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Potato crops bouncing back – Farmers Guardian – Jack Richardson

With potato crops making up for a slow start to the season, Farmers Guardian catches up with agronomists in the East and the South West for the latest advice ...

EAST: JACK RICHARDSON, FARMACY, LINCOLNSHIRE

Crop progress has been quite mixed so far, as cold, dry conditions around planting meant some crops took up to seven weeks to emerge, but then rain during May and warmer conditions in June triggered rapid canopy growth.

Larger and chitted seed emerged noticeably quicker for many later plantings, which should help crops recover lost ground and is worth noting for future seasons.

May’s heavy rain caused some slipping of recently planted ridges, repaired with re-ridging where possible.

There are signs of roots growing close to the edges of some ridges, so greening risk may be higher where ridge damage could not be repaired. Blight programmes are well underway, with early sprays based mainly around cymoxanil + mancozeb and cyazofamid for its zoospore activity.

As crops go through rapid canopy expansion and into full canopy, the systemic activity of fluopicolide+ propamocarb or oxathiapiprolin- based products offers greatest efficacy in higher disease pressure situations. Once growth stabilises, other options include cymoxanil+ mandipropamid, or where available, mancozeb, although tailor product choice to disease pressure.

Given mancozeb’s limited availability on-farm, Alternaria could be a bigger risk in susceptible varieties, possibly requiring specific protection within blight sprays, such as boscalid + pyraclostrobin or azoxystrobin.

After the tricky start to the season, it will be vital to carefully assess tuber size before applying maleic hydrazide for sprout suppression. Without chlorpropham and with dimethylnaphthalene still not approved in the UK, it is the primary option for sprout control in crops destined for long-term storage, but accurate application timing is crucial to maximise efficacy without compromising yield.

 

Desiccation

Looking ahead to desiccation, we have seen how effective diquat alternatives can be when used in conjunction with flailing. The greatest risk is prolonged wet weather in early autumn preventing topping and forcing growers to desiccate large crops with chemistry alone, incurring extra time and expense.

More growers are switching indeterminate varieties (for example, Markies) away from black land onto siltier soils that are easier to travel on later In the season, favouring earlier senescing varieties such as Ramos where later travel may be more challenging.

SOUTH WEST: TOM ROWE, HUTCHINSONS, DEVON/CORNWALL BORDER

As elsewhere, we have seen crops start slowly then race through growth stages over the past month and although there is still some catching up to do, much can change over the summer growing period.

The combination of rapid canopy growth and warmer, more humid conditions in early to mid-June ramped up blight pressure, requiring fungicide programmes to switch into more robust, systemic chemistry.

Oxathiapiprolin-based products are generally most effective at this stage and if blight pressure remains high, there may be a temptation to use back-to-back applications. However, where possible, try to alternate modes of action throughout the programme to avoid over-reliance on any one form of chemistry and manage potential resistance risks. This is especially important without the key multisite mancozeb.

Several actives are subject to limits on the number of applications which can be made in any season, so product choices must be considered carefully to balance late-season plans and stewardship considerations with the need to maintain effective blight protection.

Systemic activity

Fluopicolide + propamocarb hydrochloride offers a good alternative to oxathiapiprolin with strong systemic activity. It too has a limit on the total number of applications and, given its value for tuber blight control, it is worth retaining some allocations for later in the season.

Alternating with cyazofamid can be an effective late-season strategy that may take on added significance if crops take longer to desiccate without diquat.

The past two seasons have seen relatively early natural senescence, which has not really challenged alternative desiccation strategies. The same may occur this year, but equally, a dull, wet summer and early autumn with more prolonged crop growth could make it more challenging, especially for indeterminate varieties with long haulm longevity, such as Markies or Royal.

Even before the loss of diquat, most salad crop growers in this region have tended to flail before applying a stem desiccant, but it is an approach many larger maincrop growers are adopting.

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