Southwest Michigan fruit regional report – June 4, 2013

Wet, windy weather slows down insects, while most fruit crops look good.


Last week started cool with Monday’s high near 60 (May 27). Temperatures rose to highs in the 70s and 80s with lows in the 60s up to the weekend. Storms crossed the area throughout most of the week and temperatures fell dramatically over the weekend.

Monday morning (June 3) lows were in the mid- to upper 30s, which caused no damage. Rain fall totals for May varied from 2 to 3.5 inches. Maintaining pesticide coverage with frequents rains has been a challenge for many growers. Soils are wet with water standing in some areas. Check your local weather station and conditions at Enviro-weather.

Southwest Michigan GDD summary from March 1 to June 2


GDD 42 F

GDD 45 F

GDD 50 F

Benton Harbor (SWMREC)




Fennville (TNRC)




Average for the region




Tree fruit

Tree fruit across southwest Michigan looks good. Growers have been applying pesticides to control insects and diseases. Few new plum curculio egglaying scars have been found. Oriental fruit moth and codling moth trap catch are down, but remain strong. San Jose scale crawlers should emerge about 780 GDD50 after Jan. 1; currently, the Southwest Michigan Research and Extension Center (SWMREC) is at 510 as of June 2.

Apricots are about an inch in diameter.

Peaches are about 19 to 25 millimeters in diameter. Fruit set is variable. It looks excellent in most sites, but several growers report poor set in some orchards. Oriental fruit moth biofix was set for May 9, but some areas reset to May 14 due to the freeze on May 13. Oriental fruit moth trap catches were strong for two weeks after biofix, but not for the third week (last week). We are now well into the egg hatch period and flagging of branch terminal due to oriental fruit moth larvae that should be showing soon.

Developing fruit are susceptible to bacterial spot and rusty spot (powdery mildew) until approximately pit hardening. Peach leaf curl symptoms can be found throughout the area, but are light.

In cherries, exposed fruit is still susceptible to plum curculio egglaying.

Sweet cherries are 14 millimeters in diameter. They should be protected against plum curculio and cherry leaf spot. Sweet cherries are always susceptible to brown rot.

Tart cherries are about 12 milllimeters with hard pits. Two distinct sizes of fruit are visible. Growers should protect against plum curculio and leaf spot. Crop potential looks good for many farms. Areas near Berrien Springs, Mich., and eastern Van Buren County have a lighter set. Enviro-weather has predicted seven distinct leaf spot infection periods beginning May 4 when leaves were mature enough for infection through June 3. We had seven infection periods by this date in both 2011 and 2012, as well.

Montmorency fruit set near Paw Paw, Mich. Photo credit: Mark Longstroth, MSU Extension

Plums are 20 to 21 millimeters (Methley) or 18 to 20 millimeters (Stanley) in diameter at SWMREC. Plum growers should be protecting against plum curculio and black knot. Black knot controls are needed until active shoot growth slows in early to mid-summer. Fruit out of the shuck is prone to direct damage by plum curculio and bacterial spot.

Apples are 18 (Golden Delicious) to 25 millimeters (Zestar) in diameter. Fruit set appears heavy in some orchards. Other growers are happy with their fruit thinning and a few worry that they took too much off with earlier sprays. Natural and chemical-induced fruit drop has been occurring for about one week. Growers with too much crop potential will need to resort to chemical combination sprays at higher rates or with the use of ethrel (see the Michigan State University Extension article “Apple thinning pointers for 2013”). Cool and sunny weather forecast for this week will make thinning difficult.

Fire blight blossom blight symptoms showed up June 3 in Bainbridge Township in Berrien County. Apple scab and powdery mildew are the diseases of concern at this time. Apple scab ascospores were caught in relatively high numbers in rains this past week in Berrien County. This indicates that primary scab season is not over yet. The apple scab prediction model on Enviro-weather is indicating that all apple scab spores have matured, but not all have been discharged. This portion of the model is located at the bottom of the page below the infection predictions. Michigan State University Extension recommends that apple growers maintain fungicide coverage through the last significant rain after the model indicates that all spores have discharged. Apple scab symptoms can be seen in unsprayed trees, likely from the May 9 infection. In orchards with secondary scab lesions on the leaves, growers need to maintain protective sprays to prevent further spread of the disease.

Apples are also at risk to plum curculio and tarnished plant bug. Overwintering obliquebanded leafroller larvae have been feeding on shoot tips. Flight of the spring generation is expected about three weeks after petal fall. Codling moth males have been caught in area orchards and we set a biofix for May 18 (see the “Codling moth in apples and pears” fact sheet). Spray timing can be calculated from the codling moth model on Enviro-weather (see the insecticide recommendations at the bottom of the page, below the model). Based on the May 18 biofix, egg hatch for this insect is projected for June 4 this week using SWMREC Enviro-weather data. Spotted tentiform leafminer mines are apparent.

Pears are approximately 17 to 18 millimeters in diameter. Growers should continue to protect against pear scab and scout for fire blight and pear psylla activity.

Small fruit

In grapes, cool temperatures have slowed growth just short of bloom for most cultivars. ‘Concord’ and ‘Niagara’ are at pre-bloom at SWMREC and elsewhere. Grape berry moth numbers continue to increase, but numbers are still light. The first generation of grape berry moth overwinters as pupae in leaf litter around vineyards and emerges before bloom.

The Enviro-weather grape berry moth model tracks the predicted percentage of egglaying for grape berry moth and predicts the start of second, third and fourth generation egglaying (810, 1620 and 2430 GDD base 47 F from the biofix of wild grape bloom respectively). We reached biofix for grape berry moth in some parts of Berrien County on May 25 and other parts of Berrien and Van Buren counties on May 26-28. Biofix is calculated as 50 percent bloom on wild grapes (Vitis riparia).

As we approach bloom in grapes, the importance of timely fungicide applications with good coverage is essential. If it has not been done already, take time to replace worn nozzles on sprayers and calibrate sprayers to ensure that grape canopies are well covered and costly plant protection materials are not wasted.

Symptoms of phomopsis are becoming easier to find. Cool temperatures, rainfall and early morning dews have provided sufficient hours of leaf wetness to trigger infection. With temperatures in the 60s and 70s, six to 10 hours of leaf wetness is sufficient for phomopsis to infect shoots and leaves.

The first spots of black rot in a vineyard with a history of the disease were found late last week. The weather has been a little cool for black rot, but with temperatures in the 70 to 80 degree range, infection requires on six to seven hours of leaf wetness. Consult the 2013 Michigan Fruit Management Guide (E154) for recommended fungicides. Downy mildew needs five hours of leaf wetness at 50 F, three hours at 70F and two to three hours at 80 F.

Powdery mildew control should be applied now for problem areas or highly susceptible varieties. Begin checking leaves inside the canopy closest to the trunk for powdery mildew. Powdery mildew is favored by high humidity and temperatures in the 68 to 81 F range.

Blueberries have green fruit. Last week’s rain brought a quick end to bloom. Fruit set in many fields is heavy, but some growers complain of light set and are concerned about pollination. We should have a good handle on the crop soon. Red leaves from cool weather are still visible. This red coloration will go away when warm weather returns.

Blueberry fruit set near Paw Paw, Mich. Photo credit: Mark Longstroth, MSU Extension

Growers have been applying sprays to control fruitworms and suppress fruit rots such as anthracnose and phomopsis. The Anthracnose Disease Prediction Model Handout posted at the Michigan Blueberry Facts website explains how to use the anthracnose prediction model on Enviro-weather. Note that the output for this model has the earliest rains at the top so the most recent rains are at the bottom of the page.

Cherry and cranberry fruitworms are both flying. Cherry fruitworm biofix was May 15 in many areas in southwest Michigan. Cranberry fruitworms were down last week and we think this is due to the wet, rainy weather. A cranberry fruitworm model for timing the application of controls is available on Enviro-weather (see “Fruitworms in blueberry control options”).The use of Intrepid is restricted in Allegan, Oceana and several other counties to areas further than a mile from wild lupines (see “Why Intrepid has use restrictions and advice for complying”).

Strawberries are thimble-sized. Picking began late last week in southern Berrien County. Under these wet conditions, fungicides are important to reduce diseases later in the season. See the 2013 Michigan Fruit Management Guide (E154) for fungicide recommendations. Growers need to scout and treat for tarnished plant bugs (see “Managing tarnished plant bug injury to strawberries”).

Brambles are blooming. Blackberry bloom is well underway and summer red raspberry bloom has begun. Only fungicides are used during bloom in brambles. Avoid spraying blooming fields during the day to prevent bee injury.

Upcoming meetings

The next Monday fruit IPM meeting is on June 10 at Fruit Acres Farms at 5 p.m. These weekly meetings are good for one RUP credit and will continue through the end of June.

Weed Identification and Management for Vineyards workshops will take place June 6 (southwest Michigan) and June 7 (northwest Michigan). These half-day workshops will cover weed identification and management in grapes.

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