The consequences of the extreme temperatures and moisture deficits experienced earlier in the year have become evident this week as significant areas of potato crops are now sprouting.

Substantial stress was placed on potato crops during the hot weather, which limited both canopy development and tuber bulking. With the onset of cooler, wetter conditions, daughter tubers have now broken dormancy and developed sprouts as they themselves switch to reproductive mode.

Sprouted tubers have been discovered in fields across the country, stretching from Cork to Donegal. Every variety, including Roosters, Queens, Kerr’s Pinks, Maris Piper and Golden Wonder, are being affected.

In severe cases, sprouts have elongated to six inches or more and are now developing granddaughter tubers, a process known as chain tuberisation.

An estimated 20% of the 8,000ha of potatoes in southern Ireland were irrigated this year. While a proportion of the irrigated crops are sprouting, the problem is much worse on non-irrigated crops with poorer canopies.

No clear solution

The magnitude of the unfolding sprouting problem has never been experienced before by most growers or advisers, so there is no clear advice or solution. Some growers are applying maleic hydrazide, found in Fazor, in an effort to inhibit further sprout development. However, the active cannot be applied to tubers under 25mm in size, those still under stress or to seed crops. In other cases, particularly in seed crops, growers have decided to burn off foliage before the crop has fully bulked.

Consequences

The full consequences of this sprouting remain unknown but growers fear that the results could be disastrous. Granddaughter tubers develop in part by using nutrients from the daughter tuber, leading to small tubers at the time of harvest. The threat of glassy flesh forming on daughter tubers is also a concern. It remains unclear as to whether tubers will recommence bulking post the dormancy break, regardless of maleic hydrazide application.

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