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Johann van der Vyver Product Development Manager Hygrotech

(ANOTHER UNIQUE REGISTRATION FOR SPOREKILL)

In the previous Hygrotech Forum, we mentioned that the registration of Sporekill, for use on potato seed tubers was pending. This registration has just been approved and implies the following: “The control of bacterial soft rot and contamination of potato seed tubers, caused during washing or dip treatment process, by controlling water bo r ne E rw i ni a ca ro t ov o ra s ub s p. c ar o to vo r a” . Reinette Gouws, plant pathologist at ARC Roodeplaat describes pectolytic Erwinia (Erwinia carotovora subsp. atroseptica and E. carotovora subsp. carotovora) as the cause of the most commonly occurring bacterial diseases in potatoes, namely bacterial soft rot (Chips May/June 2003).

SPOREKILL EFFICACY The registration trials were conducted by QMS AgriScience. In all three trials, Sporekill exhibited excellent capabilities to prevent the contamination of potato seed tubers during the washing process (Table 1). Table 1: Effect of Sporekill on the water borne Erwinia carotovora subsp. carotovora as indicated by the development of bacterial soft rot on injured potato tubers incubated at a controlled temperature of 25 °C and room temperature.

Treatment

Mean percentage of tubers infected with Erwinia carotovora subsp. carotovora Trial 1

Trial 2

Trial 3

32 b

84 c

96 c

Non - inoculated control (@ 25 °C)

0a

4a

4a

Sporekill at 150 ml/ 100 L water (@ 25 °C)

0a

0a

0a

Inoculated control (Room temperature)

36 b

92 c

44 b

Delay harvesting until the skin has set to reduce tuber injuries (bacterial entry points).

Non - inoculated control (Room temperature)

0a

8a

0a

At harvest, watch tuber handling practices, and ensure good sanitary procedures to reduce the spread of the bacteria. Limit mechanical damage during harvest and handling.

Sporekill at 150ml/ 100 L (Room temperature)

0a

8a

0a

BACTERIAL SOFT ROT Bacterial soft rot is initially characterised by a small, water soaked area on the tuber. This area enlarges rapidly to form a soft, wet rot. If conditions are favourable the tuber may rot completely within a few days. Conditions that support disease development are moist conditions during storage, wet tubers, low oxygen concentration and damaged tubers. Unfortunately most of these favourable conditions for disease development are the consequence of poor harvesting practices and storage conditions. This makes control or prevention of the disease very difficult. The following preventative measures are however, often suggested and applied in the industry: Avoid excessive soil moisture just prior to harvesting, in an attempt to prevent infection through the tuber lenticels.

Cool tubers gradually and store them at a temperature of about 4°C. E ns ur e th at t ub er s are dry b e for e st or ag e. E ns ur e s uffi cie nt ve nti la tio n d ur in g s tor ag e. Treatment of the tubers after the process of washing off the soil to sterilise tuber surfaces and prevent contamination among tubers will provide a measure of control. Due to commercial harvesting and processing practices, the majority of the mentioned cultural control measures are often difficult to implement to the full extent originally intended. The final suggestion allows however, the best possibility for control and is exactly what this latest registration of Sporekill is based on.

Inoculated control (@ 25 °C)

Values in the same column followed by the same letter do not differ significantly at the standard level of significance, according to the LSD test.

This registration data also confirmed preliminary evaluations done by South Australian Research and Development Institute, University of Pretoria and Rhodes University. DIRECTIONS FOR USE Use at a dosage of 150 ml Sporekill per 100 L of water. Dip tubers for 3 – 5 minutes. Replace the solution when the water becomes too dirty. The Sporekill concentration may be regulated at the recommended dosage by using the “Spo reki ll Test Kit” . O nly tre at uncu t p otato es. For more information on this exiting new Sporekill registration contact your nearest Hygrotech branch or phone 082-9030031.

Forum - Winter 2006

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16-Artikel_-_Sporekill on seed potato against Erwinia