July 24, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, July 24, 2018, 8:00 – 9:00 AM
Guest speaker: Larry Gut, Michigan State University Tree Fruit Entomologist
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

July 24th Call Stream: CLICK HERE

Fruit rots

Fruit rots have begun to show up in traditionally susceptible varieties, e.g., Honeycrisp and Cortland. Developing apples, as Dave Rosenberger, Professor Emeritus, Cornell University, pointed out in his article, New Considerations for Controlling Bitter Rot on Apples, can suppress fruit infections, but lose this ability as harvest nears. Considering this season’s high heat and humidity, growers should watch for black rot and bitter rot infections on early ripening, e.g., Paula Red, and susceptible cultivars. Risk of infections increase where monthly rainfall totals have exceeded expected rainfall by more than one or two inches.

Codling moth

Unusually strong second-generation flights may be a result of the heavy rainfall many growers experienced in early June when larvacides were first applied. Generally, second generation codling moth pressure is a direct reflection of how well the first generation was managed. Where good control was achieved, it is not uncommon for these blocks to remain under threshold during the second generation. If growers had a hard time maintaining larvacide coverage during first generation, more moths could have completed their life cycle. This would be reflected in a larger second-generation population.

Orchards with increased second-generation codling moth pressure should consider using Altacor (chlorantraniliprole), Delegate (spinetoram) or Exirel (cyantraniliprole). These insecticides will offer the best performance for managing second generation codling moth. Assail (acetamiprid) will also do a good job, but growers should use the maximum labeled rate. Over the last ten years we have observed many instances where lower rates of Assail still resulted in second generation codling moth damaging fruit before they consumed a lethal dose. Belay (clothianidin) is rated as suppression only for second generation codling moth and imidacloprid products and Actara (thiamethoxam) offer no efficacy against codling moth.

A last consideration is increasing the volume of water. Any grower who has heavy second generation codling moth pressure AND is also applying less than 50 gallons of water per acre should consider increasing water volume to improve spray coverage. Remember, we now have those clusters of fruit pressing against each other, dense canopies and the same volume of water that worked excellent for our sprays between pink and petal fall may no longer be adequate in late summer.

Including an insecticide with a cover spray

Avoid including an insecticide with calcium or fungicide applications unless treatment thresholds are exceeded for your target pest. Orchards with apple maggot, codling moth and leafrollers that are below threshold, and have minimal pressure from other insects like leafhoppers, do not need an insecticide. Many growers are still catching parasitic wasps in pheromone trap liners and we are observing a variety of beneficial insects and predators on shoots and apples.

Mating disruption with Larry Gut, Michigan State University

Trécé announced they improved their dogwood borer (DWB) lure chemistry for the 2018 season to more accurately attract DWB and may result in increased trap captures. If using a different brand of lure, let us know how it is performing. It is recommended to set multiple traps near young trees to assess pressure. If DWB are captured, thoroughly scout the graft unions of young trees.

Is it unusual to catch a lot of DWB? How far do they fly? Are they most likely coming from larger, older apple trees, outside hosts or from young trees?

Dogwood borer captures in traps are probably coming from within the orchard, rather than outside hosts and are also not likely coming from older trees on M.7 or M.111 rootstocks. Rather, they are most likely coming from the five- to seven-year-old trees in the orchard. We can, however, get into trouble when there is the possibility of mated females traveling from outside sources to lay eggs in the block, which is a common challenge in any mating disruption system. There has been some variability in study groups, but isolated orchards, e.g., surrounded by agronomic crops, generally have the best results when using mating disruption.

Lots of rootstocks and graft unions are showing incidences of root initials. Is this a prime place for dogwood borer to lay eggs?

Correct, DWB can develop more quickly on burr knot tissue and virtually all female egg-laying behavior occurs at the graft union or below. If your graft union is right at ground level, the risk of female DWB laying eggs is reduced.

If a long rectangular orchard has high catch numbers, is there any utility in using separate pheromone traps to assess differential pressures, or will those differences be small enough that one pheromone trap will offer an accurate assessment?

There isn’t a clear-cut answer due to differences in DWB populations by location, but it doesn’t hurt to put multiple traps to monitor DWB, since we don’t know the range our lures pull from. To accurately assess DWB, sampling needs to be spread out to avoid generating false negatives. More sampling should also be conducted along the edges, for example if more mated females are coming in from the edge of the woods.

What is the host range of DWB?

Dogwood borer probably has the widest host range of any American sesiid and can reproduce on all kinds of deciduous hosts. Hosts include apple, plum, bayberry, beech, birch, black cherry, blueberry, chestnut, dogwood, elm, hazel nut, hickory, mountain ash, oak, pecan, pine and willow.

Is mating disruption for DWB deployed in a similar way for codling moth with higher density near edges?

Placing higher densities of mating disruption on the edge is not necessary when using DWB mating disruption, rather evenly distributing throughout the orchard is the best approach. An application rate of 100-200 dispensers per acre hung at chest height (about four feet off the ground) should be used; dispensers will last entire season. A higher rate, e.g., 150 dispensers per acre, is recommended for the first year of treatment and where populations are high. A low rate, e.g., 100 dispensers per acre, has worked well when internal and external pressure is low. When there is high pressure, resulting from wild hosts outside the orchard perimeter, there isn’t much that can be done to prevent mated females from traveling into the orchard.

What about an application of nematodes? We clearly have no idea how long chlorpyrifos will be around, and neonicotinoids like Assail have not been a decent replacement.

Parasitic nematodes are not likely to be effective. John Wise and Larry Gut achieved excellent results in trials using with Assail 30 SG. See the Assail label for more information.

A nurseryman from Pennsylvania, who recently presented at our Wisconsin Apple Growers Association summer field day, was shocked that DWB disruption wasn’t automatically used in orchards. Is DWB pressure increasing in Michigan and should we consider it a primary pest that is automatically managed?

Larry doesn’t know answer for sure, but that doesn’t seem to be the case. As you’d expect, DWB is a huge problem in the nursery business. This season there have been no reports of DWB in Michigan and although many orchards had issues with infestation, pressure has significantly decreased over the last several years. Larry recommends keeping an eye out and putting some traps up, and to not jump into pheromone mating disruption until you better understand DWB pressure in your orchard.

What are the performance constraints of using mating disruption in orchards smaller than five acres vs. large blocks?

Larry’s one of the few people thinking there isn’t a size constraint for mating disruption. The only constraint is what’s around you and where other hosts are. Small orchards are sometimes all borders. I don’t think there’s any problem protecting orchards of any size. There’s tons of research on mating disruption done on small plots and they’re getting good data. Small blocks aren’t an automatic no.

With codling moth mating disruption, the hurdle continues to be labor costs and every time new technology comes out, we think adoption will change. Give us a quick rundown, is there anything better than hand applying dispensers at 200-400 per acre?

The first drawback of these newer application technologies is pheromone distribution. Growers can either distribute it themselves using the high rates of hand-applied dispensers or depend on the wind with aerosol emitters – wind changes can create breaks in the pheromone distribution around orchard edges. Covering an orchard is difficult and edge effects become more of a risk as codling moth populations grow.

Among the three basic mating disruption tools, the Cidetrak CMDA Combo Meso-A dispenser, manufactured by Trécé, is the least labor-intensive, requiring only 18-36 dispensers per acre. Many growers may also be familiar with the aerosol emitter, or a Puffer, applied at a rate of one per acre. The third and oldest technology uses 100-400 dispensers per acre (rates vary by product) applied by hand or by Tangler launcher and requires substantially more labor than other options.

When comparing the Meso mating disruption to the traditional hand-applied dispenser, i.e., Isomate C TT, Larry advocates for using a median rate of the traditional dispensers, e.g., 100-200 per acre, coupled with one or two targeted insecticide applications per generation rather than using a full rate of the Meso product. His reasoning is that deploying more point sources (dispensers) will always outperform a lower density, regardless of their respective pheromone load. Larry believes that using mating disruption should be a key component in all growers’ codling moth management programs. He emphasizes that there are no new insecticide modes of action being developed and we are losing more classes of insecticides (via resistance and regulation) than we are gaining and predicts that it will become very difficult to control codling moth in the future with insecticides alone.

Is Splat and other associated technology easier to put up?

Splat is not machine applied as far as Larry knows and would still have to be applied by hand.

Are there issues with the amount of pheromone emitted being less than that of a female moth?

I used to think spreading out many pheromone sources would control codling moth better, but we need to whack codling moth with larger sources of pheromones. 400 Splat droplets won’t be as good as 400 hand-applied dispensers. To save labor, I suggest using Tangler. They’re five times as quick to apply, and the reservoir acts just like Isomate or Checkmate. Find out more about the Tangler system here, http://www.ridgequestinc.com/tangler/.

If you put up traps to judge efficacy of mating disruption, is there a potential for males to be finding gaps that the traps aren’t catching? What is the first sign you would see?

Growers should put traps where they think moths will be. Males will be upstream of aerosol emitters and we aren’t sure what the females do. It appears that the females don’t move at all, making them hard to catch. Males move toward emitters and find clean air upwind. For hand-applied codling moth disruption, the only option is to put out more pheromone traps, and even then, the probability of catching male moths is low.