There are always new challenges to consider in farming – and especially potato growing – as with the announcement Vydate (oxamyl) supply will be severely restricted due to production issues. The use of nematicides and pest control issues will therefore need careful management in the coming season.
Credit must be given to DuPont for letting the industry know of the supply problem at this stage, which now enables us all to plan early for next spring’s activities. The lack of Vydate availability next year will mean growers, in some situations, having to change their cropping practices.
Rigorous soil sampling may give us an opportunity to change fields, should we discover problem levels of PCN. We, and most of the industry, would advocate one-hectare sampling with a quad-bike which can then provide a GPS map. Fifty cores per ha is the industry standard, which allows for 2kg of soil to be sent the lab for analysis. This gives us the chance to identify more accurately low numbers, and also at the other end of the scale hotspots which can then be treated differently or not cropped at all.
By getting the sampling done in good time there is even the opportunity to select completely new fields and perhaps avoid cropping some fields with potatoes for another year or two. This will allow PCN numbers to decline naturally, or we could try to accelerate this decline by using bio-control methods.
Using hot mustard as a bio-fumigant, or sisimbrofolium to reduce cyst numbers, can be a very useful addition to any control programme. However, these are crops and should be treated as such – they must not be forced in at the last minute – if they are to achieve good results in helping PCN levels decline.
Additionally, if the sampling is done in good time and while soil temperatures are still high enough, metam sodium can be applied (by specialist contractors) to these hotspots.
Where the decision has been made to use metam sodium, growers should still use a granule in the spring to maintain PCN numbers at low levels. We are currently setting up further metam trials in conjunction with Certis and Boston Crop Sprayers. Their aim is to look at potential benefits in the other crops across the whole rotation, not just for PCN, to see if we can justify using it at lower PCN numbers, especially in crop rotations which include salads.
General ‘best practice’ would be to identify the PCN species present, and if possible a resistant and tolerant variety used. It may be problems with agrochemical supply force the industry into accepting more of these varieties. Where there is still a need to treat then it’s a choice between the two remaining granules left – nemathorin (fosthiazate) and mocap (ethoprophos) – most probably chosen on their harvest interval.
Spraing and free living nematode (FLN) feeding damage is another matter. In recent years, in-furrow treatment with Vydate has been the standard method of reducing these pest problems.
Spraing symptoms are caused by the tobacco rattle virus, which is transmitted by Trichodorus sp. nematodes. Direct feeding damage is caused by several other species including pratylenchus and longidorus.
Unfortunately, none of the remaining granules have an in-furrow recommendation currently on their label and it is unlikely they will get one going forward. This means where there is a risk of spraing or direct feeding damage a full dose, overall application of either of the remaining two granules is the only treatment method available.
Many of the long-term storage varieties favoured by the processing industry are susceptible to spraing. With the very low tolerance levels accepted by the processors it is essential to treat where there is a risk. Testing for FLN and spraing is not as easy as PCN, as the nematodes have the ability to move up and down the soil profile and so may not be detected if the soil is too dry or too cold. Also the samples, every 4ha minimum, have to be handled carefully as the nematodes can be damaged in transit to the lab. Then the TRV test - whilst being very accurate - can only say if the nematodes in the sample have the virus and not the whole field.
Generally, spraing is treated very much on a precautionary principle, but good sampling always help in best decision making.
So for next season we will definitely have to make changes. I also think there is no doubt we’ll learn new things, as the consequence of change means we will alter the things we do to grow our crops.