MSU Extension Fruit & Nuts

Weather

We experienced another cold event last Wednesday morning, May 13. Low temperatures at many of our Michigan State University Enviroweather stations dipped into the mid-20s. For many orchards, this was the coldest temperatures they have seen this spring. While the duration of cold was not as long as the May 9 freeze, the temperatures were a few degrees Fahrenheit colder. Strawberry growers have needed to frost protect a few other times early last week.

The other two cold events were May 9 and April 22. The May 9 freeze was a long cold event, many of our MSU Enviroweather stations recorded temperatures that dropped well below freezing around 9 p.m. and temperatures remained below freezing to well after sunrise.

I am finding additional damage to many fruit crops as a result of this latest freeze event. Overall, I see crop loss for tree fruits in the range of 50 to 80%. Refer to each section in the report that follows for more details on freeze damage in each of our fruit crops.

As strawberries begin bloom on early varieties, most growers are finding more black blossoms than they have ever seen. Here again, look for more details in the strawberry section of today’s report.

Forsythia bloom has finally ended across the region, we saw bloom over five plus weeks, which is longer than I can remember. It was an indication of how slow growth has been progressing this spring.

With warmer temperatures over the past week, we saw a nice jump in degree day accumulations in the last week. Our season is still running around 10 to 14 days behind normal for most of our MSU Enviroweather stations in east Michigan.

The last weather-related story of the week has been the two heavy precipitation events, the first last Thursday and the second starting Sunday morning and continuing as this report is being written on Tuesday morning, May 19. Rainfall totals from the two events ranged from 2 inches to nearly 5 inches. Most of the higher rainfall totals have been north of the Detroit, Michigan, with the Thumb receiving the highest totals, closer to 5 inches. As a result, disease pressure has increased dramatically and most soils have reached saturation. Up until these last two rain events, soils have been unusually dry this spring across the region.

Tree fruits

Apple growth stages have moved forward fairly rapidly in the past week. Most of the southern counties are seeing apples at full bloom (most started on Saturday), and the rest of the region at king bloom to approaching full bloom for a few early varieties. With warmer temperatures predicted for later in the week and weekend, I expect to see bloom move quickly in apples.

The question many growers have is concerning the amount of pollination that occurred before the cooler rains started and how viable their flowers will be after all of the rain and wind of the last few days. I believe apple growers to the south had good pollinating conditions on Saturday for most of their varieties, so they will be fine. Apple growers to the north should be concerned about the lack of good pollinating conditions and may consider holding back on doing any blossom thinning until things begin to sort themselves out in the next few days.

With last Wednesday’s cold event, most apple growers saw another loss of flower buds or bloom. I am finding a good amount of damage in some varieties of apples. The other two cold events that took some bloom were on May 9 and April 22. The range of damage varies widely across the region and by variety. If I had to place a figure on apple bud loss at this time, I would now put it to be over 50%. I want to emphasize that we still have an apple crop across the region, but it has been diminished greatly from these three freeze events over the past four weeks. Red Delicious are most impacted, with Northern Spy and Idared being some of the least impacted. This crop loss of many king blooms and now side bloom will make thinning decisions much more difficult in the next 10 days.

Oriental fruit moth trap catch is the only new insect pest to report in many apple blocks apples this week. We saw a few last week, but trap catch was not as widespread as this week. Trap catch remains low, in the range of five to 15 adult moths per trap. Redbanded leafroller adult trap catch has dropped off quickly in the past week and larvae feeding in leaves has also dropped off to nearly none being found in the last few days. I think this quick drop off is a result of the freeze event of the last week, as many farms that did not apply a pink spray in apples also saw this same drop off in larvae. Most farms are also saw a sharp drop off in numbers of spotted tentiform leafminer adults in traps—this is the end of the first generation adult flight. Very few predators were found on Monday.

Apple growers had two major apple scab wetting events this past week, both leading to heavy infection periods. The second is ongoing at this time. I also found my first few apple scab lesions on leaves on Monday of the week. These infected leaves were limited to just a few farms with just a few lesions, so it is not being found widespread at this time. I also started to see first signs of powdery mildew infections late last week and a few more yesterday. Based on these findings of the first powdery mildew infected leaves, growers need to start their protection program with their next fungicide application. Lastly on disease management in apples, the fire blight model on Enviroweather is calling for high EIP (Epiphytic Infection Potential) numbers starting with warmer temperatures on Sunday and Monday. So, fire blight protection programs need to begin with weather conditions predicting the spread of this disease.

Pears are mostly at full bloom. I have not seen any flower bud damage in pears from cold temperatures. Pear psylla adult numbers have sharply increased in the past week, mainly due to warmer temperatures.

Peaches are in the shuck this week. Some poorer peach sites have seen a good amount of flower bud damage from the most recent freeze event. In the best peach sites in the region they have seen limited damage, but on poorer sites, damage to flower buds is in the 50 to 80% range. Due to heavy rains yesterday, I was not able to check as many peach sites or flower buds as I would have preferred to check for possible crop loss.

Sweet cherries have just a few open blossoms left on the tree; most are in the shuck. I am finding even more freeze damage in sweet cherries this week from the May 13 freeze event. Damage ranges from 50 to 80% in many varieties. Some flower buds are still viable at this time, but the crop potential has diminished greatly. The best description of our east Michigan sweet cherry crop at this time is that we have gone from a great crop of sweets as spring began about five weeks ago, to a good crop of sweet cherries four weeks ago after the April 22 freeze, to short crop two weeks ago after the May 9 freeze, to a poor crop after last week’s freeze event. Growers are making fungicide applications today for leaf spot and brown rot control.

Tart cherries are at early petal fall. As is the case this week in sweet cherries, I am also finding a good amount of flower bud damage in tarts in many blocks. In cutting a limited number of tart cherry flower buds since the last freeze event, flower bud loss is in the range of 50 to 95%. Fungicides are being planned fairly soon in tart cherries for leaf spot and brown rot control.

Plums are at late petal fall to being in the shuck for European varieties, with Japanese varieties being at fruit set. I am finding freeze damage at this time in all plum varieties, but the percent of damage varies widely from 40 to 80% depending on the variety.

Small fruits

Strawberry bloom continues to slowly open on early varieties, mainly on the south sides of rows, at the ends of rows and along field edges. Most are only at about 5% bloom.

Growers are finding many black blossoms as a result of frost damage. For many growers, they are finding more black or dead blossoms than they have ever seen. It is hard to tell exactly when this damage occurred, but I think most of this damage was caused in the May 9 long and very cold frost event. There are some growers that might have missed one the milder frost events that occurred between May 9 and May 13. Do a more thorough assessment of frost or damage by cutting or dissecting more buds. Upon further examination, you may find less damage than you think you have at this time.

While new leaves continue to emerge from the crown and other leaves continue to expand in fruiting plants, strawberry growth still looks rather sparse or anemic. Few leaves have expanded to full size and most are not looking healthy. I hope that by this time next week with warmer temperatures over this coming weekend that leaves and rows will start to fill out nicely. I stated this last week as well, but it just did not happen.

Newly planted strawberry leaves continue to slowly emerge from the crown and growers can start to see the row developing nicely.

Raspberry growth has picked up in the past week. Summer red raspberry leaves on fruiting canes are 2 inches in length and newly emerging canes are about 4 inches in length. Many new canes have emerged from the soil on fall raspberries, most are 3 to 5 inches in length. However, many of these emerging canes and leaves look tough from cold temperatures.

Blueberries are mostly at late pink bud to seeing just a few open blossoms on early varieties. I have seen some damage to flower buds in Jersey from the three freeze events of this spring, but none on most other varieties.

Saskatoons are at petal fall for most varieties to some late bloom on a few of the latest flowering varieties. Due to cooler temperatures this spring, the staggered flowering of varieties was more pronounced than in most springs. There does not appear to be any freeze damage in saskatoons at this time.

Grapes are moving slowly this spring; most are at late swollen bud to a few at bud cracking open stage of growth stage.

Haskaps are at fruit set to small fruitlets.