VT Apple IPM: Management in light of a difficult crop situation

We have been collecting damage data from orchards across the state this week, and the news is generally not good. It does seem like we have three classes of damage: near-complete crop loss inland and Connecticut Valley, some degree of often substantial loss in the Champlain Valley, and a good crop in the Champlain Islands and near the lake. As far as management goes, that leaves us in three different scenarios, and those in one of the scenarios- complete crop loss- may not be crazy about hearing me discuss how the lucky ones tend to their crop this season. I’ll make some notes in a bulleted list without much formatting, as I have more orchards to scout this afternoon:

  • Apple scab- This one is easy, it is still active, with no orchards having discharged all overwintering inoculum yet. Wetting events are few and far between but all orchards need to keep covered against scab. Be sure to include a fungicide effective against rust, like a DMI (FRAC code 3) or SDHI (FRAC 7) and/or powdery mildew (strobilurin, FRAC 11) in a couple of sprays to keep those diseases at bay. This protocol should be followed for all orchards regardless of crop freeze status.
  • Keep an eye out for fire blight strikes. Any blossom infections that may have occurred from the May 12 potential infection event should be showing now or next week. If you see them, cut them out.
  • Thinning is going to be complicated a lot by crop status, of course. For orchards that have no fruit or heavily damaged fruits (meaning more than 75% )do not consider thinning this year. For orchards with less than 20% damage I would consider thinning as normal this year. The question comes with orchards that have moderate damage between 25 and 75%. Not thinning those orchards may result in heavy set of small fruit that could promote biennialism, but trees are likely to respond well to thinners applied in the next week, given both the cold damage and the warm sunny, weather that we are expecting coming up. My tactic at the UVM orchard, which experienced moderate fruit damage between 20 and 70%, depending upon cultivar, was to apply a low rate of NAA thinner with a low rate of carbaryl insecticide. This could be a gamble – we have 70 varieties across the whole orchard and it is difficult to thin based upon variety even in a ‘normal’ year. This is not an uncommon problem for retail orchards to face. I do not have the greatest confidence in this strategy this year, and have difficulty recommending blanket sending recommendations to growers given the state of the crop this year. in the end, I would trust your gut – if you have a good crop thin it, if you have a moderate crop consider thinning it lightly as we can come back in later next week when we can see better the effects of both the frost and any thinner applications you may have applied.
  • Insect management-this will also differ, depending upon the state of the crop in your orchard. For orchards with a full or even a moderate crop, I would plan to manage your insect pests as normal this year. Petal insecticide sprays should have already gone on in most orchards. Inland orchards and cooler sites may be ready for a petal fall spray now. Normally our petal fall sprays are targeted at European apple sawfly, early emerging codling moth, and plum curculio. All of those pests are fruit feeders so orchards that have no fruit or are assuming to have very little fruit may consider omitting all insecticide applications targeted toward protecting fruit. The difficult situation comes where orchards have a low set of fruit where the expense of the application on a per bushel basis could be quite high but the value of the few apples you have is also high. If there’s any question about whether or not you have sufficient crop set in your orchard, I would go ahead and treat as usual. If you have no crop or nearly no crop , then you may consider omitting those insecticides. However, I would consider maintaining some coverage primarily for shoot and leaf feeding, lepidopterous caterpillar larvae. That may mean including BT sprays in petal fall, scab, thinning, or other sprays in order to keep down leps like obliquebanded leaf roller and tent caterpillar. In orchards with little to no crop, the great reduction insecticides used this year may allow beneficial populations to increase substantially, setting you up for a better IPM program next year. I would however not ignore trunk applications of Assail or another appropriate insecticide in young plantings to avoid issues with dogwood and other borers.
  • Nutrients-for trees with little to no crop nitrogen applications should not go on this year unless trees are under vigorous. For all other trees, fertilize as you normally would. For trees with little to no crop this year potassium is not likely to be removed in any significant amount because that is usually removed in harvested fruit. However, it is important to maintain or improve the potassuim status in your orchards to ensure that you have an appropriate amount of that nutrients going into next year when it is likely orchards, will have a heavy crop load. I would consider applying magnesium potassium fertilizers in the next month or so regardless of crop status.

That’s it for now. I hope to have a better understanding of the crop situation soon, but you all likely know where you stand on your own farms. I will continue to work with the Agency of Agriculture to see what resources we can bring to the industry in this tough year.

Take care,