Tips for healthy potato crops – Farmers Guardian
As maincrop potatoes race through growth stages, the second article in our series considers how to protect crops from blight and maximise yield potential ...
EAST - JACK RICHARDSON, FARMACY, LINCOLNSHIRE
Dry conditions throughout April and May meant a more protracted planting period in this region, especially where heavier ground took longer to work down.
Many growers on heavier-bodied silts also had to start irrigating earlier than normal to get water to penetrate ridges; an increasingly common occurrence with recent dry springs, that again brings irrigation cost and efficiency to the fore.
Some growers pumping water at four-six bar to rain gun systems had started looking more closely at investing in super-efficient trickle irrigation, but soaring equipment prices, combined with disappointing returns from potato markets, has relegated many decisions to the back burner.
Meanwhile, canopies are developing rapidly and the focus is on blight protection and balanced nutrition through to tuber initiation and bulking.
Regular tissue testing over multiple seasons has highlighted common nutritional requirements during this period, so testing now focuses more on identifying any variations across soil types, allowing plans to be adjusted accordingly.
Manganese, phosphate and potash are often needed early on, while many growers favour all-round foliar nutrition products containing key macro and micro nutrients, and natural biostimulants.
In terms of blight programmes, the emergence of more aggressive strains means stronger chemistry is generally employed from the outset, with tight seven-day intervals maintained throughout. During rapid canopy expansion, fungicides require strong systemic activity, so those based on cyazofamid, fluopicolide and propamocarb hydrochloride, and oxathiapiprolin are the go-to options.
With less mancozeb being used in programmes given the ongoing uncertainty around its future, alternaria appears to be an increasing threat in susceptible varieties such as Markies.
Previously, risk has been managed with boscalid and pyraclostrobin, but the new product based on fluopyram and prothioconazole is also likely to feature this year.
Varietal susceptibility is a key driver of alternaria risk, but dry, hot conditions, combined with stressed, damaged plants, seem to favour infection. As with all diseases, early protection of susceptible varieties is crucial. For those wanting to use mancozeb, which remains the only multisite for alternaria and blight control, it is still available as a straight active this season, however it is important to plan requirements in advance.
SOUTH WEST - ANDY FINNAMORE, HUTCHINSONS, CORNWALL
Maincrop planting finished in mid-May, with most crops going into fairly good conditions, if rather dry. By late May, many areas had only received 50-60 per cent of the normal rainfall, which presented significant challenges for weed control, particularly where residual herbicides were applied to dry soils.
Many crops needed a post-emergence tidy-up which, depending on variety choice and any following crop restrictions, was primarily based on rimsulfuron and metribuzin. Residual chemistry generally worked better in earlier and later-sown crops where there was more soil moisture, but some may still require a post-em follow-up this month.
Blight control is now the priority. Spots of blight were recently seen in early crops and volunteers in cereals, so despite the lack of Hutton periods, fungicide programmes must be robust.
With most maincrop potatoes into rapid canopy development through June, systemic fungicides are the primary choice. The main options include products based on fluopicolide and propamocarb, and oxathiapiprolin. Mandipropamid may also feature as canopies stabilise and research suggests that adding a drift reduction agent to mandipropamid can improve blight control.
Mancozeb is still available this season, so where blight risk is lower and alternaria control is also required, this may be used on its own, or mixed with cymoxanil. For susceptible varieties, such as Markies or Estima, include difenoconazole.
In all cases, pay attention to application technique to optimise blight fungicides. Water volume should not drop below 200 litres/ hectare, and using angled nozzles can further improve spray penetration and coverage throughout the canopy.
There is always a balance to find between speed of operation at busy times and efficacy, but failing to control blight properly will cost more in the long run. Targeting foliar fertiliser applications to crop requirements is always important during this stage in the growing season, but particularly so where growers have trimmed seedbed fertiliser in reaction to high prices, or if dry conditions are inhibiting soil uptake.
Tissue testing during tuber initiation is the best way of determining crop requirements, but generally magnesium, calcium, phosphate and potash are key nutrients from this stage through to bulking, shown to increase tuber numbers and size. Applying phosphites at tuber initiation can also help root development and therefore improve nutrient uptake.