MSU Extension Fruit & Nuts

Weather report

The past week’s temperatures have been typical for this time of year except for Sunday, June 17, when daytime temperatures hit the low 90s. This heat was coupled with high humidity, which made the day seem even warmer. We have caught up on our growing degree-days (GDDs), and we have accumulated 1,056 GDD base 42 and 644 GDD base 50.

We also received some much-needed rainfall over the past week. At the Northwest Michigan Horticulture Research Center, the Michigan State University Enviroweather station recorded 0.14 inch on June 13. There was no rainfall on June 14. The following four days, June 15-18, all had some level of rainfall: 0.2 inch, 0.04 inch, 0.22 inch and we received just over 0.5 inch of rain on Monday, June 18. This rainfall was considerably helpful as soil moisture was low.

Growth stages at the Northwest Michigan Horticulture Research Center as of June 18, 2018

• Bartlett pear – 20 millimeter fruit
• Potomac pear – 23 millimeter fruit
• Mac – 28 millimeter fruit
• Gala – 23 millimeter fruit
• Red Delicious – 24 millimeter fruit
• HoneyCrisp – 24 millimeter fruit
• Montmorency – 13 millimeter fruit
• Balaton – 13 millimeter fruit
• Hedelfingen – 11 millimeter fruit
• Gold – 12 millimeter fruit
• Napolean – 12 millimeter fruit
• Riesling – First bloom

Crop report

The recent moisture will help size fruit, and growth on tree fruits has been excellent. Growers were likely covered up before the rainfall to protect new tissue from disease infections.

Sweet cherries are starting to color and some early varieties are past the straw stage and turning red. On our fruit team call this morning, there was some discussion on the pace of sweet cherry ripening. MSU Extension educators in southwest and southeast Michigan estimated that sweet cherry harvest will begin at least one week early compared to a normal year. The heat has moved the season along quite quickly.

Start protecting ripening fruits from spotted wing Drosophila (SWD), as the fruits are susceptible to egglaying at this time. However, SWD numbers have been low so far this season.

Most growers are done with apple thinning this season. We have heard mixed reports on thinning efforts; growers that started their programs early (bloom/petal fall) had better luck than growers that began programs at a later stage. Growers were concerned with the heat, so many held off on thinning—then temperatures turned colder. There will likely be some hand-thinning this season.

For growers that are concerned about their thinning efforts, the Hail Mary option is to use Ethrel plus Sevin plus Oil all at 1 quart per acre. This option can be used when fruit is 25 millimeters, and currently at the Northwest Michigan Horticulture Research Center, our fruit is 24 millimeters.

Strawberry harvest has begun in the north. Growers will be pleased that the wet weather is ending for the week as they move through harvest. The next rainfall event is predicted for Saturday, June 23.

Pest report

Wet and warm weather within the last week has been concerning for disease pressure and much of the region had two relatively long wetting periods spanning from June 15 to 17 and June 17 to now. As many fruits are sizing and cherries are ripening, pests have also become a primary focus of management. The forecast for the coming week suggests ample opportunity to cover for pests and diseases. However, the weather has been mostly unpredictable up to this point, making management decisions difficult.

In apples, fire blight has taken center stage as we have received many reports and visited several orchards across the region with varying levels of fire blight symptoms. Even under very intensive management programs (i.e., four or more applications of a bactericide during bloom), we have observed infections, particularly in susceptible varieties. Growers often have known “problem” blocks, but this season was optimal for fire blight and many blocks started showing signs over the last week.

Some growers have chosen to use the product Actigard to help mitigate fire blight spread within shoots this season. Actigard stimulates the trees’ natural defense mechanisms to minimize the spread of fire blight internally. In MSU trials, we have observed varying levels of success with this product, and although further investigation is needed, MSU pathologists are gaining confidence in its efficacy.

Some growers have also opted to use the more traditional strategy of making regular applications of a copper product to kill bacteria outside of the plant until trees reach terminal bud set. However, fruit finish and phytotoxicity can be a concern when using copper during hot temperatures and periods of high humidity.

Many growers have incorporated Apogee into their fire blight program this season to prevent the spread of the bacteria internally. Apogee thickens cell walls and will slow shoot growth to help prevent the disease progress. We have collected samples from several orchards this season to expand our sensitivity screening for streptomycin and Kasumin; contact us (Nikki Rothwell: rothwel3@msu.edu, Emily Ponchubay: pochubay@msu.edu ) if you would like to have samples screened.

Primary apple scab season is wrapping up, but models for the northwest region are suggesting there is still the potential for spores to discharge in future rain events. The Fruit Ridge called the end of primary over the weekend. The northwest region has been relatively dry this season, but recent wet weather would have been good for spore discharge. Early last week, some growers with scab-free orchards felt that primary would be finished after the rains over this last weekend.

Most orchards in northwest Michigan have remained relatively scab-free in recent years; however, primary may not be finished if there was a high level of scab in a block last season. Lastly, scab management should continue if there is an active scab infection on foliage/fruit at this time.

• Bear Lake (Biofix 1 May) 
• Benzonia (Biofix 1 May) 
• East Leland (Biofix 1 May)
• Eastport (Biofix 2 May) 
• Elk Rapids (Biofix 1 May) 
• Kewadin (Biofix 1 May) 
• Northport (Biofix 5 May)
• NWMHRC (Biofix 1 May) 
• Old Mission (Biofix 1 May) 
• Williamsburg (Biofix 1 May) 

We have observed active cherry leaf spot lesions in treated blocks at the station; the active lesions are primarily on leaves that were likely infected during wet weather at the end of May or in early June. Recent wet and humid weather were very good conditions for leaf spot infection and development. Low levels of infection can quickly get a foothold as the conidia on active lesions spread easily to adjacent foliage during rain.

We have also observed powdery mildew at the station on interior-canopy leaves and have received reports of this disease showing up in commercial blocks.

Sporulating American brown rot has been observed and reported from commercial tart cherry blocks. This fungus can grow and spread quickly on ripe fruit; however, green tart cherries are not typically a good host for rapid brown rot development. As sweet cherries are ripening and increasing in sugar content, American brown rot will be a concern, particularly in warm and humid weather. Several growers were challenged with brown rot management in sweet cherries last season and have a heavy inoculum load for this season.

The SDHI fungicides are the best materials for brown rot—save at least one application for pre-harvest timing. For resistance management purposes, only two applications of an SDHI fungicide per season are suggested. The product Indar applied at the highest label rate is also an option for brown rot, but recent sensitivity screening has suggested Indar may not be as efficacious as it has been previously. Obtain a copy of and review the special local needs label for Indar prior to making applications at the increased rate.

Codling moth activity picked up slightly late last week, but wet conditions over the weekend slowed flight activity. Since May 28, the Northwest Michigan Horticulture Research Center codling moth biofix, we have accumulated about 360 GDD base 50 and egg hatch is well underway.

The first flight of San Jose scale in apples and cherries has ended. We have been monitoring for crawlers visually at the station and have not observed crawler activity at this time. However, females under the waxy scale are plump, and we anticipate crawler activity this week. Catalpa trees in the area have just started to bloom. The catalpa tree at the station is not yet blooming; anecdotally, in most years, crawlers emerge when catalpa blooms.

We have only detected two spotted wing Drosophila (SWD) flies in our trap line. The first SWD was detected Wednesday, June 6, at the orchard edge of a tart cherry block on Old Mission Peninsula. The second SWD in the region was found in a tart cherry block at the Northwest Michigan Horticulture Research Center June 12.

Cherries have started to turn from green to straw color, and our previous research has shown that these ripening fruit are susceptible to SWD oviposition. Although pressure is lower at this time, begin management programs in blocks with susceptible fruit. We hypothesize that a proactive program will help to minimize pressure from this pest later in the season. With the potential for a long harvest this year, maintaining a low population could help minimize SWD challenges this year.

Obliquebanded leafroller moths took flight within the last week. The first date of sustained catch is the biofix date for this pest. Once biofix is set, egg hatch is expected at 400-450 GDD base 42.

Plum curculio activity seems to be winding down in many areas, but hot spot areas could still be vulnerable. Several materials that are effective for SWD can also provide activity against plum curculio.

American plum borer, lesser peachtree borer and greater peachtree borer activity is ongoing and some growers have started trunk applications to target this pest complex in cherries.

Rose chafer activity is ongoing and feeding damage could continue for another week or two.

Stippling from twospotted spider mites is noticeable in tart cherry blocks at the station, particularly on interior canopy leaves.

We have not detected cherry fruit fly in our traps at the station.

*Set = the date that a monitoring device was deployed