MSU Extension Fruit & Nuts

Weather

Two days of hot weather have continued to push our season ahead of normal. In terms of growing degree-day (GDD) totals, we are now between eight and 14 days ahead of normal. In terms of the beginning of harvest of our fruit crops, we are almost a week ahead of normal. For example, harvest of sweet cherry early varieties will begin this coming weekend, June 23 and 24. These same varieties normally begin harvest the last few days of June. Saskatoon harvest is coming quickly as well, as are tart cherries. This week, most all of our Michigan State University Enviroweather stations have recorded degree base 45 numbers over a thousand.

Most of the region received only a few tenths of an inch rain in the last week, however precipitation totals vary widely over short distances. The range of precipitation totals for this last week is none to over 1.8 inches.

Our soils generally remain on the dry side, with most of the Thumb area and our sandy sites being very dry. Soils seem to dry very quickly this season, so keep a close eye on soil moisture supplies for signs of drought stress, especially on newly planted and young fruit plantings. Many growers have started irrigation systems.

Tree fruits

Apples have continued to grow rapidly with the heat of the last week. They are mostly 1.25 to 1.375 inches in diameter, with Zestar 1.5 inches in diameter.

Apple growers are continuing to see that some fruit is growing rapidly and other fruit is “standing still” and is not growing at all. Most of this standing still fruit will eventually drop, but this process, commonly referred to as June drop, has not started yet. Most apple growers are finding that some blocks and varieties will require hand-thinning, with some growers starting this week. Leaf yellowing is apparent in Honeycrisp this week.

There are several new or first-time sightings of pests to report in apples this week. San Jose scale crawlers started to be seen late last week, so now is the time to control them. The crawler control window is fairly narrow, lasting just a few weeks. Brown marmorated stink bugs are being found in traps at a few farms. This seems early, but look out for them. Apple rust mites are another new pest to report this week, however their numbers are generally much lower than threshold numbers. I found my first Japanese beetle of the season in apples yesterday, June 19. Obliquebanded leafrollers are the last of the new pests to report in apples this week; adults are being caught in high numbers at several farms.

Twospotted spider mite adults were found in a few more apple blocks last week, as were white apple leafhopper adults. Potato leafhopper adults are being seen for the second week on apple leaves in just a few apple blocks. Codling moth and oriental fruit moth trap catches are much lower this week. Codling moth crawlers are being found in a few blocks. Rosy apple aphids continue to be found in a few blocks, causing leaf curling. European red mite adults are more common this week, but still well-below threshold levels.

With rain on Saturday morning, June 16, I caught no apple scab spores on the rods at my trapping location. So, based on this finding, I am calling an end to primary apple season for 2018. What this means for apple growers that have done a good job at controlling apple scab this spring is that they can begin to relax their apple scab control program for the rest of summer. Apple scab lesions continue to be found, but mostly from the early season infection periods on older leaves.

Nectria twig blight is the only new disease to report in apples this week. Just a touch of fire blight continues to be found in many orchards. At this time, these strikes are limited in numbers and can easily be broken out well-below the canker and disposed of. Pruners can also be used to remove the strikes, but remember that if tools are used they must be sterilized between cuts.

Cedar apple rust symptoms continue to be seen in a few more apple blocks this week. More powdery mildew terminal branch strikes continue to be found this week, mostly in larger trees that have not been pruned well.

Pears are 0.875 to 1.25 inches in diameter. Pear thinning has been very effective this season. All stages of pear psylla are being found in blocks where control measures have not taken place.

Peaches are mostly 1.25 to 1.375 inches in diameter. Pit hardening has yet to take place. As of this morning, brown marmorated stink bugs are being found feeding on young peach fruit in an orchard in the Flint, Michigan, area. There is a clear ooze coming from the site of the feeding injury. Look out for brown marmorated stink bugs in peaches. Peach leaf curl symptoms are visible in a few varieties.

Sweet cherries are mostly between 18 and 21 millimeters in diameter and began to get lots of color mid-week last week. Growers are hoping for another swell in fruit size before harvest begins. Some early varieties will begin harvest this coming weekend, with mainstream varieties to follow quickly. I was not correct in last week’s report saying that I thought most of this fruit that was changing color what seemed to be early would drop before harvest. Some varieties had a good amount of winter kill damage, some did not leaf out this spring and others clasped in the last few weeks.

Tart cherries are 14 to 17 millimeters with great color development in the past few days. These, too, will be early this season. Fruit drop is continuing in many blocks of tart cherries.

Plums are 0.875 inch in diameter for European types and 1.25 inches for Japanese varieties. Some European and Japanese varieties have a very light crop on them, most likely due to poor pollination.

Small fruits

Strawberry harvest continues across the region at most farms. With the heat on Sunday and Monday, they have continued to mature quickly. Most farms ran irrigation systems on Sunday and Monday to help hydrocool the berries in order to preserve berry quality.

Some farms have good berry quality this season. Unfortunately, others are having issues with poor fruit quality, small berry size and plant collapse. Some farms have not been able to harvest certain varieties due to poor berry quality. Other farms have stopped harvest already for the season. For these growers, they can begin the renovation process. The reasons for the poor berry quality issues are complex, but are mostly related to a combination of winter injury to the crown of the plant, the cold April followed by the heat of May and thrips feeding injury.

First, as a result of the mild temperatures last fall followed by very sudden cold temperatures between Christmas and New Year’s, there is damage to the crown of the plant on many varieties. This damage does not allow for the normal flow of water and nutrients to the developing leaves and fruit. Farms that spread their straw mulch prior to these cold temperatures had less damage to the crown of the plant.

Second, there was poor root development in April due to cold soil temperatures. This followed by the heat of May brought a time where demand for water and nutrients by the leaves and developing fruit far exceeded the plants ability to provide it, resulting in poor berry quality. Lastly, some growers were also hit hard by thrips feeding on flowers this spring, resulting in seedy, bronze-colored fruit that is unmarketable.

Besides the thrips damage reported above, the new pests to report this week in strawberries include twospotted spider mites and leaf spot disease. Pests reported last week and still being found include sap beetles, slugs and gray mold. Do a good job of scouting for these pests. A few spittle bugs continue being found.

In newly planted strawberries, runnering has taken place on farms that have done a good job of flower bud removal. Where flower buds have not been removed, it seems that runnering has been delayed more this year than in most years.

Raspberry growth continues at a rapid pace, with the longest new canes reaching 32 to 38 inches in length for summer and fall raspberries. On summer raspberries, small fruitlets continue to enlarge with a few of the early varieties developing good red color in the last week and getting ready to harvest soon. In fall raspberries, flower clusters are starting to form on many of the canes; they will most likely be ready to harvest early this season.

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

Saskatoon harvest is just getting started for early season varieties, with main season varieties coloring well from red to dark blue in the last week. For the main season varieties, it is looking like they will begin harvest in about a week. Fruit have sized well in the past week, with most fruit in the range of 9 to 11 millimeters in diameter. Apple curculio feeding injury continues to be found, mostly in the range of 3 to 5 percent damage in commercial blocks and 60 to 70 percent damage in unsprayed plantings.

Grapes continue to put on a good deal of new growth, with fruit mostly at the BB size. Twospotted spider mites are a new pest to report in grapes this week, but their population is generally low.