21 December 2001

Warm & wet = high risk…

Potato stores are breaking down to storage rots already

and sprouts are set to emerge any day. Vigilance is the

watchword, as we report in our latest baseline advice article

WARM, wet conditions earlier this autumn mean potato crops are at high risk from both in-store rots. Growers need to monitor crops daily, warns Adrian Cunnington of the British Potato Councils Sutton Bridge storage unit.

Weekly checks are usually enough at this stage of the season, but growers need to be more vigilant this year. "Look for evidence of any breakdown, signs of wet rots, any hot spots within the potatoes and an off smell."

Reducing temperatures quickly enough in ambient stores has been a big problem. "After a very warm October and above average temperatures in November, growers using outside air for drying and cooling have had difficulties.

"And as harvesting took place in wet conditions, there will have been an increased risk of inoculum on tubers," warns Mr Cunnington.

Soft rot

Soft rot is the main concern, particularly in regions that received a lot of rain in late October.

"Where potatoes were lifted in the wet, or tubers have been deprived of oxygen during the harvesting and handling stages, bacterial build up can be rapid. Warm storage conditions then encourage breakdown.

"At very low levels, use plenty of ventilation to dry it out and limit the spread from exudate. Of course, that may not be an option with crops being stored for processing, so youll need to consider marketing them early."

Levels below 1% are usually controllable, but need watching closely. More than 2% infection is considered excessive. "Its also important to identify any factors which may be contributing to the spread, such as condensation. These can then be eliminated."

Other Diseases

Blight and rubbery rot have also been reported. "Rubbery rot is much less common and only seen occasionally. Infected tubers smell sweet, show irregular brown patches with black margins and their flesh has a rubbery texture," Mr Cunnington explains.

"Cut tubers turn a dirty pink colour after 3-4 hours at 20C. Maris Piper is particularly susceptible and outbreaks are more likely from poorly-drained soils or where problems developed after the appalling conditions last year." Thresholds are the same as for soft rot, so vigilance is essential.

Blight came in very late, due to wet, warm weather at harvest, reveals Mr Cunnington. "Some growers didnt get the chance to finish their blight control programmes, while others were unlucky and the wet conditions allowed the fungus to infect tubers."

Blighted tubers appear bluish black on the outside with brown crystallised lesions, sometimes with cavities on the inside.

Sprouting

Sprout suppressants are likely to be needed already in many stores held at warmer temperatures, believes Mr Cunnington.

"The message this year is to treat sooner rather than later. If theres been any movement in the eye, get on and treat."

Earliest sprouting is normally found in the warmest part of the crop, 300-400mm below its surface. With CIPC, it is important to get as even a temperature distribution as possible in the store before application.

"Turn off any cooling 24 hours ahead of application. Just recirculate air within the store until fogging. Then restart any ventilation within 24 hours of application." &#42

Potato store management

1 Monitoring – check stored crops daily after high autumn temperatures and rainfall

2 Evidence – look for tuber breakdown, wet rots, hot spots and any off smells.

3 Ambient stores – difficulties lowering temperatures have put crops at risk, especially where harvesting was in the wet.

4 Soft rot – main storage disease this year, due to warm and wet conditions.

5 Rubbery rot – less common, but Maris Piper particularly susceptible.

6 Blight – tuber blight may have developed, even where no evidence of field infection.

7 Thresholds – rots below 1% controllable with cooling and drying, where market permits. At 2% and over crops need unloading.

8 Spread – identify and eliminate factors contributing to spread of rots, such as condensation.

9 Sprout suppressants – likely to be needed early. Look for any movement in tuber eye.

10 Application – turn off any cooling and recirculate air for 24 hours before fogging.

POTATO MANAGEMENT

1 Monitoring – check stored crops daily after high autumn temperatures and rainfall

2 Evidence – look for tuber breakdown, wet rots, hot spots and any off smells.

3 Ambient stores – difficulties lowering temperatures have put crops at risk, especially where harvesting was in the wet.

4 Soft rot – main storage disease this year, due to warm and wet conditions.

5 Rubbery rot – less common, but Maris Piper particularly susceptible.

6 Blight – tuber blight may have developed, even where no evidence of field infection.

7 Thresholds – rots below 1% controllable with cooling and drying, where market permits. At 2% and over crops need unloading.

8 Spread – identify and eliminate factors contributing to spread of rots, such as condensation.

9 Sprout suppressants – likely to be needed early. Look for any movement in tuber eye.

10 Application – turn off any cooling and recirculate air for 24 hours before fogging.