MSU Extension Fruit & Nuts

Weather

With the heat of May and early June, our season is between seven and 10 days ahead of normal in terms of growing degree-day (GDD) totals. This week, many of our Michigan State University Enviroweather stations have recorded degree base 42 numbers over 1,000. For crop stages, we are just about back to normal timeframes, but I still need another week or so to be sure we are back to our normal harvest windows. Saskatoons are starting to color well and sweet cherries will be next in line.

Most of the region received rain in the last week, but precipitation totals vary widely over short distances. The range of precipitation totals is from less than a tenth to over 2.5 inches. Some localized flooding was reported from rainfall over Saturday night, June 9. With these rains, many growers had an apple scab infection over the weekend.

Generally, most of our soils remain on the dry side, with some of our sandy sites being very dry. Keep a close eye on soil moisture supplies for signs of drought stress, especially on newly planted and young fruit plantings. On the other hand, other growers are reporting having trouble doing much work in the field due to wet spots remaining in orchards and small fruits.

Tree fruits

Apples have grown very rapidly over the past two weeks, mostly 22 to 28 millimeters in diameter, with Zestar 1.25 inches in diameter. We are in a growth stage in fruit where we change from metric to customary or standard system to describe fruit size. To help, one simple conversion is 25 millimeters is equal to 1 inch.

Most apple growers have seen a good amount of fruit drop in the past week. Some varieties have thinned nicely, others will require hand-thinning later this month. Growers who applied thinners earlier seem to have achieved better results than those who waited to after the extreme heat of two weeks ago. Unfortunately, not many apple growers leave a few check trees to tell if this fruit drop was the result of their thinning applications or from natural fruit drop.

There are several new or first-time sightings of pests to report in apples this week. Twospotted spider mite adults were found in a few apple blocks, as were white apple leafhopper adults. Spotted tentiform leafminer mines are just starting to be found in leaves. Potato leafhopper adults are starting to be seen on apple leaves in just a few apple blocks. Codling moth and oriental fruit moth trap catches are much lower this week. Be on the lookout for codling moth egg hatch this week.

San Jose scale male adults are being caught in traps, with numbers at most farms in the range of five to seven per trap. Be on the lookout for crawlers by mid-next week or so. Crawlers are being found in southwest Michigan. Rosy apple aphids continue to be found in a few blocks, causing leaf curling. European red mite adults continue to be found.

Powdery mildew, fresh fire blight strikes and cedar apple rust are new diseases to report this week. Powdery mildew terminal branch strikes are starting to be found, mostly in larger trees that have not been pruned well. The first of the season fire blight strikes have been seen in the last week, mostly on younger apple trees. There are so few strikes that I recommend either breaking out or pruning them out. If pruning tools are used, they must be sterilized between cuts. In the last week, cedar apple rust symptoms were found on apple leaves.

Apple scab lesions continue to be found, but mostly from the early season infection periods on older leaves. Most growers have had enough rain and heavy due this past weekend for an infection period, and therefore a scab control application. I continue to catch apple scab spores with each wetting event, with the numbers on collection rods still being in the single digits this week. So, we are still in primary apple scab season. With more showers expected later in the week, this may be enough rainfall to release the remaining spores.

Pears are 19 to 24 millimeters in diameter. Pear thinning has been very effective this season. All stages of pear psylla are being found in many blocks.

Peaches are mostly between 21 to 26 millimeters in size, pit hardening has not yet started. Peach leaf curl symptoms are visible in a few varieties.

Sweet cherries are mostly between 14 and 15 millimeters in diameter; they don’t seem to have put on much growth in the past week. Some fruit is turning red, I think this fruit will drop before harvest. Some varieties have had a good amount of winter kill damage, some not leafing out this spring and others clasping in the last week or so. I continue to find a few black cherry aphids in sweet cherries.

Tart cherries are 11 to 14 millimeters in dimeter, these too have not put on much growth in the past week. Fruit drop is continuing in many blocks of tart cherries.

Plums are 18 to 22 millimeters in diameter for European types, with a good amount of drop in the past week, and Japanese varieties are 1 inch in diameter. Some European and Japanese varieties have a very light crop on them, most likely due to poor pollination.

Small fruits

Strawberry harvest started over the weekend at farms to the south and early this week at farms to the north. They continue to mature quickly.

New pests to report in strawberries this week include sap beetles, slugs and gray mold. Do a good job of scouting for these pests in the next few days. There are reports of small, misshapen berries at several farms to the south of the Ann Arbor, Michigan, area. I will be visiting these farms later in the week to determine the cause. Thrip damage was reported in other growing regions in the last few days. A few spittle bugs continue being found.

Raspberries once again this week put on a great amount of growth, with the longest canes reaching 28 to 32 inches in length. Small fruitlets continue to enlarge; I have not seen any color development in these yet. In fall raspberries, flower clusters are starting to form on the lower growing bud berry canes.

Blueberries have not sized much in the past week, they remain 9 to 12 millimeters in diameter.

Saskatoon fruit mostly remain at 6 to 8 millimeters in diameter and most have turned red in the past week. I have seen apple curculio feeding injury at a few farms.

Grapes continue to put on a good deal of new growth, with the longest canes 24 to 36 inches in length. Flower clusters are at bloom for concord types and final bloom for vinifera types.