Vol. 20, No. 4, May 3, 2005

In this Issue
Tree fruit news
Peach tree trunks splitting due to winter damage
Resistance to sterol-inhibitor (SI) fungicides in the cherry leaf spot pathogen in Michigan
Plum curculio early season biology and monitoring
Small Fruit news
Section 18 for Topsin M granted for blueberries
Control of Phomopsis twig blight and canker in blueberries
Options for control of fruit rots in blueberries
Flea beetle injury to grape buds – see it online in the weekly scouting report
Other news
Regional reports
Dryness continues

Bill Shane
SW Michigan Research and Extension Center

Growers in southwest and southeast Michigan are reporting splitting of peach and nectarine tree trunks and scaffolds. Gaps in the bark reveal dry, cinnamon-brown cambium tissue instead of the normal cream-white appearance. Cracking seems to be occurring on all sides of the tree and not primarily on the southwest trunk side, as can occur on sunny winter days. The brittle bark is splitting now as trunks start to expand in spring growth. More splitting is expected to show up over the next few weeks. Damage seems to be more common on five- to eight-year-old trees. The damage is more prevalent on some varieties in some orchards, but more data collection is needed before we draw any conclusions.

 Tracing back, we are attributing the damage to a series of rapid temperature drops during December and January that damaged the cambium tissue and also caused some fruit bud mortality. Trees showing severe splitting will decline over the next few years as Cytospora canker moves into damaged tissues. To provide the best opportunity for tree healing, growers should maintain normal fertility and pruning programs, and if possible, provide supplemental water if soils become abnormally dry.

George Sundin and Tyre Proffer, Plant Pathology
Jim Nugent, District Horticultural Agent

Sterol inhibitor (SI) fungicides (also known as sterol demethylation inhibitor, or DMI, fungicides) were first registered for use on cherries in Michigan in 1982 for brown rot blossom blight control. They have been used for cherry leaf spot control since 1989. Trade names for SI fungicides include Elite, Funginex, Indar, Nova, Orbit and Rubigan.

In the spring of 2003, we visited a sweet cherry orchard (orchard SC1) in northern Michigan in which almost all of the trees were dead. The tree death was caused by winter injury, which was exceptionally severe on this farm due to early defoliation the previous season (mid-July 2002) caused by cherry leaf spot infection. The grower had relied on a single SI fungicide for disease control for at least the previous eight years.

We took samples from orchard SC1 and four other sites in 2003, and we sampled 41 orchard sites throughout Michigan in 2004. We used a plate assay to determine the resistance status of leaf spot isolates (Figure 1). Isolates that could not grow on a medium containing 0.2 ppm of the SI fungicide tebuconazole (Indar) were considered sensitive. Isolates that could grow at 0.2 ppm but not at 3 ppm had a phenotype of low moderate resistance. Isolates that could grow at 3 ppm but not 5 ppm had a phenotype of high moderate resistance, and those growing at 5 ppm were considered highly resistant.

Two sites were tested (Ohio and North Manitou Island) that have never been exposed to SI’s. All leaf spot isolates were controlled with 0.2 ppm, i.e., all were sensitive.

In 2004, we screened a total of 1,300 isolates from the 41 Michigan orchards and almost 100 percent of the isolates exhibited some level of SI fungicide resistance (Table 1). The only differences observed among isolates from different growing regions of the state were in the percentage of different levels of strain resistance. For example, about 40 percent of isolates from Leelanau, Grand Traverse and Antrim counties had phenotypes of high moderate and highly resistant while about 60 percent of isolates from Benzie, Manistee and Oceana counties were either high moderate or highly resistant. In southwest Michigan, the leaf spot population is predominantly low moderate resistant, but very few SI-sensitive isolates were recovered.

Thus, resistance to SI fungicides is endemic in Michigan. The effect of this resistance in terms of control failures is not fully known at this time. However, it is clear that fungicide efficacy has been reduced. An examination of disease control from fungicide efficacy trials conducted at the Northwest MI Horticultural Research Station between 1989 and 2003 shows a major decline in control (Figure 2). This loss of control may be masked in orchards where fungicide programs alternated SI's with other fungicide chemistries.

Our findings suggest that Michigan growers need to transition away from SI's for leaf spot control. It should be noted that the SI's appear to remain an effective chemistry for brown rot control, though tests for brown rot resistance in Michigan have not been conducted. Alternative chemistries for leaf spot control include chlorothalonil (Bravo) prior to shuck split and post harvest, strobilurins (Flint), strobilurin + Boscalid (Pristine), copper compounds, dodine and captan.

We have prepared a table recommending the use of various fungicide chemistries at various timings for leaf spot and brown rot control (Table 2). Articles on our experiences with Flint, Pristine and copper compounds for tart cherry disease control will appear over the next few weeks. Rotation of fungicide chemistries is critical for fungicide resistance management.

Andrea Coombs
Entomology

During overwintering, plum curculio females become reproductively mature. Once they become active in the spring, they immediately find mates and produce eggs. By fruit set or shuck split nearly 100 percent of females are mated and have mature eggs ready for oviposition. Even in early crops such as apricots, plum curculio oviposition begins at shuck split.

There are two ways to monitor for plum curculio during the early part of the season. First, traps can be deployed in overwintering sites or in hot spots. Both the pyramid and screen traps baited with plum essence and benzaldehyde have been effective at capturing plum curculio when populations are moderate to high. Pyramid traps tend to be more effective at capturing early in the season. In addition, pyramid traps are the only trap to be used if trapping in overwintering sites. If curculio are captured during the early spring, it is important to apply insecticide at fruit set/shuck split to protect fruit from resident plum curculio females that are ready to oviposit. If traps are not used, fruit can be visually monitored for oviposition scars beginning at fruit set/shuck split. Visual monitoring needs to be done on at least a weekly basis and can be biased towards known hot spots. Plum curculio can cause significant levels of damage within a short period (overnight if populations are relatively high) if evening temperatures are above 60°F.

To date, plum curculio has not been captured in sites with low to moderate plum curculio populations. Plum curculio have been captured in two commercial sites with high populations. These sites are in Genesee and Benzie counties. First catch occurred after the warm evening temperatures on April 19 and 20. In early April, there were many days with evening temperatures warm enough to induce plum curculio activity however plum curculio was not showing up in traps. This is likely due to the fact that there was no precipitation during the month of April until April 20. Damp soils are necessary for the adults to climb out of the soil after overwintering.

Evening temperatures have been below 50°F across the state since April 20 so plum curculio has not been active. According to weather forecasts for southwest and southeast, temperatures will be high enough for plum curculio activity in the later part of the week through the weekend. Peach and cherry fruit will be coming out of the shuck during this period so these fruit should be monitored for plum curculio injury. Plum curculio should also be active in west central Michigan over the weekend and into the next week. Plum curculio can also become active in northwest Michigan if the temperatures remain above 60°F into the evening.

Annemiek Schilder
Plant Pathology

A Section 18 emergency exemption has been issued by the EPA for use of Topsin M WSB (thiophanate methyl) in blueberries in Michigan (Topsin M already has a label for use in strawberries and grapes.). Target diseases on the label for blueberries are Phomopsis twig blight and canker, Fusicoccum canker, mummy berry, anthracnose fruit rot, and Botrytis blossom blight. Growers who want to use this product in blueberries should be in possession of a copy of the special label at the time of use. The specific exemption expires on September 30, 2005.

The recommended rate is 1 lb of product per acre applied by ground or aerial application. The product may not be applied through any type of irrigation system. No more than three sprays (3 lbs product) may be applied per acre per year. A worker re-entry interval (REI) of 12 hours must be observed. The pre-harvest interval (PHI) is 7 days. Applications may be started at green tip and repeated at 7-10 day intervals. However, use of this fungicide will be most appropriate from pink bud through early fruit development, as the Phomopsis, anthracnose and mummy berry pathogens are all active at that time. Topsin M should be used in combination with non-benzimidazole fungicides, such as Ziram or Captan, to reduce the risk of resistance development.

Annemiek Schilder
Plant Pathology

Phomopsis cane canker and twig blight is a widespread disease of blueberries caused by the fungus Phomopsis vaccinii. The fungus enters the canes through wounds caused by harvesting equipment or pruning activities, and can also infect younger canes and twigs directly if they are wet for a long period. This disease can predispose plants to winter injury, which is why after a severe winter you may see more flagging of canes the following summer. Included in this article are some suggestions for control of Phomopsis. The problem with Phomopsis is that infections on green canes apparently can occur all season long, although most twig infections have typically been occurring in May and June. Bud infections may also take place in the late summer or early fall and that is something that we need to investigate further. An aggressive program to combat Phomopsis would look something like this:

1)    Prune out dead and diseased canes and twigs as much as possible, including green canes with lesions. If the bushes look very bad, mow off everything and let new canes come up. Use fungicides to protect new canes from infection.

2)    Destroy diseased canes. Ideally, they should be removed from the field and burned. However, because of the labor involved, most growers just bushhog the canes and leave the remnants lying in the row middle. This is probably not a big concern, because Phomopsis spores are dispersed by rain splash and consequently won't go very far (usually within a few feet of the source). It may only be a problem if the canes are lying close to or are left in the bush. While the canes are a potential source of inoculum, if they break down quickly, the Phomopsis fungus will also be destroyed. So the better they are chopped up and in contact with the soil, the quicker Phomopsis will be gone.

3)    Prevent canes from getting herbicide burns or other wounds (e.g., from a harvester or other equipment) which may predispose them to infection. Water during dry periods (including in the fall) to reduce plant stress.

4)    Protect canes and twigs with Topsin M+ Captan or Topsin M+ Ziram on a fairly regular schedule (e.g., a spray every 2 weeks) from early pink bud through pea-size fruit. Indar (fenbuconazole) is also very good against Phomopsis, so if you are spraying Indar for mummy berry anyway, you are also covered for Phomopsis. Bravo will also work, but can't be sprayed after bloom. Other effective products are Pristine and Cabrio. In years with a warm and wet early fall, a post-harvest spray may be useful to protect newly developed buds from infection. Previous research has shown spore activity to cease in early September, so sprays should not be needed after mid-September.

5)    Lime sulfur can be put on in the fall after leaf drop or as a delayed dormant application in the spring. This will reduce inoculum and fewer fungicide sprays may be needed the following season. We are currently investigating liquid sulfur and copper as dormant sprays. These products are much less expensive than lime sulfur.

6)    Don’t feel discouraged if you do not start seeing results immediately. One needs to keep up this program for at least two years, because it may take a year for existing infections to show. A hard winter with lots of winter injury may also make the bushes appear in worse shape.

7)    There are other canker diseases out there, including Fusicoccum canker (in northern Michigan and the Upper Peninsula) and possibly cane anthracnose (found recently in Michigan). The control methods mentioned above should also be effective against these diseases. However, if you are not sure what is going on in your field, send in a sample to MSU Diagnostic Services (517-355-4536) for a proper diagnosis.

Annemiek Schilder
Plant Pathology

Fungal fruit rots, especially anthracnose caused by Colletotrichum acutatum, continue to be of economic concern in blueberries. Losses can occur before as well as after harvest. The cultivars Jersey, Bluecrop, Rubel and Blueray are very susceptible to anthracnose fruit rot, whereas Elliott is generally resistant. Alternaria fruit rot is commonly found on Bluecrop fruit before harvest and affects most varieties after harvest. Botrytis fruit rot is not as common in Michigan, but may be a problem in years when cool, wet weather prevails during the flowering and fruit development period. Botrytis fruit rot mostly shows up as a post-harvest disease. These rots can be distinguished to some extent with the naked eye: anthracnose is characterized by wet, pink to orange spore masses; Alternaria fruit rot by a dark olive-green mold layer, and Botrytis by fluffy, tan to gray mold growth on the berry surface. A fact sheet for identification of blueberry fruit-rotting has been published by MSU Extension and can be viewed on-line as a pdf, ordered through the web site (using 2847 as the keyword), or purchased through your local Extension office. The MSUE Bulletin office home page is: http://web2.msue.msu.edu/bulletins/mainsearch.cfm

The anthracnose fungus overwinters in dead fruiting twigs, but has also been found to overwinter in live, dormant buds, which subsequently die. A twig blight, which is difficult to distinguish from Phomopsis twig blight, can also result from bud infection. Pink to orange spore masses may be visible on infected tissues in the spring. More recently, anthracnose lesions have also been found on young green canes in the base of the bush. With anthracnose there are two important periods when the fruit infection risk is high because of peak spore release: 1) from pink bud to about pea-size berry (due to overwintering inoculum), and 2) from first blue fruit until the end of harvest (due to sporulating berries that infect surrounding berries). Fungicide spray programs should focus on these periods. Since anthracnose infections increase greatly at the second and third harvests, it is advisable to spray between harvests as well as to protect the later-maturing fruit if this can be done without knocking the fruit off.

Effective cultural control measures are: timely harvesting, not harvesting the berries while wet, rapid cooling of harvested berries and timing irrigation to occur at night or in the early morning to limit the duration of fruit wetness. In addition, pruning bushes will remove dead and diseased twigs, which can serve as inoculum sources, and open up the canopy to reduce wetness duration and increase spray penetration.

There are several fungicide options for control of blueberry fruit rots. Early in the season, the best control options are Bravo, Captan, or Ziram (with or without Topsin M). Around bloom and later in the season, the strobilurin fungicides Abound (azoxystrobin), Cabrio (pyraclostrobin), and Pristine (pyraclostrobin and boscalid) are good choices. They are locally systemic, rainfast within several hours of application, and have a 0-day PHI. They have excellent activity against anthracnose and are also labeled for control of Alternaria fruit rot, although the latter has not been sufficiently investigated in Michigan. If Alternaria fruit rot is a concern, good options are Aliette (fosetyl-Al) and Switch (cyprodinil and fludioxonil). Switch is a systemic fungicide with activity against anthracnose, Alternaria fruit rot, and Botrytis fruit rot. Elevate (fenhexamid) primarily works against Botrytis, while Captevate is a premix of Elevate + Captan with activity against Botrytis as well as anthracnose (due to the Captan component). Lime sulfur as a dormant spray also reduces anthracnose infection at harvest, but should not be used as a stand-alone measure.

Rufus Isaacs
Entomology

Flea beetle populations have been high this year, causing some growers to apply an insecticide for this pest, which typically causes little injury. Flea beetle injury looks different from that of cutworms, and pictures of their feeding can be seen at the Grape Team’s website – www.grapes.msu.edu (click on the link called “weekly scouting reports”).

With some varieties remaining in the bud swell stage, they may be at risk of injury when the temperatures increase, and scouting wooded vineyard borders in these vineyards would be worth the time spent. Hopefully, the new shoots will grow quickly past this risky stage in the warm weather.

Our grape IPM Project will continue in 2005, providing growers in the southwest Michigan with weekly updates on insects, diseases, degree days etc., from seven commercial vineyards. The report is posted online each Monday, and to access the latest report directly, go to: www.maes.msu.edu/tnrc/grapescout2005.pdf. This page will be updated with the latest report each Monday, so check back to see what is being seen at these sites. The current version contains photos of flea beetle and cutworm injury.

Regional reports

1 – Southwest

Mark Longstroth
Bill Shane
Al Gaus

Tree fruit
Insect activity stopped with the cold weather and trap catches were generally zero. Plant development was slow. There is little damage from last week’s winter storm. Wind burn and freeze damage is easy to find on the Northern edges of fruit plantings. Damage consists of browning petals and leaves and tattered leaves. Generally, plant growth looks weak and yellow due to the cold temperatures. Color should improve when warm temperatures return.

Peach growers are seeing vertical splitting of bark on the trunk due to winter damage. We are going to ignore the first flight of Oriental fruit moth and biofix on the adult emergence after the weather warms up. If temperatures rise into the 60s with rain, then growers should protect against brown rot. Tarnished plant bug adults are out.

Sweet cherries show good growth. Tart cherries are still blooming. Leaves are beginning to unfold and growers need to protect against cherry leaf spot. There was little damage from last week’s snow. Damage consists of browning petals and blown off flowers. Newly opened flowers appear white while older flowers are singed brown. Cold weather has reduced pollination in tart cherries. It will be interesting to see what final fruit set is.

Plum bloom is ending. Growers need to protect against black knot if it ever rains.

Apples bloom continues. We are at full bloom in Berrien County, King bloom in Van Buren and first bloom in Allegan County. Warm conditions by the weekend will be good for fire blight blossom infection. No new apple scab infection periods, but it seems likely that many areas had infections last weekend during the rain and snow. Higher exposed areas probably dried off early but there were many areas that stayed wet long enough for an infection. European red mites have hatched. No reports of leafroller larvae feeding.

Pear bloom continues. Pear psylla eggs are hatching; we can expect a heavy hatch with warmer weather this week.

Small fruit
Blueberries are at pink bud. Leaves have unfolded. Early varieties have opened in Berrien County. Cold, dry weather has held back mummy berry. Growers should apply fungicides to control mummy berry if they get a freeze.

In grapes, the most advanced Concord shoots have one leaf out. Chardonnay buds are still at bud burst. No insects and no grape berry moth. There are reports of the most exposed flower clusters being frozen. This is probably due to the melting of snow by a cold north wind after the April 24 snow.

In strawberries, Earliglo is blooming and Allstar bloom has begun in central Berrien County. Many growers have been irrigating because of the dry soil.

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. Fall raspberries have emerged from the ground.

Bob Tritten

Soil moisture is adequate to above adequate at this time. Soil temperatures have remained cool in the lower 50s on a few of the warmer sunny days.

I’ve continued to evaluate our frost and freeze injury to flower and fruit buds. Over the last week I’ve continued to check apples, peaches, sweet cherries, tart cherries and plums. With the exception of some winter injury to peaches from cold temperatures last December, it appears that we’ve, had little to no cold damage to fruit buds so far this year. Things look to be in great shape, but lets wait to see what cold temperatures come tonight.

Tree fruit
Apples are still a few days ahead of normal with most being at pink to even a few early bloom in the southern part of the region. It has continued to be clear this year that apples growing close to either Lake Erie or Lake Huron are markedly behind more inland sites. For the most part, insect activity through the week has been slow to develop. A few new insects have been seen for the first time this week, including Oriental fruit moth, rosey apple aphid and apple rust mites. Most foliage on apples and other tree fruit is in tough shape with a fair amount of wind and cold damage. Redbanded leafroller trap catches are on the rise with most being in the 25 to 40 adults per trap range. However some trap catches have been as high as 100 per trap. Spotted tentiform leafminer trap catches are also on the rise. Most are in the 200 to 300 adults per trap per week range, however some have been a bit higher. No eggs of spotted tentiform leafminer have been seen. Rosy apple aphid hatch has occurred over the last week, however numbers are fairly low. Oriental fruit moth trap catch has begun to rise at several farms with a few as high as 25 per trap. Trap catch numbers were high enough for biofix, but after this week’s cold temperature I am going to reset my models with the next sustained trap catch. Apple rust mites were found for the first time last week. They are being reported here and there, but numbers are very low. No European red mite egg hatch has occurred. Apple grain aphids continue to be seen in several blocks, as do tarnished plant bug, which are a bit higher than I like to see for this time of the year. Plum curculio catches have been rather limited over the last week, primarily due to cold weather. Dogwood borer larvae have been seen in rootstocks and crotches of apples. There are several predators to report this week, including a fair amount of ladybugs, some Amblyseius fallacis mites and a few lacewing eggs.

While a few growers had experienced their first apple scab infection period from rain a few weeks ago on April 20, most had their first infection period during the weekend of April 22-24. Most growers covered for apple scab at that time. While a few have had an infection period since then that number remains fairly low. Spore discharge has been moderate during that major infection period on April 22-24. If we get bloom over the weekend, fire blight may be a concern.

Pears are mostly at white bud. While pear psylla adults have been flying over the last three weeks, last weekend and early this week I’m starting to see nymphs and egg laying. So, all stages of pear psylla are present at this time.

Peaches are in early bloom (around 20%) at most farms. Some of the early blossoms have petals that are a bit brown from cold temperatures this spring, but it appears that the flower is intact. Note last week’s report on some winter injury, which occurred in December 2004 at just a few farms. Peaches should be in full bloom later this week if temperatures permit.

Sweet cherries are mostly at petal fall. It has been amazing to see how long bloom has stayed on sweet cherries this year. Most of the bloom that remains on sweet cherry is tattered and in pretty tough shape.

Tart cherries are in full bloom. It is becoming more apparent that we have a limited crop this year. There is a fair amount of twig and bud death due to excessive amounts of cherry leaf spot last season.

Raspberries are at late bud break for summer raspberries and fall raspberries continue to emerge slowly from the ground. As we move along here it is becoming more and more apparent that there is a fair amount of winter kill damage on summer raspberry canes. Even fall raspberries have been slow to emerge from the ground this year.

Blueberries are at late pink bud. With a little warm temperatures over the weekend I would expect to see some bloom in blueberries by early next week. It appears that we have a nice crop of blueberries coming along this year.

Phil Schwallier
Amy Irish Brown
Carlos Garcia-Salazar

Various tree fruits are showing signs of nitrogen deficiency, most likely due to the environmental condition this spring. There shouldn’t be any long-term problems associated with it, but some foliar nutrients could be added in the tank to help green up the leaves – warmer weather will most likely do that as well all on its own.

So far this season, there has only been one light apple scab infection recorded on April 20. Lesions from this infection should show up over the next week or so if at all. According to GDD32 accumulations, about 50 to 60 percent of the ascospores mature at this time.

Green fruitworm, redbanded leafroller, spotted tentiform leafminer, and Oriental fruitworm adults started flying about two weeks ago, but traps have seen little activity over the past 10 days due to the cooler weather. Even though flight has started, there’s still time to get mating disruption pheromone out for Oriental fruitmoth. Codling moth mating disruption pheromone can go up at anytime as well – ideally at bloom in apple.

A few apple grain aphids and rosy apple aphids are being seen.

Powdery mildew could be a problem the weather changes to a warmer and dryer pattern as we enter the bloom stage. Growers will need to think about adding a mildewcide in the tank for powdery mildew in the next week or so for those varieties that are susceptible to it.

Mira Danilovich

Weather
It was cold, dry week. In the last ten days we hardly accumulated any degree-days. This has been a repeat performance of last year’s events for the same time period – very cold with clear skies and frosty nights! Hard frost hit the area on April 29 and 30. The absolute minimum temperatures for these two nights registered by our weather stations were 24.5°F in Ludington, 25.6°F in Hart and 26.4°F in Manistee/Bear Lake. These temperatures were well below the critical temperatures for the stage of bud development at the moment causing various degrees of wide spread damage. For the most part, tart cherries have very little damage; apples (depending on variety) have lost a more or less significant percentage of king bloom; peaches are showing more winter injury than the recent frost damage. For now, the crop outlook is still very good. Having said that, we need to take in consideration that we are still more than two weeks away from our average cut-off date for the last late spring frost event.

GDD totals Since March 1 as of Sunday, May 1

Tree fruit
Apples are from tight cluster – king pink to pink for the early bloomers. There was one light apple scab infection for Manistee/Bear Lake area that resulted from the wetting event on April 26-28. No scab infections reported in other parts of the district. Ascospore maturation guide indicates that there is 35 percent mature spores in Manistee/Bear Lake area, 30 percent mature spores in Ludington and 40 percent mature spores in Hart that are ready to be discharged under favorable wetting conditions. Scouts are reporting a “trap shutdown” since the onset of the cooler weather conditions. The warm-up forecasted for the end of the week will bring them out in full force. It would be important to control them before the bloom.

Pears are in white bud popcorn stage with just a few flowers starting to open.

Apricots are in shuck.

Sweet cherries are in various stages of bloom, full bloom to petal fall in the southern parts of the region to less than 50 percent bloom in the northern areas. Frost damaged cherry blossoms are subject to bacterial canker infection (Pseudomonas syringae). Look for symptoms of cherry blossom blight.

Tart cherries are in white bud to very early first bloom on sandy sites. No significant frost damage at this time.

Japanese plums are in bloom. European plums are in white bud to very early bloom (NY 6).

Peaches are in various stages of early bloom. There is some frost damage to the buds. Damage appears to be variety dependant. Quick checking of the buds indicates that there has been 34% damage in Baby gold 5 and 13% damage in Ark 9.

Growers are continuing with planting trees. The comments are that the ground is dry well below 10 inches.

Jim Nugent
Jim Bardenhagen
Nikki Rothwell

Weather
Cold weather persisted throughout last week. GDD42 accumulation slipped in one week from being the most advanced since 1990 to the sixth most advanced. Still, GDD accumulation remains well ahead of normal. Precipitation was much below normal in April. Inversion (conventional) frost events occurred this past week on the mornings of April 29 and 30. Highs for the week were only in the mid 40s to low 50s.

A wetting event was reported for Thursday, April 28 that resulted in a light scab infection period in Bear Lake and on Old Mission. As of today, May 3, we have an ongoing wetting event that has not yet resulted in disease infection. Due to cold weather, we have nothing to report on insects.

Jeff Andresen
Agricultural Meteorology
Geography

A deep upper air troughing feature across eastern North America has led to cold, cloudy weather for much of the past week. Nearly all forecast guidance suggests that this feature will finally shift eastward and out of the region during the next couple of days, leading to a gradual warming trend and possibly even to above normal temperatures by this weekend.

In the short term, high pressure centered over the Great Plains on Tuesday morning (May 3) will move eastward to the Great Lakes by Wednesday morning, leading to clearing skies, lighter winds and the likelihood of widespread frost and freezing temperatures across much of Michigan. Low temperatures will generally reach the 28-32°F range with a few mid 20s possible in sheltered, low-lying areas. After a frosty start Wednesday morning, look for mostly dry and warmer weather for the remainder of the workweek. Temperatures during the next several days will warm back to normal or even warmer than normal levels with highs ranging from the upper 50s north to the low 70s south and lows ranging from the mid-upper 20s far north to the upper 30s south.

In the medium range time frame, latest forecast guidance suggests that an upper air troughing pattern across the southwestern Unites States will become the major weather influence for the Upper Midwest for the next one to two weeks. With this feature expected to lead to southwesterly flow over large portions of the central United States, the latest NOAA Climate Prediction Center 6-10 day and 8-14 day outlooks (for May 8-12 and 10-16) both call for above normal temperatures state- and region-wide. Precipitation totals during the 6-10 day period are forecast to remain near normal statewide in the 6-10 day period and range from near normal in eastern and central sections of the state to above normal in the western Upper Peninsula in the 8-14 day time frame.