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New biological control for apple maggot

for apple maggot


May 15, 2008
By Dan Woolley

Topics

There’s a promising new biological control product on the horizon for tackling apple maggot.

applemaggot1
Above: An apple maggot captured in a yellow sticky trap. Researchers with Agriculture and Agri-Food Canada are hoping to add GF-120 to the list of control products registered for use on apple maggot.
Below: An example of the type of damage possible on fruit infested with apple maggot.
Photos by Wendy Cranshaw, Colorado State University, Bugwood
applemaggot2

There’s a promising new biological control product on the horizon for tackling apple maggot.

GF-120 NF Naturalyte fruit fly bait from Dow AgroSciences is currently registered for use on cherry fruit flies and blueberry maggots in Canada and is also registered for organic use. The product is derived from spinosad and produced through a fermentation process of the bacteria Saccharopoloyspora spinosa. While it has low toxicity for mammals and birds, spinosad is neurotic to apple maggots, killing them through paralysis.

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In 2007, researchers with Agriculture and Agri-Food Canada based at Kentville, N.S., launched a project to evaluate the efficacy of GF-120 for control of apple maggot and establish the best rate and application method. The product was trialled in apple orchards within Nova Scotia and Ontario. In Nova Scotia, three organic orchards and one orchard managed under integrated fruit production (IFP) were used. Varieties involved included McIntosh, Cortland, Rhode Island Greenings plus a seedling mix. In Ontario, two organic orchards of Novaspy were used in the trials.

In each orchard, there were four replications of four treatments – GF-120 at one-time, 1.5-times and two-times the labelled rate and a Surround application – plus the control. The treatments were applied weekly following the capture of the first adult apple maggot. The orchards were monitored using yellow sticky traps.

Harvest assessments were conducted in September to evaluate the different treatments. Twenty apples were collected from 10 trees in each treatment plot while 20 apples were collected from 16 trees in the control plot. The fruit was incubated at room temperature for two weeks and then cut into quarters to record any apple maggot damage.

According to Eric Sprecht, a research technician with AAFC, the rate of apple maggot injury in the control blocks in Nova Scotia was about 70 per cent while the Ontario control block injury rate was about 40 per cent. The addition of GF-120 reduced the injury rate to about 10 per cent, he adds, making the product as effective a control of apple maggot as Surround.

The GF-120 trials are expected to continue this season.

Apple maggot infestations in Nova Scotia were down in 2007, according to Dr. Alexander Shalin, Nova Scotia’s pest management regulation co-ordinator.

Apple maggot
The apple maggot – Rhagoletis pomonella – is indigenous to North America and has been found in all Canadian provinces, with the exception of Newfoundland. It is especially widespread throughout eastern Canada and is considered a quarantine pest.

Hawthorn and apples are the favoured host plants of apple maggot but cherries, pears and other fruits have been attacked.

The adult apple maggot fly is somewhat smaller than a housefly and has clear wings with characteristic black bands, a pronounced white spot on the back of the thorax, and a black abdomen with light-coloured crossbands. Female flies have four crossbands while males have three. Larvae are cream-coloured maggots with a blunt posterior and a tapered front end that contains two black mouth hooks.

The apple maggot is closely related to the walnut husk fly and cherry fruit fly. It can be distinguished from these pests by the banding on its wings.

Every July, female apple maggots mate and lay up to 200 eggs singly under the skin of fruit. The eggs hatch three to seven days later inside the fruit and the larvae feed on the apple flesh, causing fruit damage. Browning of the larvae burrow trail occurs as the apple responds to the injury and bacteria associated with the maggots cause the fruit to rot internally.

The larvae can take anywhere from two weeks to several months to mature. The infested fruit usually drops to the ground and the larvae emerge and burrow into the surrounding soil. Larvae emergence from the fruit can occur well into December.

The larvae pupate under the soil and remain dormant through the winter. The pupae can last in the soil for several years before emerging, usually in June or July, as an adult. They reach sexual maturity seven to 10 days after emergence. Adults die three to four weeks after emergence but can live as long as 40 days under field conditions.

For non-chemical control, growers are encouraged to remove any unmanaged, wild or unsprayed host trees within 500 metres of an orchard to eliminate outside sources of apple maggot. They should inspect orchards regularly for signs of apple maggot infestations, including dropped apples. Infested fruit should be destroyed or buried at least 30 centimetres before the larvae leave the fruit to hibernate in the soil.

Growers are urged not to store apple bins under host trees to avoid risk of contamination with apple maggot larvae or pupae. Empty bins should not be returned to non-infested areas until after they are cleaned and pressure washed.

Research out of Quebec has shown that using baited sticky red spheres or yellow panels hung at 10-metre intervals along the margins of low infested orchards can protect the orchard by intercepting females immigrating from nearby sources. This control tactic has not been investigated in western North America.

For chemical control, products registered for use on apple to control apple maggot include: Calypso 420 SC, Delegate WG, Diazinon, Guthion, Imidan WP, Pounce, Ripcord, Sevin XLR, Surround WP (organic), and Zolone Flo. Growers are urged to read and follow the rates and spray timings listed on the product labels and adhere to local recommendations.

It is important to keep fruit protected as long as flies are captured.

It is also important to consider the pre-harvest intervals when selecting a control product to ensure adequate protection for the apple crop as it approaches maturity, the favoured time for apple maggot attack.


Of 88 growers inspected on 424 blocks, 5.4 per cent (32 blocks) showed a trace of the infestation, while five blocks (1.2 per cent) had a moderate rate of infestations and just 0.5 per cent (two blocks) had a heavy infestation rate.

Dr. Shalin credits increased grower attention to the issue of apple maggot damage for the decrease in infestation rather than weather conditions. In 2006, the 14 per cent infestation rate “raised alarm bells,” he says, while the seven-per cent rate in 2007 was much less than the provincial average for apple maggot.

About three-quarters of Nova Scotia’s apple maggot infestations originate in abandoned orchards or among wild apples and Hawthorne trees, Dr. Shalin explains. The Nova Scotia Department of Agriculture has a program to eradicate these trees. Funding for the program is expected increase by 20 per cent this season.