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www.actpub.co.uk THE FRUIT GROWER • SEPTEMBER 2013

Controlled Atmosphere Temperature Treatment (CATT)is a non-chemical and sustainable method of de-infesting plant material from insect pests. Strawberry

plants are treated after cold storage and before planting for48 hours at a temperature of 35C and 50% CO2. This givesexcellent de-infestation and 99.8% mortality of StrawberryTarsonemid Mites, and leads to the production of high qualitystrawberry runners in the field. Since 2009 CATT has beenup-scaled to a commercial level and widely applied by Dutchplant propagators.

INTRODUCTIONUntil 2008 methyl bromide fumigation was used in The

Netherlands to de-infest strawberry mother planting stock fromStrawberry Tarsonemid Mites (Phytonemus pallidus). After coldstorage in early spring the strawberry runners were treated in aspecially equipped fumigation chamber. This treatment washighly effective and killed at least 99.8% of the tarsonemidmites. But, because of the unfavourable side effects of methylbromide on the ozone layer, it was internationally agreed by theMontreal Protocol in 1987 to phase out the use of thisfumigant. In the Netherlands this method of fumigatingstrawberry mother plants was banned in 2008. As analternative to methyl bromide fumigation the ControlledAtmosphere Temperature Treatment (CATT) was developed and

scaled up by Wageningen UR in cooperation with the plantpropagating association Plantum (www.plantum.nl).

EXPERIMENTS AND RESULTSAfter a lot of experiments in 2006-2008 it was found that a

48 hour CATT treatment of cold-stored plants at a temperatureof 35C and 50% CO2 was most effective. Boxes containingbare-root cold-stored plants (packed in plastic bags to avoiddehydration) in -1.0C storage are removed from the cold storein early March and warmed for 48 hours to 10-12C.Subsequently the plastic bags are removed and the bundles ofstrawberry plants are placed upright just before CATTtreatment. CATT treatment provides excellent de-infestation and99.8% mortality of Strawberry Tarsonemid Mites (Phytonemuspallidus) (Figure 1). As a side effect, the Two Spotted SpiderMite (Tetranychus urticae) is also eradicated. Plant vigour andestablishment in the field after CATT treatment was comparableto plants fumigated with methyl bromide (Picture 1).

Recently it was also found that the plant parasitic nematodesMeloidogyne hapla and Pratylenchus penetrans can beconsiderably reduced by CATT. Clean source material onnematode-free soil prevents an increase in the nematodepopulation, resulting in reduced use of chemical soildisinfectants. In 2011 the standard 48 hour CATT method wassuccessfully modified to eradicate root knot nematodesMeloidogyne hapla (>99.7% mortality), which was not effectivelycontrolled by methyl bromide fumigation. However, for effective

CATT: a new method for the de-infestationof strawberry planting stockby Gijs van Kruistum and Hans Hoek of Applied Plant Research, and Jan Verschoor of Food andBio-based Research, Wageningen UR, The Netherlands.

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eradication of root knot nematodes, the temperature must beraised to 40C.

In several experiments the optimum for high mortality of bothtarsonemids and nematodes was studied. This led to anadapted CATT of 20 hours at a temperature of 35C and 50%CO2 followed by 20 hours at a temperature of 40C (Table 1).

APPLICATION AND CONCLUSIONSIn 2012 this adapted CATT method was successfully tested

under field conditions with a wide range of mother plantingstock, originating from different nurseries. 16 samples of 5,000to 10,000 strawberry plants, each of different varieties, originand plant types (SE2, A, A+ and light waiting-bed plants),treated according to the standard method: 48 hours at 35C

and the new method: shorter treatment of 40 hours andincreased temperature in the second phase to 40C.After treatment and a short storage period, thesamples, including untreated, were planted on 8 May2012. The new CATT treatment proved to be equally assuccessful as the standard method (Picture 2). Nodifferences between the varieties (Darselect, Elsanta,Figaro, Korona, Sonata, Symphony and Honeoye) wereobserved. The upper limit of 40C is critical during thetreatment as just 1.0C over this limit results in cleardamage. Uniform temperature distribution duringtreatment is required, so the plants should not to bepacked too tight in the box during treatment. Alsosufficient humidification and control of the oxygenconcentration is important. It was concluded that noharmful irreversible results of this adapted CATT methodon the vitality of mother plants and on runner

production were noticed.

SPIN-OFFCATT is now a proven commercial method, widely applied by

Dutch producers of mother planting stock. It offers productionof healthy high quality strawberry runners in the field. Twocommercial companies provide the CATT protocol as aphytosanitary treatment of strawberry runners (Picture 3). Thesecompanies (Ruvoma, Montfoort NL - email info@ruvoma.nl -

and Van Acht Cooling, Sint-Oedenrode NL - email info@van-acht.nl) are treating strawberry plants from outside theNetherlands. The application of the optimized CATT will preventfurther dispersion of plant parasitic nematodes in the strawberryproduction chain. In the international trade in plant materialsand products there is further potential for the application ofCATT for the sustainable treatment of insect, mite andnematode pests. This is confirmed by the very positive resultsof preliminary experiments on a range of pests and freshproducts at Wageningen UR. ◆

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