Vol. 20, No. 13, July 12, 2005

Tree fruit news
Post-harvest treatments available for stone fruit

Small fruit news

Annemiek Schilder and George Sundin
Plant Pathology

Fungi (molds) are the predominant organisms that cause storage rot of fruit crops. They often come in on the fruit from the field, after which they can grow, sporulate and spread through batches of stored fruit. Examples of these are Monilinia fructicola (brown rot) and Botrytis cinerea (gray mold). Yeasts may also rot fruit in storage, and tend to be more common where there is excessive moisture. Storage bins and areas may also become contaminated with mold spores. Penicillium, Aspergillus, and Rhizopus are fungi which occur in the field, but whose airborne spores easily contaminate storage areas.

As part of an integrated approach, a good disease control program during the season and timely harvesting will suppress fruit rot before harvest. Fungicide applications close to harvest will also reduce post-harvest rot. Several fungicides can be applied up to the day of harvest, e.g., Indar and Orbit, which are very effective against brown rot, and Elevate, which is effective against brown rot and gray mold. Cold storage and controlled-atmosphere storage will slow the growth of fungi and yeasts. Sorting out bad fruit and sanitation of sorting and storage areas can eliminate sources of infection. In addition, post-harvest treatments may be applied to fruit to delay or prevent rotting organisms from consuming the fruit in storage.

There are only a few post-harvest chemical options for stone fruit. However, efficacy data are too sparse to make specific recommendations for Michigan growers, so we will just list them for your information:

Scholar (fludioxonil) is a reduced-risk fungicide labeled for post-harvest treatment of stone fruit for protection against brown rot, Botrytis gray mold, Rhizopus rot and Gilbertella rot. It can be applied as a spray or dip. Only one application may be made. Treated fruit should not be stored in direct sunlight as this may degrade the chemical.

Captan (captan) is a broad-spectrum protectant fungicide that can be applied as a post-harvest dip or spray for control of various storage rots (e.g., Botrytis, Rhizopus). May leave visible residue on fruit.

Rovral (iprodione) is no longer labeled for post-harvest use.

Annemiek Schilder
Plant Pathology

As harvest is upon us, take note of the pre-harvest interval (PHI) for the various fungicides. Most fungicides that you would use at this time of the year have a 0-day PHI, but Topsin M has a 7-day PHI. Blueberries may benefit from applications of fungicides for fruit rot control close to the first harvest and even between harvests, since anthracnose rot incidence can increase greatly at the later harvests.

The main diseases of concern at this time of the year are fruit rots, such as anthracnose (orange wet spore blobs) and Alternaria fruit rot (green velvety layer of spores). Botrytis fruit rot (gray mold) is usually not a problem in Michigan, but can occur, especially in wet years. Anthracnose is often a problem in cultivars such as Bluecrop, Jersey and Rubel, while Alternaria fruit rot is more common in Bluecrop. Elliott is moderately resistant to anthracnose. While fruit rot is usually not visible until the berries ripen, it is prudent to assume you will have a fruit rot problem if you had problems last year. If the first blueberries are starting to show rot, fungicide sprays can limit new infections of neighboring healthy berries. Often, these berries look healthy at harvest, but start to rot soon after in the lugs while awaiting processing. Rot may be slowed down by refrigerated storage, but will resume on the supermarket shelves, lowering fruit quality. Applications close to the first harvest or between harvests can still be beneficial in preventing these late infections. In fact, an application between the first and second harvest may be recommended as well under high disease pressure.

The strobilurins (Abound, Cabrio, Pristine) are all highly effective against anthracnose, with Pristine having the most broad-spectrum activity since it contains two different active ingredients. However, it probably is also the most expensive of the three. Pristine will also have excellent activity against Phomopsis, while Cabrio has good and Abound fair activity against this disease. All have moderate to good activity against Alternaria fruit rot and become quickly rainfast since they are locally systemic. Switch (cyprodinil and fludioxonil) also has some systemic properties and provides simultaneous control of anthracnose, Alternaria and Botrytis fruit rots. Thus it may be a good choice if several fruit rots are a concern, e.g., in ‘Bluecrop.’ Aliette (fosetyl-Al) is a highly systemic fungicide that provides good control of anthracnose, Alternaria fruit rot and Phomopsis. Of course Topsin plus Captan can still be used, provided the 7-day PHI of Topsin is taken into consideration. While Topsin is very active against Phomopsis, Captan will do most of the work against anthracnose. Therefore, if anthracnose is the disease you wish to control, a Captan or Captec spray alone may suffice. Just remember that Captan is a protectant that can be washed off in heavy rain. As such, it also does not provide any post-infection activity.

Editor’s note: This article was submitted by Annemiek Schilder, Plant Pathology, but was modified from article by Joe Fiola, Univ. MD Cooperative Extension.

Even though we have not seen much if any downy mildew in grapes yet this year, this disease can still pose a significant threat, especially to newly planted vines. In mature vines, late-season disease development can lead to premature leaf drop and potential effects on brix and cold hardiness.

Maintain an open canopy.

First primary infections may occur about two to three weeks before bloom and continue through fruit set. In Michigan, the first symptoms of disease may appear much later, especially in dry years.

Be careful with young vines as downy mildew can defoliate and greatly decrease winter survival.

Be extra careful with young vines in grow tubes as the tubes provide excellent conditions for disease development.

It is important to prevent an epidemic from starting or nip it in the bud as soon as you can, which means frequent scouting to catch symptoms early.

Disease can spread rapidly: generation time may be as short as four to five days if weather is favorable.

Young clusters are highly susceptible to infection but become resistant with age (This is particularly an issue in some wine grape varieties, e.g., Chancellor.). We rarely see cluster infections in Niagara grapes.

Sprays from two to three weeks before bloom through four weeks after bloom provide thorough protection of clusters.

Annemiek Schilder and George Sundin
Plant Pathology

With a few exceptions, Alternaria fungi are considered opportunistic pathogens that are only able to grow on damaged or senescing plant tissues. This is also the case in fruit crops, where Alternaria occurs mostly on overripe or damaged fruit. Typically, as a fruit ripens, it loses most of its defense mechanisms and can be easily colonized by pathogens that it would otherwise be resistant to. Alternaria fruit rot can be recognized as a dark-green to black, velvety layer of fungus spores in soft or sunken areas of the fruit.

Alternaria fruit rot occurs on both sweet and tart cherries. This disease is typically a minor problem in orchards but can become important if fruit become overripe or are injured, for example by cracking. Large circular, slightly sunken lesions appear on fruit that eventually become flattened and wrinkled. These lesions become black in color because of sporulation of the fungus. Alternaria rot can also be a problem in storage again with infection initiated in injured fruit. Since this is typically a minor disease problem, there is little information on effective fungicides for control. The best way to control this disease is to avoid letting fruit become overripe on trees.

On blueberries, Alternaria fruit rot is a problem as berries ripen in some years. The cultivar Bluecrop appears to be particularly susceptible. In the field, the rot usually occurs at the calyx end. While in storage, it also colonizes the berries through the stem scar. If fruit is stored in the dark, the fungus does not produce many spores (since it needs light for that) and appears more fuzzy and grayish than on field-infected fruit.

Alternaria is a fungus that is ubiquitous in the environment, growing and sporulating on many types of plant debris, including decaying flower parts, leaves, etc. However, spore-trapping experiments in Michigan have shown that the spores are not abundant in blueberry fields until the berries start to ripen. Attempts to infect healthy blueberries with spores have been largely unsuccessful, leading researchers to believe that some damage (e.g., chemical or physical) to berries may be needed for infection. Best ways to control the disease are timely harvesting and rapid post-harvest cooling of fruit. Several fungicides are available with good to excellent activity against Alternaria, e.g., Aliette (fosetyl-Al) and Switch (fludioxonil and cyprodinil). Other products (e.g., Cabrio and Ziram) may also be effective. Applications are recommended beginning at the green fruit stage.

Eric Hanson
Horticulture

Editor’s note: This article was submitted by Mark Longstroth. It was published in previous years in the Fruit CAT Alert and is timely now.

It is time to start thinking about collecting tissue samples for analysis of plant nutrient levels. Tissue analysis is a valuable and usually under-utilized tool in fruit nutrition programs. Results provide a means of accurately identifying nutritional problems difficult to diagnose by soil testing or observing plant appearance. More importantly, growers can identify and correct potential nutrient shortages before growth or yield is affected.

Start dividing the farm into uniform sampling units, based on differences in soil types, past fertilization or management practices or varieties. If these factors are generally uniform, designate sampling units of up to 10 acres each. Farms on variable soils or history will require more samples to provide an accurate picture of the nutritional health over the farm. For routine monitoring, sample every two to four years. On larger farms, different blocks may be sampled during successive years on a two- to four-year cycle. If you are trying to diagnose a suspected nutritional problem, collect one sample from plants beginning to develop the problem and a second from nearby healthy plants.

The proper sampling time is between mid-July (southern Michigan) and mid-August (northern areas). Sample grapevines at veraison (fruit color change). Samples from orchards and blueberry, raspberry and strawberry plantings should consist of 50 to 100 leaves collected from different plants throughout the sampling area. Collect full-sized leaves from the middle of current-season shoots – not spur leaves. If leaves do not detach readily when pulled in a downward direction, wait a week or two and try again. Collect raspberry leaves only from primocanes (current season canes). For grapes, collect only the petioles (stems) of the most recently matured leaves. Concord leaves turn tan on the underside as they mature. Wash the tissues by swirling them in a dilute detergent solution for several seconds, then rinse briefly in tap water. Let samples air‑dry on a table top for a day or two before sending them to the lab - wet or moist leaves will rot during shipping.

Labs may offer analysis of single nutrients, such as N, but the cost of complete analyses is usually not that much more. The MSU Soil and Plant Nutrient Lab (517-355-0218) provides tissue analysis and an interpretive report. Send samples to the Soil and Plant Nutrient Lab, A84 PSSB, MSU, East Lansing, MI 48824.

Some other labs offering tissue analysis include A & L Great Lakes Laboratories in Ft Wayne IN (219-483-4759, http://www.algreatlakes.com/) and Brookside Labs in New Knoxville, OH (419-753-2448, http://www.blinc.com/).

The cost of tissue analysis discourages many growers from regularly using this service. I think the potential savings clearly justifies the cost. A single sample (analytical costs $20 to $25) represents up to 10 acres, so the cost monitoring is only $2 to $3 per acre. Often, the results indicate that fertilizers are not needed or rates can be reduced. Identifying a nutritional problem before yields or quality are impacted can save hundreds of dollars per acre.

John Wise
Trevor Nichols Research Complex

Bayer CropScience recently announced the registration of a new miticide, Envidor 2SC, for use in grapes, pome fruits and stone fruits. It is labeled for control of the European red mite, two-spotted spider mite, apple rust mite and pear rust mite.

The active ingredient, spirodiclofen, controls mites by inhibiting lipid synthesis and is active by contact to all life stages. Envidor has a novel mode of action and is not known to have risk of cross-resistance with other currently registered miticides. Envidor 2SC has a rate range of 16 to 18 fluid oz per acre, seven day pre-harvest interval for pome and stone fruits (14 days in grapes), and is restricted to one application per acre per season for all labeled fruit crops.

Craig Anderson
Michigan Farm Bureau

Requirements depend on head rack rating
1)    If rated at 80 percent of the weight of tanks being hauled – use one strap per tier.

2)    If not rated at 80 percent of the weight of tank being hauled – use two straps per tier.

§      Stake rack doesn’t meet 80 percent
§      Burst rating is based on slamming on brakes, not an accident

3)    If have an angle iron rack to haul tanks on, only need one strap on each side front to back.

Straps must be rated at least 50 percent of weight of tanks being strapped; i.e. two tanks in tier equal 4,000 lb need strap rated at 2,000 lbs. New two-inch straps are rated at 3,300 lbs.

Rack sides need to use bolts of grade 5 to 8 (10,000 lb.). It needs to hold 80 percent of gross load; i.e. 12,800 lb. for eight tanks.

We will be having a research field day at the Trevor Nichols Research Complex on Tuesday, September 27 From 1:00 PM to 5:00 PM. The field day will focus on insect and disease research and efficacy trials that were carried out this season at the TNRC by Larry Gut, Rufus Isaacs, Mark Whalon, Annemiek Schilder, David Epstein and John Wise. The TNRC is located at 6237 124th Ave. in Fennville, Michigan.

See our Web page for directions: http://www.maes.msu.edu/tnrc/

Regional reports

1 – Southwest

Mark Longstroth
Bill Shane
Al Gaus

Weather
The last two weeks were warm with highs in the 80s and 90s and lows about 60. Strong thunderstorms moved across the area July 4 with some general rain following. This was the only significant precipitation. Areas close to the lake received one or two tenths of an inch while inland areas received a half or more. Drought stress symptoms are widespread and winter injured plants are collapsing. Soil temperatures are about 75. This week’s forecast is for continued warm weather with highs in the 90s and lows about 70.

Tree fruit
We are catching picture wing fruit flies such as apple maggot, blueberry maggot and cherry fruit flies. Japanese beetles are increasing. These pests emerge from the soil, and we expect their numbers to increase following any significant rain. Potato leafhoppers have been found. The second generation of Oriental fruit moth is flying. Redbanded leafroller trap catches increased sharply. Codling moth and obliquebanded leafroller trap catches are declining. Aphid and mite numbers are building in many crops.

Apricot harvest is underway with Goldcot being harvested in Berrien County. Fruit are relatively clear of bacterial spot due to dry conditions.

Early peach harvest has begun. PF1s are being harvested in Berrien County. With current dry conditions, sugar content of peaches is high and flavor very good. We are past peak egg laying for the second generation of Oriental fruit moth the end of egg hatch should be about 2100 to 2200 GDD45. We are picking up about 35 GGD per day, so egg hatch should last another 10 to 14 days. Trunk sprays for peach tree borer are applied in July. Two-spotted spider mites are building and green peach aphids numbers are increasing.

Cherry harvest is ending. A few late season sweet cherry varieties such as Sweetheart and some Balatonâ tart cherries remain to be picked. There were no reports of brown rot. Cherry fruit flies are being trapped in abandoned cherry plantings. Very few symptoms of cherry leaf spot have been found. Cherry growers should watching the weather and protecting against cherry leaf spot if rain seems likely.

In plums, white apple leafhopper injury can be found. Second generation eggs will begin to hatch soon so growers should be scouting for nymphs. Brown rot has shown up on fruit damaged by insects.

Apple fruit are about two inches in diameter. We are catching apple maggot adults. See the article on apple maggot monitoring and control in the June 28 Fruit CAT Alert. Fire blight has appeared in some new locations but generally is confined to older orchards with a history of the disease. Green apple aphids are becoming common and can spread the infection to healthy trees. Codling moth trap catches are low. The first generation of codling moth should end at about 1000 GDD after biofix. We biofixed for codling moth on May 20 at 334 GDD50. We are now at 1312 GDDs, almost 1000 GDD after biofix. The second generation of codling moth begins to emerge 1200-1250 GDD after biofix. We are picking up about 30 GDD a day so we can expect an increase in adult trap catch next week. Obliquebanded leafroller biofix was June 6 at 935 GDD42. We are at 2000 GDD42 and the end of egg hatch is 1000 GDD after biofix, so egg hatch should end this week. See the article on summer leafroller control in the June 21 Fruit CAT Alert. We are finding leafroller larvae in abandoned orchards. The second generation of Oriental fruit moth is laying eggs. European red mite numbers are increasing, and this hot weather may make them explode. The treatment threshold for European red mite from mid-July to mid-August is 7.5 mites per leaf. The mines of the second generation of spotted tentiform leafminer are showing up. White apple leafhopper eggs will begin to hatch soon so growers should be scouting for nymphs. Examine 50 leaves from 10 different trees and treat if the average is more than one nymph per leaf.

In pears, European red mites are turning pear leaves black. Pear psylla numbers are bu

Bob Tritten

Weather
Dry and hot weather persisted over the last two weeks with high temperatures in the 90s and nighttime lows in the low 70s. Degree day totals have continued to roll along rapidly. Our season is back to normal in terms of degree days and a bit ahead of normal in terms of growth stages. Some areas received around a half-inch of rain over July 4 and late last week, however many have not had significant rain for three to four weeks. Hail was reported with several of the thundershowers that have moved through. Our soils remain very dry. Fruit growers are irrigating on a regular basis, particularly in Lenawee and Monroe counties.

Strawberry and sweet cherry harvest have pretty well been wrapped up, tart cherries and raspberries are being harvested and blueberries are just beginning to be picked.

Tree fruit
Apples continue to size very well with most being around 1.75 to 2 inches. The big news of the week is high trap catches of apple maggot. People have reported trap catches as high as 30 on yellow boards and 10 on a red sphere traps. I started to hear reports of apple maggot catch in small apple blocks on June 29 and started catching them in abandoned apple blocks on July 1. The first apple maggot catch in commercial orchards was late last week on July 7 or 8. These unusually high and early trap catches are a bit puzzling. I encourage growers to do frequent scouting in their orchard to determine first catch and levels. Codling moth trap catches are generally in the four to eight range in most commercial blocks and near zero in mating disruption blocks. I stand corrected in my last report stating that codling moth is currently between generations. This second flight may be the end of the first generation or what has been referred to of late as the “B generation.” Time will tell in the next week or so. Aphid populations have generally dropped off dramatically over the last two weeks with predators doing a good job. Most apple growers have applied a pesticide to control them. Obliquebanded leafroller trap catches are high with an average number of four to nine per trap. Oriental fruit moth trap catches continue to be low. Potato leafhopper burn is just starting to be seen in a few scattered apple blocks. I would expect higher numbers fairly quickly. European red mite numbers have reached threshold levels in small areas of many blocks. There appears to be a fair amount of adults with lesser amounts of mite eggs. Apple rust mite numbers are also very high. Two-spotted spider mite populations continue to build in most apple blocks. San Jose scale is now being seen on fruit. I encourage growers to continue to monitor blocks closely that have had high scale populations in previous seasons. We continue to see a good number of predators. Fall webworm larvae are starting to be seen. Assassin bugs are the only new predator report this week. I continue to see good numbers of ladybird beetles in all stages, Stethorus punctum, minute pirate bugs, big-eyed bug, syrphid fly, solider bug, six-spotted thrips, velvet mites and Amblyseius fallacies.

Apple scab appears to be under control in most blocks. It is possible to find scab in almost every block of apples. Fire blight shoot strikes continue to be seen more prominently, however I found very few new strikes in the last two weeks. Cedar apple rust is starting to show in several apple blocks. Necrotic leaf blotch leaf yellowing and drop is starting to be seen in Golden Delicious.

Pears continue to size well with most being around 1.5 to 1.75 inches in diameter. Pear psylla seems to be under control in most blocks. Aphid populations in pears have declined over the last week. We are starting to see a light to moderate crop of pears.

Peaches continue to size quite nicely with most being in the range of 1.75 to two inches in diameter. Bacterial spot infected foliage continues to turn yellow and drop to the orchard floor. X-disease continues to show up in peaches, also causing premature leaf yellowing and drop. Two-spotted spider mites continue to be seen at fairly low levels, however their numbers are building and growers should scout for them carefully. Oriental fruit moth numbers have been fairly low in peaches over the last week. Some peach varieties are starting to turn color in anticipation of harvest in a week to 10 days. I’m starting to see some split pit in early peach varieties. Many varieties of early peaches that have a light crop have a wide range of fruit sizes at this time. Lastly on peaches, I am seeing a bumpy, warty growth that is generally on the suture of the peach. It is possible that this suture mark may be the result of peach leaf curl, however I’m not seeing any infected foliage in these blocks. Stayed tuned for details in the next issue of the Fruit CAT Alert.

Sweet cherry harvest is pretty well wrapped up. Most folks had a light to moderate crop of sweet cherries with the exception of Romeo, which has a good crop. Last week I also saw very high populations of cherry fruit fly being caught on yellow sticky boards. There were even some reports of cherry fruit fly larvae being found in fruit. Next year earlier scouting and monitoring of the cherry fruit fly needs to take place in order to determine population levels. It seems as if last season there was an increase in trap catch and in infected fruit, this year that trend has continued. Birds were a serious problem in sweet cherries. I encourage growers to consider making a post harvest fungicide application to control cherry leaf spot.

Tart cherry harvest continues with most growers being about 80 to 90 percent complete. Tart cherry has also suffered from leaf spot infected foliage drop over the last couple years. I encourage growers to make a post harvest fungicide application here as well.

Plums continue to size fairly well with most being around 1 to 1.25 inches in diameter. No new pest problems to report.

Raspberry harvest is now under way for most midseason summer red raspberries, black and purple raspberries. I’m seeing a fairly good crop despite the winter injury, which occurred last year. No major pest problems to report with an exception of high bird populations. Fall red raspberry growth continues with most being around 2 to 2.5 feet in height. I’m starting to see some potato leafhopper burn in fall red raspberries.

Blueberry harvest is just now getting under way for early varieties. While picking is light, it appears that we have an excellent crop of blueberries coming along. I encourage growers to continue to monitor blueberry maggot populations very closely as adults have been caught in southwest Michigan and at one blueberry farm here in southeast Michigan. Remember that it is a close relative of apple maggot, if not the same pest, and we are seeing very high populations of apple maggot this year. Birds are feeding on blueberries.

Grapes are sizing quite nicely with Concord having about 2.5 feet of growth.

Phil Schwallier
Amy Irish Brown
Carlos Garcia-Salazar

We continue to see powdery mildew in apple and other fruit crops and the forecasted weather will continue to advance mildew.

Codling moth trap numbers were down the last two weeks, but have shown a slight increase over this past weekend, which may indicate that second generation is starting to fly. Controls for second generation will need to go on in another 7 to 10 days depending on the material being used and the trap numbers in individual blocks. Obliquebanded leafroller flight has declined to zeros. Larvae are very easy to find and are quite high in some blocks. Controls should be continued for another week or two for leafrollers.

There are many European red mite eggs present in some blocks. With the hot and dry weather predicted over the next week, mites could explode, so scout blocks closely and keep track of mites.

A few apple maggots were caught over the weekend, indicating that they are ready to emerge – expect a significant emergence if we get some heavy rains to drive them out of the soil.

In most places around West Central Michigan the harvest of early blueberry varieties has continued. However, the variety Jersey is in the fruit coloring stage and Elliott still is in late green fruit stage. Weather conditions in the region remain dry and hot. In the last 12 days the amount of precipitation registered in the area has been around a half inch, and approximately 1.5 inches accumulated since June 1. This amount of precipitation has not been enough to supply the blueberry water consumption needs. At the same time, daily temperatures have remained in the upper 80s and 90s increasing the stress on blueberry fields. A major consequence of these conditions are an outbreak of Phomopsis twig blight and canker in most blueberry fields in West Central Michigan, and a much smaller crop than the estimated at the end of the bloom period. Based on the conditions observed in their own fields, crop estimates by some growers indicate that this year’s harvest may be 20 percent less than the previous year. In 2004, the blueberry production was 72 million pounds.

 Regarding insect pests, the cherry fruitworm flight is over and the cranberry fruitworm is coming to an end in most fields. At this time, the blueberry maggot and Japanese beetle are the predominant insect pest problems in blueberries. And as in previous years, there is a chance for finding a mix of cherry maggot and blueberry maggot adults in yellow sticky traps. Thus, care needs to be taken when inspecting the traps to correctly distinguish the blueberry maggot from the cherry maggot flies. Before initiating pest control actions against the blueberry maggot, growers having problems in distinguishing the blueberry maggot from other flies should request the assistance of the local Extension educator or other pest consultants available in the area.

Mira Danilovich

Sweet cherry harvest is underway. Quality is excellent! Tart cherry harvest started more than a week ago. Fruit is looking excellent. Blocks that are still more than a week away from harvest need to be protected from the cherry fruit flies. Scouts are finding higher numbers of cherry fruit flies in their traps. There was couple of cherry leaf spot infection periods as a result of the rains at the beginning of the month. There are some symptoms of the cherry leaf spot, but overall, the trees are looking very good with a full “head” of leaves.

Apples are sizing well. We are finding some scab lesions on the fruit, but it is not in alarmingly high numbers. Most of the blocks have had very good primary scab control. Powdery mildew has been more common throughout the area as a result of increased humidity. We are finding symptoms of fire blight scattered in parts of the district. There are reports of nectria twig blight in Romes and Spys.

Codling moth numbers have dropped though we had a second “spike” towards the tail end of the first generation. The codling moth egg hatch is expected to be over by the end of this week. In a few blocks, we are starting to find small larvae in the fruit. Blocks need to be covered. Scouts are reporting finding potato leafhoppers. Applying the model for the obliquebanded leafroller egg hatch appears to have started. We are finding some very small larvae scattered throughout the area. Second generation spotted tentiform leafminers are out and getting stronger. European red mites and some two-spotted mites have been reported in large numbers in a few blocks. Green apple aphids are being found in low numbers throughout the district. There are increased numbers of various stages of ladybugs, lacewings, syrphid flies and various predatory mites.

Peaches are looking good. We are finding a touch of powdery mildew in some blocks, but nothing major. Green peach aphids are present in relatively high numbers. Lesser peachtree borer and greater peachtree borer numbers have decreased significantly since last week due to spray applications.

Jim Nugent
Jim Bardenhagen
Duke Elsner
Nikki Rothwell

Cherry fruit is not sizing well. Hot conditions have made it difficult at times to find conditions safe for ethephon application. Ethephon is very active in hot weather. Some tree damage is evident caused by ethephon application during a period of high heat. Sweet cherries seem to be particularly hard hit by the drought as they are carrying an exceptionally heavy crop load.

With the continuing dry weather, we have seen no cherry leaf spot infection. With dry pre-harvest weather, American brown rot has been spotted in a few isolated locales. We have reported brown rot in organic blocks and areas where the fruit is extremely heavy and spray was not able to penetrate the clusters. However, this disease has also been detected in orchards where we had inoculum presence from a wetter period earlier in the season. If brown rot inoculum is present in the orchard, consider slowing the sprayer for better fungicide coverage. We are still seeing powdery mildew in tart cherries. American plum borers are at 17 borers per trap. Lesser peachtree borer numbers are very low this week, but greater peach tree borers have increased tremendously to 17.6 borers per trap. Two-spotted spider mites are increasing in untreated cherry blocks, and some numbers suggest an eightfold rise from the previous week. Cherry fruit fly seems to be a more complex pest than normal this season due to its unpredictable behavior. We have captured many flies in the unsprayed entomology block, but we have only seen a handful of flies in commercial settings. Reports of cherry fruit fly catches increased slightly after the July 4 rain and only in high-pressure blocks. With little or no rain predicted in the coming week, we expect few cherry fruit fly to emerge under these droughty conditions. We are recommending that growers in high-pressure areas remain protected for the weeks leading up to harvest. Blocks that have traditionally had little cherry fruit fly activity may not need to be as diligent as usual. However, if a grower is not trapping at their orchard, preventative applications are needed.

Jeff Andresen
Agricultural Meteorology
Geography

Upper air ridging and surface high pressure across the Great Lakes region has persisted for much of the past several weeks, leading to abnormally hot and dry weather in Michigan. Unfortunately for those areas in need of rain, this pattern is expected to continue for much of the next week and possibly longer.

Seasonal precipitation deficits (since April 1) currently range from about two inches in east central sections of the state to more than eight inches in some spots across southwestern Lower Michigan. Normal rainfall for this time frame is generally in the 9.5 to 11.5 inch range from east to west across the state.

In the short term forecast, the remnants of Hurricane Dennis will come close to southern areas of the state as it drifts slowly eastward through the Ohio Valley late Tuesday through early Thursday, but given dry air in place under the ridge, rainfall will likely be limited to the southern half of the Lower Peninsula and remain scattered in areal coverage with totals less than 0.25 inches where rain does fall. The next chance for any significant rainfall will likely be late Sunday or Monday, when a cool front is expected to pass through the region. Temperatures will remain at much above normal levels for the next several days with daytime highs ranging from the mid- to upper 80s to the low 90s. Low temperatures will range from the mid- to upper 60s north to the low 70s south.

The NOAA Climate Prediction Center 6-10 day (for July 17-21) and 8-14 day (covering July 19-25) outlooks both call for broad upper air ridging across western sections of the country with weak troughing across the east and a continuation of drier than normal weather expected in Michigan for both forecast periods. Mean temperatures are forecast to remain above normal statewide during the 6-10 day time frame and range from near normal levels in northwestern sections of the state to above normal in the southeast during the 8-14 day period. It is important to note that forecaster confidence in these time frames is lower than normal due to disagreement among some of the individual forecast model used to create the outlooks.