MSU Extension Fruit & Nuts

Weather

With a stretch of eight hot days and much warmer than normal nighttime temperatures, our season continues to march along at a very rapid pace. With the exception of strawberries, all of our fruit crops have lush amounts of new growth with larger than normal sized leaves and long extension of new shoots.

Our season has yet again moved forward this past week with the much above-normal temperatures, to a point where we are now between seven and 10 days ahead of normal in terms of growing degree-day (GDD) totals. It is unusual to see that most of our Michigan State University Enviroweather stations have added over 120 GDD base 50 in just one week’s time.

For crop stages, we are just about back to normal time frames, but the degree to which we are back to normal is really crop-specific. For example, strawberries bloomed seven to 10 days behind normal, and yet with all of this heat between then and now, they have caught up on themselves. How these wide swings of temperatures will impact harvest windows of fruit crops later in the summer is yet to be seen.

Most of the region has had under a tenth of an inch to well over an inch of rainfall in the past week, with wide swings of precipitation totals over very narrow bands. Overall, 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. This week, I have seen signs of drought stress on apples that are in their third leaf.

Tree fruits

Apples have grown very rapidly in the past week, they are mostly in the range of 12 to 18 millimeters in diameter, with Idared and Zestar being 15 to 20 millimeters in size.

Most apple growers have made two thinner applications in the past week. For the brave growers who made thinning applications in the hot weather, they have seen a good amount of drop. Most of these growers have now gone back in for a second application on selected varieties. Most growers in this first group are pleased with fruit set.

For growers who waited for cooler temperatures to make their thinner application, they are waiting to see drop begin. Many growers in this second group are now applying another thinner to see if they can get more drop. Do a close inspection of every variety and block to determine the need for and the rates of this last thinner application for the season. This is the hardest decision of the season for apple growers, and with the wide swings in temperatures after bloom this season, it has been particularly one of the toughest ever for many growers.

Many growers have seen a big jump in codling moth trap catches this week, even in pheromone disrupted blocks. Many trap catches are in the range of 15 to 25 moths per trap. This spike of high trap catches was most likely caused by the hot weather. San Jose scale male adults are being caught in traps, so be on the lookout for crawlers fairly soon. Crawlers are being found in southwest Michigan. Some farms are also seeing some good populations of leafroller larvae feeding on young fruitlets and terminal leaves.

There are no new insect pests to report in apples this week; I am seeing more plum curculio adults and feeding injury on fruit and rosy apple aphids continue to be found in blocks that either had an early petal fall spray and where they have not been controlled. White apple leafhopper adults and European red mite adults continue to be found. A few tarnished plant bugs continue to be found. Oriental fruit moth adult trap catch remains low for most growers. Redbanded leafroller and spotted tentiform leafminer trap catch remain low.

Apple scab lesions are on leaves at a few more farms this week. Most growers have had enough rain and heavy due in the past week for some wetting events, but only a few have resulted in apple scab infection periods. I continue to catch apple scab spores with each wetting event, with the numbers on collection rods now being in the single digits. So, we are still in primary apple scab season. With showers expected on Thursday and Saturday, this may be enough rainfall to release the remaining spores.

I have not seen or heard of any fire blight strikes yet this season, even with very high EIP numbers in the Maryblight model over the past week. In the last week, cedar apple rust symptoms are on many ornamental tree species, but none in apples.

Pears are 16 to 20 millimeters in diameter. Pear thinning has been very effective in the past week. All stages of pear psylla are being found in many blocks.

Peaches are mostly between 16 to 18 millimeters in size. I am finding a few more green peach aphids in the past week and continue to find a few green fruitworms in peaches.

Sweet cherries are mostly between 12 and 14 millimeters in diameter, they don’t seem to have put on much growth in the past week. Some fruit is starting to turn 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 12 millimeters, these too have not put on much growth in the past week. Fruit drop is continuing in many blocks of tart cherries.

Plums are 12 to 18 millimeters in diameter for European types, with a good amount of drop in the past week, and Japanese varieties are 20 to 25 millimeters in diameter. Some European and Japanese varieties have a very light crop on them, most likely due to poor pollination.

Small fruits

Strawberries have matured very quickly in the past week due to the hot temperatures. Harvest is expected to begin in the southern tier of counties late this week or over the weekend, with other regions to follow fairly quickly. Last week I predicted that it looked like we would have a late strawberry harvest this season, but with the very warm day and night time temperatures, things have quickly moved forward. Strawberries are a hard crop to predict the beginning of harvest and have fooled me several times over my 40 seasons; this season seems to be a record for the fewest days between bloom and harvest.

Strawberry clipper injury on young fruitlets was seen late last week for the first time this season. However, I saw very little feeding injury, so wide spread control measures are not in order. Do a good job of scouting for this pest in the next few days. This is very late to see this damage.

A few spittle bugs continue to be found. I have not seen any tarnished plant bugs or slugs in strawberries. Warm weather conditions are generally not favorable for angular leafspot infection.

Raspberries once again this week put on a great amount of growth, with the longest canes reaching 24 to 28 inches in length. Small fruitlets are now forming in summer raspberries. In fall raspberries, flower clusters are starting to form on the lower growing bud berry canes.

Blueberries have sized very quickly in the past week and are now 9 to 12 millimeters in diameter.

Saskatoon fruit mostly remain 6 to 7 millimeters in diameter and have started to turn from green to red. I have not seen any apple curculio feeding injury yet this season.

Grapes continue to put on a good deal of new growth, with the longest canes 18 to 24 inches in length. Flower clusters are at the early bloom stage for concord types and first bloom for vinifera types.