University of Vermont

By Terence Bradshaw

The time has come to hang apple maggot fly (AMF) traps in Vermont orchards. Last year, we saw higher populations state-wide, for which I don’t really have a good explanation. 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.

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 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. 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

It is summer lepidoptera season, and treatment should be on everyone’s minds, especially for codling moth (CM) and obliquebanded leafroller (OBLR). CM are active and eggs hatching or soon to hatch across the state, so growers who have caught CM in their traps or who often have issues with this pest (that’s most everyone) should apply something effective against them soon. Very specific materials like insect growth regulators (Intrepid, Rimon) or granulosis virus (Madex, Cyd-X) can be used that are very safe to non-target insects. One or two applications of a material should suffice for first generation. OBLR are just showing up in traps, and treatment should be timed at 360 degree days (base 43°F) after first catch. There is a NEWA model for this pest, and a material like Bt (Dipel, etc.) is effective (but not against CM).

Mites are a no-show statewide. Keep scouting leaves, as their populations can grow very quickly, especially as the weather heats up.

Diseases: keep checking on your scab, if you have none (I mean none), then it’s okay to relax. The summer diseases sooty blotch and flyspeck are of concern now, but they require 270 hours of leaf wetness for lesions to form, so fungicide coverage between that period should be maintained. Keep in mind that one inch of rain washes off half of your coverage, after two inches, it’s gone.

Enjoy the holiday this week and remember that trees shouldn’t be sprayed when it’s over 80-85, and application of sulfur, captan, and other potentially phytotoxic materials should be avoided when hot weather is in the forecast for the next couple of days.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

Orchards in the highest elevation and coolest areas are at or just past petal fall, so all the advice I’ve had for other growers applies there as well now. All orchards should have started or, more likely, completed chemical thinning by now. Fabulous thinning weather occurred last week and those who applied the usual materials should see the effects by now. If a little more ‘nudge’ is needed to break up clusters, carbaryl , 6-BA 9 (Maxcel, etc.), and NAA (Refine, etc.) will still work so long as the fruit you’re thinning are under 15 mm diameter. If you have a lot of larger fruit, up to 20 mm, then Ethephon + carbaryl can help in a pinch, but be careful, as that mixture is relatively unpredictable. Wes Autio and Win Cowgill have a factsheet on such rescue thinning for more information.

Regular readers may have noted that I (almost) took a week off from updates- I also took a week off from spraying. Where petal fall insecticides were applied against plum curculio (PC) and European apple sawfly, you’re probably good until another is needed for PC due to rain washoff or codling moth rears its head. As for the former, PC is only ‘programmed’ to lay eggs and cause fruit damage for about 308 degree days (base 50) after McIntosh petal fall, and we’re only about 1/3 there at the UVM Hort Farm. It would be wise to check for PC damage to fruitlets and consider reapplication at the first sign of fresh damage.

Figure 1Plum curculio damage on a developing fruitlet. This damage is about a week old, note the dried surface and lack of sap. Fresh stings after an insecticide has been applied indicate potential need to reapply.

As for the latter pest, codling moth have now been trapped in most scouted orchards in the state. To best manage the first generation of this pest, calculate degree days (base 50°F) from the date of first capture in pheromone traps. Most materials should be applied at 200 degree days after catch, which should be in the next week or so. Cornell entomologist Dr. Art Agnello offers the following specific recommendations for CM management in the latest Scaffolds newsletter: “The best products for controlling both CM and OFM in apples and stone fruits are those in IRAC Group 28 (containing a diamide; i.e., Altacor, Exirel, Minecto Pro, Voliam Flexi or Besiege) or IRAC Group 5 (mainly spinetoram, Delegate; spinosad, formulated as Entrust, is an organically approved option). Two applications from either of these groups on a 10–14-day interval would be recommended starting at 220 DD50 from biofix; we’re already beyond this point in Highland and Geneva, but sites in WNY range from 81-247 DD50, depending on proximity to the lake (refer to “Model Building” numbers in this issue). Products with insect growth regulator activity, such as Rimon, Intrepid or Esteem, would also be suitable options this week in apple sites at the lower end of these values. Other products with activity against internal leps include the neonic Assail, the biological Grandevo (also organically approved) and, in orchards where resistance has not developed to the newer pyrethroids, also Baythroid, Danitol, Endigo, and Leverage. Most older broad-spectrum materials like Imidan, Lannate, and the older pyrethroids, which were formerly more effective, are generally not as good choices because of insecticide resistance issues…Now would also be an appropriate time for an application of a granulosis virus product in pome and stone fruits such as Cyd-X, Madex, Virosoft CP4 or Carpovirusine (apples and pears only), in addition to the larvicides discussed above. These are biological insecticides, which must be ingested to initiate the infection, after which the virus replicates inside the larva until it is killed; this releases more virus particles into the orchard. This is a very useful approach for long-term population reduction, particularly when used in at least 2 applications per generation. Madex, and now Virosoft CP4 (see “Chem News” in this issue) contain an isolate that is also effective against OFM.”

As for diseases, all sites should be done with primary apple scab season. That doesn’t mean that scab management is done, just that there are no overwintering spores left in leaf litter. If you have NO scab, you’re done managing this disease for the year. However, I suspect that many orchards missed an infection period or had spotty coverage, and that there is a good bit of scab out there. If you have scab, plan on maintaining some level of preventative fungicide (Captan is about all you have, sulfur if organic) for the next month or so until fruit and foliage become resistant. Do not use single-site fungicides like DMIs, strobilurins, or SDHIs (FRAC codes 3,7, 9,11) on active lesions to reduce development of fungicide resistance.

There have been some reports of fire blight showing up from the marginal infection periods that occurred May 20, 23, or 26. Keep your eyes out, especially in blocks that have had a history of the disease or on susceptible cultivars like Gala and Paulared, and cut strikes out as you see them.

If using nitrogen fertilizers in your orchard, plan on wrapping up applications in the next week or two to give trees time to harden off for winter. Potassium fertilizers can go on any time now.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

Finally, it looks like we’ll be entering an extended stretch of warm, sunny weather starting Thursday and especially Friday and lasting through the weekend. In South Burlington, we’re expecting temperatures just near 80°F by Sunday. That is great weather to drive plum curculio and European apple sawfly activity, so I suggest treating against those pests Tomorrow or Friday. I’ll be going out Friday morning when the wind is looking more favorable for spray application. But remember, if you’re one of those high elevation sites with petals and bees still present, you need to wait.

All for now.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

This week I’ll just say, “more of the same…” Apple scab primary ascospore season is done or nearly done in Vermont orchards. Check carefully for apple scab in your orchards before stopping fungicide coverage. Lesions can take two weeks to appear, so you may not see the latest infections for a bit. By now, growers who have been using more than three pounds per acre of mancozeb should put that away for the season, captan will be the protectant fungicide of choice. Sulfur should be the standard in organic orchards, although lime sulfur may be appropriate, especially if there are active lesions that need to be burned out and you want some thinning activity. Remember, lime sulfur is extremely caustic and corrosive to metal, to take care of yourself and your equipment if you use it.

Keep an eye out for fire blight strikes as you walk your orchards. We were generally on the ‘no conditions for infection’ side of the line in most orchards, but there is a chance that some got through, especially in warmer sites with a history of the disease where streptomycin was not applied. Prune out strikes as you find them.

Insects: still quiet. Codling moth has shown up in some sites, which means a targeted application of an effective product 250 degree days (base 50 °F) after the biofix of the first date caught in a pheromone trap. In the meantime, where you have 100% petal fall and no bees in the orchard, an insecticide application targeted at plum curculio and (if present) European apple sawfly may be warranted. Dogwood borer are rearing their heads more and more. If you have them (check burr knots on trunks, especially young trees on M9 or M26 rootstock), consider a coarse, soaking trunk spray. Best bet now is probably Assail; the old standby Lorsban (chlorpyrifos) is no longer registered for use in Vermont, and for good reason. Organic growers may consider Pyganic, and probably several applications.

Thinning: weather isn’t looking very good for 6-BA thinners like Maxcel until later this week. If planning to use those materials on smaller-fruited cultivars like Empire and Fuji, wait a bit. NAA thinners should be effective, but plan on using higher rates given the cool weather. Keep an eye on developing fruit following thinner applications, fruit will be susceptible to hormone sprays up to 17 mm diameter, after which we need to take more drastic and unreliable measures.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.

By Terence Bradshaw

As has been the general case this year with the drawn-out, cool weather, we have bloom (and p-bloom) bud stages all over the place depending on elevation, proximity to the lake, cultivar, and latitude. For growers in upland sites just entering bloom, see my posts from the past couple of weeks that have been aimed at bloom-time management. Remember, no insecticides; mow flowering weeds in the groundcover to make your trees more attractive to bees; and watch for fire blight. Keeping an eye on that very weather-specific disease can be more difficult in upland areas where NEWA stations are less prevalent. However, a look at stations in East Dorset, East Montpelier, Morrisville, and Berlin (‘Montpelier’ airport) shows EIP (potential bacterial population) below infective level all week, although a warmer-than-expected Wednesday or Thursday may change that. Overall, I wouldn’t be too concerned about fire blight for those sites, but would keep an eye on things.

Growers in warmer areas, however, may need to be concerned. Shoreham was flagged as having had an infection event yesterday, and an application of streptomycin today (like, now) to open blossoms may be prudent, especially on susceptible cultivars. Remember that blossoms are pretty much done as far as disease susceptibility is concerned once the petals fall, or 80 degree days (base 40) after they open, or 3-5 days given the weather we’ve been having.

Apple scab is the main disease to stay concerned about statewide. This is proving to be a challenging year for the disease, with infection periods occurring every week since bud break and reports of numerous tractors stuck while spraying. The good news is that we’re on the tail end of the primary apple scab infection season when the overwintering spores resulting from last year’s infections on leaf litter are close to expended. If you manage to keep covered with fungicides during that window and all infections are prevented, then apple scab season ends when those spores are gone. However, any infection in the tree canopy will lead to development and release of conidial spores which creates a secondary phase of the disease. My point is, keep protected until you know that you are scab-free and the spores are all expended. Some stations (Bennington, Cornwall, Shoreham) called for the end of primary season last Thursday, many more are indication that we’re within 1-2% of the spore load left. For those orchards, I recommend maintaining a good coat of fungicide through this week, and likely next. Depending on the material you choose, this application will cover you against powdery mildew, rust, and moldy core which can be a problem in cool, wet bloom periods. In 7-10 days, get out and do a thorough assessment of foliage for scab lesions. Pick the worst-case spots- tops of trees, that corner of the orchard where you turn and can’t get good coverage on that one last tree, the shady spot where the trees stay wet longer. Only after you know you’re clean can you let your guard down.

Speaking of letting your guard down, many of us did on the insect front going into bloom because trap counts were low for most insects across the state. We’re now seeing high numbers of European apple sawfly on traps in many orchards, and I expect a petal fall spray will be warranted against them. Pay attention when making this spray- petal fall means that all blossoms are gone, your migratory bees are pulled out, and flowering weeds attractive to wild pollinators are mowed. There are a number of materials that are effective against EAS, and all are toxic to bees to one degree or another. For organic growers, now is the time to get a good, solid coat of Surround kaolin clay onto your trees to deter plum curculio. I always preferred to apply this base layer in two coats, one at ~50 lb Surround per acre followed by another 25 lb per acre to get a good build up going into petal fall and the beginning of the real incest management season.

Thinning. This is always tricky to give advice on, and the variable conditions across the state make the job even harder. Many orchards have a larger-than-normal potential crop, and pollination should have been sufficient given the handful of good ‘bee days’ where conditions were right for bee flight and fertilization. This is a good year to consider multiple ‘light coats’ of thinners. NAA + carbaryl are a typical mix to apply at petal fall on many cultivars. For smaller-fruited cultivars, 6-BA thinners may be used instead of NAA to increase cell division and final fruit size, but they need warm sunny weather to work best. NEWA has a good model (two of them, actually) for helping to determine the potential effectiveness of thinner applications based on weather before, during, and after application.

This is the most critical time to keep your eyes open out in the orchard. Stay alert for signs of fire blight and apple scab. Check traps daily for codling moths to help determine the biofix date that you’ll use for subsequent management decisions. Keep an eye on fruit clusters for signs of thinner activity (yellowing stems, sepals that don’t close up). Get you nitrogen and other nutrients on, multiple lighter coats are better in rainy years than one big one to minimize leaching and runoff. Watch for and enjoy the sunshine. This weather can’t last forever.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

The UVM Tree Fruit and Viticulture Program is supported by the

University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM

Grant, and USDA Risk Management Agency Funds.