West central Michigan tree fruit update – June 25, 2019

Warmer weather brings increase in insect activity and more disease is showing up in tree fruits.

Weather is finally warming up in the area, giving some much needed heat to our crops. However, frequent rains have continued to be a frustration for growers as they try to get out in to fields and keep covers tight, and more scattered showers are likely on the way in the next week. An increase in heat has also brought on an increase in insect activity, and more disease showed up in tree fruit over the past week as well.

Growing degree day accumulations since January 1 for west central Michigan

Station

Degree Days Base 42 Degrees F Current

Degree Days Base 45 Degrees F Current

Degree Days Base 50 Degrees F Current

Benona / Shelby

946

756

488

Elbridge / Hart

999

802

523

Fremont

1099

891

596

Hart

973

777

500

Ludington

929

735

465

Mears

993

791

507

New Era

1044

835

540

Shelby - East

1016

815

530

Apples continue to size quickly with all of the rain. King fruits have moved to 25-30 millimeters in the Hart area. The thinning window is over in the area, but some growers will be doing some further hand-thinning on varieties that are still set too heavily. Summer applications of NAA are beginning – the optimal timing for these applications is five, seven and nine weeks post bloom.

Some scattered fire blight strikes have shown up in the past week at a few orchards on susceptible varieties including Gala and Idared. The strikes that have been submitted to the tree fruit MSU Extension lab have been shoot blight, not blossom blight. While we have not necessarily had any specific weather events that would constitute a traditional trauma event (hail, severe wind storm), we have had several very windy days and quite a few storms move through in the presence of frequent rain and warmer temperatures over the past two weeks. This, combined with the lush growth that is present on most apple trees this season, likely resulted in some microfractures to new shoots during conducive weather, leading to the shoot blight strikes that have shown up. Fewer bacterial cells are required to initiate a shoot blight infection than what are required to initiate blossom blight, so it does not take much to get a shoot infection going during a conducive weather event.

Growers with isolated shoot blight strikes are advised to wait for a warm, dry day and then cut it out of the tree. Growers with high density apples should be particularly careful to prevent the fire blight from making it in to central leaders, leading to loss of trees. High rates of Apogee (4-6 ounces, at least two applications timed 14 days apart) can be used to thicken up the cells in shoots and slow down the movement of the fire blight bacteria. Copper applications can also be used in processing or non-bearing trees, but should be avoided in fresh market apples due to concerns of fruit russet. Streptomycin is not recommended in these situations, inoculum levels when bacterial ooze is present on shoots are so high that this practice is more likely to select for resistance than achieve successful control.

Use the sooty blotch/fly speck model to keep track of accumulated wetting hours. A summer fungicide should be timed around the 240 accumulated wetting hour mark indicated by the model. This wet growing season means that many orchards will need a cover sooner than in a typical year.

Tart cherries are starting to show some light yellow color at early sites. The crop continues to be highly variable in the region, and many orchards have poor fruit set this year. More cherry leaf spot continues to show up, yellow leaves are visible in some orchards at this time. Phytotoxicity in tart cherries has also shown up in the past week. The lush, tender foliage on trees this year may have been slightly more sensitive to some of the sprayer combinations that we tend to associate with these issues. Growers who want to try an application of copper this year are either at or rapidly approaching the optimal timing – just after plum curculio sprays and before spotted wing Drosophila (SWD) sprays, during moderate weather.

The sweet cherry crop is looking lighter as the past week has gone by, significant amounts of fruit have dropped off in many orchards. Fruit cracking has also been observed, especially in places where the crop has thinned out to a higher degree. Growers do not normally need to think about brown rot when sweet cherry fruits are still green, but crack damage or other physical damage to sweet cherries at this stage can result in brown rot infections. Keep an eye on brown rot as fruits start to color up, particularly on early varieties. Yellow color is already visible in several varieties. Warmer weather on the forecast accompanied by intermittent rain and high humidity will highly favor the development of this disease.

In peaches, no shoot flagging has been observed yet. The first generation of oriental fruit moth should be just about over at this time in most orchards.

Insect report

Codling moth. Orchards have been setting biofix since the first of June, dates generally ranging from June 1-7 in sites with a history. The first application for codling moth is to be timed 100-250 growing degree days base 50 from biofix for the first generation, depending on product. Most growers are using materials that mean shooting for roughly the 250 mark, and a first material for codling moth is already out in many area orchards. Warmer weather at dusk again this week should mean that codling moth is active.

Oriental fruit moth. Most orchards set biofix in late May or early June, with a regional biofix estimated for May 20. The first management application is recommended around 200 growing degree days base 45 from the first biofix. No shoot strikes from larval feeding have been observed yet. Flight of the first generation should be nearly over.

Plum curculio. Warmer weather last week brought on significant plum curculio activity. Another warm week ahead along with a late start to spring means most growers will want to consider being covered for this pest through the end of the week.

Mullein bug. Images from several sites and several samples indicate that this pest has caused some damage this season. This is a sporadic pest of apples and can cause injury to fruits between bloom and about 10 millimeter fruit. If you see damage from mullein bug in fruit now, it is too late to do anything about it but you are encouraged to read this article on mullein plant bug to familiarize yourself with optimal management of hot spots going forward.

Greater and lesser peach tree borer. Flight of both of these pests is ongoing. Trunk sprays of Lorsban have been going out over the past weeks.

Spotted wing Drosophila. The first four female SWD were captured in Weare and Clay Banks townships two weeks ago as of tomorrow (June 26). However, our trap line was empty last week and came up empty again this week. Keep a close eye on SWD numbers as early sweet cherry varieties start to color up.

Obliquebanded leafroller. First flight typically begins around 900 growing degree days base 42 from March 1. We are around that mark in west central Michigan at this time, and a strong flight has been reported in the past several days at Trevor Nichols Research Center. Area scouts are likely to see this pest in flight this week.

European red mite and two spotted spider mite. Numbers are low of these mites at this time due to the frequent rain events this season.

San Jose scale. Crawlers have been found over the past week at Trevor Nichols Research Center and will likely be active in west central within the week. Materials targeting crawlers can be timed in late June and early July this season.


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