Northwest Michigan fruit regional report – July 9, 2013

As sweet cherry harvest starts off, rain moved into the region after three weeks of droughty conditions.

Rain moved into the region following three weeks of hot and extremely dry conditions. The region is in much need of precipitation as soil moisture is very low at this time. Most growers are anticipating beginning sweet cherry harvest at the end of this week, and some early varieties can be found at fruit stands and local grocery stores. We had some local sweet cherries for the National Cherry Festival last week.

This rain is a welcome relief for the tart cherry crop, but we are hoping that it will not result in cracking in sweet cherries. The drought-like conditions will help minimize cracking as the fruit size is small as a result of lack of moisture and drought-stressed trees can take up a fair amount of water without cracking. However, cherries with frost scars and light crops may sustain some cracking damage. The other issue is the amount of rainfall across the region, which varied from site to site. Michigan State University Extension has had reports of 2 to 3 inches of rain in southern Leelanau County on Sunday night (July 7) into Monday morning (July 8), while the Northwest Michigan Horticultural Research Center (NWMHRC) only received 0.5 inches of rain in that same time frame. Substantial rain is predicted for the region today, July 9.

Daytime temperatures have been in the 80s with nighttime temperatures only falling into the mid-60s. With the recent hot days, we have moved ahead of our 20-year average for degree day accumulations. So far this season, we have accumulated 1527 base 42 and 972 base 50. The heat coupled with the recent rain and now humid conditions will be a challenge for growers to protect ripening fruit.

Apples. With the recent rains, we can call the end to primary apple scab. The model is still saying we are at 98 to 99 percent discharge of apple scab spores, but with the droughty conditions for the previous three weeks that was followed by a decent amount of rain, growers that are scab-free can lighten up on their scab programs for the remainder of the season. Growers with scab lesions on the leaves will need to continue a good scab program to prevent fruit scab.

Codling moth numbers are down despite the recent warm nights, and this dip in moth numbers is likely the small separation we see between first and second generation. Growers must continue to protect fruit against this internal feeder. Obliquebandedleaf roller numbers are also slightly down here at the NWMHRC compared with last week’s trap counts; we caught an average of 6.5 moths per trap. No apple maggot flies were caught this week.

Cherries. Cherry leaf spot is a disease favored by warm and wet conditions, so growers that had an infection started prior to these recent rains will need to keep new tissue covered. The goal is to keep leaves on well into September to ensure good fruiting and healthy trees for next season. Most orchards are looking good, but some growers have expressed concerns about some cherry leaf spot in their orchards even with the dry conditions in the past few weeks. We hypothesize that the wet and foggy mornings contributed to cherry leaf spot infections, even with good spray programs.

We have not seen sporulation in orchards with European brown rot infection. We know little about European brown rot, but data from other countries showed that European brown rot can infect ripening fruit. We will keep an eye out for this type of infection as we move closer to harvest in tart cherries.

American brown rot is the disease of concern at this time. Sweet cherry harvest will begin in earnest this week, and growers will need to keep this fruit protected if this wet and warm weather continues. American brown rot can move quickly through an orchard as fruit approaches ripening if the conditions are optimal, and we can lose an orchard within 24 hours with the perfect storm. With the high value sweet cherries are predicted to fetch this season, growers should make the best use of the 24 (c) Special Local Need Permit for Indar this season. We can use up to 48 ounces per season, and the recommended rate per acre is 8 to 9 ounces.

Growers that had sporulating green cherries infected with canker or June drops that took a long time to drop should pay particularly close attention to this disease. However, all sweet cherry growers need to protect fruit as these current conditions are perfect for American brown rot infection. For growers that cannot use captan as we approach harvest, Elevate might be a great tank-mix partner for Indar for resistance management. Elevate is rated fair against American brown rot, but data from California rates this product higher. MSU’s George Sundin thinks that Elevate as a tank-mix partner is a good idea at this time.

Cherry fruit fly counts are up across the region, and growers will need to protect ripening fruit against this pest. Again, MSU Extension recommends that each grower trap in his or her own blocks due to the variability in population size. Our first insects were caught last week here at the NWMRHC, and this week we caught a total of 64 flies on three traps. Cherry fruit fly catches are also widespread throughout the area’s orchards.

Many insecticides are rated as good against cherry fruit flies, but growers should be sure to check the pre-harvest interval (PHI) as we are fast approaching harvest. Another issue that growers need to be aware of is the different imidacloprids on the market – the PHIs vary among the products, amounts of active ingredients also vary and some of the products are not labeled in cherries. All imidacloprid products are not the same, and growers should be sure to read the label of their particular imidacloprid before application.

This week we trapped an average of 19 obliquebanded leafroller moths per trap in cherries, and we anticipate summer generation larvae are now hatching. Growers need to add a lepidopteran material to the tank targeting these obliquebanded leafroller larvae. As mentioned in past weeks, obliquebanded leafroller larvae are a contaminant pest as they can end up in a tank at harvest if not controlled, and our crew has been finding larvae here at the NWMHRC and in commercial blocks this season. These pests have contaminated both sweet and tart cherries at harvest. Growers that are sizing or coloring fruit need to make sure fruit is protected up through the time of harvest. Multiple new insecticides are rated as excellent against obliquebanded leafrollers, but growers need to pay attention to the PHIs.

No spotted wing Drosophila have been caught in northwest Michigan this season in our 60-plus traps.

Wine grapes. Berry development is coming along nicely, revealing a good fruit set in most sites. It is a very important time to tuck shoots and maintain a thin leaf canopy wall. Conditions have been conducive for powdery mildew infections, with high humidity and the weekend rainfall. Refer to previous FruitNet articles for treatment recommendations. There will be a few more weeks of opportunity for powdery mildew to infect the berries.

Rose chafer numbers are finally dropping off – they lasted longer than expected this year. In general, there was little feeding injury to fruit clusters this year. Potato leafhopper numbers are still very low in the sites we have visited. Eggs of the large, foliage-feeding hornworms will likely start to hatch in the week ahead.

MSU entomologist Rufus Isaacs will be on-hand to discuss insect management issues for the next MSU Extension/Parallel 45 meeting on Friday, July 12, from 3-5 p.m. at the 2 Lads Vineyard and Winery on Old Mission Peninsula. Two recertification credits have been requested from the MDARD for this program.

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