June 12, AppleTalk Conference Call

AppleTalk Conference Call Summary
Tuesday, June 12, 2018, 8:00 – 9:00 AM
Presenter: John Aue, Threshold IPM
Moderator: Peter Werts, IPM Institute of North America; questions or comments, pwerts@ipminstitute.org

June 12th Call Stream: CLICK HERE

Thinning and hail

The orchards are looking fantastic and surrounding fields, hills and woods are lush and healthy as well. Apple trees and wild deciduous species are both showing minimal stress, which is surprising given the amount of stress trees were under during bloom. Thinners seemed effective regardless of parameters such as rate, timing, weather, fruit size and carbohydrate balances.

Many growers have experienced hail damage ranging from light events up to a storm in Iowa that yielded golf-ball-sized hail stones. As we have previously discussed, hail damage is not as severe shortly before thinning because damaged fruitlets are likely to be removed by thinning agents. As fruits becomes larger, hail will be much more destructive. John suspects the rebound in tree phenology throughout the season may have played a significant role in easy thinning. Fruit damage aside, hail damage increases susceptibility to an infection from fire blight. Streptomycin is generally applied as a protective measure within 24 hours of a hail event, but this isn’t necessary if you don’t have a history of fire blight or if trees aren’t already showing evidence of fire blight. Once the terminal shoots are set and no longer growing, the risk of a fire blight infection will drop significantly.

Insect updates

Codling moth and obliquebanded leafroller

The start of the codling moth (CM) flight generated relatively high numbers in many orchards this season, due to consecutive hot days.  This gave us a very strong biofix and most growers who caught >10 moths/trap/week applied a larvicide right at 250 degree-days (DD), base 50°F. Now most growers have observed a dramatic drop in codling moth populations over the last two weeks. Most larvicides will be washed off with 0.5-2 inches of rain depending on application intervals.  We often discuss that reapplication only needs to occur once two inches of rain have been received, however, a half to one inch of intense rainfall in a short period of time may generate an equal amount of wash off as two inches of rain accumulated over several less intense rain events.  Consider the number of CM you have caught in the seven to ten days since the application. If trap captures have been below the threshold, larvae from the first batch may have finished hatching. Egg hatch reoccurs every 250 degree-days in a ‘bell-shaped’ distribution, meaning each flight will generate a new hatch after 250 DD. A Larvicide should be applied at 250 DD after a large CM flight. Codling moth traps should continue to be checked at least weekly.

Most neonicotinoids will not suppress populations of obliquebanded leafrollers (OBLR), which have started flying in some places. Belay (clothianidin) is one exception and is labeled for OBLR, but not other leafroller species.  Belay has been a popular neonicotinoid to use, where plum curculio and first-generation codling moth management overlap.  Growers who have used Assail (acetamiprid) or other neonicotinoids for plum curculio or first-generation codling moth should note these will not manage populations of OBLR or other leafrollers.  Once the OBLR flight has been observed, additional larvicides for CM should consider efficacy against this generation of OBLR.  Two popular classes of insecticides which will manage codling moth plus the spectrum of leafrollers and other internal-feeding lepidoptera, e.g., oriental fruit moth and lesser appleworm, include spinosyns, i.e., Delegate (spinetoram) and Entrust (spinosad) or the diamides, i.e., Altacor (chlorantraniliprole) and Exirel (cyantraniliprole). A good option for organic growers would be to apply Bacillus thuringiensis (Bt) for OBLR plus the codling moth, e.g., Virosoft or CYD-X (Cydia pomonella granulovirus).

European corn borer and oriental fruit moth

Jentsch lab, located at the Hudson Valley Research Lab, posted recently on European corn borer and oriental fruit moth (OFM) in nonbearing trees, https://blogs.cornell.edu/jentsch/2018/06/11/insect-management-for-newly-planted-trees-european-corn-borer-and-oriental-fruit-moth-june-11th-2018/. Both oriental fruit moth and European corn borers lay eggs on apples and bore into shoots, but can also bore into fruit. Massive flights of European corn borer have already been seen in our region over the last few days. This will result in egg-laying in orchards and will need attention. Growers should familiarize themselves with pictures of damage from both insects. Conversely, oriental fruit moth is an uncommon pest to our region and growers should not have much concern for OFM.


Thrips are generally only a problem in non-bearing trees and sometimes can be a problem on terminals of high-density plantings and are generally not a concern on large M7. On the rare occasion they can cause light blemishes known as pansy spot on green and yellow colored fruit.  The pansy spot injury that is rarely observed is dependent on the thrips entering the orchard between bloom and petal fall. The terminals of susceptible trees should be inspected for thrips where the leaves are unfolding on the new shoots. Typical damage consists of scarring on the mid-rib of the leaf and the curling of growing points. Trees can be treated with Delegate or Entrust at the maximum rate. A non-ionic surfactant should be added to help spread the insecticide into the tightly closed growing points.

Potato leafhoppers

Potato Leafhoppers (PLH) are also a problem for young trees and unlike thrips, Entrust and Delegate are not effective treatments. Potato leafhoppers come to the region during spring storms where warm air masses from the Gulf of Mexico pick them up, as the system moves north. To date, numbers reported in other host crops, as per the Wisconsin Department of Agriculture Trade and Consumer Protection Pest Bulletin, were still relatively low. The first large leafhopper immigration into orchards tends to occur after the second cutting of hay, which is happening now.

San Jose scale

Scale crawlers have not been caught on monitoring tapes but will likely appear in orchards soon. Trees have responded dramatically to warm weather after a delay earlier in the season. San Jose scale is likely delayed this year, when compared to tree phenology or the calendar. A growth regulator or a summer oil shouldn’t be applied before crawlers are seen. For San Jose management information, read ‘Scaling it Up as Buds Break,’ from The Jentsch Lab, April 2 2018, http://blogs.cornell.edu/jentsch/2018/04/02/san-jose-management-scaling-it-up-as-buds-break/.

European red mites

Localized European-red-mite hot spots have been found in several orchards, suggesting oil applications in some places didn’t provide the desired level of suppression. Fluctuations in predator mite population, other applications or external weather could all be factors as well. Mites should be monitored as they continue to multiply at rapid rates under our current conditions of high heat. As the season progresses, the threshold needed for treatment increases. Mites observed now in hot spots should be sampled to track the populations’ changes over time.

Threshold counts should include all motile mites, which may be difficult to see especially for smaller nymphs. European red mite populations tend to distribute themselves in high heat, allowing for easier counting. Magnification may be necessary to spot all young motile mites for an accurate count. Remember, predator mites can consume European red mite eggs and young. Beneficial mite predators at sufficient numbers on the tail end of a European red mite explosion will often lead to a higher ratio of red females to young or eggs, particularly motile young. Sequential sampling thresholds require inspecting leaves for all motile forms. The models were created to achieve no damage, so orchards with damage from mites may be past time for action. Download the sequential sampling forms in pdf form here, https://nysipm.cornell.edu/sites/nysipm.cornell.edu/files/shared/erm-sampling-chart.pdf.

Dogwood borer

The dogwood borer (DWB) flight should be starting soon.  DWB larva have been found in some orchards, which suggest the flight is still to come. Growers who have planted a lot of new trees in the last five years should be scouting and monitoring DWB. Deploy traps now, and place four feet off the ground. The DWB pheromone casts a very wide net and attracts multiple species of native clear-wing moths. If moths are caught in traps they need to be appropriately identified to confirm species.  There is not a trap-based threshold for DWB, rather if you are catching DWB adults you need to be looking for evidence of DWB larvae, e.g., frass around the graft union. Initial stages of DWB infestation may be random, damage may not affect tree immediately but four to five years down the road trees will begin to decline. Trapping gives us an early warning system to begin scouting, rather than waiting for visible symptoms.

The last couple of weeks has been an excellent time to scout for active dogwood borer (DWB) larvae.  Overwintered larvae are currently large (~0.5”) and reddish brown, gummy and/or crumbly frass can be found where they are feeding. This frass looks very similar to what we see from codling moth larvae.  The standard recommendation is to scout for larvae in blocks with trees on dwarfing rootstocks that are prone to producing burr knots, e.g., M.9, M.26, since DWB females find these burrknots to be an attractive medium on which to lay their eggs. Another critical area to scout is beneath tree guards on all dwarf trees even if they don’t look in decline or have reduced vigor. Tree guards, regardless of style, e.g., wraps, corrugated, grow tubes, can cause the “protected” bark to remain humid and damp long after the surrounding environment dries. The dampness can be exacerbated by tall weeds or grass in the tree rows. These conditions can cause the bark to crack or degrade, which create an area for the female moths to lay eggs and hatching larvae to burrow into the bark. When scouting for larvae also look for empty pupae casing near to or protruding from borer holes. Even if borers are not found other surprises may exist below the tree guards, e.g., woolly apple aphids, ants, etc.

Usually DWB injury is found right above or around the graft union. DWB have also been observed in the scaly bark that is not covered by tree guards, e.g., winter injury or herbicide injury, or even on pruning cuts just above the tree guards. Small diameter dwarf tree, e.g., 3-6 years old, are more prone to girdling that can be caused by continuous infestation; feeding often needs to happen for several years before trees shows decline in vigor and possible death. Even if feeding does not impact the vigor of the tree it can produce an entry point for disease, e.g., black or white rot.

When applying chlorpyrifos as a trunk spray use large volume of water and high pressure to thoroughly coat the bark. If good coverage is achieved effective protection can be achieved for 2-3 years. Low pressure backpack sprayers are not suitable for this application.

For more information and photos visit:

Apple maggot

Apple maggot (AM) have been caught as early as June 14th in some years. If you have had injury from AM or have early ripening cultivars, e.g., Lodi, yellow boards or red spheres for apple maggot monitoring can begin to be deployed. Yellow boards can provide an early warning system by attracting apple maggot during their feeding period. If bait is used in addition to visual traps replace volatile lures according to the manufacturer’s directions, e.g., seven to ten days. It is advised to set up a minimum of three traps per ten acres at the beginning of July; trap density should gradually increase to one trap every 200-300 feet along the orchard perimeter, as the season progresses. Locate traps along perimeter where wild hosts are present and near early ripening cultivars. Hang traps at eye level, and make sure they are visible. Traps are usually hung in early-season varieties that exist on the interior of block around July 4th. Putting a trap or two out now can give a good heads-up as well.

Beneficial insects

Lot of beneficial insects are out there in good populations including spiny soldier stink bugs, green lacewing eggs, gall midge larvae, lady beetles (Coccinellidae), assassin bugs, predatory mites and spider mite destroyers. These insects certainly don’t control plum curculio or codling moth but are mostly beneficial for controlling aphids. To see photos of these insects, download these ‘Early Season Apple Injury and Common Beneficial Insects’ slides in pdf form, http://www.ecofruit.wisc.edu/appletalk/wp-content/uploads/sites/343/2018/06/Apple-Injury-and-Benefical-Insects.pdf.

Disease updates

Powdery mildew

Powdery mildew has been observed at orchards around the region in the last two weeks.  This disease flourishes in hot and dry conditions. Spores are easily washed from infection sites, but the fungus can grow on terminals, in the absence of frequent rain events. At one time, we considered this a rather rare disease in the upper Midwest, but shoot infects have now become quite common place.  In the southern United States, powdery mildew is much more severe and can spread to fruit and cause russeting. At this point, there’s no need to worry if powdery mildew appears on trees other than to note its location for next year. Single-site fungicides and sulfur provide protection against powdery mildew, whereas captan does not. Where we don’t have active-scab infections, any of the single-site fungicides may be used without concern of losing efficacy for primary scab management. Note: Sulfur applications when made during hot weather, e.g., over 80°F, may cause russeting during application. If applied under cooler conditions and warm weather follows several days later, the risk for russeting decreases. Russeting potential decreases significantly when the sulfur is out of solution and dry on the plant surface.

Secondary scab

We are well past primary scab season and secondary scab infections are now releasing millions of conidia during rain events. Secondary scab will likely be located only on varieties where scab has been a problem the previous year and control was not achieved during primary ascospore release. Avoid treating secondary scab with single-sight fungicides, e.g., Aprovia, Flint, Rally and Sovran that were used during primary scab season. Captan should be the only fungicide used to reduce the spread of scab, once secondary infections are found. Organic growers have the option of wettable sulfur or bio-fungicide, to slow down secondary scab spread. Young tissue on trees remains highly susceptible to scab and just because it is hot, apple scab can remain a persistent problem. If you have no scab, intervals between sprays may be stretched and rates can be adjusted. However, consider that protecting tissue from black rot and white rot would still warrant applications of Captan at five pounds per acre.

Sooty blotch and fly speck (SBFS) and bitter rot

Captan or Topsin-M (thiophanate-methyl) or a generic equivalent, are best fungicide options for managing the SBFS complex.  These do not have any resistance concerns, where secondary scab may be present and functions exceptionally well against summer diseases. Fruit rots, including bitter rot, require either a full rate of captan or a half rate of captan plus a single-site fungicide, e.g., strobilurin, sterol inhibitor or SDHI.  Single-site fungicides should not be used on any varieties for SBFS, bitter rot or other summer diseases, where secondary scab is present.

Sooty blotch and fly spec reproduce the same way as apple scab. Ascospores spread from brambles into trees, where the first infections begin occurring in the weeks after petal fall. The disease model predicts when symptoms show up, not when infection occurs. The first application should be made between 175 and 250 leaf-wetting hours that were longer than four hours in length since petal fall or the last application of single-site fungicide. If humidity is high, closer to 175 is recommended, which will typically happen in early July. Overgrown trees that should have been pruned will show symptoms first, but once the symptoms appear, they can’t be removed. Two applications of Topsin or a single-site fungicide applied after the accumulation of the leaf-wetting hours should be sufficient to get through the season. Summer disease infections can be eradicated with minimal resistance because it’s a complex of about 70 different pathogens.