Southwest Michigan fruit update – July 14, 2020

William Shane<shane@msu.edu>, Mark Longstroth<shane@msu.edu>, Michael Reinke<reinkem3@msu.edu> and Katherine East, Michigan State University Extension - July 14, 2020

Summer fruit harvest is continuing. The brief rains and cool weather was a welcome break, but heat and humidity will return.

Dew on Vignoles grapes — Heavy dew events can be common this time of year. These are good conditions for developing diseases like downy mildew. Photo by Mike Reinke, MSU Extension.

Weather

Last week started hot with highs near 90. A cold front moved through the region on Friday, July 10, bringing rain and cooler temperatures. Much of southwest Michigan saw up to an inch of rain. Highs over the weekend were in the upper 70s. The coming week will become warm and humid. Highs will climb into the 90s by the weekend with lows in the 70s. Rain is likely Wednesday, July 15, into Thursday. Recent rains have provided a brief break, but soils are already drying out. This time of year, most plants need almost 1.5 inches of rain a week.

With the warm week, we picked up a lot of growing degree days (GDD) last week: 239 GDD base 42 and 184 GDD base 50, respectively 34 and 26 per day.

Southwest Michigan GDD summary from March 1 - July 12, 2020
Station	GDD 42 F	GDD 45 F	GDD 50 F
Benton Harbor (SWMRC)	2008	1735	1327
Lawton (Lawton)	1994	1717	1305
Fennville (TNRC)	1834	1568	1173
Average for the SW region	1974	1701	1293
Average last week	1735	1482	1109

Tree fruit

Trees on sandy ground have been showing drought stress. Oriental fruit moth flight is underway. Codling moth and obliquebanded leafroller are between flights. Lesser and greater peach borer flights appear to be in decline. Grasshoppers are causing problems on foliage of young trees close to mowed fields. Deer are browsing on young plantings.

Peaches and nectarines early variety Desiree is firm ripe and Harrow Diamond and Earlystar are about five to seven days away. Due to a light crop and spring freezes close to bloom, the potential for split pits appears to be greater this year for large pit varieties prone to this problem. The estimated harvest date for Red Haven in central Berrien County for 2020 is Aug. 4. Oriental fruit moth larvae entries into fruit are expected soon. Leaf drop and fruit marking due to bacterial spot is showing up on susceptible varieties.

In cherries, sweet and tart cherry harvests are complete. Cherry leaf spot symptoms are common in the tops of many trees. To prepare the trees for the winter and next year’s crop, continue to protect the leaves from cherry leaf spot. See: Low spray programs for tart cherry.

Cherry ochard — Cherry leaf spot symptoms are becoming more evident. With harvest complete, resume your leaf spot programs to protect the trees through the season. Photo by Mark Longstroth, MSU Extension.

In plums, spot picking of very early variety Kuban Comet is underway. Japanese (Shiro) plums are starting to lose their background green with harvest about five days off. Plum curculio scars and bacterial spot seem to be the primary fruit problem. Black knot from last year’s infections is becoming easy to find.

Apple fruit range from 1.5 to 2 inches in diameter. Current hot, sunny conditions could start to induce sunscald symptoms on exposed fruit. Use of sunlight-blocking treatments may be warranted. The sooty blotch and flyspeck model on Michigan State University Enviroweather predicts when symptoms will appear. The model predicts that symptoms could start showing now in some sites in southwest Michigan. There is a lot of variation between sites; check several sites to assess risk. NAA treatment to enhance return bloom generally should start approximately five weeks after full bloom with two additional spray treatments at seven and nine weeks after full bloom.

Apple maggot emergence is increasing. Traps should be placed to monitor susceptible sites. Potato leafhopper and green aphid populations are building on tender leaf tissue. Obliquebanded leafroller larvae are rolling leaves.

Apple scab on apples — Apple scab is becoming more noticeable as fruit are sizing. The primary season for scab management is from bud break through second cover, but infections can occur at any time. Regular fungicide applications through the season can help reduce infections on the fruit. Photo by Mike Reinke, MSU Extension.

In pears, Bartlett fruit are 1.5-plus inches in diameter. Pear scab and watching for fire blight symptoms are the primary disease concerns now. Pear psylla are becoming easier to find. Removing watersprouts at this time will help to remove places for psylla to multiply.

Small fruit

Spotted wing Drosophila (SWD) numbers are expected to rise in southwest Michigan with this cooler weather. We expect SWD numbers will climb quickly with ripe blueberries, raspberries and wild fruit such as Bush Honeysuckle (Lonicera).

Most grapes are at berry touch or bunch closing. The disease focus now is preventing downy mildew and powdery mildew infections. Choose fungicides carefully to control both diseases. Downy mildew favors wet conditions, especially heavy dews in the morning. We are starting to get heavy dews in the morning. Powdery mildew favors high humidity and warm weather.

Grape berry moth should have begun last week, around July 5, so controls should be applied if they haven’t already. For information on what to use and when, see: Mid-season management of grape berry moth.

Blueberry harvest has begun for Duke and other early varieties. The Michigan blueberry crop is estimated at about 85 million pounds. This is similar to last year’s harvest. Phomopsis cane collapse continues to appear. There are no effective sprays to stop shoot collapse. Under the hot, dry conditions, growers struggled to maintain their irrigation. Growers with overhead irrigation should also focus on protecting against anthracnose. For fungicide recommendations, see: Blueberry growers need to focus on Anthracnose fruit rot as bloom ends.. Use systemic fungicides, which are absorbed into the plant reducing fungicide wash off from sprinkler applications.

Cranberry and cherry fruitworm flights and egglaying have ended. Some leafroller larvae and other insects are out, but not in numbers that need control. Blueberry maggot are being caught but since most growers maintain a strict coverage for SWD, blueberry maggot has become a minor pest. SWD numbers vary a lot with some growers reporting large numbers and others only a few. SWD numbers usually climb quickly in late July.

Strawberry harvest has ended. Growers are renovating their fields. You can spray 2,4-D herbicides before or after mowing depending on weed pressure. If the weed canopy is above the strawberry leaves, spray before mowing. If the weeds are below the strawberry leaves, spray after mowing. The rows need to be narrowed to 10 or 12 inches. Cultivate the row middles before applying residual soil herbicides to control germinating weeds. We are already seeing new growth in some renovated fields. See: Renovate perennial strawberry fields to maximize yield next year. Protect against potato leafhopper, as this pest will stunt plant growth.

Bramble harvest of black and red raspberry continues. SWD is the major insect pest of brambles and can destroy the crop quickly. Treat SWD as a disease and focus on keeping it out rather than letting this pest become established. Pick ripe fruit frequently so that ripe fruit are not available to the pest for very long.

Currants are ripening. Champagne and red varieties are being harvested.

Cranberry bloom is ending.