East Michigan fruit update – July 21, 2020

Robert Tritten, Michigan State University Extension - July 21, 2020

Two precipitation events moved over the region in the past week, bringing some much-needed relief to drought. Summer red and black raspberry and blueberry harvest continues.

Weather

Two much needed rain events moved over the region in the past week, one last Thursday and the other Sunday morning. Precipitation totals vary greatly over short distances from these two rain events. Thursday’s nice slow rain brought between a quarter to nearly an inch of rain, it really helped to soften the soil. Sunday mornings quick windy thunderstorms brought about the same amounts of rain. While drought conditions have eased at most farms, soils remain dry.

There were some light amounts of scattered hail reported in Sunday’s thunderstorms. The hail was mostly pea sized and rounded. There was some light amount of fruit damage as a result of the hail events.

With another week of warm to hot temperature last week, we saw another good jump in growing degree day (GDD) accumulations. Most of our Michigan State University Enviroweather stations have seen a rise of another nearly 200 GDD base 50 accumulations again this past week. With the heat of the last week, our season moved ahead a few days to being five to seven days ahead of normal for both growth stages and GDD.

East Michigan growing degree day (GDD) totals for March 1 to July 20, 2020
Location	GDD42	GDD45	GDD50
Commerce (Oakland County)	2121	1830	1395
Deerfield (Monroe County)	2304	1994	1535
Emmett (St Clair County)	2085	1796	1369
Flint (Genesee County)	2271	1968	1514
Freeland (Saginaw County)	2100	1810	1381
Lapeer (Lapeer County)	2096	1803	1367
Pigeon (Huron County)	2013	1735	1329
Romeo (Macomb County)	2152	1857	1417

Tree fruits

Apples have continued to size, but their growth rate has slowed over the past two weeks. Most apple fruit are now 1.75 to 2.25 inches in diameter. Hand thinning continues for many apple varieties. Lodi harvest has started at a few farms.

More fruit color is being seen on several varieties this week. This coloring may be the result of some mild sun scald injury. As the week progressed last week, the coloring appears to be heat related but is not severe.

There are no new insect pests to report in apples this week, but there are several developments on insects that we have seen this season. Apple maggot trap catch has jumped up this week on red ball traps, most likely as a result of recent rain events. Growers will need to cover fairly quickly for apple maggot. Yesterday I started to see San Jose scale damage on fruit. Last week I saw high numbers of green apple aphids on fruit. Where growers applied an insecticide to control them in the last week, their numbers have been dramatically reduced. Codling moth trap catch is on the rise for the start of the second generation adult flight.

Woolly apple aphids are moving to terminal branches. Apple rust mite and European red mite populations are continuing to build. Some bronzing of leaves is starting to be been seen from both of these insects. Potato leafhopper numbers have dropped off again this week in most apple blocks, however the curled leaves remain. Beneficial or predator numbers continue to build, this week I am finding good numbers of lacewing eggs and lady beetle adults.

Sooty blotch and fly speck symptoms are a new disease being seen in apples this week. Silver leaf symptoms continue to be seen on infected trees. I continue to have isolated reports of new fire blight strikes. Be on the lookout for new strikes. Limb collapse, wilting and browning from black rot infections in the wood tissue have been seen over the last month. Two weeks ago, the first black rot leaf infections started to be seen, and last and this week I am seeing some fruit infections.

Leaf mottling is more common on Honeycrisp leaves. The mottling is caused by the accumulation of large starch granules in the leaves that reduce photosynthesis.

Pears are mostly 1.75 inches in diameter. Pear blister mite feeding symptoms on leaves is a new insect to report this week. Sucker removal is continuing in pear blocks.

Peaches are between 1.875 and 2 inches in diameter. Fruit coloring is starting to be seen, with Red Haven harvest expected to begin in two weeks or so. This week I started to see flagging from oriental fruit moth in peaches. Rusty spot is a new disease to report in peaches this week, however it is being seen in very light amounts.

Sweet cherry leaf spot disease symptoms and leaf drop are common again this week.

Tart cherry leaf spot disease symptoms and leaf drop is less common than on sweets, but are continuing to be found.

Plums remain at an inch in diameter for European varieties with coloring developing. Japanese varieties are at 2 inches in diameter and some harvest is expected soon. Most plum blocks have a poor crop due to freeze/frost damage.

Small fruits

Strawberry renovation wrapped up last week. Growth has started again in most fields. Growers with dry soils will need to begin irrigation soon in renovated fields.

Leaves on newly planted strawberries continue to emerge from the crown, along with runners that are rooting. Rows are starting to fill out. Drought stress symptoms are easing up in newly planted strawberries.

Potato leafhopper leaf cupping damage is common in newly planted strawberries.

Raspberry harvest continues for summer red raspberries and black raspberries. Berry size is small where soils have been dry over the last month. Where irrigation has not been applied in black raspberries, the berry size is so small that they are not marketable. New growth in both summer and fall raspberries has slowed due to dry soils. Fall red raspberry flower trusses are starting to form. Growth in fall raspberry plantings have canes the are shorter than normal this season. A few berries are continuing to be harvested on the bud berry canes or shorter fall red raspberry canes.

Spotted wing Drosophila (SWD) trap catch started across the region five weeks ago, and again this week’s trap catches remains low. Regardless of this low trap catch, I have more reports of growers finding small SWD larva in fruit. So, even though pressure from SWD is low, protection programs need to be ongoing.

Gray mold started to be seen in summer raspberry fruit late last week.

Blueberry harvest continues on early varieties. Berry size continues to improve, with the largest harvestable berries being 15 to 18 millimeters in diameter. Remaining berries are coloring well.

Spotted wing Drosophila (SWD) trap catch started across the region five weeks ago, and again this week’s trap catches remain low in blueberries. Regardless of this low trap catch, SWD protection programs need to be underway in blueberries. Blueberry maggot trap catch has been on the rise this week in blueberries.

Grape growth has moved quickly again this week, with concord being at berry touch. Growers are doing some cane removal this week. Vinifera varies are approaching berry touch. Japanese beetle adults are being found in low numbers in many vineyards. Grape berry moth larva feeding was seen in more grape varieties this week.

Saskatoon harvest wrapped up over a week ago. Japanese beetles are feeding in some saskatoons.

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