Northwest Michigan fruit regional report – June 24, 2014

Several days with rain in the last week have sized fruit well and posed challenges for maintaining good spray coverage.

Weather report

This past week has been much like the rest of the season with some warmer days and some cooler days. This week has been marked by more rainfall than in previous weeks, however, growers have been in the orchards a lot this season trying to keep new tissue covered against fungal pathogens. Last week, the high daytime temperature was on Monday, June 16 when we reached almost 84 degrees Fahrenheit. By Friday, we dropped down to a high of 60 degrees F—a swing of 24 degrees.

We have accumulated 1040 growing degree days (GDD) base 42 and 600 GDD base 50. We are still about one week behind our average. As mentioned, we had four days of rain last week. On June 16, we had 0.07 inches of rain, 0.38 inches on June 17, and 0.13 inches on June 18. It rained again on June 20, and we recorded just under a half inch of rain that day. Rainfall has been variable across the region. Rain was in the forecast for the start of this week as well, and we only received 0.02 inches of rainfall yesterday. We have a chance of rain today and into tomorrow. Conditions between the rains have been humid, and there have been some infection periods for diseases.

Crop report

Fruit is sizing well across the region, particularly with last week’s rainfall. Early varieties of sweet cherries are beginning to color, and birds are already evident in these blocks. The sweet cherry crop continues to look good, and the rain will help with size in orchards that have a heavy set. The tart cherry crop is variable across the region. Some orchards have a fairly large crop while others are much lighter. Blocks that had a heavy set in 2013 are considerably lighter this season. There also appears to be variability within a block, and some trees have a big crop but neighboring trees are light. Estimates are between 75-90 percent of the 2013 crop. Overall estimates have gotten lighter in the past few weeks. The official guesstimate will be held in Grand Rapids, Michigan on June 25.

Some growers are still wrapping up apple thinning efforts for 2014. Many orchards to the south are finished, and growers are feeling confident they did a decent job of thinning. However, some orchards to the north are still in need of more thinning. The phenological difference between northern and southern regions of this part of the state seems to quite spread out this season. We anticipate harvest will be long for all tree fruits due to this spread.

Strawberry harvest has begun in Manistee and Antrim counties. Growers expect to start picking strawberries later this week in Leelanau, Michigan.

Pest report

Variable rainfall in the last week has posed challenges for maintaining good coverage to protect leaves and developing fruit from diseases and insect pests. There were rain showers on Friday June 20, and average temperatures were cool in the mid to upper 50s throughout the northwest region. The duration of the rain event was not long in most areas, and because temperatures were cool, there were few disease infection periods in most areas on Friday. However, this rain event was longer in Bear Lake and Benzonia, and the cherry leaf spot model on Enviro-weather reported high cherry leaf spot infection periods for both locations. Low cherry leaf spot infections were reported for East Leland and the Northwest Michigan Horticulture Research Center on Friday. We received very little rain Sunday June 22 and Monday June 23 and once again the event was short and did not result in cherry leaf spot infection periods in most areas. However, the cherry leaf spot model for Bear Lake and Benzonia is currently reporting low cherry leaf spot infections triggered by rain on Monday.

According to the apple scab model on Enviro-weather, Friday, June 20 rain also resulted in heavy scab infection periods in Bear Lake and Benzonia; no apple scab infection periods were recorded for other locations in our region. Bear Lake and Benzonia are also currently in the midst of a light apple scab infection period that initiated during rain on Monday. Apple scab spores are still discharging at our monitoring site in Leelanau County. We counted an average of 12.5 spores per spore rod that were discharged during Friday’s rain and the apple scab model on Enviro-weather is reporting that 93 percent of spores have been discharged. We are not calling the end of primary scab infection at this time. However, growers that have had little to no scab in their orchards for the past few seasons are likely finished with the primary scab infection period. We will continue to monitor scab spores following rain this week if the rain predicted for Tuesday, June 24 and Wednesday, June 25 is correct. We hope to call the end of primary this week. Other fruit growing regions of the state have called the end of primary apple scab.

In general, orchards are looking pretty clean in terms of disease symptoms. We have received a few reports of isolated incidences of powdery mildew on tart cherry, and some cherry leaf spot lesions are beginning to appear on leaves. The weather conditions are worrisome for American brown rot infection, and growers should be diligent about controlling this disease if we continue to have warm and wet conditions. American brown rot can infect fruit that has been injured (bird pecks, canker, etc.) Reports of apple scab severity and incidence have also been very low.

Codling moth numbers are on the rise here at the station. This week we found an average of 6.5 moths per trap; in the previous two weeks there was only one moth per trap. Growers who already set biofix and reached ~100 GDD were spraying Rimon last week to target codling moth eggs. Some growers reapplied sprays following rain last week. In some orchards where codling moth biofix was set earlier, the 250 GDD timing for controlling codling moth larvae may be approaching. We did not find oriental fruit moth in traps at the NWMHRC this week.

Adult moths of obliquebanded leafroller are emerging and were found in traps in apples, 7.5 moths per trap, and cherries, 5 moths per trap, at the station. Although we are finding obliquebanded leafroller in our traps, this pest has a broad host range which makes it difficult to interpret trap catch numbers because we cannot be certain that obliquebanded leafroller are infesting fruit trees or if they are coming from a nearby host plant. Nonetheless, Michigan State University has developed some rules of thumb for obliquebanded leafroller trap catch to determine biofix: a consistent catch of 20 or more moths per trap for two to three weeks usually indicates that obliquebanded leafroller may be a problem, and low-catch of less than 20 moths per flight period generally indicates a non-problematic pest density.

Growers are continuing to protect developing fruit from plum curculio. Fruit damaged by plum curculio and other pests and non-pollinated fruit have started dropping.

In cherries, borers are still active and the numbers of moths captured in traps are declining. We found all three borer species in traps at NWMHRC this week: American plum borer at 6.7 moths per trap, lesser peach tree borer at 13.7 moths per trap, and greater peach tree borer at 1.7 moths per trap.

Cherry fruit fly adults are emerging and were observed on leaves at the NWMHRC late last week. We have not detected any cherry fruit flies on traps at this time. Cherries are sizing and some early ripening varieties began taking on color last week. Cherries are likely not susceptible to cherry fruit flies this early, but as the fruit ripen and soften they will be susceptible to cherry fruit fly damage in the near future. Birds have moved into early ripening sweet cherry blocks.

Spotted wing Drosophila have not been detected in our region, but were found in Southwest Michigan last week.

Rose chafers began emerging throughout the region last week and are mating. At the station we have received several calls regarding this pest. Although there are insecticides that provide good control of the beetles, rose chafers are highly mobile and can re-infest treated areas quickly.

Wine grapes

Some delayed reactions to winter cold injury are now evident; shoots that started out well but have now failed to thrive. For example, in a Riesling block at the NWMHRC, healthy shoots on the fruiting wire are well over a foot in length and continuing to show vigorous growth at the tip; affected shoots have stopped growing at four to five inches. The problem is likely cane, cordon or trunk injury resulting in reduced ability to support shoot growth. The shoots having problems now will possibly die as the season progresses, or at best the fruit they bear will lag behind in development.

Many varieties are approaching bloom. The next three to four weeks is a very important time for protecting fruit from powdery mildew, downy mildew and black rot, depending on the susceptibility of particular varieties. In vineyards where a lot of basal shoots have been retained to promote vine recovery from cold injury, there is a very dense canopy of leaves low on the vines. This will result in reduced air flow, high humidity and slow drying of foliage, encouraging fungal disease. This situation also makes it difficult to achieve good pesticide penetration into the canopy. Adjustments to nozzle orientation, spray volume and/or sprayer speed may be needed to make efficacious pesticide applications under these conditions.

Rose chafer adults are now active in vineyards, with relatively high populations in some areas. Potato leafhoppers have been found in some downstate sites, so they may appear in local vineyards soon. There have been a few reports of grape tumid galls, which are red swellings on the leaves, stems or tendrils caused by the presence of tiny gall fly larvae. This is a spotty problem that seldom requires treatment.


Saskatoons are in the green berry growth stage, with some red starting to show on the most advanced fruit. Apple curculio adults and larvae are feeding on fruit, along with saskatoon sawfly larvae. Leaf-curling aphid activity is continuing, but the level of infestation seems lower than the previous year. Several insecticide choices are available, but Sevin should not be used now as it will cause fruit drop.

Saskatoon-juniper rust infections of fruit are now evident, and protecting fruit from further infection is very important at this time. As ripening and harvest is approaching, the fungicide choices now need to have a short pre-harvest interval, such as Abound (0 days), Pristine (0 days) and Quash (7 days).

Dr. Rothwell’s work is funded in part by MSU’s AgBioResearch.

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