East Michigan fruit update – July 7, 2020

Robert Tritten, Michigan State University Extension - July 07, 2020

Drought conditions have worsened. It has been nearly a month since most farms received rain. Black raspberry harvest is staring, summer red raspberry and saskatoon harvest continues, and tart cherry harvest is nearly complete.

Weather

Drought and dry soils are more widespread over the region this week. Most fruit farms saw their last rain on June 10. Overall, soils are dry to very dry. Signs of drought stress in fruit crops are more common this week, especially in newly planted fruit crops, in shallow rooted fruit crops, and this week in plantings that are well established. Sod in most orchards has turned brown, looking more like some in August. Lanes and driveways are very dusty. Fruit farmers are devoting more and more of their time to irrigation.

Evapotranspiration rates have been very high with the heat of the last week. With another week of hot temperatures, we saw another good jump in growing degree day (GDD) accumulations. Most of our Michigan State University Enviroweather stations have seen a rise of 200 GDD base 50 accumulations in the last week. Our season moved ahead to being a few days ahead normal for both growth stages and GDD.

East Michigan growing degree day (GDD) totals for March 1 to July 6, 2020
Location	GDD42	GDD45	GDD50
Commerce (Oakland County)	1,675	1,426	1,061
Deerfield (Monroe County)	1,830	1,562	1,174
Emmett (St Clair County)	1,640	1,393	1,036
Flint (Genesee County)	1,808	1,547	1,163
Freeland (Saginaw County)	1,639	1,391	1,032
Lapeer (Lapeer County)	1,653	1,403	1,037
Pigeon (Huron County)	1,563	1,328	991
Romeo (Macomb County)	1,698	1,445	1,075

Tree fruits

Apples that are well-established have continued to size well despite dry soils. Apple size on younger trees has started to slow due to dry soils. Most apple fruit are now 1.625 to 1.75 inches in diameter. Most apple varieties have around 24 inches of new terminal growth. Hand thinning is underway for many varieties, especially Honeycrisp.

I have no new insect pests to report in apples this week. Apple maggot trap catch started in the region last week, and just a few more are being caught in traps this week. Low numbers of adults are being caught on both yellow sticky boards and red ball traps. Drought is limiting apple maggot emergence. Apple rust mite populations are continuing to build quickly with this hot weather. While numbers are still below threshold, they will bear watching as this hot weather continues.

Potato leafhopper numbers have continued to rise at most farms in the last week, with a good amount of leaf curling. San Jose scale crawlers have waxed over, meaning that the crawler control window is closed for this first generation. Trap catch of obliquebanded leafroller adults is down sharply. European red mite and twospotted spider mite numbers continue to slowly build, but neither are at threshold levels. A few white apple leafhopper adults continue to be found feeding on leaves, as well as a few woolly apple aphids around pruning scares. I continue to see a few codling moth larvae in apples. Trap counts of adults are generally low at this time.

Beneficial or predator numbers continue to build. This week I found minute pirate bugs, red velvet mites, lady beetle adults and larvae, and lacewing adults.

Apple scab fruit lesions continue to be found, and in some cases growers are finding fruit lesions where there are no leaf symptoms. This is odd. I keep an eye on apple scab on ornamental crabapples each summer to give me an idea how prevalent apple scab might have been if left uncontrolled and to give me an idea of apple scab pressure for next season. Many of the traditional crabapple varieties that are not apple scab resistant have lost a good percentage of their leaves already due to apple scab infections. So, my three conclusions from these observations are that it was a fairly tough apple scab season, that there will be a good amount of pressure next season and that most growers did a good job in controlling it this season.

I have had several reports from apple growers this week of new fire blight strikes. Be on the lookout for new strikes. I am seeing entire limbs that are wilting and browning from black rot infections in the wood tissue, and this week I saw my first black rot leaf infections. More growers are finding cedar apple rust symptoms on fruit in the last week, it is common this season. Some apple blocks continue to have high numbers of powdery mildew infected terminals on mildew prone varieties. Protection programs need to be ongoing on mildew prone varieties.

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

Pears are mostly 1.5 inches in diameter and approaching 1.75 inches. Pear psylla adult numbers continue to slowly raise as suckers continue to elongate. Sucker removal is continuing in pear blocks.

Peaches are between 1.375 and 1.5 inches in diameter. Pit hardening has taken place. Thinning is wrapping up at most farms. Green peach aphids continue to be found in many peach blocks. I have not seen any flagging from oriental fruit moth in peaches but I expect to find some soon. Peach leaf curl symptoms are common across the region, but as new leaves develop, the symptoms appear to be diminished.

Sweet cherry harvest started and was wrapped up quickly last week for the few farms with a pickable crop. Leaf drop due to cherry leaf spot disease and some from drought is starting to be more common. I found a few cherry fruit fly larvae in fruit last week as the crop was being harvested. This was a new pest to report.

Tart cherry harvest has come and gone for most farms, but a few have enough crop to be still harvesting. Harvest will be wrapping soon at these farms. Leaf spot symptoms are just starting to be seen in tart cherries.

Plums remain at an inch in diameter for European varieties, with Japanese varieties at 1.5 inches. Most plum blocks have a poor crop due to freeze/frost damage.

Small fruits

Strawberry renovation is continuing this week. Growers with dry soils will need to get their irrigation systems back into strawberry fields quickly to begin irrigation when renovation is wrapped up. Leaves on newly planted strawberries continue to emerge from the crown, along with flower trusses and runners. Deflowering is taking place. Drought stress is common in newly planted strawberries.

Raspberry harvest continues for summer red raspberries. Berry size is small where soils have been dry over the last month. Black raspberry harvest is just beginning. Where irrigation has not been applied in black raspberries, the berry size is so small that they are not marketable. Growth has continued to be good on fall bearing raspberries that have been irrigated, the tallest canes are 32 inches in length. Flower buds are starting to be seen on the bud berry canes or shorter fall red raspberry canes.

Light amounts of raspberry cane borer and raspberry sawfly larva feeding damage is being found at just a few farms. Spotted wing Drosophila (SWD) trap catch started across the region three weeks ago, but trap catch number have remained low, most likely due to hot temperatures. However, even though pressure from SWD is low, protection programs need to be underway.

Blueberries are continuing to color well; berry size mostly remains the same at 8 to 12 millimeters in diameter. Blueberry maggot trap catch has been seen in southwest Michigan, but again this week none over here on this side of the state. I expect to see trap catch soon, especially when we get rain.

Grape growth has moved quickly again this week, with Concord and Vinifera varieties at buckshot sized fruit. Many new canes are 60 inches in length. Japanese beetle adults are being found in low numbers in many vineyards. Grape berry moth larva feeding was seen in low numbers in a few grape varieties early this week. Populations are very high in southwest Michigan.

Saskatoon harvest continues. The remaining fruit are continuing to size and color well. Most fruit are between 12 and 15 millimeters in diameter. Heavy bird feeding continues in saskatoons, mostly from cedar waxwings and robins.