MSU Extension

Weather

Most of our southeast Michigan region received around 1 inch of a nice, gentle rain that started on Sunday night (June 9) and carried over into Monday (June 10). Combined with the rain received the week before, it has helped to regenerate the moisture in the surface layers of our soils. Cool temperatures have slowed fruit growth and development a bit, but our season remains normal for both growth stages and growing degree day (GDD) totals.

East Michigan Growing Degree Day Totals for March 1 to June 10, 2013

Tree fruits

Apples are approaching 1.25 inches in the south and 22 to 25 millimeters in the Flint, Mich., area. Despite cooler temperatures, most apples have grown 7 millimeters in the last week, which is average for this time of the season. More and more apples are showing up as time goes on, even in freeze-damaged blocks.

Many apple growers are just beginning to see fruit dropping to the orchard floor as a result of thinner applications. Almost all apple growers will need to do a fair amount of hand-thinning this season, as thinners did not do the entire thinning job in most apple blocks. I do not believe we are at the start of June drop yet. Apple growers need to wait for a week or so to begin hand-thinning.

Fruit that was scarred from the May 13 freeze are becoming more viable in the last week. I expect we will see much more of this damage than normal this fall at harvest.

San Jose scale crawlers are now being seen in apples. Growers with this pest looking to control it in the crawler stage will need to move quickly. I saw my first potato leafhopper adults for the season on apples – and strawberries – last Thursday (June 6) on grower visits in Monroe and Lenawee counties. Remember that potato leafhopper adults do not overwinter here, but are blown in on weather fronts from the south and mid-westerly states, and will continue to move into other parts of the region on these weather fronts. We have had a pattern of these fronts moving up here in the last few weeks. Once here, there are no distinct generations of this pest and it will be present continuously in orchards from now through har­vest.

Codling moth trap catches are down this week, and I am not sure if this decline is the dip between the A and the B first generation peaks or the start of the decline of the overall first generation. At any rate, Michigan State University Extension suggests we are just at the start of egg hatch and that growers could delay an insecticide if their trap catches have not been too high this season. Where trap catches have been high, we are approaching the time where an insecticide application needs to be made. Due to cool temperatures this season, I am not as confident with the May 22 biofix date and model as I am in a normal season. Consult the codling moth model on Enviro-weather for more details.

Oriental fruit moth trap catch dropped this week as well. I have not seen any terminal flagging due to oriental fruit moth. Recall that I set a regional biofix date of May 16 for oriental fruit moth. I am finding very few plum curculio “stings” on any tree fruit this season. Rosy apple aphid leaf curling remains, however the pest has been controlled well this season by predators in most apple blocks. Oystershell scale crawlers are now waxing over, so the control window is closed. European red mite and two-spotted spider mite numbers remain low at most farms; here again predators are doing a great job controlling them. Mullein bugs continue to be found in apples, but I believe they are now predators. There are record -setting numbers of predators being seen this season.

I have seen a few scattered fire blight shoot strikes at five orchards since late last week. Apple growers need to be on the lookout for it now and be prepared to break out these strikes as they are first being seen. Apple scab spore discharge continues, although spore numbers have declined to an average of 14 spores per rod as a result of yesterday’s rain event (June 10). All of our Enviro-weather stations recorded a heavy infection period with yesterday’s rain event, so growers need to remain covered for apple scab; we are not at the end of primary apple season. According to the apple scab maturity model, all of the spores have matured and have been released for the season. I can find just a touch of apple scab leaf infection at most apple farms.

I continue to see a few twig infections of powdery mildew, mainly on susceptible varieties.

Pears are 17 to 18 millimeters for growers that have a crop. Frost ring scars are more visible on pears in the last week and are common in most blocks. Pear psylla adults continue to fly and egg hatch continues.

Peaches are 15 to 21 millimeters in size. Some blocks are being abandoned due to the lack of a crop. The foliage in these blocks that have been yellowing and stunted thus far this season have begun to look much more like normal in the last week. Tarnished plant bugs continue to be seen in peach blocks. Peach leaf curl-infected leaves continue to be seen in light amounts. I continue to see very low to no oriental fruit moth trap catch in peaches. Bacterial spot infection on leaves continues to be found at many farms.

Sweet cherries are 16 to 18 millimeters in size. Cherry leaf spot disease symptoms are being seen in many blocks. Spotted wing Drosophila traps need to be set in sweet cherries at this time in order to detect first catch of adults.

Tart cherries are 11 to 12 millimeters in size. Cherry leaf spot disease symptoms are being seen in most tart cherry blocks. Spotted wing Drosophila traps need to be set in tart cherries at this time in order to detect first catch of adults.

Plums are 20 millimeters in size for European types and 17 millimeters for Japanese types where growers have a crop this season. Growers need to continue to be on the lookout for black knot infections as I am finding much more of it in the last two weeks.

Small fruits

Strawberry harvest for early maturing varieties for U-Picks started this past weekend for growers in the southern tier of counties and a few fields will be ready in the Flint, Mich., area in the next few days. Berry harvest for wholesale and ready picked sales began last Thursday (June 6) in these same southern counties. It appears that there will be a gap in harvest between early ripening varieties and the main crop of berries at most farms this season. Wet field conditions have also been a problem. Cool weather has also delayed ripening a bit.

New pests to report in strawberries include a few tarnished plant bugs, a few potato leafhopper adults, a few spittle bugs, strawberry leafrollers in isolated spots at a few farms and slugs at many farms. I had one report of high numbers of pill bugs feeding in strawberries at one farm, but I believe they were feeding in holes in berries that were already opened up by slugs. This pill bug is truly not an insect, but a crustacean that feeds on decaying organic matter.

I am also starting to see bird feeding damage to mature to over-mature fruit in a few strawberry fields. Several weeks ago I reported seeing the bacterial disease angular leaf spot in a few strawberry fields. Late last week I found it return in one of those fields where I had seen it previously. Growers need to carefully scout for it at this time.

Raspberries are at 11 to 14 inches of new growth for summer-bearing types with bloom ending in most varieties and green fruit in early flowering types. Canes of fall-bearing types are about 18 to 24 inches tall where they were not killed back to the ground from the May 13 freeze event. Spotted wing Drosophila traps need to be set in summer raspberries at this time in order to detect first catch of adults.

Blueberries are 10 to 12 millimeters for Blueray and Bluecrop and 5 millimeters for Jersey and most other varieties. Petal fall sprays were applied in the last week at most farms. There continues to be quite a difference in the amount of foliage growth between varieties, for example Jersey and other main season varieties had considerable more leaf growth than Bluecrop or Blueray. Spotted wing Drosophila traps need to be set in blueberries at this time in order to detect first catch of adults.

Grape cane growth continues at a rapid pace with new canes receiving 30 inches of new growth. Wild grape were in bloom mid-last week, concord types are just starting bloom and French hybrid types are nearly ready to begin bloom. Bloom has been very slow to develop in grapes this season due to cooler temperatures. Grape berry moths have been very active in wild grape vines.