Regional reports on Michigan fruit – May 29, 2012

MSU Extension educators’ pest and fruit updates for Michigan.

This week’s regional reports:

Southwest Michigan – Mark Longstroth, Bill Shane, Diane Brown, Michigan State University Extension

Southwest Michigan


Last week was hot with highs rising from the 70sto 90s and lows rising into the 60s. Dry conditions continue and soils, especially sandy soils, are dry.Weather for this week is forecast to be cooler with highs below 70 and lows near 50. There is little chance of rain in the upcoming week. The potential evapotranspiration for the last two weeks has been between 0.2 and 0.3 inches of water a day. We have lost almost 3 inches of water in the last two weeks. Growers who can irrigate should be applying an inch of water every four to five days to replace the lost water. Our growing degree day accumulations are currently about two weeks ahead of an average year.

Southwest Michigan Growing Degree Day Totals from January 1 through May 27


GDD 42

GDD 45

GDD 50





Trevor Nichols




Small fruit

Fruit are developing quickly and the season is early.

Strawberry harvest is well underway. Fruit size and quality are excellent. Harvest at the beginning of June is several weeks early for strawberries. Tarnished plant bugs are present in low numbers and could cause cat facing of fruit. Both nymphs and adults feed, but nymphs cause the most damage. Common leafspot symptoms are showing up in some plantings.

fruit cluster
Ripe strawberries. This picture, taken June 2002, accurately
represents normal strawberry development in mid-June and the
current conditions in southern Michigan strawberries in 2012.
Photo credit: Mark Longstroth, MSUE

In brambles, bloom is ending in raspberries. Early raspberry fruit is about a half-inch in diameter.Blackberries are blooming. At the Southwest Michigan Research and Education Center (SWMREC), the cultivar ‘Black Butte’ has fruit 0.5 to 1 inch long and ‘Apache’ has 0.5 inches fruit.

In grapes, Concord and Niagara bloom began last week and is well advanced in some vineyards. Wine grape bloom varies, depending on variety. Marquette, the earliest- developing variety at SWMREC this year, was at about 50 percent bloom on Friday (May 25); Brianna was at first bloom. Leaves with phomopsis symptoms are increasing. Black rot was found at SWMREC in Pinot Noir and Chardonnay.

black rot chard
Black rot leaf lesions on Chardonnay. Notice the tiny black dots
inside the leaf lesions that are fungal fruiting structures.
Photo credit: Diane Brown, MSUE

Grape berry moth trap catches increased substantially last week at high pressure locations. The highest trap count was107, up from 57 the previous week. We set biofix for grape berry moth (50percent bloom on wild grape, Vitisriparia) in southern Berrien County on May18, and northern Berrien County on May 21. Biofix in Van Buren County should be similar. Grape flea beetle larvae are feeding on foliage. Control is not necessary unless damage is high. Grape tumid gall was found on the variety Marquette.

tumid gall marquette
Tumid gallon Marquette flower cluster. Notice the leaf galls
in the background. Photo credit: Diane Brown, MSUE

Blueberry fruit is sizing rapidly. Soils in sandy fields are dry; many growers are irrigating. Growers with overhead irrigation should control anthracnose during the green fruit stage. Many growers need to apply follow-up sprays to control cherry fruitworm and cranberry fruitworm. For more scouting information, see the Blueberry Insect Scouting Report for May 21-27, 2012.

Cranberry bloom is underway.

Tree fruit

Fruit are scarce and hard to find. San Jose scale crawlers are expected to emerge at the end of this week or early next week, based on degree days and the blooming of catalpa, an indicator for this insect stage. The hot weather of the last few days is causing trap catches of many moth pests to increase sharply.

Apricot fruits are 1.5 to 2 inches in diameter.

Peach fruit are 1.25 inches in diameter.Growers report misshapen fruit where one side is larger than the other. Oriental fruit moth catches decreased last week,indicating the end of the first generation. Flagging of terminal ends by burrowing larvae has been reported. Bacterial spot symptoms are showing up on leaves of susceptible varieties. Rusty spot, caused by the powdery mildew fungus, is common on fruit.

Sweet cherry fruit are coloring and birds are feeding on ripening fruit. Harvest of early season cherry varieties such as Chelan and Cavalier or Rembrandt should start mid-week. Many fruit are misshapen and the fruit surface is often pitted.

Tart cherry fruit are 14 to 16 mm and beginning to yellow. Growers need to control cherry leaf spot to maintain the health of their trees.

Plum growers should protect against black knot as long as shoot growth continues. Japanese plum plums are 7/8 to 1inch in diameter.

Apple fruits are 1.25 to 1.5 inches in diameter and June drop is underway. Codling moth trap catches remained steady for the week. Codling moth biofix was set as May 7. Degree day accumulation since biofix for codling moth through Monday (May 28) at the Bainbridge Enviro-weather station was 287. This is the window for use of insecticides targeting hatching larvae for sites having enough fruit to justify treatment.

Obliquebanded leafroller was set as May 19. Oblique banded leafroller numbers increased considerably last week. Fire blight symptoms are relatively scarce in the area in part due to dry conditions. A year like this with no diseases is an excellent time to prune fire blight out. Scabascospore catches in the last rains were relatively low, indicating that primary scab season is over. Growers should check their blocks to see if leaf scab symptoms are present. Powdery mildew symptoms are easy to find on susceptible varieties.

Pear fruit are about an inch in diameter for Harrow Sweet and other varieties with fruit. Growers should check their blocks to see if leaf scab symptoms are present. Pear psylla is present in low numbers.

Upcoming meetings

Our next Monday fruit meetings will be June 4 at Fruit Acres Farms at 5 p.m. Fruit Acresis located on the northeast corner of Friday and Carmody Roads about 1.5 miles south of the Coloma Exit on I-94. One RUP credit is available at the meeting.

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Southeast Michigan – Bob Tritten, Michigan State University Extension

Southeast Michigan
Southeast Michigan


Summer-like weather in the last week pushed ahead ripening of strawberries and produced a tremendous amount of growth in tree fruits. Look for cooling temperatures as this week progresses. Dry soils are a concern for many fruit growers,especially in newly planted fruit crops. Growers are working hard to get irrigation to these fruit crops.

Tree fruit growers continue to find a few isolated fruit on a few varieties, but most are not finding enough fruit to commence pest control operations for the season.

Growers continue to sort out strategies to replace income losses for the year and to source fruit from other growing regions. As I have shared in my fruit crop updates over the last month, there has been a significant crop loss in all tree fruits across the region.

Fruit farms in the southern tier of Michigan counties still have some viable tree fruit crops as well as a few fruit farms located very close to Romeo, Mich.There seems to be no consistence from farm to farm or block to block in terms of the varieties that have a crop and the fruit load. Overall it appears that there is just over half of an apple crop and even fewer peaches. In apples,June drop is underway, about two weeks ahead of normal.

Strawberry harvest began on Memorial Day (May 28) for farms in Monroe and Lenawee counties and will begin later this week for farms in the Detroit area. Our opening of the strawberry harvest is a week to 10 days ahead of normal.

Our early warm season is still running about two weeks ahead of normal in terms of growth stages and even more than that in terms of degree day totals.

Most of the region received two rain events over the past week with very little rainfall;most fruit farms received only a few tenths of an inch of rain.

East Michigan Growing Degree Day Totals for March 1 to May 28





Commerce (Oakland)




Emmett (St Clair)




Flint (Genesee)




Lapeer (Lapeer)




Petersburg (Monroe)




Pigeon (Huron)




Romeo (Macomb)




Tree fruits

Apples were hard for me to find in my travels yesterday (May 28) to check for fruit development and pest activity. The few Empires (about a dozen apples on two limbs on just a few trees) that I have found are approaching 1 inch in diameter. Most apple trees have between 8 and 12 inches of new growth, with some terminals reaching 16inches of new growth. Growers who have used Apogee this season (most have made two applications) are wondering if it is working. As with thinning decisions in the normal years, growers need to leave some check or untreated trees in order to tell if Apogee is helping to reduce terminal growth.

Overall,insect pressure has been low over the past week with the exception of continued high codling moth trap catches. Codling moth adult trap catches have been high at most farms the past two weeks, even in mating disruption blocks. Trap catches have been in the range of 15 to 20 moths per trap. I set the regional biofix date for May 10. With recent, warmer nighttime temperatures, now is a good time to control codling moth. Plum curculio fruit sting have is now being seen, especially in orchards that are not being sprayed. Aphid populations have exploded in unsprayed apple blocks in the last week, but predator’s numbers are increasing rapidly.

We have not had a rain event at either of our apple scab monitoring stations in the past week to determine if we are at the end of primary apple season. So, until we get rain at these two locations, I cannot say for certain that we are at the end of primary apple season. However, I believe that we are at the end of primary at most farms where rain has been more prevalent in the past few weeks.Most of our weather stations have not had an apple scab infection period in the past week, with the exception of Emmett and Pigeon. If growers still have a crop, they will need to continue apple scab control until I can determine that we are at the end of primary apple scab season.

I am starting to see some sheet scab in blocks that have not been sprayed in the last three to four weeks. Powdery mildew-infected terminal branches have become much more evident in the past week – some varieties are heavily infected. Frog eye or black rot leaf symptoms are being seen in several apple blocks, and some black rot-infected limbs are now starting to flag or die back.

Pears have put on a tremendous amount of new growth in the past two weeks. Pear psylla populations continue to grow quickly in unsprayed blocks. Suckers need to be removed to help reduce pear psylla populations.

Peach leaves where there is no crop are just now starting to look better. Oriental fruit moth trap catch remains low. Green peach aphid populations continue to increase. For trees with no crop, this year is a good opportunity to do some major pruning to reduce tree height. Be careful not to remove more than a quarter of the leaf surface.

Sweet and tart cherry growers are now starting to find a few handfuls of cherries. Leaf curling is extensive from black cherry aphids, especially in sweet cherries. Predator populations are building quickly to control them. Cherry leaf spot disease needs to be controlled in blocks that do not have a crop and maybe cherry fruit fly in problem blocks.

Plums were severely damaged by the last freeze event. Most blocks have little to no viable fruit remaining.

Small fruits

Strawberry harvest started yesterday (May 28) at farms in the southern part of our region, and begins later in the week for farms in the metro Detroit area. This will be the earliest that some farms have ever opened for harvest. I continue to see evidence that slug populations are building in strawberries. Growers need to do a good job of scouting for them. I have not seen any new strawberry clipper damage in the last two weeks. No new angular leaf spot disease symptoms have been seen. Growers need to keep a close eye out for this disease and be ready to control it if the need arises.

 Raspberry bloom continues for summer fruiting types and new canes of fall bearing types are now 15 to 18 inches ofnew growth. Summer bearing raspberries had a great deal of tip burn or die back from the April freeze events. Now is the time to set spotted wing Drosophila traps.

Blueberries are at 10 to 12 mm in size for most varieties, with some freeze damage in blueberries growing in low laying sites. Now is the time to set spotted wing Drosophila traps.

Grape flower clusters are very close to bloom. Canes that were damaged in the many freezes appear tohave been killed. I would wait for a few more weeks to remove those canes for signs of emerging buds.

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Grand Rapids Area Tree Fruit– Amy Irish Brown and Phil Schwallier, Michigan State University Extension

Grand Rapids Area
Grand Rapids Area

Crop update

Fruit is hard to find and it’s difficult to determine a proper crop stage. In blocks with little fruit, it is likely that “June drop” will not be significant enough to notice. Overall, trees are starting to really look healthy again as new leaves emerge without freeze injury.

Horticultural tasks to consider

Some areas received rain over the weekend, but it is still on the dry side and irrigation should be considered, especially for newly planted trees that were looking wilted over the weekend. A good rule of thumb for newly planted trees is 10gallons of water per tree per week. It is best if you can break that up into two applications over a week’s time, but more important that you get it applied, even if it is only once per week.

Pruning and training should include feathering newly planted trees and 1-year-oldtrees. This is a good week to get this done as there should be little risk for fire blight situations.

Removal of tree guards should be done where they are too tight against the trunks to avoid girdling problems. Painting of tree trunks should be done as well.

Fire blight update

You should continue to be vigilant for situations of blossom blight in newly planted trees that are just coming into bloom. The rains Sunday and Monday (May27-28) did trigger a blossom blight infection for any open apple bloom according to the Mary Blyt model.

Apple scab

There were no additional spores on the rods with the rains over the holiday weekend(May 26-28). The last two rains came in the night, so it is possible that there could still be some spores to be released. However, given the fact that there have been no spores released in the last two rain events, the poor fruit set inmost tree fruit blocks, and we have been dealing with scab for nearly 11 weeks,I am calling an end to primary scab for 2012.

Powdery mildew

In some high pressure apple blocks, there is a very high level of powdery mildew present. I can’t remember the last time it was this easy to see just driving by an orchard. Continue to monitor all blocks for mildew. The warm, humid weather from last weekend and in the forecast for this weekend (June 2-3) will only enhance mildew infections. Until terminal bud set, mildew must be managed so as not to end up with high inoculum levels for 2013.

Tree fruit insects

Plum curculio activity should be over for the year.

Oblique banded leafroller adult flight is just beginning on the Ridge. In low oblique banded leafroller pressure situations, it is likely you could severely reduce your manage mentinputs in blocks with little fruit. There are many parasitoids of oblique banded leafrollers and they should be able to help this year. In high pressure blocks,you will have to make the determination of whether controls are needed based on the crop you have. Keep in mind that with less overall fruits, the fruit that is there is likely to have a higher infestation rate for worm pests overall.

Codling moth. We have accumulated 300 DD50 since the May 3 biofix on the Ridge, indicating that egg hatch should be underway from that date. Some sites may have set a later biofix than my regional May 3 date. I’ve heard May 18 or May 19 as dates for specific site biofix. This is a difference of 120 DD50 accumulated, so you need to adjust your management accordingly. In blocks with little crop this year,you should consider using delayed timings for applying needed management sprays for first generation codling moth – at least 350 DD50 post-biofix rather than the traditional 250 DD50 for egg hatch.

Oriental fruit moth. A regional biofix was set for oriental fruit moth on April 15 and we’ve accumulated 522 DD45 since then. This indicates we are about a week past peak egg hatch on the Ridge for oriental fruit moth. By early next week (June 4 or5), egg hatch should be over for first generation oriental fruit moth.

Borers. American plum borer and lesser peach tree borer flight has begun. Trunk sprays can be started in stone fruits now. Dogwood borer frass can be seen in M9 clonal rootstocks – no adult flight yet, but it is expected to begin soon. Timing for dogwood borer frass trunk sprays is at peak adult flight – usually around July 4, but expect it to begin earlier this year.

Black cherry aphids can be found in very high numbers in some sweet cherry blocks. Where there is no crop, let the predators and parasitoids move in for this pest.

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Grand Rapids Area Small Fruit– Carlos García-Salazar, Michigan State University Extension

Grand Rapids Area
Grand Rapids Area

Good weather conditions in the Grand Rapids, Mich., area have allowed major small fruit crops to continue developing without many problems. So far, maximum daily temperatures have been around the upper 70s with some days reaching the low 90s. Rains have been absent for the most part, only scattered rain showers have been observed with less than 0.5inches accumulation. Regarding degree days, up until May 29 there are 650 DD (base 50°F) and 1130 DD base 42°F accumulated since March 1.

Crop growth stages

Strawberries are in in petal fall and the first harvest for early varieties may start this week.So far, birds are the main problem. They are attracted to ripening fruit and are damaging early ripe fruits. Meanwhile, raspberries are blooming and no problems are reported.

For blueberries, the bloom period has concluded in all varieties. All varieties are in the green fruit stage except Elliott that is in the fruit set stage. Blueberry fields north of Allegan County are showing a heavy fruit set,especially in the varieties Jersey and Elliott. At this time it is evident the impact of frost events that occurred at the end of April. Fields where growers limited the use of frost protection to only the major frost and freeze events of April 27-29 are showing a large number of plants with heavy fruit set, but sparse and weak foliage (Photo 1).

Bluecrop with abundant fruit and
sparse foliage after spring frost.
Photo credit: Carlos García, MSUE

A good nutritional program is needed to restore the plant reserves and balance the competition between foliage development and fruit production. Fields severely affected by frost need to be pruned to allow the new growth to develop during the current season (Photo 2). This new growth will allow the bush to produce berries for the next year’s crop.Despite these problems, blueberry fields north of Allegan County are showing a very good crop.

Photo 2
Young bush severely affected by spring
frosts requiring extensive pruning to
eliminate damage growth and prevent
dieback. Photo credit: Carlos García, MSUE

At this time of the season, insect pest control is one of the main priorities. The cherry and cranberry fruitworm adults continue flying and according to the cranberry fruitworm phenology model, the fruitworm egglaying continue favored by the excellent weather conditions of the past seven days. Special attention needs to be placed to fruitworm control in those fields with advanced green fruit development. Since beehives have been removed from most fields, the use of insecticides such Guthion and Imidan can be applied to reduce the cost of fruitworm control. If Guthion or Imidan are going to be used, growers need to check the label carefully to apply only the allowed amount for this season. See the 2012 Fruit Insecticide Registration Update for a guideline for the recommended doses.

Guthion (8) (azinphos-methyl)is no longer labeled for use on peaches, nectarines, plums, cane berries and cranberries. The year of 2012 will be the final EPA Phase-out of Guthion for apples, pears, cherries and blueberries. The maximum yearly amount of Guthion50 WP to be applied has been reduced to 3 lbs. on apples, 3 lbs. on pears, 1.5lbs. on blueberries and 1.5 lbs. on cherries. The pre-harvest interval (PHI)for apple and pear use is 14 days with a 21-day PHI if the last application is greater than 2 lbs. of Guthion 50 WP per acre.

Imidan 70W (9) (phosmet) is an organophosphate insecticide labeled for use in many fruit crops, including tart cherries. New commercial product will include a reduced legal rate of 2.125 lbs./acre for use in tart cherries. Older product that lists the rate of 2.5 lbs./acre can still be legally used.

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Northwest Michigan – Nikki Rothwell, Duke Elsner, Erin Lizotte, Michigan State University Extension

Northwest Michigan

Weather report

The late May weather continues to be unusual with extremely warm temperatures and dry conditions followed by some intense rainfall and thunderstorms on Sunday(May 27). Daytime temperatures for this past week were in the mid-70s into themid-80s, and conditions were extremely dry. Growers without irrigation were concerned with the dry conditions as newly planted trees were starting to show signs of drought stress. These warm conditions were coupled with substantial winds, and the fire danger throughout northwest Michigan was at an extreme danger.

As of today, May 29, we have accumulated 924GDD base 42 and 515GDD base 50 – these accumulations are still well above our average (571GDD base 42 and 283GDD base50). On Sunday morning (May 27), a thunderstorm rolled through the region and brought intense rainfall; the Northwest Michigan Horticultural Research Station (NWMHRC) received 1.75 inches of rain on Saturday into Sunday. The rain came so fast and many orchard roads and newly planted orchards have wash-out areas.

Crop report

Fruit that is out there is starting to size. With little fruit on the trees, we expect that the fruit will size quicker than usual, particularly with the recent rainfall. The rainfall over the weekend was a welcome relief to the droughty conditions that we have had over the past three weeks; however, the rain came fast and resulted in quite a bit of runoff rather than a nice,metered, soaking rain. Growers are considering apple thinning, and many are opting to hand-thin rather than use chemical thinners because of crop variability and the potential to drop all of remaining fruit. We expect to better estimate the apple crop in the coming week with the sizing fruit. The sweet cherry crop appears to be smaller than we originally anticipated; growers are starting to determine the size of the crop in order to decide to harvest or not. Strawberries are sizing, and the crop is still looking good.

Pest report

Cherries. With some much needed rainfall over the weekend, the region had a cherry leaf spot infection. Symptoms from earlier infections are already visible around the region. Growers should be aware of the increased risk for early defoliation due to these early season infections and need to be scouting their orchards for leaf spot at this time. If leaf spot is visible, growers must be diligent about keeping the remainder of the leaves protected as we still have a long season ahead of us.

Regardless of the crop load, growers should plan to continue to manage for cherry leaf spot and powdery mildew. Early season cover sprays (ideally at first cover timing) are critical to season long powdery mildew management, so growers who have not yet applied a strobilurin fungicide (Pristine, Gem, or Adament) for powdery mildew should consider it as they are effective against both cherry leaf spot and powdery mildew; this spray should go on immediately as these hot and dry conditions are conducive for powdery mildew infection. There have been reports of powdery mildew in apples across the state. The sterol inhibitor fungicides (Indar, Elite, Orbit) are also effective powdery mildew materials,but will not be effective against leaf spot due to widespread resistance in all the major fruit producing areas of Michigan. Light crop loads this year will likely lead to increased shoot growth and succulent leaf area that is highly susceptible to powdery mildew.

Additionally,the Cherry Industry, Michigan State University, EPA, MDARD and Syngenta have worked together to obtain a 24(c) special local need registration (SLN) for use of Bravo Weather Stick (chlorothalonil) beyond shuck split. Traditional timing of chlorothalonil for cherry leaf spot has been prohibited past the shuck split timing prior to this newly registered use. With the 24(c), growers must follow a series of restrictions in order to use this product legally throughout the growing season to ensure that post-shuck split applications do not result in illegal residues.

Growers should be aware that cherries harvested 21 days after the last application of Bravo will have illegal residues, and to ensure the residues on the fruit are reduced to a legal level (less than 0.5 ppm), growers MUST carefully follow all label directions. The cooling pad procedures on the SLN label are key to reducing residues to a legal level. Illegal residues not only violate federal law, but they have serious consequences for growers, processors, and the Michigan tart cherry industry. Although a more permanent solution is underway for the 2012 season, growers should obtain the Training Affidavit by going to MDARD’s Cherry SLN webpage and complete Steps 2 and 3.

MSU Extension will be available to help growers work through this educational step to be able to use chlorothalonil beyond shuck split by using the MDARD website. Growers with questions or those in need of assistance can call the Northwest Michigan Horticultural Research Station at231-946-1510. However, if orchards have no crop and will not be harvested in 2012, chlorothalonil can be used as the label states for non-bearing orchards. This distinction needs to be clear—to harvest or not to harvest—to comply with the 24 (c) label for 2012. Additionally, this special label is for Bravo Weather Stick only and will not apply to other products containing chlorothalonil.

The symptoms of bacterial canker remain prevalent on sweet cherries around the north; canker has also been reported in tart cherries. These spring conditions were favorable for bacterial canker (prolonged periods of cold, frosty, wet weather) and allowed the bacteria to multiply within the overwintering sites and be disseminated by rain. Freeze and frost damage caused by the weather allowed for an easy entry point and infection. Unfortunately, there is no effective treatment for bacterial canker at this time.

American plum borer adult flight slowed this week, reinforcing that earlier high trap counts indicated peak adult emergence for first generation at the station. Lesser peach tree borers continued to emerge in large numbers this week with 40 moths per trap; this is a very high trap catch for the station based on historical data. These lesser peach tree borer trap catches indicate that we are likely at the peak emergence in that species. Lorsban trunk applications are also recommended for lesser peach tree borers, but growers who applied Lorsban for American plum borers recently should keep in mind that trunk applications should be applied at least two weeks apart.

Growers should be scouting for oblique banded leafroller larvae as leaves continue to expand; we have observed a few larvae in terminals throughout the region and caught the first adult moth this week. Growers can scout their orchards by examining 20 clusters per tree in five trees per orchard for larvae or feeding sites. An insecticide should be applied if they observe more than two larvae or feeding sites per tree. Growers who have not had luck finding the larvae canal so hang delta traps with sticky liners and lures to determine if obliquebanded leafroller adult moths are present in their orchards. The materials that target the larval stage of obliquebanded leafroller a include Delegate, Belt, Altacor,Voliam flexi, Entrust and Bts. During this growing season, growers may end up targeting the second larval generation of obliquebanded leafrollers, expected around harvest time. Growers in northwest Michigan should not expect organophosphates or pyrethroids to provide effective control of obliquebanded leafrollers because of insecticide resistance.

Plum curculio activity continues this week with fresh and older, crescent-shaped, egglaying scars visible on green fruit. Many of the non-organophosphate insecticides (pyrethroids, neonicitinoids and oxadiazines) for plum curculio management require treatment to begin around petal fall to provide adequate control. The MSU Tart Cherry Postponed Insecticide Treatment Strategy(P.I.T.S.) model for the control of plum curculio is estimating the accumulation of approximately 350 degree days since tart cherry biofix (full bloom April 20 at NWMHRC). Control is recommended at 375 GDD from the biofix date. The MSU P.I.T.S. model should only be used in carefully scouted orchards using the on-farm biofix date and weather data from the closest Enviro-weather station. If growers have a short crop that they plan to harvest this year, increased competition for those fruit as egglaying sites will warrant earlier plum curculio control to protect the remaining fruit. Growers who have no harvestable crop may consider reducing their plum curculio management as the issue of internal larvae in the fruit at harvest is not of concern. Refer to the E-154 2012 Michigan Fruit Management Guide for more information on plum curculio management materials.

Apples. Thewet weather over the weekend triggered an apple scab infection period around the region. Based on a March 20 biofix (McIntosh green tip), the Enviro-weather apple scab modelis estimating that approximately 95 percent of primary scab spores have been discharged around the region, and 100 percent are mature and ready to be discharged. EBDCs and Captan are both excellent scab protectants, and provide five to six days of protectant activity when used at full rates. Growers should remember that spray intervals should be tighter when relying on these materials. Keep in mind that EBDCs have a 77-day PHI, so they are best use dearly in the growing season. Growers should also note that strobilurin resistance has been confirmed in all major apple growing regions of the state and the mutation confers complete resistance – fungicides containing strobilurin will not work against apple scab and increasing the rate of a strobilurin is not an effective option.

Regardless of crop load, growers should carefully consider their scab management program as inoculum can build quickly over a season and make control difficult insubsequent seasons. Refer to the E-154 2012 Michigan Fruit Management Guide for more options. Growers should also carefully consider their powdery mildew management as high levels of infection are being reported from other regions of the state. Strobilurin or sterol inhibitor fungicides are the recommended materials for mildew and should be applied on a protectant basis.

Codling moths flight continued at the station this past week. We have continued to accumulate degree days quickly with the hot weather over the past week leading to the accumulation of 250 DD50 as of May 29. Growers should track the progress on their farms using the Enviro-weather codling moth model and on-farm biofix dates. The codling moth model is designed to help growers accurately apply insecticides at the recommended treatment timings which range from 100 to 250 DD50 post-biofix, depending on pest pressure and insecticide mode of action. Ovicidal insecticides are positioned early to coincide with first generation egglaying (100 DD50),followed by larvicides (250 DD50) which are targeted at first generation egg hatch.

The adults we are currently catching are primarily mating during a four-hour period beginning around dusk. The mild evening temperatures over the past week are ideal conditions for mating. If the cooler evening temperatures forecasted are correct, then we should see activity slow as codling moth flight during this critical period drops quickly when temperatures fall below 60°F. Growers should be confident that low catches are accurately assessing codling moth activity during these cool periods. The positive effects of this slowed activity is compounded as female fecundity (ability to reproduce) decreases by approximately 25 percent for every 24 hours a codling moth female is delayed from mating after she has emerged from her cocoon. Based on the unusual patterns of emergence we have observed in other pests this season, growers should be carefully monitoring for codling moth and weighing the pros and cons of treatment in no crop situations. There are a number of effective codling moth materials. Refer to the E-154 2012 Michigan Fruit Management Guide for more information.

Growers should be on the lookout for obliquebanded leafroller larvae feeding on leaves in the terminals. Growers who haven’t had luck finding the larvae can also hang delta traps with sticky liners and lures to determine if obliquebanded leafroller adult moths are present in their orchards. Oriental fruit moths continued to emerge at lower levels this week.

Grapes. Shoot growth has progressed nicely over the last two weeks. Many sites have reached10- to 12-inch shoots; sucker removal is underway and tucking will begin soon. In some places, young vines with less extensive root systems have suffered from our very dry conditions unless they have been irrigated.

Insect activity in vineyards has picked up quite a bit. Potato leafhopper adults are numerous in some sites, with leaf deformity starting to become noticeable. Stippling from three-banded leafhoppers and other Erythroneura species is heavier than normal on wild vines in our area. The stippling leafhopper species are rarely problems on the cultivars grown in our area.

Adults of the eight-spotted forester moth are flying and more numerous than usual. This moth is a day-flying species, often thought to be a butterfly when seen. Larvae will appear on vines over the next few weeks. Larvae will feed on clusters, so the higher numbers of this insect this year may call for treatment this year.

larvae Adult
Left, Forester moth larvae. Right, Forester moth adult.

The first generation of grape plume moth larvae is approaching maturity. These are far more common on wild grapes, but they sometimes appear in managed vineyards.The larvae tie together terminal leaves on shoots and feed inside the tangle of leaves.

The first reports of powdery mildew have come in during the last week. The heavy rainfall on May 27 likely triggered a big release of powdery mildew spores, so it will be very important to keep on top of scouting for this disease and protecting vines that are now in a very susceptible stage of growth.

Saskatoons. The crop looks good in the sites I monitor. I have not seen any activity from the sawfly pest that attacks the berries to this point. Our relatively dry conditions have kept Entomosporium leaf spot at low levels, but the rains of early this week may bring about a change in that situation.

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