Plum Curculio: Betwixt and Between

Plum Curculio sting in Ginger Gold, mid-May 2017

Plum Curculio (PC): Cool temperatures have kept the lid on migrating populations of PC over the past two weeks, delaying and or reducing oviposition of fruit in many locations in the Hudson Valley. Since petal fall on the 8th of May and the first sting from PC on fruit on May 15th, we are more then two weeks out with only 10% PC injury in our untreated Ginger Gold in a heavily infested corner of our research orchard in plots along hedge row and woodlands. In most years we would be looking at 50% injury by now. Many growers have commented on similar observations this week.

An interesting article in Science (May 12, 2017) titled Where have all the insects gone? suggests a dramatic decline in insect biomass points to an overall decrease in world wide populations of insects. This phenomenon may play a part in this conversation … but for now, we’ll focus on the impact of weather on the low levels of insects in the orchards we have seen to date.

PC activity is highly dependent upon temperature. We have only had three consecutive days in which the mean temperatures have been above 60F, the temperature at which PC begins migration to orchards. Since PC usually do not feed or oviposit when night temperatures fall below 50F, the 5 nights above 50F we’ve had to date did provide opportunity for some feeding that are reflected in low sting numbers in fruit to date.

If the weather is extremely warm after petal fall, the oviposition cycle may be completed in 2 weeks. However, in cooler seasons as we are presently experiencing, PC may continue to oviposit for 4-6 weeks. If this trend holds we will be looking at the end of migration and oviposition in early June.

The model used to calculate the end of PC emergence begins at 95% petal fall of McIntosh. The majority of eggs deposited into fruit by overwintering plum curculio in the Northeast is completed in apples once 308 DD base 50 has been reached. (developed in studies conducted by by W. H. Reissig, J.P. Nyrop, and R. Straub (Environmental Entomology; 1053-1060; 1998; titled “Oviposition Model for Timing Insecticide Applications Against Plum Curculio (Coleoptera:Curculionidae) in New York State”).

I would recommend maintaining residual protection from the high rate of an effective insecticide for PC. Take note that residual activity is no longer effective when 2 inches of cumulative rain occurs within the first 10 days after application, 1.5 inches of cumulative rain occurring from 10-14 days after application, or 14 days has passed since the previous application with no rain event. Rains today and tomorrow will significantly impact residual with 0.75″ having fallen over the past 8 hours and 0.5″ predicted for the next 24 hours. If your next application is applied over the next few days, consideration should be made for the new big pest, the codling moth.

Adult codling moth

Codling moth: The Tortricid complex of Red Banded Leaf Roller (RBLR), Oriental Fruit Moth (OFM), Lesser Apple Worm (LAW) and Codling Moth are now in flight with the Obliquebanded Leafroller (OBLR) still in pupation. The most import of the internal lepidopteran being codling moth, has taken flight as of May 12th in Highland. To date we have accumulated 157.0 degree days for the CM model using 220DD accumulated degree days (base 50°F) to forecast larval emergence. We are predicting 1st CM larva emergence to be on the 31st of May this season.

Of all the complaints I’ve heard over the past 8 months, the loss of sound fruit at pack out appears to be from codling moth. Over the past few years we have seen a rise in CM numbers in traps and in orchard infestations, culminating in 2016, in which the third generation emergence in September gave rise to very high losses.

Conventional material options are listed in the Cornell Guidelines.

An additional option is to apply a granulosis virus formulation at 200-250 DD 50°F. High moth pressure requires 2-3 sprays for the first generation, but in lower pressure orchards (with counts of less than 5 moths per trap per week), you can control CM with a single spray timed at 350 DD 50°F.Codling moth granulosis virus. Formulations include Cyd-X, Cyd-X HP, Madex HP by Certis; Carpovirusine by Arysta LifeScience. Cyd-X 0.06SC is applied @ 0.25-0.4 qt/acre and Carpovirusine 0.99SC @ 0.25-0.4 qt/acre.

Codling Moth Granulosis Virus contains an insecticidal baculovirus, Cydia pomonella granulovirus, which is specific to the larval form of the codling moth, and is registered for use in apples, pears, and (Cyd-X only) plums. This biological insecticide must be ingested in order to be effective, after which the viral occlusion bodies dissolve in the larval midgut and release infectious virions. These enter the cells lining the digestive tract, where they replicate; eventually, the other tissues are infected and the larva stops feeding and eventually (within 3-7 days) dies. After death, the larva disintegrates, releasing billions of new occlusion bodies, which may infect other codling moth larvae upon ingestion. No adverse effect to fish, wildlife or beneficial organisms has been observed; it has a low bee-poisoning hazard.

Insecticide Resistance Development in Codling Moth:

The organophosphate class of insecticides, including Guthion (azinphos-methyl) and Imidan (phosmet) have been used since the 1960’s, for over 50 years, to manage the codling moth. The development of resistance by codling moth to Imidan is likely if its reoccurring use has been for Plum Curculio and or OBLR management during mid-summer. Consistent use during the past ten years or more increasing resistance potential. Those specific timings would provide some level of control of CM while providing various rates of residual exposure. Low rates of residual increase the selection for resistance during the early and mid-summer generations of the pest. A scenario, such as the switch from Guthion to Imidan in season long program use would affect the same target site (nerve receptor sites for ACh, acetylcholinesterase) within the insect to contribute to resistance.

In the Hudson Valley to date I don’t believe resistant strains are widespread, even though we are hearing of increasing reports of CM damage to tree fruit. The broad availability and use of insecticides that include the different IRAC classes of active ingredients for plum curculio from PF to 2nd cover and mid-summer management of OBLR, would reduce region-wide resistance of CM to any one specific insecticide class. We have seen the use of these materials to include Avaunt, Exirel, Calypso, Carbaryl, pre-mixes including pyrethroids or pyrethroids alone. Insecticides of various classes for the overwintering OBLR used at PF would likely impact CM to a lesser degree when used at petal fall timing.

There haven’t been recent studies to detect phosmet resistance to CM in NY that I’m aware of. In Michigan, a study in 2008 detected a 7-8 fold level of resistance in orchard site specific CM populations to codling moth (see abstract from work done by John Wise in Mich. State below). However, no resistance to acetamiprid (Assail) and spinosad (Delegate, Spintor, Entrust) was detected in the study.

That said, it’s very likely we have codling moth populations resistant to older insecticide classes, including pyrethroids and OP’s in orchards throughout the Northeast.

Insecticide rotation: I would suggest the use of specific materials for CM be employed during 1st-2nd cover and again in mid-July, when model predictions for larva emergence are called for AND in orchards with reoccurring fruit injury from CM. The use of Assail to manage apple maggot during 2nd generation CM larval emergence has been a good option, as it’s been shown to be one of the better materials against both CM & AM. The use of Delegate, Altacor at 1st – 2nd cover would reduce the resistance potential while picking up a few lingering overwintering OBLR. Mating disruption and granulosis virus are also good choices in conventional and organic production systems.

Remember to rotate classes for EACH GENERATION and not each spray during a generation, to reduce the potential for insecticide resistance.

Pest Manag Sci. 2008 Sep;64(9):881-90. doi: 10.1002/ps.1576. Resistance of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), larvae in Michigan to insecticides with different modes of action and the impact on field residual activity.

Mota-Sanchez D1, Wise JC, Poppen RV, Gut LJ, Hollingworth RM.

The codling moth is one of the principal pests of apple in the world. Resistance monitoring is crucial to the effective management of resistance in codling moth. Three populations of codling moth in neonate larvae were evaluated for resistance to seven insecticides via diet bioassays, and compared with a susceptible population. In addition, apple plots were treated with labeled field rate doses of four insecticides. Treated fruit were exposed to neonate larvae of two populations from commercial orchards.

RESULTS: Two populations of codling moth expressed two- and five fold resistance to azinphos-methyl, seven- and eight fold resistance to phosmet, six- and tenfold resistance to lambda-cyhalothrin, 14- and 16-fold resistance to methoxyfenozide and sixfold resistance to indoxacarb, but no resistance to acetamiprid and spinosad. The impact of the resistance to azinphos-methyl, measured as fruit damage, increased as the insecticide residues aged in the field. In contrast, fruit damage in methoxyfenozide- and lambda-cyhalothrin-treated fruit was observed earlier for resistant codling moth. No differences in efficacy were found for acetamiprid.CONCLUSIONS: Broad-spectrum insecticide resistance was detected for codling moth. Resistance to azinphos-methyl, lambda-cyhalothrin and methoxyfenozide was associated with reduced residual activity in the field. Broad-spectrum resistance presents serious problems for management of the codling moth in Michigan.