Regional reports on Michigan fruit – June 5, 2012

MSU Extension educators’ pest and fruit updates for Michigan.

This week’s regional reports:

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

Southwest Michigan


Last week was cool. A cold front dropped high temperatures on Wednesday (May 30) and Thursday (June 1) into the 50s, and steady rain fell both days. Precipitation totals varied from 0.5 to 1.5 inches of rain. This rain was an infection event for most diseases with wetting periods of 30 to 60 hours and average temperatures between 48 and 50 degrees Fahrenheit. Soils are moist.

Weather for this week is forecast to be warmer with highs around 80. There is little chance of rain in the upcoming week. The potential evapotranspiration next week should be about 0.2 inches of water a day. Our growing degree day accumulations are currently about two weeks ahead of an average year. Southern sites are only about five days ahead of northern sites in the region.

Southwest Michigan growing degree day totals from January 1 through June 3


GDD 42

GDD 45

GDD 50





Trevor Nichols




Small fruit

Fruit are developing quickly and the season is about three weeks early. Insects are early, too. Japanese beetles should emerge soon. Rose chafers usually come out in early June, but we have not seen many this spring.

Strawberry harvest continues. Cooler weather has slowed down growth. Strawberries are normally harvested in late June and the heat causes the fruit to ripen rapidly and later pickings get small quickly. Fruit size and quality are excellent. Tarnished plant bugs and slugs have been reported. Common leafspot symptoms are showing up in some plantings.

Brambles are at the green fruit stage and harvest is about two weeks away. Insect pests to scout for include raspberry sawflies, leafrollers and raspberry cane girdlers. At the Southwest Michigan Research and Education Center (SWMREC), the cultivar ‘Black Butte’ has fruit 0.5 to 1 inch long and ‘Apache’ has 0.5-inch fruit. Potato leafhopper numbers have been increasing in the fall raspberry plantings and seem to be more severe in the variety Polka.

raspberry fruit
Green-red raspberry fruits will ripen in a few weeks.

In grapes, Concord and Niagara bloom is underway. We will soon be at berry shatter. Growers should be monitoring vineyards for rose chafers, which can cause considerable damage to flowers and developing berries.

Wine grape bloom began last week. Leaves with phomopsis and black rot symptoms can be found in unsprayed vineyards. Although we have not yet detected powdery mildew in vineyards we scout, growers with susceptible varieties should be watching for this disease. Grape berry moth trap catches increased sharply last week. We set biofix for grape berry moth in southern Berrien County on May 18 and northern Berrien and Van Buren counties on May 21.

In blueberries, initial fruit growth has slowed and the second phase of growth by cell division should begin soon. Many growers have complained of fruit drop, apparently of freeze damaged fruit. Many of the small damaged fruit are black inside, suggesting that the cold had traveled down the style into the pistil and killed the ovaries. Fruit set is light in many fields. Yields appear to be very variable across the region with large differences in the same variety, depending on the location. Recent rains have recharged soil moisture, but growers should be irrigating as they would in early July when warm weather returns.

Growers with overhead irrigation should apply controls for anthracnose during the green fruit stage. With the approach of harvest, traps to monitor blueberry maggots and spotted winged Drosophila should be deployed. For more scouting information, see the Blueberry Insect Scouting Report for May 28-June 3, 2012.

Cranberry bloom continues.

Tree fruit

San Jose scale crawlers are active. Growers needing to manage this pest should have appropriate controls out now. Useful plant phenological indicators for San Jose scale crawlers include northern catalpa and Japanese tree lilac at full to late bloom. If you have either of these trees near your orchards, they can be used to provide a very visual reminder of when to look for San Jose scale crawlers. Plum curculio stings are common in orchards with fruit and multiple stings from egglaying are common.

Apricots are colored and firm. Harvest should begin this weekend.

Peach fruit are 1.5 inches in diameter. Oriental fruit moth catches continued to decline, marking the end of the first generation. Flagging of terminal ends by burrowing larvae is becoming easy to find. Rusty spot is very common on fruit of certain varieties and appears as white, circular areas that will eventually turn brown.

Sweet cherry harvest is underway and birds are feeding on the fruit.

Tart cherry fruit are colored and growers with fruit are wondering if they have enough to harvest. Harvest should begin in about two weeks. Last week’s rain was a heavy cherry leaf spot infection.

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

Apple fruits are 1.25 to 1.5 inches in diameter and June drop is ending. The spring freezes have caused russeting and distortion of many fruit. Codling moth biofix was set as May 7. Obliquebanded leafroller biofix was set as May 19.

Fire blight symptoms are relatively scarce in the area in part due to dry conditions. Most sites showing fire blight symptoms have overwintering cankers. Primary apple scab season is over. Growers should check their blocks to see if leaf scab symptoms are present. Powdery mildew symptoms are easy to find on susceptible varieties and grower should consider control to prevent loss of fruit buds in the winter.

plum curculio
You can see 13 of the 24 individual plum curculio
egglaying scars on this one apple.

Pear fruit are about an inch in diameter on Harrow Sweet. Pear psylla is present in low numbers.

Don’t forget to join us for our upcoming southwest Michigan meetings. For a list of upcoming meetings and more information, see Upcoming fruit meetings in southwest Michigan.

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Southeast Michigan – Bob Tritten, Michigan State University Extension

Southeast Michigan
Southeast Michigan


Cooler temperatures have been welcomed by strawberry growers across the region, where harvest continues at most farms. Rain late last week was also welcomed by all fruit growers, as most farms received between 0.5 and 1 inch of precipitation. However, soils at most fruit farms remain dry and growers continue to irrigate newly planted fruit crops.

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

East Michigan Growing Degree Day Totals for March 1 to June 4





Commerce (Oakland)




Emmett (St Clair)




Flint (Genesee)




Lapeer (Lapeer)




Petersburg (Monroe)




Pigeon (Huron)




Romeo (Macomb)




Tree fruits

Apples continue to be hard to find in most of the region; the few that I was able to find yesterday (June 4) are at 1.125 inches in diameter and all were heavily damaged by plum curculio. Most apple trees have between 10 and 15 inches of new growth, with some terminals reaching 18 inches of new growth. Growers who have used Apogee this season (most have made two applications) are now seeing that it, indeed, is having an impact on reducing terminal limb growth. Growers using Apogee are encouraged to leave some check or untreated trees in order to tell if it is helping to reduce terminal growth.

Overall, insect pressure remains low this season, with the exception of continued high codling moth trap catches at many farms. Even mating disruption blocks have had high trap catches. With recent, warmer, nighttime temperatures, now is a good time to control codling moth.

San Jose scale crawlers are just starting to be seen at several farms, so we are approaching a key time to control them. Plum curculio fruit stinging continues to be seen where there are apples, especially in orchards that are not being sprayed. Aphid populations have been reduced by predators in the last week.

In rain late last week and Saturday (June 2), we continued to catch a few apple scab spores at both of our apple scab spore release monitoring stations, so we are not at the end of primary apple season. However, I believe that we are at the end of primary at fruit farms where rain has been more prevalent in the past month. Most of our Enviro-weather stations had two or three apple scab wetting events in the past week, with most having one or two infection periods.

I am seeing more apple blocks with the start of sheet scab. Powdery mildew-infected terminal branches and individual leaves have become much more evident in the past week; some varieties are heavily infected and some terminal limbs are starting to die from this disease. I am encouraging apple growers to keep a close eye on powdery mildew infections in valuable and susceptible varieties, even in blocks with no fruit. Some growers without a crop are considering sulfur applications to help control it. It is hard on foliage, however.

Cedar apple rust spots are just starting to be seen in apples. Most growers are seeing frog eye or black rot leaf symptoms in several apple blocks, and some black rot-infected limbs are now starting to flag or dieback. Sooty blotch and fly speck symptoms are just starting to be seen in a few apple blocks in the Petersburg, Mich., area, where the threshold of 240 hours of wetting has been reached.

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

Peach leaves where there is no crop are looking more normal in appearance. Oriental fruit moth trap catch remains low. Green peach aphid populations have been reduced by predators in the past week at most farms. For trees with no crop, this year is a good opportunity to do some major pruning to reduce tree height. Be careful not to remove more than a quarter of the leaf surface.

Sweet and tart cherry leaf curling is extensive from black cherry aphid, especially in sweet cherries. Predator populations are building quickly to control them. Cherry leaf spot disease needs to be controlled in blocks that have no crop and maybe cherry fruit fly in problem blocks.

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

Small fruits

Strawberry harvest continues at most farms in the southern and mid-area of the region, with excellent demand from consumers. Our season continues to be almost two weeks ahead of normal with most farms opening earlier than ever before. I continue to see evidence that slug populations are building in strawberries. Growers need to do a good job of scouting for them. Growers are finding more fruit damage from earlier tarnished plant bug feeding than in most years.

Raspberry bloom and fruit set continues for summer fruiting types and new canes of fall bearing types have 16 to 20 inches of new growth. Summer bearing raspberries had a great deal of tip burn or dieback from the April freeze events. Now is the time to set spotted wing Drosophila traps.

Blueberries are 12 to 14 mm in size for most varieties with fruit coloring on early varieties. Some early fruit drop continues on freeze-damaged varieties. Now is the time to set spotted wing Drosophila traps.

Grapeflower clusters are very close to bloom. Canes that were damaged in the many freezes appear to have been killed. Now is the time to prune these damaged canes.

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

Grand Rapids Area
Grand Rapids Area

Crop update

Growers are carefully assessing their blocks now to determine whether they have enough harvestable fruit to continue maintaining. Most apples are at about 25 mm in size. We did not see a significant “June drop” this year as was expected with the very light crop.

Horticultural tasks to consider

Some areas received rain again over the weekend (June 2-3), but it continues to be dryer than normal for this early in June. Irrigation is highly recommended in newly planted trees. A good rule of thumb for newly planted trees is 10 gallons of water per tree per week. It is best if you can break that up into two applications over a week’s time, but more important that you get it applied, even if it is only once per week.

Pruning and training should include feathering newly planted trees and one-year-old trees. The weather outlook indicates that this is a good week to get this done as there should be little risk for fire blight situations.

Fire blight update

We’ve moved past all risk for blossom blight for the year. However, trauma blight is something you should keep in the back of your mind. If we get weather with hail or high winds that tear foliage, preventative fire blight sprays will be needed. The risk for trauma blight remains until terminal bud set which is normally in mid-July, but could be delayed this year with little fruit to hold back vegetative growth.

Apple scab

There were no additional spores on the rods with the rains over the weekend in the general Sparta, Mich., area. This has been a rather light apple scab year overall, with some areas having only four infection periods and others having six to seven. It’s not unusual to have an average of eight or nine infection periods during primary scab season. Very little scab can be found in blocks that were covered well prior to the freeze event in late April and through the first weeks of May. Unsprayed apples are starting to defoliate from scab infections, so your fungicide sprays were not wasted.

Powdery mildew

As is typical, in years with lighter scab pressure we tend to see more powdery mildew. Fungicides get stretched out in years with fewer rain events for scab, and mildew does not need free moisture to grow – high humidity and high temperatures are enough. We’ve had bouts of favorable mildew conditions along with higher levels of inoculum from 2011 and a mild winter. All add up to the perfect storm for higher mildew levels in apples for 2012. Every passing week it is easier to see mildewed blocks just driving by.

Tree fruit insects

Obliquebanded leafrollers. Adult flight has been steady for the last week. A regional biofix was set for May 26. We have accumulated 169 degree days base 42 since then. Peak moth flight is predicted for later this week, with early start of egg hatch predicted for June 14 or 15. In blocks with viable fruits, cover sprays will be necessary by June 15 where pressure was high in 2011. In low pressure blocks, you could scout for larvae and then manage them – this usually falls about a week after the early egg hatch prediction based on the degree day model or around June 22.

Codling moth. We have accumulated 356 DD50 since the May 3 biofix on the Ridge, indicating that egg hatch should be underway from that date. Some sites may have set a later biofix than my regional May 3 date. I’ve heard May 18 or 19 as dates for specific site biofix. This is a difference of 120 DD50 accumulated, so you need to adjust your management accordingly. In blocks with little crop this year, you should consider using delayed timings for applying needed management sprays for first generation codling moth – at least 350 DD50 post-biofix rather than the traditional 250 DD50 for egg hatch.

Oriental fruit moth. A regional biofix was set for oriental fruit moth on April 15 and we’ve accumulated 610 DD45 since then. Egg hatch should be nearly over for first generation oriental fruit moth. We are right in between first and second generation and cover sprays will not be needed again in stone fruits for a few weeks.

Borers. American plum borer and lesser peach tree borer flight have begun. Trunk sprays can be started in stone fruits now. Dogwood borer frass can be seen in M9 clonal rootstocks – no adult flight is reported yet and it should begin any day. Timing for dogwood borer frass trunk sprays is at peak adult flight, usually around July 4. It could be earlier this year.

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

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

Grand Rapids Area
Grand Rapids Area

Weather conditions during the last seven days have been without major incidents for fruit production. Daily maximum temperatures have been on average 68 degrees Fahrenheit with a minimum temperature of 48 degrees Fahrenheit. There have been some rain showers that produced an accumulation of 0.68 to 1 inch. So far, degree days accumulated since March 1 are 710 DD (base 50) and 1,222 DD (base 42).

Strawberry harvest is in full swing in the Grand Rapids, Mich., area and the low temperatures from the past seven days are helping to bring plenty of customers to U-picks. The harvest is good; berries harvested are of good size, color and flavor. Major problems so far are related to insect leaf feeders in tender plants and some sap beetles in mature fruits.

Because of the earlier reports of spotted wing Drosophila flies on strawberry fields around Allegan County, we recommend to start monitoring this insect in strawberry fields that are harvesting at this time. (See MSU Extension Bulletin E-3104, Spotted Wing Drosophila: A new invasive pest of Michigan fruit crops, for information on monitoring.) For adult flies, the most effective monitoring devise is the current trap loaded with a mixture of sugar and yeast. For larvae, the fruit-dunk flotation method in a solution of water and sugar is a good detection method. If you need assistance with the procedure, please contact Carlos Garcia at 616-260-0671.

Strawberry growers interested in learning how to monitor and manage spotted wing Drosophila are welcome to join our June 12 meeting in Fennville, Mich. For more information, see Spotted wing Drosophila biology and management workshop held June 12.

Raspberries are blooming and so far the main problems are associated with leaf feeders such as the raspberry sawfly.

Regarding blueberries, the conditions of the crop are good despite early problems with spring frost damage. Currently, all varieties are in the green fruit stage with different degrees of growth.

Insect problems in blueberries are few, with the exception of the common pest problems, fruitworms. At this time, the cranberry fruitworm flight has continued at a low intensity and the cherry fruitworm adult emergence is coming to an end.

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

Northwest Michigan

Weather report

The big weather news in northwest Michigan, as well as most of the state, was the cold and rainy days on June 1-2. Daytime temperatures from May 30 to June 2 only rose to the mid-50s, which seemed very cool considering we hit the high 80s on May 28. Temperature swings have been extreme throughout the season thus far. Although frost was forecasted in the state, no fruit growing areas recorded any temperatures below freezing. Degree day accumulations are still well ahead of our 20-plus-year average: 1007 GDD base 42 and 550 GDD base 50; our average accumulations are 700 GDD base 42 and 357 GDD base 50. Rainfall was variable among the different Enviro-weather stations, and the Northwest Michigan Horticultural Research Station (NWMHRC) recorded 1.49 inches on June 1 and 0.69 inches on June 2. The rainfall total for NWMHRC is 12.44 inches since March 1.

Crop report

With the recent rains and small crop on most tree fruits, fruit is sizing. Sweet cherries are about 15 mm, and fruit is straw-colored with a bit of reddish tint starting to show. Many growers are considering harvesting sweet cherries in blocks with adequate fruit. Bacterial canker has taken its toll on trees throughout the region, and fruit has been lost to this disease this season. There are very few tart cherries to report.

Apples are quickly passing the thinning window as the fruit is about 20 mm for most varieties. Many growers are opting to hand thin this year to minimize the potential of over-thinning in a year with few fruit. Some varieties look better than others: Honeycrisp, Gala, Jonathans and Golden Delicious blocks have a small but harvestable crop load. MacIntosh, Red Delicious and Northern Spy orchards have few fruit. Strawberry harvest will be getting underway this week, and the crop looks great heading into the season.

Pest report

Cherries. With the continued rainfall, the region experienced a number of cherry leaf spot infection periods with the symptoms from earlier infections already visible around the region. These early infections have not caused the leaves to yellow, but pose a significant obstacle to retaining leaves going into this fall. As temperatures warm, the infection will become more obvious as leaves yellow and drop from the canopy. Leaf spot currently appears as red-purple lesions on the upper leaf surface. If you flip the leaf over, there is often a white dot in the middle of the lesion; these are the secondary spores. Cherry leaf spot lesions have also begun to drop out of some leaves, giving a shot hole appearance. If leaf spot is visible, growers must be diligent about keeping the remainder of the leaves protected as we still have a long season ahead. Regardless of the crop load, growers should plan to continue to manage for cherry leaf spot.

Powdery mildew symptoms are also being reported in tart cherry. Light crop loads this year will likely lead to increased shoot growth and succulent leaf area that is highly susceptible to powdery mildew. Growers who have not yet applied a strobilurin fungicide (Pristine, Gem or Adament) for powdery mildew should consider applying as they are effective against both cherry leaf spot and powdery mildew. The sterol inhibitor fungicides (Indar, Elite, Orbit) are also effective powdery mildew materials, but must be tank-mixed with a different leaf spot material as the sterol inhibitor fungicides are not effective against leaf spot due to widespread resistance in Michigan. Fungicides for powdery mildew must be applied on a protectant bases as there are no effective burn-out materials.

The Cherry Industry, Michigan State University, EPA, MDARD and Syngenta have worked together to obtain a 24 (c) special local need registration (SLN) for use of Bravo Weather Stick (chlorothalonil) beyond shuck split. Traditional timing of chlorothalonil for cherry leaf spot has been prohibited past the shuck split timing prior to this newly registered use. With the 24 (c), growers must follow a series of restrictions in order to use this product legally throughout the growing season to ensure that post-shuck split applications do not result in illegal residues. For more information, see the May 29, 2012, Northwest Michigan Regional Report.

The cool, wet weather this week all but halted insect activity in the north. No borers were trapped this week and only two obliquebanded leafroller adults were trapped across the entire station’s trap line. Obliquebanded leafroller larvae are becoming more visible. Growers can scout their orchards by examining 20 terminals per tree in five trees per orchard for larvae or feeding sites. An insecticide should be applied if they observe more than two larvae or feeding sites per tree. Growers who haven’t had luck finding the larvae can also hang delta traps with sticky liners and lures to determine if obliquebanded leafroller adult moths are present in their orchards. The materials that target the larval stage of obliquebanded leafroller include Delegate, Belt, Altacor, Voliam flexi, Entrust and Bts. During this growing season, growers may end up targeting the second larval generation of obliquebanded leafrollers expected around harvest time. Growers in northwest Michigan should not expect organophosphates or pyrethroids to provide effective control of obliquebanded leafroller.

Plum curculio activity continues this week with the delayed P.I.T.S. (Postponed Insecticide Treatment Strategy) model predicting that many area farms are in the ideal treatment window to prevent larvae in cherries at harvest. The P.I.T.S. model should only be used in carefully scouted orchards using the on-farm biofix date and weather data from the closest Enviro-weather station. Growers who have no harvestable crop may consider reducing or delaying their plum curculio management as the issue of internal larvae in the fruit at harvest is not of concern. Refer to the E-154 2012 Michigan Fruit Management Guide for more information on plum curculio management materials.

Rose chafers are out in high numbers and may be of particular concern in young orchards with limited leaf area. Established trees with light crops loads will be able to tolerate a substantial amount of foliar feeding. The first spotted wing Drosophila were trapped in west central Michigan this week. If growers have not yet done so, they should be hanging their yeast traps now. For more information on trapping and monitoring spotted wing drosophila, visit theMSU Spotted Wing Drosophila website.

Apples. The wet weather triggered a protracted apple scab infection period around the region. Based on a March 20 biofix (McIntosh green tip), the Enviro-weather apple scab model is estimating that we are approaching the end of scab season. However, spores continue to be caught in other regions of the state and so protecting tissue against primary scab should continue in the region. EBDCs and Captan are both excellent scab protectants and provide five to six days of protectant activity when used at full rates. Growers should remember that spray intervals should be tighter when relying on these materials. Keep in mind that EBDCs have a 77-day preharvest interval (PHI), so they are best used early in the growing season. Growers should also note that strobilurin resistance has been confirmed in all major apple growing regions of the state and the mutation confers complete resistance – fungicides containing strobilurin will not work against apple scab and increasing the rate of a strobilurin is not an effective option.

Regardless of crop load, growers should carefully consider their scab management program as inoculum can build quickly over a season and make control difficult in subsequent seasons. Refer to the E-154 2012 Michigan Fruit Management Guide for more options. Growers should also carefully consider their powdery mildew management as high infection levels are being reported from other regions of the state. Strobilurin or sterol inhibitor fungicides are the recommended materials for mildew and should be applied on a protectant basis. Once mildew is established, there are no adequate burn-out materials.

Codling moth flight stopped completely at the station this past week due to the cool and wet weather. We have continued to accumulate degree days towards the larvicide treatment window, but degree day accumulation is highly dependent on the biofix date (the first date of sustained codling moth trap catch) for each apple block. Growers should track the progress on their farms using the Enviro-weather codling moth model and on-farm trap catch data. The codling moth model is designed to help growers accurately apply insecticides at the recommended treatment timings which range from 100 to 250 DD50 post-biofix, depending on pest pressure and insecticide mode of action. Treatments for first generation codling moth should only be applied when a single trap location reaches a cumulative catch of five moths or more. Ovicidal insecticides are positioned early to coincide with first generation egglaying (100 DD50), followed by larvicides (250 DD50), which are targeted at first generation egg hatch.

The cooler evening temperatures over the past week have slowed activity and the zero trap catches reflect how quickly male moth activity drops when temperatures fall below 60 degrees Fahrenheit. Growers should be confident that low catches are accurately assessing codling moth activity during these cool periods. The positive effects of this reduced flight is compounded as female fecundity (ability to reproduce) decreases by approximately 25 percent for every 24 hours a codling moth female is delayed from mating after she has emerged from her cocoon. Based on the unusual patterns of emergence we have observed in other pests this season, growers should be carefully monitoring for codling moth and weighing the pros and cons of treatment in no crop situations. There are a number of effective codling moth materials. Refer to the E-154 2012 Michigan Fruit Management Guide for more information.

Growers should be on the lookout for obliquebanded leafroller larvae feeding on leaves in the terminals. Growers who haven’t had luck finding the larvae can also hang delta traps with sticky liners and lures to determine if obliquebanded leafroller adult moths are present in their orchards – we caught the first two moths in apples this week. First generation oriental fruit moth emergence has all but ceased with only one moth trapped this week. Rose chafers are out in high numbers and may be of particular concern in young orchards with limited leaf area. Established trees with light crop loads will be able to tolerate a substantial amount of foliar feeding.

Grapes. There have been some reports of powdery mildew in some locations, but no infections have been seen in the unsprayed row at the research station. Spore release was quite likely following the weekend rains and infection potential is still high through the end of bloom. Bloom of wild grapes has occurred in the past week. This is the biofix for the grape berry moth Enviro-weather model.

Potato leafhopper adults are now more widespread in the area. Cool weather has limited their reproduction thus far; nymphs should appear soon. Rose chafers have appeared in some sites and in a few areas the numbers are very high. The first symptoms of grape erineum mites have been seen.

Saskatoons. Growers should be on the lookout for rose chafer infestation.

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