Vol. 20, No. 3, April 26, 2005

In this Issue
Tree fruit news
2005 TNRC trapline data – Green fruitworm
Status of streptomycin resistance in the fire blight bacterium Erwinia amylovora in Michigan
Alternatives to streptomycin for fire blight management
Apple scab infection period and snow in eastern Michigan
Mullein bug
Small Fruit news
Cane anthracnose found in some blueberry fields
Other news
Control options for mites in fruit crops (pdf)
Optimizing pollination of fruit crops with bees
Regional reports
Weather news

Status of streptomycin resistance in the fire blight bacterium Erwinia amylovora in Michigan

George Sundin, Plant Pathology
Amy Irish-Brown, MSU Extension Educator

Streptomycin resistance in the fire blight bacterium Erwinia amylovora was originally detected in the early 1990s in southwest Michigan. Most of the resistant strains contained an extra sequence of DNA that encoded streptomycin-resistance genes. This distinguished the mechanism of resistance from that found in E. amylovora from the Pacific Northwest, in which the strains became resistant to streptomycin due to a chromosomal mutation. In the mid- to late 1990s, the streptomycin resistant strains from southwest Michigan slowly spread westward towards the lake, and resistance was noted in an isolated orchard in Kent County. In addition, a small number of resistant strains (~ 10%) were found from these locations that harbored the chromosomal mutation.

In 2004, we surveyed eight apple blocks in the Fruit Ridge area, most of which were concentrated around 10 Mile Road and Kenowa Avenue. Streptomycin resistance was detected in seven of the eight blocks sampled. Genetic analyses of the strains indicated that most of the strains contained the same streptomycin-resistance genes found in strains from southwest Michigan and a small number harbored the chromosomal mutation.

This survey and genetic testing indicates that streptomycin-resistant strains are moving between orchards and between growing regions in Michigan. We will broaden our sampling area on Fruit Ridge in 2005 for resistance detection, but our results suggest that it is quite possible that additional orchards will be identified that contain streptomycin-resistant E. amylovora. We will also sample additional locations throughout the state; we tested isolates from one orchard in Oceana County in 2004 that tested negative for streptomycin resistance.

What control measures should be adopted in orchards that contain streptomycin-resistant fire blight bacteria? Two caveats must be mentioned at this time: 1) streptomycin is the best control agent available for blossom blight control; and 2) we don't know the percentage of streptomycin-resistant strains in blocks testing positive for resistance. Thus, the current recommendation is to tank-mix streptomycin and Mycoshield (oxytetracycline) both at full label rates (1.5 pounds per acre) for bloom sprays.

A Section 18 emergency exemption was granted by EPA for Mycoshield use (see the April 12 Fruit CAT Alert). Mycoshield is not as effective in controlling blossom blight as streptomycin as oxytetracycline is bacteriostatic (inhibits bacterial growth) and is not bactericidal. That is why it is still prudent to include streptomycin in a spray application. A mixed spray of streptomycin and Mycoshield would be expected to kill streptomycin-sensitive strains and inhibit streptomycin-resistant strains. Growers in the Fruit Ridge area who have had success with streptomycin, including in 2004, should continue to use streptomycin or consider comparing control in streptomycin treated versus streptomycin + Mycoshield treated blocks.

Alternatives to streptomycin for fire blight management

George Sundin
Plant Pathology

Streptomycin-resistant strains of the fire blight pathogen Erwinia amylovora have now been detected in orchards from southwest Michigan and the Fruit Ridge area (please see accompanying article). As these strains move into and colonize new orchards, this will detrimentally impact our ability to manage fire blight, as streptomycin is the best blossom blight management tool that we have.

The best management tactic for fire blight is to grow varieties with reduced susceptibility on resistant rootstocks such as Bud9. Growers should also experiment with the new Geneva series rootstocks such as G.16 or G.30. Susceptible scion varieties of young trees on resistant rootstocks will still sustain fire blight strikes, however, these trees should not be killed by rootstock blight. The list of management alternatives for fire blight is small, and I will review the attributes of existing options in this article.

Oxytetracycline
Oxytetracycline is an antibiotic that differs from streptomycin in that it is bacteriostatic and doesn't kill E. amylovora but does act to inhibit its growth. Oxytetracycline is equally active on streptomycin-resistant and streptomycin-sensitive strains; however, oxytetracycline is not as effective as streptomycin in fire blight control. Mark Longstroth, Bill Shane, and myself submit an application yearly for a Section 18 Emergency exemption (the exemption has been granted for use of Mycoshield 2005). Use the full rate of 1.5 lbs. per acre; this antibiotic does not dissolve well, so volumes of at least 100 gallons per acre are recommended. Also, a surfactant such as Regulaid at one pint per 100 gallons will enhance efficacy.

Serenade
Serenade is a biological control agent composed of a combination of spores of a Bacillus strain and the antibiotics that this strain produces in culture. Although Serenade is a biological control agent, it should be used as an antibiotic for bloom sprays. We have tested the efficacy of Serenade for two years in field trials under heavy disease pressure on inoculated trees. In both years, Serenade provided 50 percent control. We saw better control with Serenade in an on-farm trial relying on control of natural inoculum. My current recommendation is that Serenade best fits as a middle spray in a blossom blight control program (Table 1).

The reasoning for this strategy is that the antibiotics will work to reduce fire blight populations initially, and a Serenade application will further reduce those populations. The last spray exiting bloom should be an antibiotic, which would provide the best inoculum reduction as the disease moves into the shoot blight phase.

¹ The first spray timing is dependent upon weather conditions and is best monitored using blossom blight predicting programs such as MaryBlyt. The length of time between sprays is dependent upon the occurrence of fire blight-conducive weather conditions.

² Antibiotic = streptomycin, Mycoshield, or streptomycin + Mycoshield tank mix. Both streptomycin and Mycoshield should be applied at 1.5 lbs. / Acre.

The spray timing for Apogee for shoot blight control is petal fall of the king bloom. The effects of Apogee show up around 10 to 14 days later. A single application of Apogee at the high rate is most effective for fire blight control under conditions of high pressure during bloom. Please see Phil Schwallier's article (April 27, 2004 Fruit CAT Alert) for information on other horticultural aspects of Apogee use.

Copper
Copper is an excellent bactericide for fire blight control as the pathogen E. amylovora is highly susceptible to copper. Unfortunately, the use of copper is restricted by phytotoxicity concerns to an early season application (see article in the April 12 Fruit CAT Alert). This early application should be used yearly for the foreseeable future, as inoculum reduction in orchards will become more and more important.

BlightBan A506
BlightBan A506 is a biological control agent registered for use in Michigan, and we are currently examining parameters for optimizing its use. We have not yet seen the disease reduction with BlightBan observed in the Pacific Northwest. BlightBan is a Pseudomonas fluorescens bacterium that protects blossoms against infection through competitive inhibition of the fire blight pathogen. The BlightBan organism has to arrive at the blossom first to be effective. Thus, the spray timings for BlightBan are 20 to 30 percent bloom and 70 to 80 percent bloom. BlightBan is compatible with and can be tank-mixed with streptomycin but should not be tank-mixed with Mycoshield and only applied at least 48 hours after a Mycoshield application.

Apple scab infection period and snow in eastern Michigan

George Sundin
Plant Pathology

The heavy, wet snow that fell on the eastern side of Michigan during the weekend (April 23-24) resulted in an apple scab infection period. An extended wetting period of approximately 55-60 hours, along with average temperatures in the 34-38°F range, signify an infection event according to the Mills table as modified by Jones.

Since this snow event was preceded by a few weeks of warm, dry weather, it is possible that primary spore discharge was relatively high. Wet snowfall initiated the wetting event, and several hours of potential spore release passed before the snow accumulated on the ground, covering leaves. The subsequent snow cover would be expected to reduce the number of spores reaching the foliage. It is hoped that growers had covered trees with a scab fungicide in the days prior to last weekend.

Mullein bug

David Epstein and Larry Gut, Entomology
Amy Irish-Brown, MSU Extension Educator

Information for this article was obtained from research at Washington State University, the Ontario Ministry of Agriculture and Utah State University.

Mullein bug, also known by its scientific name, Campylomma, is a sporadic pest of apple that appears to be increasing as a problem in Michigan. Interestingly, it acts as a pest early in the season, but can also be an ally throughout the summer months as a predator of European red mite and green apple aphids. Apple growers around the state reported an unusual type of damage to small fruits early in the 2004 growing season; small upraised bumps with a cork-like appearance, surrounded by conical depressions, caused by the feeding punctures of mullein bug. As injured fruit sizes through the summer, distortion of the fruit often occurs. Washington State reports that injury can sometimes resemble russet in certain varieties, such as Gala.

Damage to fruit from the mullein bug occurs around bloom-time. Fruit can receive individual or multiple stings and the large majority of these injured fruit abort just prior to or during June drop. Affected fruit that do remain on the tree develop the small corky warts or bumps. Washington reports that feeding beyond bloom time does not usually result in damage.

The mullein bug has two to three generations per year in Michigan, and divides its time largely between two main plant hosts – the mullein plant and apple. Research at WA State University in 2004 showed that the most susceptible apple cultivars are Golden Delicious, Red Delicious and Gala. Other varieties it favors are Northern Spy, Empire and Spartan, Cortland, Gala and Jonagold. Damage is often most visible on light-colored fruit, such as Golden Delicious. McIntosh and other cultivars seem to be largely unaffected but it is not known whether mullein bug does not generally attack fruit of these other cultivars, or if they are immune to mullein bug stings.

Mullein bug nymphs are tiny, oval-shaped and translucent-green in color. They look somewhat like an aphid without “tailpipes,” and have distinctive pink or reddish eyes. Campylomma nymphs can also be confused with white apple leafhopper (WALH) nymphs. Two features distinguish Campylomma from WALH, a rounded tip to its abdomen and 4-segmented antennae. Campylomma nymphs and adults are fast moving, especially when disturbed.

Monitoring for the pest phase of mullein bug should start around pink and continue through the bloom period. Once you see the damage, it’s too late to target controls in apple. Visual searches and limb tapping of nymphs onto beating trays are the most common methods for determining pest levels. Washington State research reports that beating trays recover approximately 70 percent of nymphs. Campylomma distribution in an orchard is generally clustered, necessitating a high number of limb taps to accurately determine infestation levels. Where a block of mixed cultivars is present, sampling from the most susceptible varieties is suggested. Sample at least 25 trees per block and one limb per tree. Choose limbs with fruit clusters since mullein bug are often most present on these. Once tapped onto the beating tray, nymphs move quickly, so be prepared to sight identify them. Action thresholds developed in British Columbia and used in Washington, are an average of one nymph per tap in Golden Delicious and four nymphs per tap for Red Delicious. Washington research in 2004 showed that an average of 1.2 nymphs per tap would produce ca. 1% fruit injury at harvest in Gala. Blocks with damage last season should be scouted closely for mullein bug during bloom and for two to three weeks after petal fall.

Fruit is susceptible to injury from bloom until fruit reaches about half-inch in diameter. In western states there appears to be a consensus of opinion that chemical controls applied by late bloom are the most effective. Washington State reports that insecticide activity against Campylomma injury is clearly enhanced by early (pink) application. Assail may be the most active of the new compounds (in terms of nymph suppression), and also provided among the best levels of damage prevention. The ability to make an application during bloom may also be a deciding factor.

*Washington State University Tree Fruit Research and Extension Center

**Utah State University Extension

Monitoring of beneficial insects and mites during the summer months should include mullein bug counts. Several weeks after petal fall the nymphs become predaceous on European red mite and aphids. Nymphs with red bellies are an indication that they have been feeding on mites. Numbers of mullein bug nymphs and adults should be recorded when conducting green apple aphid terminal infestation counts and in predator limb tap sampling throughout the summer, to give an estimate of the importance of mullein bug as a predatory insect in the orchard, especially in non-susceptible cultivars. During the summer, mullein bugs will leave the tree to feed on herbaceous plants, especially mullein. In the fall, adults return to the apple tree to mate and lay overwintering eggs. Pheromone traps are used in western apple production regions to assess this movement back into the orchards and provide an early indication of potential problem orchards for the coming spring.

For more detailed information and some great pictures of mullein bug, visit this Ontario Ministry of Ag website: http://www.gov.on.ca/OMAFRA/english/crops/facts/mullein.htm; Washington State University Tree Fruit Research & Extension Center website: http://www.tfrec.wsu.edu/index.ph

Cane anthracnose found in some blueberry fields

Annemiek Schilder
Plant Pathology

This spring, it is not just Phomopsis that is infecting blueberries. One might also see unusual lesions on green blueberry canes that are dark brown to black with lighter brown centers, circular or oval and fairly sharply delineated. Lesions vary in size, from the several millimiters to 3 cm in length. In contrast, Phomopsis lesions tend to be more elongated, often girdle the entire stem and are flattened with more diffuse margins. The lesions may also be mistaken for Fusicoccum canker, but they can occur on any area of the cane and are not necessarily centered on a leaf scar. So far, the lesions have only been observed in a few Jersey fields, but may be present in other varieties as well. What is most striking are the pinkish masses of Colletotrichum spores occurring in concentric circles on the surface of these lesions. Spore masses can be seen on canes in the field now, but if you are not sure, keep the pieces on a moist paper towel in plastic container for a day or two. Anthracnose lesions will produce pink spore masses, whereas Phomopsis will produce creamy white spore blobs in a random pattern. Both can start to look like curly strings if the humidity is just right, but Phomopsis spores have more of a tendency to do so. Anthracnose lesions are initially fairly superficial, only killing the bark, but are assumed to develop further to girdle and kill larger portions of canes.

The occurrence of anthracnose cane lesions is rare, though it has been reported before by researchers in Japan and was observed in Ontario last year. It may be related to the unusually rainy weather that we had during the 2004 season, which may have provided sufficient wetness to allow infection of young green canes at a time that spores were abundant, e.g. during fruit ripening and harvest season. It is not clear when the infections actually took place. While studies have not been done specifically to determine the best methods to control cane anthracnose, they are likely to be similar to those that would be employed for Phomopsis: pruning out diseased and dead canes, applying lime sulfur as a delayed dormant spray, and fungicides on a regular basis through the season.

Since the fungus is sporulating already, it would be prudent to apply protectants, such as Bravo, Captan or Ziram at this time. Make sure to focus sprays at the base of the bush and provide good coverage. The goal is to protect young and emerging green canes from infection. During and after bloom, strobilurins are should be effective as well.

Optimizing pollination of fruit crops with bees

Rufus Isaacs and Zachary Huang, Entomology
Amy Iezzoni, Horticulture

Pollination is a critical phase of the production cycle for most specialty crops, and in Michigan alone the total annual value of fruit and vegetable crops dependent on bee pollination is about $300 million. Bees are the most important delivery vehicle for pollen, and their activity ensures that the flower stigma receives sufficient pollen for fertilization to occur. Well-pollinated crops ripen earlier, produce larger and more even fruit, and improve grower profit. Investment in pollinators is essential for reaching the potential of many fruit crops. To reach this potential, growers need to know how to optimize pollination of their particular crop(s) and varieties being grown.

Table 1 provides the recommended densities of honeybee hives for optimal yields in some common Michigan fruit crops. These numbers come from a series of studies over the years and are averages. Growers using densities lower than these numbers risk their yields and quality, unless the native pollinator community is abundant and healthy.

Use the “early” strategy for tree fruit crops
For tree fruit crops, it is advantageous to have bees working the flowers as soon as they open. This provides multiple benefits. It improves the odds that fertilization will occur before the ovules start to lose vigor (this can happen in only three days on some crops), flowers are more likely to receive the multiple visits needed to deposit enough pollen, and in many crops the first flowers that open set the best fruit. An additional benefit is that having bees in place in orchards at the time of first bloom makes it most likely that all the ‘king bloom” flowers that produce the best fruit will be pollinated. Also, if the weather turns bad, some fruit will be produced.

Use the “late” strategy for small fruit crops
Generally, flowers of small fruit crops are less attractive to honeybees than some other flowers due to the shape and the relatively low “reward” from the flowers, so a different strategy is required than you might use for apples which need bees early. The crop should be starting to bloom before bringing bees in, so that bees stay on the crop to forage, and don’t move elsewhere. If brought in too early, bees will learn to forage on other patches of flowering plants and when the crop blooms, they may not be attracted back to the crop. So, moving bees into fields after 5 percent bloom but before 25 percent of full bloom is recommended. For blueberries, having 4 to 8 honeybees per blueberry plant in the warmest part of the day during bloom is sufficient to achieve good pollination. The "late" strategy is especially important for cranberries, which is not very attractive to bees. Luckily, cranberry flowers will stay open for a while if not pollinated, proving opportunities for pollination when the weather is good. In cranberries, it is better to wait until 10 percent bloom in order to maximize the yield. If too many flowers start turning rosy, pollination was too low and the number of honeybee hives should be increased next year.

Hive placement
If possible, place the colonies in sheltered locations so their entrances face the early morning sun. This will encourage earlier bee activity as the hive warms in the morning. Pallets of hives or individual hives should be spread out around the field to maximize the spread of floral visitation by bees, with a maximum of 300 yards between colonies.

Other managed pollinators
Growers are becoming more interested in bumblebees, which can now be purchased commercially from a supplier based in Michigan. These have the advantage of visiting more flowers per minute than honeybees and being active in the cooler damp conditions we often experience in Michigan. For some crops, such as blueberry, they also provide the buzz pollination required to maximize release of pollen from the flower. While the cost per bee is higher, each bumblebee is much more efficient than each honeybee. Increased interest in native bees has also lead to the commercial development of blue orchard bees (species of Osmia) for pollination, and this is growing slowly but steadily as growers learn more about how to manage them.  

Native pollinators
Many other helpful insects are active in fruit crops during bloom, working flowers and providing free pollination services. Native bees (such as the mason bees, sweat bees and bumblebees) can be seen moving among flowers during spring, and their activity generally remains high when weather conditions turn too cold or wet for honeybees. These native bees may be insufficient to provide the complete pollination required for good yields, however, and until we learn more about them they should not be relied on to stand alone as your sole pollination source. By providing the right nesting habitats, and food for the bees after your crop has flowered, you can enhance the local populations of native bees around your crop. This is a long-term process and you’ll need several years of experimenting before these bees can become a reliable part of your pollination planning.

Pest management during pollination
Avoid use of insecticides when flower buds are open to prevent killing pollinators. Some products are bee safe, but the label should be followed carefully if using them during bloom. Beehives should be removed immediately after pollination if post-bloom pesticide applications are planned. By monitoring for pest problems carefully during bloom, growers can help minimize the need for pest control. If an insecticide application is necessary during bloom, compounds that are least toxic to bees should be used and applied when bees are not foraging, with careful observation of the pollinator-restrictions on the label.

Plan ahead for how to optimize pollination
We cannot control the weather, but planning ahead will help maximize the chance of pollinators working flowers during some part of bloom. A diverse combination of pollinators is expected to provide the best insurance against low fruit set from a cool spring. Honeybees will remain the dominant pollinator of fruit crops, and with bumblebees and blue orchard bees now available commercially, a combination approach is more possible than in the past.

Over the past few years, fruit set in Balaton has been disappointing in years with cold weather during bloom. Apparently normal-looking flowers simply failed to set fruit. We strongly suspect that this poor fruit set is due to ovule senescence prior to fertilization. Therefore, to improve fruit set in Balaton, we recommend the following strategies:

1)    Increase early pollen availability, and
2)    Improve pollen transfer.

Honeybees should be placed in the orchard in ample time for the bees to visit the first open flowers as the first flowers may have the best potential to set fruit. In addition, we recommend a minimum of two honeybee hives per acre since under cool conditions, Balaton fruit set may be improved with Montmorency or sweet cherry pollen.

Table 1. Recommended density of honeybee hives (per acre) for common Michigan fruit crops

Regional reports

1 – Southwest

Mark Longstroth
Bill Shane
Al Gaus

Apricot crop potential looks good.

Peach bloom is ending. Winter fruit bud loss was easy to assess during bloom. The crop was reduced for some varieties and sites, and in some areas there will be no peach crop. Growers are seeing vertical splitting of bark on the trunk due to winter damage. Oriental fruit moth adults have emerged. Biofix for SWMREC was April 15 at 175 GDD45. The cool (50F), wet conditions forecast are too cold for brown rot infections, but if temperatures rise into the 60s then grower should protect against brown rot.

Tart cherries began to bloom last Tuesday with full bloom Wednesday. Leaves are beginning to unfold and growers need to protect against cherry leaf spot. There seems to be little damage from the frost. But by Monday afternoon, browning of the petals in cherries was easy to see. Pollination should have been good for sweet cherries but cold wet weather started soon after full bloom in tart cherries. This means that only flowers pollinated before Friday are likely to set fruit.

Plum bloom is ending. Growers report that Japanese plum leaves look poor either due to the cold or the high winds, probably both. Growers need to protect against black knot now that shoot growth has started.

Apple blooms began to open last week. The warm conditions were good for fire blight development but cooling conditions before the rain reduced the risk of infection. The cool conditions forecast for this week will not be good for fire blight development. The weekend rain snow event did result in marginal apple scab infection periods. Higher exposed areas probably dried off early but there were probably areas that stayed wet most of the weekend. Many growers covered up for apple scab last week. Growers should reapply protectant fungicides while rain seems likely. European red mites have hatched. There were heavy flights of redbanded leafroller and spotted tentiform leafminer, but few reports of leafroller larvae feeding.

Pear bloom continues. Most of the flowers have opened. Pear psylla adults are out.

In grapes, the most advanced Concord shoots are about one inch long. Now is the time to apply the first EDBC spray to protect against phomopsis. There is winter damage to vinifera wine grapes as many buds are not moving. Grape flea beetle damage has been reported.

Strawberry growers are complaining of poor weed control from residual herbicides applied last year. Others are applying grass herbicides.

Summer raspberry leaves are out. We are seeing a wide range of winter injury symptoms. Some varieties are leafing out normally and others show few live buds or only new shoot growth from the ground. Flower buds are plainly visible in Prelude.

2 – Southeast

Bob Tritten

It appears that an area south of Flint and up in the Thumb had the greatest amount of snowfall, with a total of 8 to 12 inches on the ground at the close of Sunday afternoon. With warm temperatures on Monday, most of the snow has melted and bees were flying again.

I did an extensive survey of tree fruits to see if any cold weather injury had been evident, and I could find no damage. I checked apples, peaches, sweet cherries, tart cherries and plums. More details on some winter injury on peaches under that section of this report. The unusual snow event of the weekend also brought an extended light to medium apple scab infection for most apple growers. Most growers began to cover for that event on Monday. It was interesting to see tractor and sprayer tracks in the snow at orchards on Monday morning. This was the first time I had ever seen that.

A few growers experienced their first apple scab infection period from the rain event last Wednesday, April 20. This truly depended on the amount of rainfall received in that event. Most growers, however, received only in the 0.05 to 0.11 inch of rainfall that did not trigger a wetting event. Most growers had an apple scab wetting event starting on Friday afternoon (April 22) when the rain started and continued through Sunday night. Even though temperatures were very cold, the event was wet long enough for the entire period that it triggered a light to moderate infection period. Most growers have now covered for this apple scab infection period.

Apple scab spore discharge was present from the Friday rain event at one of our monitoring stations. The levels were light to moderate. I am a bit concerned about fire blight development with the extremely warm temperatures of last week. This will bear some watching as we get closer to bloom time in apples.

Pears are mostly at bud burst to open cluster. Pear psylla adults have been flying for about three weeks now. I’ve not observed any egg laying. Now is still a good time to remove the suckers from the inside middles of the pear trees to help lessen pear psylla populations later this spring.

Peaches are mostly at pink bud with a very few early blossoms opening. It appears that over the entire region we have an excellent crop of peaches coming along. There is an exception to this in the Armada area as they received extreme winter cold temperatures in the winter of 2003-04. These trees looked very weak last year and don’t appear to have produced many live flower buds this year. I have also run across one peach orchard that had a complete bud kill from cold weather that occurred in December 2004. A temperature of -13 degrees was reported at this orchard. Recall that last fall we had a very mild fall that did not allow peaches to harden down as they normally would have. The sudden drop of cold temperatures killed virtually all of the flower buds.

Sweet cherries are in full bloom. Blossoms opened very quickly on Tuesday, April 19 and most of them continued into bloom on Wednesday and Thursday, even though temperatures were cooling. Hopefully, we had enough pollination in those three days to save the crop. Again, in extensive checking of flower buds on sweet cherries, it appears that they have survived the cold weather event of the weekend quite nicely. We will need to wait into the mid part of the week however to tell for certain.

Tart cherries are at bud burst. At some orchards there appears to be a fair amount of winterkill of small twigs and flower buds. This was most likely due to the excessive leaf drop caused by cherry leaf spot disease last season. It’s still a bit early to determine the crop potential.

Raspberries are at bud break and fall raspberries continue to emerge from the ground. Raspberries also appear to have been stunted this year with a fair amount of winter injury. I am a bit concerned about this and continue to watch this plant develop. Stay tuned for details in the next few weeks.

Blueberries are at bud burst at most farms. It appears that we have a nice crop of blueberries coming along again this year. Blueberry pruning continues to take place at most farms.

3 – Grand Rapids Area

Phil Schwallier
Amy Irish Brown
Carlos Garcia-Salazar

Most apple varieties are in the open cluster to early pink stage at this time. Sweet cherries are in bloom. Peaches are nearing full bloom across the Ridge. According to 30-year averages from the Sparta weather station, degree day totals are running about 10 days ahead for GDD42 and 14 days ahead for GDD50, even with the colder weather of the past weekend.

Overnight temperatures over the weekend probably caused some bud damage to all tree fruit crops in the low pockets of orchards – it’s a bit early to tell how extensive the damage is. Most weather stations in the area reported the lowest temperatures on Sunday morning (April 24) of around 30°F. It was colder in the low areas, but there was limited frost.

Since first green on April 6, the Sparta and Belding weather stations have recorded two rain events that have resulted in one apple scab infection for the rains on April 20. Spore numbers were low for the April 20 rain event and quite high for the April 22 rain event. According to GDD32 accumulations, about 30 to 40 percent of the ascospores mature at this time.

Green fruitworm and redbanded leafroller adults were flying last week. A few consultants are reporting seeing quite a few tarnished plant bug and their feeding evidence can be seen on apple fruit buds – small droplets of sap around their feeding site. Spotted tentiform leafminer should start to fly at any time if not already. Oriental fruit moth traps should be up in both peaches and apples – they should be flying. Pheromone for OFM mating disrupted blocks should be going on now.

Some growers have already applied pink sprays last week when it was so warm. If growers haven’t applied a pink spray and have had problems with rosy apple aphids or spotted tentiform leafminer last year, a pink spray should still be considered, if possible, before bloom. Be mindful of bees in blocks nearby that might be in place.

With bloom getting close, apple growers will need to think about adding a mildewcide in the tank for powdery mildew in the next week or so for those varieties susceptible to it.

Another problem resulting from the winter damage is the weakening of affected plants. Wounds caused by winter damage make the plant susceptible to Phomopsis twig blight and canker (Figure 1). At this moment in West Central Michigan the most serious blueberry health problem is the Phomopsis that is widely spread in this area. Affected fields in Ottawa and Allegan County showed that Phomopsis infections are already present in the new growth. In some cases, especially in the variety Bluecrop, Phomopsis is affecting up to 90 percent of the last year’s growth.

4 – West Central

Mira Danilovich

Weather
What a difference a week makes! From summer-like temperatures, back to winter. Snow did not amount to much ... about a half-inch on the grassy area and that was all. For the most part temperatures stayed above the critical temperatures for the current developmental stages. Certainly, in some low-lying areas the temperatures may have been significantly lower than what our automated weather stations have shown indicating that there might be some damage to the opening buds in those areas. Overall, except for a minor frost-burn to the petals, the rest of the bud is good and viable.

GDD totals since March 1, as of Sunday, April 24

Pear psylla continues to be very active. Yesterday was still quite chilly but they were hanging onto the opening bud clusters. It appears that there is an increased number of tarnished plant bugs flying around and sap feeding. Scouts are reporting finding newly hatched European red mites, rosy apple aphids, strong flight of redbanded leaf roller and spotted tentiform leafminer before this Arctic blast.

Last week we had two wettings but only one resulted in scab infection period throughout the district. I need to point out that there is a bit of a discrepancy between the data posted on the PestNet West Central Wetting Event Summary and what I am posting on the code-a-phone messages when it comes to the duration of the wetting events. The reason being that the wetting sensors are not placed within the canopy but are mounted on one of the weather station’s posts. They are out on the open and, consequently, are drying out much faster. To compensate for this, I am adding an hour to each wetting event. This will explain why I am calling for scab infections in Ludington and Hart when the chart shows only infection in Bear Lake/Manistee. Following Mac Hardy model, there are 23% mature spore in Bear Lake/Manistee, 18% in Ludington and 27.5% in Hart areas.

So far, we did not have cherry leaf spot infections. With the low temperatures that we had over the weekend, cherries in low-lying sites may have been damaged by some frost. It is important to realize that any frost damage to the flower buds at this time may set us up for bacterial canker infections. All stone fruit would fit into that category. With flowers opening up, brown rot is of concern as well. Blocks need to be covered.

5 – Northwest

Jim Nugent
Jim Bardenhagen
Duke Elsner

GDD50             115

Last week was a roller coaster! Exceptionally warm temperatures during most of the week advanced crops well beyond normal. The weekend then ushered in a blast of snow and cold. Temperatures remained below freezing for 31 hours with continuous strong wind. Fortunately, during this period temperatures remained mostly around 30ºF, never getting below 29ºF. By comparison, the 2002 wind event lasted 11 hours at 27-28º F, wiping out the tart cherry crop and badly damaging the sweet crop. A wetting event was reported for Monday, April 25. The amount of precipitation varied around the northwest from, 0.02 inches to 0.75 inch at the NWMHRS.

Tree fruit
Freeze damage occurred in cherries. The wind event over the weekend reminded us of 2002 with the following differences: 1) temperatures this year were 2 to 2.5 degrees F warmer, 2) the duration was nearly 3 times longer, and 3) the stage of bud development was a little more advanced this year. Cold temperatures on Monday have made assessment difficult at this time (Tuesday morning). We will have better assessments in a couple of days. Fortunately, preliminary evaluations are looking quite good. We have seen some damage in sweet cherries, but so far damage does not appear to be too bad. Preliminary evaluations of Montmorency tart cherries are showing damage ranging from some to none, depending on the orchard site. Early evaluation of other fruit crops looks good.

Although we had a wetting event, apple scab infection periods were none to borderline for our region.

Weather news

Jeff Andresen
Agricultural Meteorology
Geography

An intense, but slow-moving area of low pressure brought an extended round of late winter weather to all of the state during the past weekend, leading to subfreezing temperatures, strong winds and heavy snowfall in some areas. Fortunately, the presence of clouds and wind kept air temperature above 30°F in most areas, although some upper 20-degree readings were reported in a few spots. This unusual weather system was directly associated with the development late last week of a deep upper air troughing feature across eastern North America, which will likely continue to be the dominant factor in weather conditions over the next week and possibly longer.

In the short term, a weak cool frontal boundary will make its way across the state Tuesday (April 26), setting off mainly scattered rain showers through Wednesday. Precipitation with this feature is expected to be light, with most totals remaining below 0.25 inches. Given nighttime temperatures in the low and mid 30s, some light snow is possible in central and northern sections of the state. Drier weather is likely Thursday through Saturday, with partly to mostly cloudy skies expected each day. Another area of low pressure will approach the state from the southwest by late in the weekend, bringing the next chance for any significant precipitation. Mean temperatures during the next several days will remain 3-6 degrees below normal, with highs ranging from the upper 40s north to the upper 50s in the south and lows ranging from the low 30s north to the upper 30s south. Should skies clear or winds die down during the late night or early evening hours, scattered frost is a possibility during the next week (especially in sheltered low-lying areas), although no significant large scale frost or freeze is anticipated at this time.

In the medium range time frame, latest forecast guidance suggests the continuation of the upper air troughing pattern across the region for the next two weeks. Specifically, the latest NOAA Climate Prediction Center 6-10 Day and 8-14 day outlooks (for May 1-5 and 3-9) both call for a below normal temperatures state- and region-wide. While I personally believe the below normal temperatures during the 6-10 day time frame are a good bet, there is some evidence of at least a temporary change in the jet stream pattern to allow warmer temperatures back into the region about 1 to 1.5 weeks out. Precipitation totals during the 6-10 day period are forecast to range from below normal in western sections of the Upper Peninsula to above normal in southeastern Lower Michigan. Below normal precipitation totals are forecast state- and region-wide for the 8-14 day time frame.