MSU Extension

Weather report

Seasonable temperatures were abundant across the region last week. Daytime temperatures ranged from the mid-70s into the low 80s, and nighttime temperatures fell into the high-50s into the 60s. All days in the past week were sunny with low humidity and moderately windy conditions. We have accumulated 727 growing degree days (GDD) base 42 and 397 GDD base 50. The last rainfall was on June 3 when we received just under 1 inch of precipitation. Soil conditions are dry and we could use some rain. Although rain is predicted for June 11, the amount will not be substantial to improve soil moisture. Growers have been running irrigation systems with the lack of rainfall.

Crop report

Wine grape shoot growth high in the canopy has reached the 6- to 12-inch growth stage. The crop potential looks very good in some hybrid varieties. Powdery mildew and downy mildew are the important diseases at this time. Potato leafhoppers may show up at any time now, and rose chafers are due as well.

Young larvae of saskatoon sawfly have been found during the last week. A number of different leafroller caterpillars are also feeding near shoot tips, but they are not likely to be a problem for shoot growth.

The cherry crop is looking good here in Northwest Michigan. We had terrific weather for pollinating sweet cherries, and as a result of good pollination, we anticipate a nice sweet crop. The fruit is sizing, and at this time there is considerable size difference between fruits on the same tree. Tart cherries are out of the shuck and are also sizing well. The pollination window for tart cherries was much condensed due to the hot weather during bloom. Growers are currently estimating their crop size and initial predictions are that the crop is a good size, but not a limb buster.

Many apples are at petal fall or at the 10-millimeter size – we also had good pollinating weather for apples. Some growers are thinning according to the precision orchard management approach, and many thinning sprays began at bloom this year. The carbohydrate model has not shown much stress in the past week, and growers that had a jump on thinning with bloom and petal fall applications may be in a good situation if we do not have stress at the key thinning period of 8-12 millimeters.

Unfortunately, we are still observing decline of apples due to the severe winter. Again, there is not a distinctive pattern to this decline as we see damage showing up across varieties, rootstocks and ages of trees. Many of these trees pushed this spring and put out leaves, but now are declining. We anticipate further decline of trees as we move into the season.

Strawberries were blooming last week and growers are likely looking at a season without having to frost protect. Strawberry harvest is anticipated to begin in early July, which is later than in most years. We have seen some damage to peach trees from the winter, but many growers think they will have a crop this season without a lot of thinning efforts.

Pest report

Many apple varieties are past bloom and not susceptible to the blossom blight phase of fire blight at this time. However, if susceptible varieties have open blossoms, they will need to be protected from possible fire blight infection prior to rain predicted on Wednesday, June 11. The Section 18 exemption for Kasumin use in counties where streptomycin-resistant fire blight has been detected (i.e., Leelanau, Grand Traverse, Antrim counties) ends on Sunday, June 15. The use of Kasumin in not permitted after petal fall and only three sprays of Kasumin are allowed each season.

The biofix date, such as the date of green tip on McIntosh, was May 9 at the Northwest Michigan Horticulture Research Center (NWMHRC) and according to the MSU Enviro-weather apple scab model for the NWMHRC, apple scab spores are 99 percent mature and 81 percent discharged at this time. Rain that is predicted this week could result in an apple scab infection and growers should protect tissue prior to rain. We will continue to monitor spore discharge following possible rain this week at the scab monitoring site in Leelanau County; we hope this information will assist growers in determining when to call the end of the primary apple scab infection period. We will need a few more rain events with good amounts of precipitation for the remaining apple scab spores to discharge. Other regions of the state have not called an end to primary scab.

At the NWMHRC, we have observed development of cherry leaf spot conidia on the undersides of bract leaves in both Balaton and Montmorency tart cherries and sweet cherries. Last week, we received reports that cherry leaf spot lesions were present on bract leaves in many tart cherry orchards in the region, and conidia are rapidly developing on infected leaves in those orchards with our recent warm conditions. Conidia on infected leaves will spread to nearby leaves during wet periods. In orchards where early cherry leaf spot infection has occurred, growers will need to be diligent about adequately covering new tissue throughout the season. Newly expanded leaves are susceptible to cherry leaf spot and should be protected prior to possible rain on Wednesday, June 11.

Prior to shuck split, Michigan State University Extension recommends the fungicide chlorothalonil for cherry leaf spot management. Growers need to be sure to check labels for re-application intervals for fungicide sprays. Growers should also check with processors for any additional restrictions on fungicide use, particularly with the 24 (c) for use of Bravo WeatherStik past shuck split. MSU Extension recommends a first cover timing application of Luna Sensation at 5 fluid ounces per acre plus Captan at 2.5 pounds per acre, or Merivon at 5.5 fluid ounces per acre plus Captan at 2.5 pounds per acre. These fungicides are excellent for both cherry leaf spot and powdery mildew.

We have received a few isolated reports of American brown rot sporulation on sweet cherry fruit that is visible on last year’s mummies. Insect feeding, bacterial canker on green fruits, and other damage to developing sweet cherry fruit make those damaged fruit more susceptible to American brown rot infection. Spores developing on mummies have the potential to infect neighboring fruit. We have also seen blossom blight and canker symptoms in sweet cherries.

Codling moths were detected in the region early last week and the first capture of codling moths at the NWMHRC was this week, Monday, June 9. After two consecutive codling moth capture dates, the biofix for codling moth should be set for the first date that moths were caught. GDD accumulation should be set to zero at the biofix date and begin accumulating after the biofix date is set to determine optimal codling moth management timings. Please refer to the article “Codling moth is back with a vengeance in 2014” for more information on codling moth management.

Many growers sprayed for plum curculio last week and plum curculio scars have been observed in apricots, sweet cherries and tart cherries at the station. Growers should be protecting fruit against plum curculio as this insect can target fruit as it’s just emerging from the shuck. Growers should check their “hot spots” for oviposition scars as plum curculio stings are evident in most cherry blocks at this time.

Spotted tentiform leafminer numbers are down this week at 30 moths per trap and the optimal time for managing this pest has almost passed. This is the third consecutive catch of oriental fruit moth at one moth per trap.

Adult moths of American plum borer, lesser peach tree borer and greater peach tree borer were detected this week. This is our third consecutive week of American plum borer capture at 11.7 moths per trap; the second consecutive lesser peach tree borer capture at 11.7 moths per trap; and the first capture of greater peach tree borer at 1.7 moths per trap. Some growers have sprayed trunks with Lorsban last week to target borers.

We have observed green fruit worm larvae and obliquebanded leafroller larvae actively feeding on leaves and developing cherries at the station. Adult moths of obliquebanded leafroller have not been caught in pheromone traps at the station at this time. If growers are controlling the overwintering larvae of obliquebanded leafroller, they should make applications as soon as possible – smaller larvae are much easier to kill than larger older caterpillars. MSU Extension recommends a spray targeting overwintering obliquebanded leafroller larvae at the petal fall timing, which may be too late for most orchards. If growers missed this spring spray, we will have another opportunity to control summer generation obliquebanded leafroller prior to harvest.

Cherry fruit fly traps went up Friday, June 6, at the station; we have not detected cherry fruit flies at this time. Here at the station we have accumulated 397 GDD and should begin seeing cherry fruit fly emergence within the next one to two weeks.

Growers should check with processors for restrictions on insecticide use to avoid possible issues with maximum residue limits.

Dr. Rothwell's work is funded in part by MSU's AgBioResearch.