Vermont Apple IPM- Summer pest management

Sorry about the delay in getting this out, graduating a kiddo from high school is more of an event than I’d planned. Anyway, there are a few orchard items I want to touch on. First and probably foremost, the heat we are expecting this coming week could provide substantial stress to trees, not to mention farmers and farm workers. Plan ahead and take care of yourselves. If you have irrigation, is should absolutely be running this week. Even with drip irrigation, well-watered trees will have cooler canopies due to increased transpiration and evaporation from leaves. High temperatures combined with many pesticides can lead to phytotoxicity ranging from minor leaf burn to fruit finish damage to tree defoliation- I’ve done them all. Pay attention to any warning on labels and do not spray during the heat wave. I’d say Sunday is your last day to apply anything this week before it gets too hot.

Heat stress on trees not only contributes to general tree decline, but also predisposes fruit to certain rots. I have visited some orchards and haven’t seen any apple scab, so most can step back from regular sprays for that disease. However, protection should still be applied to reduce fruit rots. Captan is the standard summer fungicide for its efficacy against the cosmetic diseases sooty blotch and flyspeck as well as against fruit rots, and is more effective when mixed with topsin, a strobilurin fungicide (FRAC code 11, e.g., Flint, Sovran, Merivon, Prostine, etc.), or a phosphite fungicide (e.g. Rampart, OxyPhos, Prophyt, etc.). Summer fungicides should be applied every 10-20 days depending on rain, and I find that most well-managed orchards that market direct to consumer and don’t store fruit for long with trees pruned and grass mowed to allow for good airflow can get by with 2-3 post-scab summer fungicides. That’s a lot of qualifiers, but it works for us and for many other farms. Farms that will store fruit or process on a packing line and thus have greater likelihood of disease development in storage and / or lower tolerance for cosmetic diseases may need to cover more, and would do best to follow the NEWA SBFS model.

Insect pests of note right now include the tail end of codling moth egg hatch and increasing obliquebanded leafroller activity , so a second application against them would be warranted in orchards that have a history of damage (most, by now) or trap capture over ~5 codling moths per week. A lepidopteran-specific material like Delegate, Intrepid, Altacor, Belt, Exirel (DON’T mix that one with captan) would best target those pests. Plum curculio should be done ovipositing in most all orchards. Now is the time to get started coating apple maggot fly traps to be hung shortly. These are some of the easiest pests to manage using an IPM strategy, so there’s really no excuse. The idea is to assess the population in the orchard before applying prophylactic sprays. By using red sticky traps, you can time treatments for best effectiveness, and maybe even skip treatments if the populations are low enough. Traps are red plastic balls that you coat with Tanglefoot adhesive. Kits including traps and adhesive are available from Gemplers and Great Lakes IPM. We will also be distributing some traps, but will need to do so on our (limited) drives as they don’t ship well when the adhesive has been applied.

Traps should be hung at least four per 10-acre block, preferably at the orchard perimeter and especially near sources of the insect, like wild or unmanaged apples. Placement in the tree should be about head-height, and surrounding foliage should be trimmed away- this trap is largely visual, and you should be able to see it from 10-20 yards away. The traps may be baited with an apple essence lure that improves their attractiveness dramatically. For monitoring to time sprays, unbaited traps that catch one fly per block (as an average of all the traps in the block) would warrant treatment; the lure (Gemplers, GL IPM) makes them much more attractive such that you can wait until an average of five flies per trap are caught before treating. For most growers, the main insecticide used against AMF is Assail, Imidan also works but it has a long reentry interval and tends to leave visible residue on fruit. Remember to rotate your insecticide chemistries to avoid resistance development in pest populations. Resistance isn’t a huge issue with apple maggot fly that has one generation per year, but codling moth and other lepidopteran pests are still about and subjecting successive generations of them to the same class of materials can induce resistance. For organic growers, Surround works well, but its use in midsummer may increase European red mites, and it can be hard to remove at harvest; spinosad (Entrust) works pretty well too. First AMF treatment is still a few weeks off, most likely.

I have seen one pretty bad case of European red mites already, and hot, dry weather is also conducive to mite flare-ups. A weekly or, if the numbers indicate, bi-weekly scouting will help to indicate if there are high enough mite numbers to consider treatment. Information on monitoring: Mites should be treated based on the following thresholds: in June, 1-2 mites per leaf; July, 5 mites per leaf; in August, trees are more tolerant of feeding so treatment should only be applied if there are over 7.5 mites per leaf.

It’s time to wrap up any ground-applied nitrogen fertilizers, but potassium and magnesium fertilizers can be applied any time in summer. It’s also a good idea to start your regular foliar calcium sprays, especially on bitter pit-prone cultivars like Honeycrisp and Cortland.

That’s all for now. Stay cool out there this week- it’s a good time to do fieldwork ‘farmer’s hours’ in early morning (or ‘hobby farmer’s hours’ in the evening).

The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.

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