Three-step plan to maximise sprout control in potatoes

In-store sprout control for potatoes has become much more complicated and costly since the loss of chlorpropham (CIPC).

But a cost-effective option is now available, so long as it is managed correctly: maleic hydrazide – marketed as Fazor by UPL.

Field trials and an extensive literature review by potato consultant Mark Stalham suggests potato store managers who pay attention to detail and abide by good practice will reap the rewards.

“If you get it right, you can save on in-store product applications. Over the last three years, we have been trying to give recommendations by repeating old work to prove it is still correct and doing new trials to add to our knowledge.”

Step 1: Get the timing right according to your variety

The ideal spray window begins five weeks before the onset of senescence. The uptake rate decreases significantly three weeks before the rapid phase of senescence begins, which will make getting the desired maleic hydrazide levels challenging.

We are looking for 12-14 parts per million (ppm) of aleic hydrazide in tubers, but we know that 6 ppm can control sprouting. There will be a variation of levels in tubers across a plant; what we need is for every tuber to be at least 6ppm.

The window is a lot closer to desiccation than many growers think. The later you go, the less effect maleic hydrazide will have on yield.

Work we did last year showed that applying maleic hydrazide five weeks before senescence produced lower yields than three weeks, albeit not statistically significant.

All the varieties in the trials were longer-season processing varieties for McCains in groups three and four on the determinacy scale. The ideal spray window for determinate varieties probably narrows to three to four weeks before the onset of crop senescence.

Step 2: Apply maleic hydrazide in the evening and by itself

To get maleic hydrazide translocated into the leaf, it needs to remain in a soluble solution for as long as possible. A fine spray dries within minutes if applied at midday.

We need to apply it at the time when the canopy retains most of its humidity, which is as late as possible in the day. Leaving it overnight gives it more chance of being translocated.

Many potato agronomists have a view that maleic hydrazide takes a long time to get into the plant. Our work last year showed that within 36 hours, the crop can translocate enough MH to get good sprout control, and by seven days, it’s over.

Fields should be treated specifically for sprout control rather than tank-mixing maleic hydrazide with blight sprays. It’s about preventing what is an expensive problem to control in-store by applying a cheaper product in the field at the right time.

For scenarios where the weather is highly changeable, we split the maleic hydrazide into two doses at half rate. This did not impact overall maleic hydrazide levels in tubers where conditions for both applications were good 48 hours after each.

It did no harm but is another dedicated pass through the field at an odd time of day.

Step 3: Grade out tubers smaller than 45 mm

Bigger tubers have higher MH concentration levels than smaller ones. Bigger tubers are the first to initiate, usually on stems with a bigger diameter.

A bigger diameter stem leads to a wider diameter stolon, meaning a more significant plumbing system. Further up the stem, the largest leaves tend to feed the biggest tubers predominantly.

Bigger leaves shade other leaves, leading to reduced and more variable absorption when maleic hydrazide is applied to the canopy. We looked at the size of the tuber versus the maleic hydrazide levels. There isn’t a correlation until you get to very small tubers.

Small tubers often have insufficient maleic hydrazide. What happens is they break dormancy because of low maleic hydrazide, forcing you to treat the whole store, even though the bigger tubers may not break dormancy for several weeks.

There is a significant shift in maleic hydrazide levels at tuber sizes around 35mm.  However, it is a gradient, and there are differences in varieties. Because of this, you should grade out anything smaller than 45 mm for main crop potatoes.

This will ensure the greatest consistency in maleic hydrazide levels across a store. Getting maleic hydrazide applications right will save growers considerable amounts of in-store sprout control hassle.

I worked with an agronomy group to measure maleic hydrazide concentrations across two crops. The crop that averaged 14 ppm across four 10-tuber samples got through to April without any other sprout control.

When timing and application are done well, you can get six months of storage.

In-store sprout control affects dormancy

Starting in-store sprout control programmes with a product that has contact activity on the sprouts will get the most out of maleic hydrazide.

Argos orange oil suppresses sprouting in potato tubers by physically damaging the sprouts, says Geoff Hailstone, potato technical lead for UPL.

“Pure orange oil produces a physical mode of action on contact, drying and disrupting the soft tissues on which it is applied. Even sprouts that the naked eye cannot see are removed.

“By only treating once sprouts are seen in store, Argos’s contact mode of action takes full advantage of the crop’s natural dormancy and the effect of the maleic hydrazide from an application of Fazor.

“A product like DMN needs to be applied preventatively so it could be applied before it is necessary.”