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THE DROUGHT ISSUE: Dealing with in-field sprouting and secondary growth

Publication Date: 
27 July 2018

At a recent AHDB event, Dr Mark Stalham of NIAB CUF discussed calls he has received regarding the prevention of in-field sprouting and secondary growth. With thunderstorms in the forecast, these are genuine risks. He said:

"Many crops, particularly those that are unirrigated, will have effectively stopped growing in the last week or ten days. A deluge of water could cause growth cracks.

"The heat-stress tubers are under, particular when many have poor canopy cover, means we have seen in-field sprouting and we will continue to see that as long as the hot weather continues.

"We've had calls asking if the use of MH as a growth inhibitor would help. Crops under this much stress are highly unlikely to take-up MH to the required amount to prevent these problems. All that is likely to happen is that you would further restrict yield."

Watch a video of Mark Stalham discussing in-field sprouting and secondary growth.*

We have also been discussing the use of MH at SPot Farm West. Dr Anne Stone, Knowledge Exchange Manager for the West has reviewed the conditions required for effective use of MH, decribing a challenging situation for growers:

Maleic Hydrazide.  Uses on Potatoes

Note by Dr Anne Stone 11.07 18

Maleic hydrazide (MH) is a plant growth regulator which inhibits cell division but not cell expansion. It is used for several distinct purposes, though more than one benefit can apply to a single crop. The most widely used commercial product containing MH is Fazor.

Sprout suppression in store. Either alone or as a precursor to products applied in store, maleic hydrazide extends storage length. If used correctly it doesn’t affect fry colour, dry matter or cooking quality.

Volunteer control. The same restriction on sprouting which improves storage delays growth of ground keepers, making them more likely to be supressed by crop competition when they eventually emerge.

Control of secondary growth. When drought greatly reduces tuber growth before foliage senescence, and is followed by availability of water, growth resumes leading to dolls on existing tubers, new little tubers on stolons and growth cracks. These can be associated with glassiness or jelly end rot. MH applied soon after the weather breaks can reduce secondary growth, preserving crop quality and increasing marketable yield.

Variety. The response to timing, phytotoxic effects and the effect on secondary growth depends partly on variety (De Blauwer et al 2012, Fazor label).

MH is usually applied to varieties for processing. Most customers of varieties sold fresh do not currently allow suppliers to use MH, except with derogations which are given to certain varieties kept long term, e.g. King Edward. 

Timing. The label recommends application to actively growing foliage when the smallest tubers required to reach marketable size are not less than 25mm long, typically 3-5 weeks before haulm destruction. It should be applied to actively growing foliage not to stressed crops. Ideally there should be 24 hours rain free, after application since MH is the least rain-fast of any product applied to potatoes. The first 12 hours are the most critical.

In practice these conditions are sometimes not achieved. In the suitable period for application either drought stress or frequent rain may prevent MH from being effective. If its necessary to apply in a heat wave, spraying should be done in the cool of early morning or late evening, and in as much water as possible.

Application less than three weeks before senescence or desiccation will not only be ineffective but may possibly cause a residue exceeding the MRL in a low yielding crop. Application too early can reduce the larger ware fraction, desirable for chips and bakers; so crisping crops are most commonly treated. Labels in USA typically recommend applying when the smallest tubers required to reach marketable size are 38-50mm diameter.

The Fera pesticide usage survey for 2016 found that 16% of the ware area sampled was treated with MH. It was applied in July, 20% and August, 80%.

Adjuvants. The approval holder, Arysta, states they have found mineral oil adjuvants can obstruct MH uptake, hence the label advice to apply it on its own. Growers may apply with blight sprays for convenience, so Arysta provides information on compatibility, attached. Some agronomists recommend mineral oil or other adjuvants which they believe improves uptake, especially if there is rain within 24 hours of application.

Sources:

  • Fazor label. Arysta UK.
  • Project R 275 Maleic Hydrazide in potato volunteer control Buckley et al 2006.
  • Maleic hydrazide: sprout suppression of potatoes in the field. De Blauwer et al Commun Agric Appl Biol Sci. 2012;77(3):343-51

*This video was shot on a phone in a windy field, sorry for the noise quality*

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