Up until now, the codling moth (Cydia pomonella) has been one of the most difficult insect pests to control on an organic apple orchard. If no insecticides are used, the numbers of codling moth can increase up to ten times in one season from the first to the second generation. Codling moth damage has meant that most organically produced apples have been unsuitable for export.

Photo 1: Codling moth damage on Granny Smith apple

However a HortResearch scientist has now shown that pheromone mating disruption, in combination with Codling Moth Granulosis Virus (CMGV), can keep codling moth populations low enough to produce organic fruit of export quality. Mating disruption trials have been carried out in Auckland, Waikato, Hawke’s Bay, Horowhenua, Nelson, Canterbury and Central Otago. The most successful trials were undertaken by Dr John Clearwater in northern areas of the North Island. In this article, we discuss the results and recommendations from one of these trials in West Auckland.

Auckland Orchard Study
Dr John Clearwater has been monitoring three organic orchards since 1992.

The first orchard (Orchard 1) is an established organic orchard. By using CMGV and pheromone dispensers, damage from codling caterpillars was reduced to 0-1% in year two and 1-4% in year three. The second orchard (Orchard 2) was previously sprayed with a conventional programme but organic methods were used from 1992 onwards. Despite a large initial build-up of codling moth, the population was controlled. The third orchard (Orchard 3) has had no synthetic insecticides applied for over thirty years and was a good comparison to study the damage codling moth can do in an uncontrolled orchard.

IMPORTANT FINDINGS FROM STUDY:

1. Control of codling moth can be maintained using CMGV and pheromone disruption.
One and a half applications of Shin-Etsu Isomate-C transparent dispensers were used. The first application was placed in the orchard in early spring, the second preceding the appearance of a smaller second generation which was detected through monitoring, (usually late February to early March).

The dispensers cost 25 - 30 cents each and 1000 dispensers are needed per hectare.

One spray of CMGV was used per season. CMGV is highly specific to codling moth and is applied with conventional airblast sprayers. Timing of the spray is very important as it breaks down quickly in sunlight. The spray must be applied when the young caterpillars are hatching and boring into apples. Careful monitoring (described below) indicates the best time to apply the CMGV spray. One spray costs approximately $130 per hectare.

2. Monitoring by different methods indicates when the codling moth populations are building up.
Six methods were used in the trial to monitor the codling moth populations : tree bands, windfall apple collections, time search information, two types of pheromone-baited sticky traps and harvest assessments.

Tree bands are made of corrugated cardboard and are taped to the largest limbs in the tree. Contrary to some popular opinion, they don’t control codling moth but they do provide an excellent way to monitor the insects. The mature caterpillars crawl into the corrugations of the bands, spin cocoons and turn into prepupae. The number of prepupae gives an estimate of the size of the next generation. If there are large numbers of prepupae, the grower will need to increase the number of CMGV sprays to combat the next generation. In these trials, the first bands were placed in the first week of December and they collected information on the first generation. The second bands were put in place in the first week of February and removed at harvest.

The value of these bands was illustrated in Orchard 2 in the last year of the trial. The orchardist had applied the second batch of dispensers 18 days late. This allowed many of the second generation moths to mate and produce overwintering prepupae that would threaten the orchard next season. The bands acted as an effective warning systems by detecting these prepupae.

Photo 2: Corrugated bands on the trees to collect prepupae

The flight activity of male codling moths can be measured using standard pheromone sticky traps. Sticky traps are for monitoring purposes only and, unlike the pheromone dispensers, they do not cause mating disruption. Because the dispensers emit much more pheromone than the traps, the traps are not a useful indicator of the effectiveness of the dispensers. A failure of mating disruption may be imminent, but the standard sticky trap will remain empty lulling the orchardist into a false sense of security.

Photo 3: Pheromone sticky trap

Time search means looking for the first appearance of the caterpillars. Once the sticky traps indicate that the first flight of the male moths has begun, it is time to start looking for the caterpillars. The first sign of the codling moth caterpillar is small piles of light brown frass (droppings) of the surface of the fruitlets.

Photo 4: Pile of frass on apple fruitlet

3. Relative sizes of codling moth generations vary between organic and conventional orchards
Typically there are two generations of codling moth in the upper North Island. See codling moth lifecycle chart. In a conventional orchard, the second generation is larger than the first. However, in these trials, the first generation was larger (except for Orchard 2 when it was in the transitional stage converting from conventional to organic). More damage was caused by the first generation than the second when measured on the untreated orchard, (Orchard 3), see Table 1.

Table 1
Percentages of codling moth damage to apples remaining on the tree, per generation. Recorded in an unsprayed orchard over two years.

	Generation 1	Generation 2
Gala	20-25% damage	16-18% damage
Granny Smith	22-35% damage	6-10% damage
Golden Delicious	16-18% damage	8-10% damage

Apple varieties are effected according to when they are harvested. In the northern North Island, the Gravenstein strains are subject to only the first generation of codling moth. Gala strains and Golden Delicious are picked with many of the second generation caterpillars still inside the apple. By the time Granny Smith are harvested, the second generation is complete.

In the West Auckland orchards sampled, trapping showed that the first flight of male moths peaks in November and December. The caterpillars first enter the fruit in large numbers in December. Larvae and pupae develop during January and the adults emerge in early February to start the next generation. Careful monitoring will pick up these stages and allow the dispensers and CMGV sprays to be targeted accurately.

4. The organic programme works even if neighbouring orchards are unsprayed
One of the pheromone-treated orchards (Orchard 1) had unmaintained orchards around half of its boundaries in the last year of the trial. These abandoned orchards suffered heavy damage, losing 35% of the harvested apples to codling moth. Despite the large populations of codling moth in these surrounding orchards, control was still maintained in the pheromone treated orchard. This is very encouraging as it shows the control system is robust.

5. Damage in harvested fruit is not a complete measure of codling moth control
The “control” orchard (Orchard 3) had been free of synthetic insecticides for over 30 years. No pheromone dispensers or virus sprays were used on this orchard, so it could be compared with orchards where mating disruption was used. On this control orchard, a range of 12-40% (depending on the variety) of the harvested apples were damaged by codling moth. This figure does not take into account the apples which fell from the tree before harvest which had codling moth damage. If these windfall apples are included, then up to 78% of all Granny Smith apples on the untreated orchard had codling moth damage, compared with 8-10% in the one of the treated orchards. Table 2 shows the level of codling moth damage on all the fruit from the trial orchards over the three years.

Table 2.
Total undamaged fruit (at harvest as well as windfalls) from the trial orchards.

Orchard 1 : Established organic orchard treated with pheromone dispensers and CMGV.

Orchard 2: Conventional spray programme up until 1991/92 season and then pheromone dispensers/CMGV programme.

Orchard 3 : No synthetic insecticides for 30 years, no pheromone or CMGV treatment.

	1992/93		1993/94		1994/95*
	%	No. of fruit	%	No. of fruit	%	No. of fruit
	Undamaged	sampled	Undamaged	sampled	Undamaged	sampled
Oratia beauty
Orch 1	96.7	(572)	93.7	(158)	88.4	(983)
Orch 2	88.5	(602)	72.8	(439)	80.6	(1541)
Orch 3	-	-	43.0	(807)	37.0	(1017)
Gala
Orch 1	-	-	-	-	-	-
Orch 2	84.2	(2654)	87.5	(4125)	74.6*	(1963)
Orch 3	-	-	29.2	(2534)	25.2	(1918)
Golden Delicious
Orch 1	81.0	(3369)	90.6	(2660)	87.4	(3054)
Orch 2	-	-	-	-	-	-
Orch 3	-	-	31.6	(2127)	45.3	(2699)
Granny Smith
Orch 1	77.9	(2962)	92.2	(2773)	90.5	(3113)
Orch 2	77.0	(666)	86.4	(1356)	68.5*	(629)
Orch 3	-	-	22.9	(3165)	26.7	(1150)

* Late placement of the second batch of dispensers contributed to extra codling moth damage.

Further information
For further information on the West Auckland codling moth trials contact Dr John Clearwater on j.clearwater@xtra.co.nz

Acknowledgment
HortResearch acknowledges ENZA New Zealand (International) for their support.

Source
New for HortNET, June 1996. Written and submitted by Helen Percy from Client Reports 95/85 and 93/184.