GRAS fumigants for phytosanitary pests

CONTACT DETAILS:  +27 83 601 3037 /
LEAD INSTITUTION:  Citrus Research International
BENEFICIARY:  Citrus, Grape, and Pome Industry

Objective 1: Develop specific Vapormate treatments that will guarantee freedom from external phytosanitary pests such as the grain chinch bug, mealybugs, scale insects and Fullers rose beetle.

Objective 2: Develop the most effective combination of fumigation with Vapormate or carbon dioxide and a short cold treatment at 2.0°C for the control of the internal phytosanitary pests fruit fly and false codling moth.

Scope for Objective 1: Preliminary research and international registrations with Vapormate have given an indication of approximate dosage and treatment times required for the control of external pests so the approach here would be to bracket the “best guess” treatments with more severe and less severe treatments and evaluate them against approximately 1000 individuals. Treatments that cause 100% mortality at these levels will then be taken further to Probit 9 levels with 95% confidence as required by the USA (no survivors in 93 613 insects) if sufficient numbers of that insect are available.

Scope for Objective 2: Preliminary research has shown variable levels of penetration into fruit of different citrus cultivars with both Vapormate (comprising ethyl formate and carbon dioxide) and carbon dioxide alone. Further research is therefore required to determine whether apparent differences in permeability between cultivar types are consistent or whether fruit condition and time after harvest could be playing a role.

Different selections of the same cultivars harvested at optimal times will be infested with FCM and fumigated simultaneously at the same dosage and for the same period to determine relative permeability between selections and cultivars. Similar comparisons between different ages of the same cultivar will be conducted by comparing fruit picked at optimal harvest time with fruit that has been in cold storage for 1 week.

Once the optimal dosages have been required per cultivar type, the required length of cold treatment will be determined to obtain 100% mortality of 3rd instar FCM for that cultivar. The degree of gas penetration will therefore be based on mortality of insect larvae within the fruit relative to larvae that are in permeable growth medium.

We are more concerned about controlling the 1st, 2nd and 3rd instars that are difficult to detect than the 4th and 5th instar which are known to be more tolerant to cold but would usually be detected in the packing process. If we get consistent results for certain cultivar types and if the required short cold treatment after fumigation is still significantly shorter than the cold period required to kill the larvae without fumigation, we will then conduct a confirmation treatment with high levels of fruit infestation, but as the fumigation needs to be conducted with fruit, Probit 9 will not be attainable because around 500 cartons of fruit would need to be infested and treated.