Sugar for the control of codling moth
Pest and Disease ManagementThis article was first published in Australian Fruit Grower Magazine – Autumn 2022.
Inexpensive and environmentally friendly, Algerian research shows sugar can be used in the control codling moth.
Back in the 1990s it was found that there are many compounds, including sucrose, excreted by apple trees onto their leaf surfaces to deter insects from laying eggs.
Using this information, by 2011, trials in France, Italy, Greece and Algeria had demonstrated that the application of sugars to trees reduces codling moth populations in apple fruit by up to 60 per cent.
Codling moth damage. Photos: Dr Gordon Brown
A summary of results of trials conducted from 2009 until 2014 was presented by Arnault et al. in 2016 (Table 1).
This shows that in the nine trials reviewed, located predominantly in Algeria:
- the level of fruit damaged by codling moth ranged from 12 to 47 per cent in the untreated plots
- 100ppm sucrose reduced this to between 11 and 28 per cent
- in the granulosis virus trial, between 7 and 26 per cent of fruit was damaged
- thiacloprid insecticide reduced damage to between 3 and 23 per cent
- the addition of sucrose to either granulosis virus or thiacloprid improved performance of both products.
Table 1. Percentage of harvested fruit damaged by codling moth in nine different trials.
Since then, research, still concentrated in Algeria, has further confirmed both sucrose and fructose at 100ppm (100g/1000L) applied at 21-day intervals during the growing season reduces fruit infection by codling moth by 65, 70 and 41 per cent (three publications). It was found that sucrose and fructose have similar efficacy. Further, the sugar treatment substantially reduced the number of cocooned codling moth larvae caught in trunk bands in two of the trials (not studied in the third trial). This implies the sugar treatment reduces the primary population of codling moth in the following spring.
In this edition of AFG magazine we will study the latest piece of Algerian research, by Tiffrent and Lombarkia, on this inexpensive and environmentally friendly treatment.
This research was conducted on apple trees in 2019. There were four treatments: an untreated control; trees sprayed with fructose at 100ppm; trees sprayed with glucose at 100ppm; and trees sprayed with Deltamethrin, a pyrethroid insecticide.
Treatments were applied every 21 days from flowering to harvest. Sucrose was not used in this trial, although in previous research it was found to give similar results to fructose. The reason for incorporating glucose instead of sucrose in this trial is not given by the authors although in their discussion they mention that in previous laboratory research by other researchers it was found that glucose appears to inhibit egg laying on leaves to a greater extent than sucrose. Sucrose (table sugar) is composed of both glucose and fructose.
Codling moth catches in traps ran at about 10 moths per trap per day with a peak of 70 moths for the second generation indicating a high pest load in the trial site. This is reflected in the percentage of damaged fruit with close to 60 per cent of the fruit in the untreated control being damaged (Figure 1), far higher than any of the reports listed in Table 1.
The level of control offered by the sugar applications was also far lower than that observed in the previous studies. The authors do not attempt to explain the poor performance of the treatment in this trial. It should be noted that even the level of control achieved with the Deltamethrin insecticide was poor. While the level of control of codling moth was lower than in previous studies, it should be pointed out that both fructose and glucose significantly reduced the level of codling moth damage resulting in a 10 per cent increase in marketable fruit.
This was a small piece of research; however, it stems from the finding that apple trees excrete sugars onto their leaf surface as a natural deterrent to codling moth egg laying. Numerous subsequent trials have shown that applying micro amounts, a soup ladle of sugar per 1000L (100ppm) at a cost of about 10c/1000L, reduces the incidence of codling moths in harvested fruit and that its addition to standard pesticides increases the level of control achieved.
This is an environmentally friendly method of controlling codling moth and is an acceptable method for organic fruit growers especially if used in conjunction with Grandex®, Cyd-X® or Madex® (granulosis virus). It is interesting to note that Madex® has a recommendation to add sugar to their product if being used on large trees. Given the cost of this treatment and the fact that its effect is present when added to standard insecticides sprays it would seem prudent to start using this treatment in future seasons. It is possible that in years to come the combined treatment will allow for reduced amounts of traditional insecticide being applied in a season.
Take home messages
- Sucrose regularly sprayed onto apple trees reduces the incidence of codling moth in harvested fruit.
- Sucrose added to insecticide sprays increases the level of control of codling moth over the pesticide alone.
- 100g/1000L of sugar or a soup ladle per 1000 litres is all that is needed.
- This is an environmentally friendly method of codling moth control which can be used by organic growers.
Further reading
Assessment of control strategy by spraying low doses of sugars on apple orchard against Cydia pomonella (Linnaeus, 1758.)
