Southwest Michigan fruit update – June 9, 2020

William Shane<shane@msu.edu>, Mark Longstroth, Michael Reinke<reinkem3@msu.edu> and Katherine East, Michigan State University Extension - June 09, 2020

Blueberry bloom is ending. Strawberries are starting to color. Tree fruit are rapidly increasing in size

Strawberries coloring up — Strawberries are beginning to color up. Early varieties may be ready to start harvest by this weekend. Photo by Mike Reinke, MSU Extension.

Weather

Last week was hot and dry with high temperatures in the 80s. Lows were in the 60s. Saturday, June 6, was cooler. Highs were in the low 70s and lows in the 50s. Scattered showers on Wednesday, June 3, brought up to a quarter inch of rain to small sections of the area. No other rain was recorded in the region. Soils are drying out. Warm temperatures will continue through Tuesday, June 9.

The remnants of Tropical Storm Cristobal will bring rain and wind Tuesday night and Wednesday, June 10. Warm, wet rains will be infections periods for many spring diseases. Beginning Wednesday, the rest of the week will be cool and dry with highs near 70 and lows near 50.

With a warm week, we picked up more growing degree days (GDD) last week: 190 GDD base 42 and 135 GDD base 50, respectively 27 and 19 per day.

Southwest Michigan GDD summary from March 1 - June 7, 2020
Station	GDD 42 F	GDD 45 F	GDD 50 F
Benton Harbor (SWMRC)	939	746	513
Lawton (Lawton)	919	748	511
Fennville (TNRC)	815	654	432
Average for the SW region	910	741	507
Average last week	720	572	372

Tree fruit

June drop of fruit is underway, assisted by recent warm and dry weather. Oriental fruit moth and redbanded leafroller flights are ending. Codling moth, San Jose scale and obliquebanded leafroller flights are underway. The warm weather the last couple weeks has been ideal for plum curculio activity and reports of fruit damage are common. Potato leafhopper adults (bright green) have moved into the area from southern overwintering sites. Tarnished plant bug adults have been active.

Peaches and nectarines range from 20 to 25 millimeters in diameter. Crop potential looks better in many sites now that growing fruit are more conspicuous. Mycoshield is preferable to copper for suppressing bacterial spot populations now that fruit are exposed. Leaf symptoms of bacterial spot are showing up on susceptible varieties. Peach leaf curl symptoms range from slight to severe and are generally worse on showy bloom types. Peach scab and rusty spot control should begin starting at shuck split. Rusty spot is primarily a fruit disease problem whereas peach scab infects both fruit and green twigs. Tarnished plant bug damage to fruit is being reported. Both lesser and greater peach tree borer adult moths are being caught.

Oozing in peaches — Tarnished plant bug are active in many fruits. The oozing from these peaches is the result of damage from this pest. Photo by Bill Shane, MSU Extension.

In cherries, sweet cherries are 15 to 20 millimeters in size. Tart cherries are approximately 13 millimeters and the crop is generally light to very light due to the spring freeze. Pit hardening is complete. Brown rot has been seen in sweet cherries. Sweet cherries are always susceptible to brown rot. Brown rot management is important when warm temperatures and rain occur together, especially during bloom. Regardless of the crop load, growers need to protect the leaves from cherry leaf spot. See “Low spray programs for tart cherry” for more information.

In plums, European (Stanley) and Japanese (Shiro) plums are approximately 19 to 22 millimeters in diameter, respectively, in central Berrien County. Crop potential is generally better for European plums than Japanese types. Sprays for black knot are targeted on protecting new shoot growth from bloom to the end of shoot growth. Bacterial spot symptoms are showing up as water-soaked lesions with brown center on fruit. Young fruit are prone to russet at this point. Plum curculio egglaying scars showed up a couple weeks ago on fruit in multiple orchards in the area.

Bacterial spot symptoms in plums — Bacterial spot symptoms are showing up in plums. Notice the water soaking around the black spots. Photo by Bill Shane, MSU Extension.

Apple fruit range from 15 to 28 millimeters in diameter, depending on the variety, with natural drop underway. The Maryblyt model predicted multiple fire blight infection periods during bloom. Blossom blight symptoms are expected to show up anytime. Maintain sprays to control powdery mildew and apple scab. Scab symptoms are very common on unprotected crabapples. Scab ascospore counts are continuing to go down.

Cornell University has just released a new version of the apple carbohydrate model for thinning apples, version 2019. Cornell has a detailed explanation on their NEWA blog site. The thinning recommendations will be based on the GDD from bloom, percent of spurs that are flowering, and the thinning index (i.e., the average carbohydrate balance over seven days versus the older model, which used only four days). This new version has been added to MSU Enviroweather with the older model still available for comparison.

In pears, Bartlett fruit are approximately 22 millimeters in diameter. Crop load potentials are low to fair due to low temperatures on May 9. Pear scab and watching for fire blight symptoms are the primary disease concern now. Pear psylla are becoming easier to find.

Small fruit

Grape shoots are about 12 to 18-plus inches long. Clusters are elongating and flowers are separating. Vinifera wine grapes have not started bloom. Early hybrid varieties such as Marquette and Frontenac are in full bloom. Traces of bloom have been found in Niagara as well.

Starting prebloom through bloom, sprays for downy mildew and black rot are critical to protect blooming grape clusters from disease infection. The warm, rainy weather this week increases risk from these diseases, as well as phomopsis. Phomopsis leaf and cane damage has been found. Protect new leaf tissue from powdery mildew infection, which is favored by high humidity and warm weather.

Grape tumid gall is attacking hybrid grapes as well as some juice grapes. Wild grape bloom is widespread. Wild grape bloom is used as the biofix date for grape berry moth models.

Blueberry bloom has ended in many varieties and fruit in many fields are the size of small peas. Some late varieties are still in late bloom/petal fall. We should now be able to evaluate damage from the May 9 freeze and how effective pollination was. In some fields, the growing tips of the shoots were killed by the freeze. These dead shoots can be sites for possible disease infection. Separating freeze damage from disease can be difficult. See “Twig and blossom blights in Michigan blueberries” for more information. There is regrowth starting in many places.

After full bloom, the disease focus shifts to controlling anthracnose infections of green fruit. Anthracnose is also responsible for some blossom blight and probably a lot of the shoot tip dieback we see in the interior of the plant to new shoots from the crown late in the season. See “Blueberry growers need to focus on Anthracnose fruit rot as bloom ends” for more information.

In late bloom and early green fruit, focus on anthracnose and the cherry and cranberry fruitworms, which emerge during bloom. Both cranberry and cherry fruitworm are now being caught in traps. Biofix was near Monday, June 1, for both these insects. Use the predictive tool on Enviroweather to time fruitworm control sprays. See “Fruitworm control in blueberries for 2020” for more information. There are some leafroller larvae and other insects out but generally not in numbers that need control. Gall wasp is not generally a problem is southwest Michigan, but they have emerged as well.

Strawberry bloom is ending. The fruit are starting to turn color in the early varieties. Harvest will start soon. The major strawberry fruit pest now is tarnished plant bug.

Bramble bloom is ending. Fruit can be seen. Avoid using pesticides during bloom. Broad mites have been reported in raspberries. Scout for leafroller and sawfly, which feed on the leaves. If bloom has ended, a broad-spectrum insecticide is effective.

Brambles — Raspberry bloom is close to an end. Fruit are becoming noticeable. Insect and mite pests are becoming an issue in some fields. Make sure bloom has completely ended and bees are out of the fields before spraying. Photo by Mike Reinke, MSU Extension.

Currants are finished blooming. Fruit are pea size.

Cranberry buds have opened. There is about a half-inch of new shoot growth.

Aronia bloom has ended.

Upcoming meetings

Our regular Southwest Michigan Monday Fruit IPM Updates are available online. Our next meeting is Monday, June 15, at 5:30 p.m. You need to register to receive the login and password for these meetings. The webinars are free and one pesticide applicator credit is available for each meeting. We have over 70 growers attending our Monday meetings. These meetings run through the last week of June.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).