Potato Review

www.potatoreview.com POTATO REVIEW MAY/JUNE 2022 23 BAYER CONFERENCE Biomass images can be filtered in a similar way to identify crops in need of closer monitoring and plan seasonal workloads, for instance spraying. Decreasing biomass rates can also show rate of crop senescence pre-harvest. Yield mapping Yield maps are perhaps most valuable for identifying areas of contrasting performance for later investigation. FieldView allows growers to produce a virtual potato yield map which can give an indication of the variability within a field to evaluate performance in different areas. “It is possible to scrutinise performance within a field. By drawing a polygon around the desired area, the yield and other data such as moisture content can be displayed. This has value for assessing on-farm trials such as changes to seed spacing, bed or row width, fertiliser rates or between varieties, but there is still more to come,” Edward said. John Weir, Gateside, Fife. 65 hectares of mainly pre-pack whites and Maris Piper has been using FieldView for about a year. He said: “What I like about it so far is the excellent accessibility. It is available all the time and the images are updated regularly with an email notifying me that there are new maps to view. From these I can investigate crop development and compare it with yield maps from previous years to understand differences in crop growth and identify areas in need of closer inspection. It means you arrive at the field with a clear indication of which parts of the crop need to be inspected. Our crop walking is better targeted as a result. “I’ve been using it to look at the potato enterprise in a range of different ways and so far, I have not uncovered any irregularities. As we strive to be more efficient with the use of inputs such as water and fertiliser, the scope for failing to meet crop needs increases so we must be aware of the need to monitor crop development regularly and promptly respond to any issues. “My principal interest in FieldView is in investigating the potential of variable seed spacing. I am largely at the data gathering stage, but I will use FieldView to monitor crops and overlay my planting prescription to see what relationships there are and whether I am happy with the decisions I made. I will then further analyse the crop again pre- harvest when I will perform crop digs at pre-determined locations. The information will then be overlayed with vegetation maps to extrapolate a yield forecast. This can then be compared with the actual yield at harvest.” Latest learnings on Alternaria highlight value of IPM The spread of fungicide-resistant strains of early blight (Alternaria spp.) and the difficulties they create in ensuring crops are suitably protected continues to concern researchers. Speaking at the Bayer potato conference, Dr Juergen Derpmann of Bayer Crop Science, Germany described how novel genotypes of Alternaria solani were evidence of the need to follow best practice in crop protection. “We know that such isolates with a mutation in cytochrome b. gene at position F129L, were detected at high frequencies in Germany, the Netherlands and other countries across Europe. This demonstrates a reduced sensitivity to most strobilurins, such as pyraclostrobin, azoxystrobin and famoxadone,” he said. “Monitoring has also identified isolates showing several mutations in different parts of the enzyme succinate dehydrogenase, which are leading to resistance to some SDHI active substances - namely boscalid. Analysis of samples collected from across Western Europe reveal that isolates exhibiting these genotypes are now becoming widespread,” he added. More recent research indicates that SDHI-fungicides show an incomplete cross- resistance pattern in Alternaria species, for example, isolates carrying the sdhB-H278Y mutation were resistant to boscalid (a pyridine-carboxamide) but were controlled by other active substances in the same mode of action group of SDHIs belonging to another chemical group, such as fluopyram (a pyridinyl-ethyl-benzamide). DMI fungicides such as prothioconazole (a triazolinthione) have demonstrated a stable sensitivity against the dominant Alternaria spp. over many years, with no shift in sensitivity seen in-vitro test systems. This supports the use of Caligula ( fluopyram + prothioconazole) as an effective fungicide with a built-in resistance management strategy for use against Alternaria spp. Growers are encouraged to consider cultural control measures as part of an integrated strategy for disease control. However, focussing only on plant host resistance is recognised to be of limited value because of the evolutionary potential of the pathogen. As resistance genes in the plant can also be overcome by pathogen adaptation, it follows that repeated production of the same varieties is unsustainable in the long term. Also, eliminating weeds such as Black nightshade (Solanum nigrum) which is considered a potential alternative source of inoculum, can reduce the inoculum pressure within the crop. As the popularity of this plant species increases due to its capacity to reduce potato cyst nematode (PCN) populations, the inoculum pressure facing crops is likely to increase.