Apple Maggot: Threshold Reached As Heavy Rains Increase Emergence In The Mid-Hudson Valley. July 11th, 2020

Apple maggot trapping using baited red spheres in high pressure orchard.

Brief: Continued insect pest management should focus on Apple Maggot, our greatest concern this week. We are finding increased levels of emergence in baited red sticky spheres hung along the orchard perimeter. Thresholds have been exceeded in orchards with adequate soil moisture and highest populations from infestations of fruit in 2019.

Obliquebanded Leafroller (OBLR) is well past peak of egg hatch with late instar larva remaining in untreated orchards in the Mid-Hudson Valley. Scouting in fruit clusters is recommended if earlier applications to manage OBLR were omitted. San Jose scale (SJS) adults of the 2nd generation continues to emerge. Second generation crawler emergence is predicted to occur approximately 1450DD after March 1. We are presently at 948DD with predicted SJS 2nd generation emergence expected after August 1st. Wooly apple aphid (WAA) continue to increase in commercial blocks. This is especially true in blocks treated last year with late season BMSB management using pyrethroids and left untreated this season. WAA should be managed before they over-run the orchard near harvest

July is proving to be hot and relatively wet with 1.92 inches of rainfall in Highland, NY over the past 11 days, providing increased soil moisture for apple maggot to continue emerging from the soil over the weekend. Additional rain forecast over the next few days will likely increase the rate of AM emergence this coming week.

Apple Maggot (AM): In this weeks assessment of our AM traps (see 2020 scouting report) we captured an average 1.1 adults per trap per day (8.0 / week) with one block exceeding the 5 adult per trap threshold (17 adults/wk).

At this point in time each orchard block should now have baited AM sticky sphere traps out to determine AM pressure in blocks containing early maturing varieties.

Ginger Gold and Honey Crisp are highly susceptible to early maggot infestations and should be managed accordingly. High relative humidity during the morning hours will increase deposition of material while cool temperatures reduce the likelihood of detoxification using pyrethroid based pre-mix insecticides.

Application windows for the next 48 hours: NOAA Weather

Introduction: The apple maggot, Rhagoletis pomonella, also known by mature tree fruit growers as the “railroad worm”, causing ‘trails beneath the skin of infested apple, is a native of eastern North America. The fly originally bred in large fruited hawthorns (Crataegus sp.) and as colonization from Europe and tree fruit production began in earnest in the 17th century, the apple maggot adopted the apple as a principle host. The fly has been a major fruit pest in the northeastern United States and Canada for the past 200 years.

During the early 1980s, the AM became established in California, Oregon, Washington, Idaho, Utah, and Colorado, becoming a serious threat in the major apple production areas in these western fruit growing regions. Complete control of this insect is necessary as fresh market apple must be free from AM injury and larval presence during storage and shipment overseas.

AM normally has a single generation a year, although there are two exceptions: AM may have a partial second generation in the southern part of its range, and some individuals remain in the soil two winters before emerging as adults.

AM emergence.R.W Dean and P.J. Chapman ‘Bionomics of the Apple maggot in Eastern N.Y.

AM emergence.R.W Dean and P.J. Chapman ‘Bionomics of the Apple maggot in Eastern N.Y.

Red sphere traps are very attractive to mature adult female AM flies, ready to oviposit. Through the development of the red sticky sphere and attractive lures using ammonium acetate, butyl hexanoate (fruit odor) ammonium carbonate (food odor), or blends, the trigger for apple maggot management can be postponed until mature flies capable of laying viable eggs are captured in traps. When placed along wooded edges and abandoned blocks in commercial apple, traps can provide optimum timing for management of early maturing, highly attractive varieties such as Ginger Gold, using a threshold of 5 flies per trap.

P.J. Chapman and R. Dean found dramatic variability of AM emergence from season to season. There is considerable variability between farms with infestation levels differing between farms based on a number of variables.

These include weather, soil moisture and site, with apple variety preference of early egg laying puncture of fruit coinciding with varietal maturity.

Evaluations of apple maggot emergence from 1931 to 1969 in Hudson Valley Orchards showed that in 31% of the years monitored for emergence, AM emerged beyond the 20th of August. Yet there was little or no emergence of new flies after the 1st of September.

AM seasonal ovipositional preference as per variety.

AM seasonal ovipositional preference as per variety.

This reassured apple producers that applications beyond the 15th of August were not needed AS LONG AS effective reside was present up to the 1st of September. In 1973 (the year of R. W. Dean and P.J. Chapman’s publication) the organophosphates such as Imidan and Guthion were the insecticides of choice in managing AM.

One of the challenges we face today is the lack of residual efficacy of newer insecticides to actually kill the AM fly. This may not be as important as one might think.

Generally, the neonicotinoids prevent the fly from laying eggs into the fruit, yet they produce lower levels of mortality of the fly, allowing adult AM to be present in the orchard late into the season. If there is significant rainfall there is often a reduction in residual activity that may lead to AM punctures with few or no eggs present in the sting or puncture of the apple.

The bottom line is that traditional IPM based use of the baited red sticky sphere, which has been successful at monitoring the onset of AM emergence and treatment threshold, is not a strong tool for use in signaling reapplication, due to low direct mortality of the newer insecticide tools.

Apple Maggot presentation. Harvey Reissig 2010

Apple Maggot presentation. Harvey Reissig 2010

Once AM spheres have been ‘reset’ (cleaned), AM flies may reach the 5 fly per trap threshold more quickly using neonicotinoids that have high egg laying deterrence but low adult toxicity. Instead, the use of neonicotinoids such as Actara and to a lesser degree Assail, will need to be applied at a 10-14 day window despite high trap captures immediately after orchard treatments into September.

Assail is a very effective insecticide at managing the AM fly, and has a great fit for the onset of 2nd generation Codling moth.

In general Assail has excellent efficacy against the internal lepidopteran complex such as OFM late into the season.

To drive this point home, in page 9 of a presentation by Dr. H. Reissig in 2010, Harvey confirmed the ability of AM to ‘sting’ fruit yet produce very few eggs employing many old and new insecticides against the AM.

In this comparative study, he demonstrated the efficacy of Assail and Guthion to be about equal in control of AM tunneling from larva.

2006 AM Field Screening Tests; HVRL

2006 AM Field Screening Tests; HVRL

Additional studies by Jentsch reinforce these findings, shown in 2006 field efficacy studies conduced at the Hudson Valley Lab research orchard.