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codling moth and Entrust

Posted by Brian Caldwell 
codling moth and Entrust
February 16, 2021 07:43PM
We seem to have lost effectiveness on codling moth with Entrust on one of our two sites. I sprayed twice at max rates last summer to hit the second flight, timed by pheremone traps, and we still had 15-20% CM damage.

The other site was fine, almost 0 CM damage.

I'll be switching to Cyd-X virus this year.

Has anyone had success with Grandevo on this pest?

Hemlock Grove Farm
Zone 5 in New York
Re: codling moth and Entrust
February 17, 2021 04:00PM
You're like the last guy on the planet that I'd expect this to happen, Brian! Seems you've been reminding the rest of us since forever about resistance issues with Entrust. How applications need to be rotated with different materials so the target species doesn't develop individuals with a genetic end-around to the spinosad toxin. It would be useful for you to expound on this. Or maybe you're suggesting that the formulation itself has somehow been changed? Shelf life enters in here as well as I've experienced a lessening of effectiveness by year three.

Not to change your Codling Moth focus... but I found it interesting how Mike Biltonen pointed out (somewhere) that use of Entrust for sawlfy year after year is justified despite the resistance risk. A single application approximately a week after petal fall in this case targets one generation per year thus "sawfly survivors" have not necessarily been given a drawn-out chance to counter the effectiveness of spinosad. I agree, having long used Entrust for this purpose.

I hope you get feedback on Grandevo as part of a proper rotation against lepidoptera species.

Lost Nation Orchard
Zone 4b in New Hampshire
Re: codling moth and Entrust
February 17, 2021 09:39PM
Resistance management depends on a lot of factors including the type of material being use, the pest being treated, other alternative strategies being employed, and luck. Resistance occurs when materials are used consistently without a break such that the grower is "selecting" for the resistant population. In some cases, this resistant population is usually a very small percentage of the overall original population and is also a very weak genetic variant, otherwise it would have been the dominant portion of the population to begin with. This means that in some cases, but not all, that if you cease using that material they have grown resistant to, the population will "recover" and become susceptible again as the "fitter" part of the populations - the susceptible ones become dominant again. In some cases this recovery can happen in a season, some times it takes decades.

- Type of Material - almost all of the materials used in organic growing are generalists - almost but not all. That is, they act or work by attacking different part of the biological organisms life cycle and development. Organisms (e.g., apple scab) that are treated with materials that work on a single site (e.g., some conventional fungicides) develop resistance much quicker when those materials are used i) alone or ii) repeatedly without a break because they are always banging away on the same weakness. Tank mixing with a different class of material and rotating materials with a different class of material ensures a reduced risk of resistance simply you're attacking the organisms from different biological angles. Rarely, can an organism be naturally resistant to 2 different modes of action. Regardless, in the case of Entrust, tank mixing with another non-spinosad material ensures continued susceptibility.

- Pest being treated - some organisms - like bacteria and some insects - have very short turnover times in terms of generational fecundity. Others, have a single generation per year. The shorter the life cycle, the quicker the turnover, the more likely the organism is to develop resistance. The weaker, susceptible populations are killed off and with each successive generation the less fit but resistant population becomes more dominant. The more turnover per season, the quicker resistance builds. Now, this doesn't mean that an organisms with a single life cycle/generation per year is NOT susceptible to resistance, it just means it is more unlikely and, after all, really depends on the specifics of the situation. In general though, the more specific the material, the generations per season, the more likely resistance will develop.
- Other materials. Already discussed above, but tank mixing and rotating sprays with different class materials breaks up these cycles and reduces the potential for any resistance issues.

Speaking more specifically to Brian's case - Using ONLY Entrust would increase the likelihood of resistance to spinosad type insecticides. Using DiPel, CyDex/Madex, PyGanic, Grandevo, mating disruption together or in rotation with Entrust should have ensured a reduced potential for resistance issues. That said, there are a number of factors that could have gotten in the way of this.

One is that local use of Delegate (a synthetic analog of spinosad) and/or local use of Entrust itself in neighboring areas could have pre-empted any other strategies Brian had. Codling moth are not limited to Brian’s orchard, but are all over the place and migrate in from outside – so depending in neighboring practices, this could have been a factor as well. That said, Brian didn’t mention the use of any alt strategies in the same or previous years. This could have helped reduce resistance potential, but will certainly help reduce the resistance issues and in a few years Spinosad could be back in the regime.

Codling moth is a 3-4 generation pest (3 gen in the Finger Lakes) and so has up to 3 opportunities per season to shift the genetics of the local populations to resistant subpopulations. Euro Apple Sawfly is a single generation pest and so has one opportunity per season, so the pressure is lower. Lastly, the later generations of codling moth tend to be the worst. The early or overwintering generations tend to be more susceptible to sprays, while the later are less susceptible just because they are stronger as there is developing fruit, more foliage, etc. through the season. Not sure what gen caused Brian’s damage.

My approach is thus (always use mating disruption and granulosis):
Early 1G CM – apply PyGanic around full pink as the first generation is coming out of its winter phase as an adult, so Bt will not work and I do not want to waste an Entrust spray for CM at this time. That said, I am also putting out mating disruption and pheromone traps to begin to monitor this pest. The 1G is not a damaging gen, but it will be the first mating gen of the season. Timing the first flight and using mating disruption allows for both timing of sprays and monitoring of population thresholds. Low flight number indicate a reduced need for any controls. There is a possibility that this first spray could coincide with an early Entrust spray for early PC or EAS, but that will depend on your specific area. In any case, mixing with PyGanic reduces the potential for resistance and increases potential for control. At first flight, eggs are laid and eggs hatch around early-June.

Larval feeding between mid-June and mid-July

Mid 2G CM – between the 1G and this stage, the eggs have hatched and larvae are active. If you time properly the egg hatch, then a combination of Entrust plus Bt should control this generation. Remember that MD is working along this whole time too. After a period of feeding (this is right around fruit set and so they are loving life now if they can find your fruits), they will pupate before developing into the 2G gen of adults in early July, after which they go through the whole deal again – lay eggs, hatch, larvae, pupae, adults.

Larval feeding between mid-July and mid-August

Late 3G CM – early August you get the third flight of the adults and the potential for the third and strongest generation. Here I wouldn’t use Entrust but switch off to a Grandevo + Dipel or PyGanic spray, unless this also aligns with your apple maggot spray (where you might be using Entrust again). By now, you may have applied Entrust 4 times – pink, PF, 2C, and now mid-August (AMF). The more overlap with the codling moth generations, the more likelihood for resistance.

There may be a 4th generations in warmer climates (not Brian’s orchard).

You may need to repeat these sprays more than once (so mixing them up is an even better idea) and the 2nd and 3rd gen may overlap actually, so they aren’t necessarily distinct generations. I hope this makes somewhat of sense – but the bottom line is: monitor populations with traps, use biofixes to time egg hatch, use mating disruption to reduce breeding, use granulosis and generalist insecticides, and rotate rotate rotate.

* specifics and timing depend on YOUR specific conditions and location.
**I probably missed/forgot something in here, so don’t hesitate to call me out or ask questions.

Mike Biltonen, Know Your Roots
Zone 5b in New York
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