MSU Extension

Weather

Last week was hot with high temperatures in the 80s and 90s and lows in the 60s. Scattered showers and thunderstorms moved across the region several times during the week. Some areas received no rain. Most areas received about a third of an inch, but some received over an inch. Evapotranspiration last week was about 0.15 inches of water a day.

The weather this week will be wetter and then cooler. The region should receive widespread rain Tuesday, Sept. 8, as a cold front moves slowly across Michigan, then highs will fall into the 70s about 10 degrees below normal for the weekend. The following week should see warmer, more seasonal weather. Last week, our daily growing degree day (GDD) accumulation was very high; 31 GDD base 42, 29 GDD base 45 and 24 GDD base 50 per day. This week, our daily GDD accumulation will be less; 20 GDD base 42, 17 GDD base 45 and 13 GDD base 50 per day. Even with the warm weather, we are lagging a week or two behind normal in heat accumulation.

We have begun our transition into fall with cooler temperatures. Trees that lose their leaves early have begun changing color and drop leaves. We will soon begin to see Lake effect rains caused by cool, dry air moving across a warm Lake Michigan and absorbing water from the warm lake. This water will then fall as rain as the air moves over the cooler land.

The outlook for September and October is for warmer and dry conditions, but not a great deal different than normal. There is a strong El Nino in the Pacific and this often means the Michigan winters are dryer and milder. After two exceptionally cold winters with widespread winter injury, this is good news for fruit growers.

Tree fruit

Michigan State University Extension does not recommended pruning in the fall as this will inhibit development of winter hardiness. At this time, shortening day length is a signal that fall is approaching, but pruning stimulates a wound response and growth in the plant. This will ultimately reduce winter hardiness. Oriental fruit moth trap numbers are up, indicating the third generation is flying. Obliquebanded leafroller adult flight of the second generation continues. The Trevor Nichols Research Center trap catch for San Jose scale males have extended for seven weeks, indicating continued risk for crawlers and the potential of scale damage in sites where this insect is established.

Detection of brown marmorated sting bugs (BMSB) has increased in the Stevensville, Michigan, area in Berrien County, near the area where the pest was first detected in the region. This insect has been detected on tree fruit in the Kalamazoo and Niles areas. Adult BMSB increase their feeding in late August and September, preparing for overwintering. Adult BMSB will soon begin clustering on buildings.

Peach harvest this week includes Encore, Victoria, Autumn Star and PF Big George. Most of the peaches in the area have been harvested. Oriental fruit moth damage to fruit was responsible for much of the problems seen this year with brown rot. Some growers experienced problems controlling brown rot with less than full rates of DMI fungicides (Indar, Orbit, Elite and Rally). This could indicate building resistance of the pathogen. Growers should include fungicides with different modes of action (SDHI and strobilurin) to avoid fungicide resistance problems with brown rot.

Oriental fruit moth trap catches are up in some fields. Spotted wing drosophila (SWD) is a potential problem in peaches picked on the mature side of tree ripe. Suspected infested fruit should be stored at 35 degrees Fahrenheit or lower for at least 96 hours to kill developing eggs, larvae, pupae and adults. Lorsban trunk sprays for peachtree borers can be done post-harvest and still provide yearlong protection against this insect according to work at Cornell University.

Sweet cherry growers need to maintain protectant fungicide coverage to reduce cherry leaf spot. Pruning should be finished by now so that trees have time to recover before cold weather arrives.

Tart cherry trees exhibiting wilting or poor vigor foliage should be examined for gumming, sawdust-like frass and chewed areas due to American plum borer and peachtree borer larvae feeding on the trunk at or slightly below the soil line.

Plum harvest of Stanley plums is over for most farms, with Italian, Vision and Empress underway or starting soon. Apple maggot, oriental fruit moth, codling moth and obliquebanded leafroller can infest fruit if it is not protected. Apple maggot adults continue to be caught in good numbers at the Trevor Nichols Research Center. SWD is also a potential problem for thin-skinned plums picked tree ripe. Young plum trees should be examined for potato leafhoppers, an insect that can build quickly and stunt growth. Brown rot is the primary disease problem for plum fruit requiring control now.

Apple harvests of McIntosh, Gala and Honeycrisp are underway, with Empire on the horizon. Starch and pressure tests for maturity insure that apples are really ready for harvest and moved to the correct marketing window. A starch test reading of 3 using the Cornell University scale is recommended as the minimum for fruit picked for immediate sales and consumption of Gala. Spot-picking of Honeycrisp began last. Weekly apple harvest maturity reports will be posted at the MSU Extension News for Fruit webpage.

In general, apple finish and size looks very good. Stop drop sprays are a necessary tool for managing harvest. Growers should be aware that apple maggot adults continue being caught in good numbers for the last six weeks at the Trevor Nichols Research Center. Growers need to include fungicides in some of their cover sprays to control sooty blotch, flyspeck and apple scab. In orchards where apple scab is present on fruit and leaves, growers need to prevent pinpoint scab showing up in storage. Growers with a light crop or with bitter pit-susceptible varieties need to include calcium in their cover sprays early on to reduce bitter pit. Large applications of calcium just before harvest are not effective. We are still catching good numbers of codling moth adults of the second generation flight. Oriental fruit moth trap catches are high in some orchards. Growers should be scouting for obliquebanded leafroller larvae.

Pear harvest of Bartlett has generally ended. Gem harvest has begun and Harrow Sweet harvest is expected to begin in about a week. As pears ripen and soften, they need to be protected against codling moth and oriental fruit moth. Obliquebanded leafrollers can also target fruit. See a good fact sheet on harvest and storage of pears from Ontario.

Grape harvest of Concords is scheduled to begin towards the end of September. National Grape Co-Operative currently plans to harvest Niagara grapes for about a week before Concords and then switch to Concords. They plan to finish Niagara harvest after Concord harvest. The third generation of grape berry moth is winding down. Grape berries are resistant to fungal disease infections at this time, but downy mildew can infect leaves and defoliate the vine. Growers need to protect leaves of susceptible varieties. Wine grape growers should maintain botrytis fungicide with wet conditions. In wine grapes, scout for potato leafhoppers.

Blueberry harvest is ending in southwest Michigan. ‘Elliott’ harvest is winding down. SWD numbers are high. Growers finished for the season are applying long lasting materials such as chlorothalonil. New shoot growth can be seen in fields where soil moisture is good. Fruit buds are starting to form. Growers should avoid heavy pruning in fall as this can reduce the winter hardiness of bushes in the upcoming winter.

Strawberry fields look good. Protect leaves against potato leafhoppers and foliar diseases. We are in the window for the fall application of herbicides to suppress weeds in the June-bearing strawberry plantings. Fall harvest of everbearing strawberries needs to be protected from SWD. Soft fruit is an excellent indicator of the presence of SWD.

A stained receptacle or soft fruit are sure signs of SWD larvae in the fruit. Photo by Diane Brown, MSU Extension

Raspberry harvest of fall bearing red raspberries and primocane bearing blackberries is underway. Raspberries and blackberries are very attractive to SWD and growers need to pay close attention to this pest. Soft fruit is an excellent indicator you have SWD. Our traps are catching flies and trap numbers rise and fall, depending on the availability of fruit, especially wild berries near fruit plantings. SWD is a pest of ripening fruit and numbers increase as wild berries ripen and the fly moves from one ripening host to another. It has multiple generations every year, so the population increases through the growing season. Growers with ripening fruit need to time their SWD controls with harvest and pay close attention to the preharvest intervals (PHI) on the pesticide label. See the SWD recommendations for caneberries at the MSU Spotted Wing Drosophila website. With the wet spring, warm, rainy conditions and heavy morning dews, botrytis or gray mold can be a serious problem in fall raspberries. Fall leaf rust can also affect the fruit.

See also

• Peach harvest dates available on MSU Enviroweather
• Sooty blotch and flyspeck disease of apple and pear
• Bitterpit control in apples
• Predicted 2015 apple harvest dates
• Stop drop sprays to help manage apple harvest
• Recommendations for harvest and storage of pears (Ontario, Canada)
• Don’t let bunch rots ruin your grapes
• SWD Website for more information
• Where else does Spotted Wing Drosophila like to feed?
• Protect strawberries from foliar diseases after renovation
• Management of botrytis gray mold in fall raspberries