MSU Extension

Weather

Last week was warm. Tuesday (July 2) was cooler with a high below 70. The passage of a warm front brought rain and high temperatures into the upper 80s. Scattered showers fell across the region the rest of the week as the storm track ran to the east of the region, so rainfall varied across the region. Soil moisture is good. With this wet growing season, fruit growth has been excellent. We continue to be a week behind the five-year average in growing degree days (GDD), but the timing of some harvests seems to be occurring on time. Check your local weather station and conditions at Enviro-weather.

Southwest Michigan GDD summary from March 1 to July 7

Tree fruit

Japanese beetle adult trap catch numbers have increased over the past week. Spotted wing Drosophila (SWD) adult male and female flies continue to be caught in low numbers, but could increase sharply as small and tree fruits ripen. No reports of brown marmorated stink bugs.

Apricot harvest is winding down. Bacterial spot has been the most important disease this year.

Peach fruit size is increasing rapidly. Harvest of Desiree, PF1 and a few other early peach varieties has begun in a few sandy sites in Berrien County, starting with fruit with split pits. Bacterial spot with leaf drop and fruit gumming is the most significant disease on peaches and nectarines right now and is more common on sandy sites. Brown rot control programs and possibly insect control of SWD need to be ramped up as we approach harvest. Oriental fruit moth trap catches are continuing to rise for the second generation flight.

Sweet cherry harvest is continuing with mid-season to late season varieties such as ‘Ulster’, ‘Hedelfingen’, ‘Summit’, ‘Attika’ and ‘Kristin’. Fruit flavor has been good to very good. Fruit cracking from the rain is the biggest concern. Disease concerns are cherry leaf spot and brown rot, and the insects to monitor and manage are cherry fruit flies and spotted wing Drosophila.

Tart cherry harvest is still continuing. Fruit quality has been generally good to very good with minor soft and wind-bruised fruit problems. In spite of the troublesome bloom time frosts, the fruit maturity is relatively uniform. Growers should protect against fruit flies, including spotted wing Drosophila, and the diseases cherry leaf spot and brown rot. The Trevor Nichols Research Center started detecting the traditional cherry fruit fly in their traps in the first week of July this year.

Plum fruit are 0.875 (Stanley) to 1.5 inches (Shiro) in diameter at the Southwest Michigan Research and Extension Center (SWMREC). Continued fruit drop has lightened the fruit load on some varieties. Bacterial spot spread on fruit has slowed and growing fruit is cracking at the necrotic spots. Fruit with insect damage and bacterial spot are more prone to brown rot infections. If time permits, hand-thinning of damaged plums will reduce the potential for brown rot as harvest season approaches.

Bacterial spot on Japanese plums. Photo credit: Bill Shane, MSU Extension

European plums self-thinning. Photo credit: Bill Shane, MSU Extension

Apple fruit at SWMREC are 1.75 inches in diameter for ‘Golden Delicious’; 2 inches in diameter for Gala; 2.25 inches in diameter for Red Delicious; and 2.75 inches in diameter for ‘Zestar’. No reports of sooty blotch and fly speck symptoms on apples and pears. Trap catches for oriental fruit moth and codling moth vary considerably from orchard to orchard, but are generally increasing for the area as a whole. Fire blight severity is generally low in the area. Yellow sticky traps for monitoring apple maggot fly emergence should be deployed soon.

Pears (Harrow Sweet) are approximately 1.5 inches in diameter. Growers should monitor for pear scab symptoms, fire blight and pear psylla activity. Pear psylla numbers are generally low. Small, green, immature pear fruit are generally not real attractive to codling, but will occasionally be damaged by this pest.

Small fruit

In grapes, the Concord grape berry weight model predicts when grapes will be at half of their final weight at 1,200 GDD base 50 past April 1. It appears that we will reach 1,200 today (July 9) for Berrien Springs, Benton Harbor and Lawton, and July 10 for Paw Paw. Trap catches for grape berry moth are still low in monitored fields, but are expected to increase in the coming weeks. Check the grape berry moth model on Enviro-weather for the station closest to your vineyard.

Second generation grape berry moth egglaying has begun. The Enviro-weather grape berry moth model predicts the start of second, third and fourth generation egglaying – 810; 1,620; and 2,430 GDD base 47 F from the biofix of wild grape bloom respectively. We set biofix for grape berry moth in some parts of Berrien County on May 25, and May 26-28 in other parts of Berrien and Van Buren counties. For Benton Harbor, using a biofix date of May 27, 810 GDD occurred on Friday, July 5.

Excellent coverage of clusters before bunches close is needed to achieve optimum control of grape berry moth. Insecticides that are active on eggs and young larvae such as Intrepid, Alticor and Belt should be applied as soon as possible if they aren’t already on. The optimum time for the application of broad spectrum products such as Imidan is 910 GDD and is predicted to occur Tuesday, July 9, for Benton Harbor.

Growers of hybrid and vinifera grapes should watch for Japanese beetle activity. Adults have started to appear, but we have not seen much damage yet. We are still in the stage of fruit development that is critical for disease control.

The continuing wet weather is favorable for black rot infections. The black rot model on Enviro-weather shows that the most recent infection periods for black rot occurred July 2-3 for Berrien Springs, Lawton and Scottdale; July 5-6 for Bainbridge/Watervliet and Hartford; and July 6-7 for Fennville. Certain vinifera cultivars remain susceptible to black rot through veraison.

The frequent early morning ground fog and dew created a favorable environment for the development of downy mildew. Similarly, high humidity is favorable for the development of powdery mildew. For grape cultivars that are susceptible to bunch rots, this is a good time to make a preventative application of fungicide. Consult the Michigan State University Extension E154 bulletin, 2013 Michigan Fruit Management Guide, for recommended fungicides.

In blueberries, Duke, Bluetta, Earliblue and others are being harvested with first and second pickings. Fruit size and quality is excellent. Ample rain this growing season has resulted in good fruit growth. Shoot growth continues in many fields. The season seems a few days early as some growers are already harvesting Spartan, Blueray and other early mid-season varieties. Bluecrop has ripe fruit and some growers are starting their first picking. Some growers report problems getting adequate labor.

First picking of Blueray. Photo credit: Mark Longstroth, MSU Extension

Cane collapse from Phomopsis is becoming more common as harvest nears. Growers with ripening fruit need to scout for blueberry maggots and spotted winged Drosophila (SWD). SWD have been trapped in low numbers across southwest Michigan. Not all SWD traps are catching flies, but growers who are not monitoring for this pest should be applying controls. Growers should also be applying sprays to suppress anthracnose and alternaria fruit rots to maintain fruit quality.

Strawberry harvest ended two weeks ago at most farms. Many growers have begun renovation.

Bramble harvest is underway with the harvest of summer red raspberries and black raspberries. Growers should be monitoring their raspberry plantings now for SWD. We trapped both male and female SWD in Berrien County. Last week, there were three adult SWD trapped at SWMREC. One of the signs of infestation in raspberries is a red stain present on the receptacle when the raspberry is picked. Insecticides to control SWD in brambles and other insect problems should not be applied while bees are actively foraging.

Raspberry receptacle with red stains is indicative of fruit
infestations by SWD. Photo credit: Diane Brown, MSU Extension

Upcoming meetings

The annual Viticulture Field Day will be held at SWMREC July 31. For more information, contact Diane Dings at dingsd@anr.msu.edu.

A hop production workshop is scheduled for August 7 at SWMREC from 8:30 a.m. until 3:30 p.m.