Adexar Proline Acanto Proline Seguris 0.25 Flexi Proline Acanto Proline Seguris 0.37 flexi Phoenix Proline Phoenix Proline Phoenix Aviator Phoenix Aviator Mean LSD (P<0.05) CV% *experimental treatment only in order to assess sensitivity of Ramularia to SDHIs. SDHI fungicides should always be mixed with a fungicide with a different mode of action effective against the target disease. For experimental reasons Phoenix was applied outside of the latest label application timing of GS39. The T2 spray was applied toward the GS49 end of the spray window.

5 Autumn sown barley fungicide programme T1 - GS30-GS31 (pseudo stem erect - first node) A Proline + Phoenix mix has given superior control of Ramularia over other triazole + SDHI options and the highest margin over fungicide cost in FAR trials. This mix should also be effective on scald although this disease was not present in the trials. Consider: Proline 0.4 L/ha + Phoenix 1.5 L/ha Proline + Phoenix is less effective against leaf rust. Leaf rust has been present in only one of six FAR autumn sown barley trials over recent years. However, if rust is present or the cultivar has a susceptibility to rust consider: Proline 0.4 L/ha + Acanto 0.25 L/ha + Phoenix 1.5 L/ha Proline 0.4 L/ha + Seguris Flexi 0.3 L/ha + Phoenix 1.5 L/ha Aviator Xpro L/ha + Phoenix 1.5 L/ha Adexar L/ha + Phoenix 1.5 L/ha. In lower disease pressure scenarios, such as a dry spring or more disease resistant cultivars, the lower rate in the range may be more appropriate. Since the dose rate of the triazole in these pre-formulated mixes of Aviator Xpro 0.5 L/ha or Adexar 0.6 L/ha is less than half the label rate for the triazole, consider topping up the triazole component in order to better complement Phoenix and the SDHI (e.g. add Proline at 0.1 L/ha to the lower rate of Aviator Xpro or add Opus at 0.2 L/ha to the Adexar). Phoenix (multi-site protectant) and Ramularia control: In FAR trials, Phoenix (active ingredient folpet) mixed with Proline has given superior control of Ramularia and higher yields compared with triazole plus SDHI treatments. Phoenix could also assist in controlling Ramularia strains with reduced sensitivity to the SDHIs. The fungicide Phoenix has a label recommendation for control of scald only in barley, with a maximum of two applications up to GS39. A change to the label is currently being sought to add Ramularia. An update of the FAR Cereal Disease Management Strategy (Revised 2018) will be delivered in the next few weeks. In the meantime, we will put excerpts into Crop Action.

6 Number of aphids 5. Aphid suction trap data Weekly suction trap capture of cereal aphids The number of cereal aphids caught in the Lincoln suction trap from the 04 th September to the 10 th of September 2018 was 5. The number of cereal aphids caught this year is shown in the graph below (blue line), along with: - The weekly average number of cereal aphids caught in the Lincoln suction trap between (green line), and - The weekly number of cereal aphids caught in the Lincoln suction trap in 2005, a year of very high BYDV incidence (red line). The cereal aphids caught in the Lincoln suction trap do not represent secondary spread of BYDV within a crop. Directly searching your crop will provide the best information about the incidence of cereal aphids in your crop. Searching is best done on sunny afternoons, looking at the underside of leaves year average Degree weeks Generally the warmer the temperature, the faster an aphid will develop into an adult. Below are the degree weeks at a base of 5.8 C (the minimum threshold for aphid growth). Degree weeks calculate the number of hours above the minimum development temperature (5.8 C) based on hourly temperatures for that week. The higher the degree week the more favourable conditions are for aphid development. However other factors, such as amount of rain, can affect aphid growth and survival.

7 Degree weeks at 5.8 C The data are collected from the NIWA CliFlo database, Lincoln station (17603). Below are degree weeks calculated for: so far, including the last week (blue line), and - The average degree weeks between 2006 and 2017 (green line), and - The weekly degree days in 2005, a year of very high BYDV incidence (red line) year average Contact us Rob Craigie rob.craigie@far.org.nz Richard Chynoweth richard.chynoweth@far.org.nz Phil Rolston phil.rolston@far.org.nz Jo Drummond jo.drummond@far.org.nz Ivan Lawrie ivan.lawrie@far.org.nz NOTE: This publication is copyright to the Foundation for Arable Research ( FAR ) and may not be reproduced or copied in any form whatsoever without FAR s written permission. This publication is intended to provide accurate and adequate information relating to the subject matters contained in it and is based on information current at the time of publication. Information contained in this publication is general in nature and not intended as a substitute for specific professional advice on any matter and should not be relied upon for that purpose. No endorsement of named products is intended nor is any criticism of other alternative, but unnamed products. It has been prepared and made available to all persons and entities strictly on the basis that FAR, its researchers and authors are fully excluded from any liability for damages arising out of any reliance in part or in full upon any of the information for any purpose. All previous Crop Actions and other publications can be viewed on the FAR website: Please contact the FAR Office if you would like to unsubscribe from Crop Action, or change your address.