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Vol. 20, No. 10, June 14, 2005 In this
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| When to prune out fire blight: To prune or not to prune | The question of pruning out fire blight strikes during the growing season, leaving them until the winter or using the "ugly stub method," has long been debated. The answer to this question depends upon the number of strikes and the weather conditions suitable for infection. While growers usually consider pruning out blight when it is severe, I think the greatest benefit comes from pruning out blight in years when there is only a little blight. Under dry conditions when only a few strikes occur, immediately pruning down to non-infected two-year-old wood will reduce the potential spread of the disease. This strategy also works when infections are light or are located in only an isolated area of the orchard. We had a lot of orchards where the grower walked away from older trees (more than 10 years old) and the blight killed all the young wood less than three or four years old. By late July the trees had grown new shoots and you could hardly tell they were infected from the road. Some growers pruned out all the fire blight-affected wood that winter and others waited a year and did their pruning after the tree's growth had settled down. Both strategies seemed to work well and I think waiting a year was cheaper, but you do have a much-increased risk the following spring if you leave it in for a year. This strategy works with old trees. Unfortunately, leaving the disease in the orchard serves as an inoculum source if a severe storm rolls through resulting in a "trauma blight" event. The "ugly stub" method would work better than leaving the diseased strikes in the orchard until winter. Dave Rosenberger, in the Hudson River Valley, advocates the "ugly stub method." Pruning out blightPruning out strikes during years when fire blight is not a major problem allows growers to reduce the small amounts of bacteria that will be present in their orchards in the years that the bloom conditions are right for the spread of the disease. I tell my growers to scout for and prune out strikes when the weather is dry and don't go out until the dew has dried. If you decide to prune out strikes in a young orchard, the strikes should be pruned out as soon as they appear. Failure to do so increases the likelihood that blight will continue to spread both to adjacent trees and into the rootstocks of affected trees. Pruning out infections in mature trees may not be practical, but mature trees with a full crop will set terminal shoot buds earlier than young trees. When trees set terminal buds, blight stops spreading both between trees and within the affected trees. Remove strikes before the cankers extend into the tree. Trees must be examined at least two or three times weekly until the epidemic slows as tree growth slows. In sections where trees are severely affected, it may be more cost-effective to immediately remove entire trees, especially if trees are a susceptible cultivar like Gala. Pulling out badly affected trees will allow blight removal crews to focus their efforts on trees that can be salvaged. Blight removal crews should be trained to recognize the early symptoms of blight on terminal shoots. Remove such shoots by cutting back into two-year-old wood at least 8 to 12 inches below any visible symptoms. If a spur or shoot on the central leader shows signs of blight, immediately remove the central leader down to 8 to 12 inches below any visible symptom. Immediate and aggressive removals reduce the need for repeated pruning in the same tree and may result in fewer trees lost to root stock blight. Make cuts into at least two-year-old wood where bacteria will be less able to multiply. Also, leave "ugly stubs" by cutting branches between nodes and at least several inches away from the central leader. Small cankers that form on these stubs can then be removed during winter pruning whereas a canker that forms at a flush cut on the central leader will be missed during winter pruning. Prune during dry weather. An Extension specialist in California failed to transmit fire blight with pruning tools when he purposely made cuts through active cankers in dry weather. However, he did transmit blight on pruning tools when pruning was done in wet weather. Blight removal operations should be suspended in wet weather, but that is not always possible. As a precaution, perhaps pruning tools should still be disinfected if blight removal must be done in wet weather. I do not generally recommend disinfecting pruning tools since they need to sit in the disinfectant for several minutes so just dipping tools in disinfectant does nothing. In the ideal world, blight removal would only be done in dry weather. However, when a week of rain is predicted just as the first symptoms of blight appear, one must weigh the risks of spreading blight by pruning in wet weather versus the risks of giving the epidemic a full-week, or even a two or three day head start. With highly susceptible cultivars like Gala, I would remove blight as quickly as possible, even if that meant that some removal would be done in less than ideal weather. Should prunings be removed from the orchard?My recommendation is to toss prunings in the row middles and allow them to thoroughly dry before mowing them. Dry means that the bark no longer slips on the cut branches, and the cambium is brown. With today's tightly spaced orchards, I am concerned that carrying prunings out of the orchard may spread more blight than occurs when prunings are left to dry in the row middles. Avoid hand thinning, bud pinching and other manipulation activities until after terminal bud set. Delaying hand thinning may result in some loss of fruit size, but risks of spreading blight out-weigh the benefits of early hand thinning. You can spread blight on your fingers while pinching buds (or hand-thinning). Pinching is done to succulent shoot tips highly susceptible to blight, whereas cuts made to remove blight are made in wood that is at least two years old. Streptomycin or other antibiotic sprays should not be applied during summer to reduce the spread of the disease. These summer applications will result in rapid development of streptomycin-resistant strains of the blight pathogen. Streptomycin should only be applied immediately after a hailstorm if there is active blight in the orchard. I have posted several articles on fire blight including pictures of symptoms and a longer version of this article on the web. Go to my Fire Blight Links at: http://web1.msue.msu.edu/vanburen/fblinks.ht |
| Fruitworms continue and other blueberry pests surface | The warm weather in the past week has brought out a peak flight of cranberry fruitworm, with increased egglaying detected in scouting at Van Buren County blueberry farms. During scouting on Monday June 13, between 1 and 7 cranberry fruitworm eggs were found per 40-bush sample, indicating that egglaying of this pest has increased. At the same time, between 4 and 7 cherry fruitworm eggs were found in these same samples. Fruit infestation by larvae is just starting, with the first consistent evidence of multiple-berry damage indicating that fruit protection from fruitworms is critical in the next few weeks. Other regions of the state are also likely to have fruitworms developing on the fruit in the next few weeks, so fields where fruitworms have caused problems in the past will need to be monitored closely for fruitworms and managed with effective insecticides if sampling indicates a risk of fruit infestation. Tussock moth larvae have been found developing in bushes at all of three farms scouted in Van Buren County this week. Although this early generation of larvae do not cause significant feeding injury, control of these insects is expected to prevent infestation by larvae just before harvest later in the growing season. Insecticides registered for control of fruitworms should also control tussock moths, but it is critical to get excellent control of bushes. Blueberry aphid colonies are easier to find on the lower branches of bushes, particularly on the newer growth. Aphids are on the lower surface of leaves, and some colonies are becoming parasitized by parasitic wasps. Colony size is increasing with between 1 and 20 aphids per colony. This is a pest to scout for in fields this month, as fruitworm management actions may help suppress aphids in the coming weeks. Fields showing shoestring virus symptoms, or susceptible new fields near virus-infested fields should be a priority for aphid management to prevent aphids from transmitting virus to uninfected bushes. The recently registered neonicotinoid insecticides, Provado and Actara, are both highly effective aphid controls. Although these will not provide any control of fruitworms, they can help with Japanese beetle and blueberry maggot control later in the growing season. Crescent-shaped dark scars on the cheek of berries indicates feeding or egglaying by plum curculio. We have found scars at each of three farms scouted yesterday (Monday 13), and if eggs have been laid inside the berries, white maggots will develop inside the fruit. Monitoring traps for obliquebanded leafrollers trapped moths over the past week, so growers monitoring for this pest should be setting biofix. See the article in the June 7 issue Fruit CAT Alert for details of the OBLR degree day model for timing sprays for control of this leafroller. |
| Cluster scouting reveals berry moth eggs and larvae | Bloom by the Concord and Niagara juice grapes is the typical timing for egglaying by the first generation of grape berry moth, and this year is no different. Catches of male moths in traps continue to be high, and we usually expect female moths to be laying eggs as counts peak in the traps. Weekly scouting of clusters has revealed that egglaying and early egghatch by this pest has started in the past week. As part of our research, we have been scouting almost 2,000 grape clusters each week across Berrien and Van Buren counties. Last week there were very few eggs (less than 0.1% of clusters) and no larvae. In scouting this week (on Monday, June 13) across all these sites, we found an average 3.5% of the clusters infested with a grape berry moth egg and 0.1% with berry moth larvae. Some vineyards had up to 22% of clusters with eggs, while the lowest were 1.3%. These findings indicate that the 10-day post-bloom spray timing for fungicides would be a good time to also target a spray for berry moth control in vineyards with a history of berry moth infestation. This timing should provide coverage of the clusters during the first period of egg hatch and larval development. In vineyards that have had light pressure from this pest, growers should scout before deciding whether an insecticide is needed. With the cooler weather predicted in the coming week, it would be best to select a product with a good length of activity. To see an earlier article on grape berry moth control, see the May 24 issue of the Fruit CAT Alert. |
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| When it rains, it spores: watch out for grape diseases | Black rot and Phomopsis The relatively dry weather so far has kept most grape diseases at bay, but the situation may be changing with more frequent rain events and warm temperatures in the past week. Since most juice grape vineyards carry a large crop, it is worth protecting. So far we’ve been lucky in that disease pressure has been relatively light: a well-deserved break for growers. A few foliar black rot lesions were observed in some vineyards. The current weather conditions are ideal for black rot infection of developing fruit, as the fungus prefers temperatures around 80°F. At this temperature it only takes about six hours of wetness to get fruit infection. Continue to protect the fruit from infection by applying effective fungicides (sterol inhibitors or strobilurins) at the first, second and maybe even third postbloom timing. This should cover the susceptible period, which lasts until about five weeks after bloom in Labrusca grapes. It may be a few weeks longer in certain susceptible wine grapes. It is also important to continue protecting the fruit against Phomopsis infection, at least until bunch closure. Best fungicide options are strobilurins (Abound, Sovran, Pristine) although ProPhyt has provided good control of Phomopsis in small plot trials in the past. Powdery mildew and downy mildew Keep scouting for downy and powdery mildew that may develop on the leaves or clusters anytime between now and the end of the season. Fungicides applied for black rot control at this time will generally keep powdery mildew at bay as well. Earlier sightings of yellow spots that resembled downy mildew were most likely caused by herbicide drift. Apparently Gramoxone, Chateau and Round-up can cause these kinds of spots. As a general rule, if white sporulation cannot be seen on the underside of the lesions after a humid night or after incubating freshly picked leaves in a moist plastic container overnight, it is most likely not downy mildew. Since Ridomil Gold Copper now has a 42-day pre-harvest interval, and we have phosphorous acid fungicides like ProPhyt and Phostrol available, we have more tools to control late-season downy mildew outbreaks. Pristine is another excellent option for downy mildew control, but should not be used on Labrusca-type grapes because of possible crop injury. A careful, weekly inspection of vine foliage and clusters to detect early downy mildew development is crucial for maintaining control, since most fungicides work better when applied before infection and are therefore most effective as protectants. Don’t wait until an epidemic is raging by only observing vines from the seat of your tractor or truck. At that point it will be very difficult to control the disease, since the downy mildew fungus can multiply very rapidly. Botrytis bunch rot The current weather conditions may be conducive to development of the Botrytis bunch rot fungus on blossoms of susceptible varieties, so a bloom spray is recommended if conditions remain wet and warm during bloom. A bloom spray would be in addition to later sprays (bunch closing, veraison, pre-harvest). I can tell that Botrytis has been happy over the past week by watching my poor geraniums melt away in my garden. Effective fungicide choices for Botrytis control are: Vangard, Elevate, Endura and Scala. The two newest fungicides, Endura and Scala, should be applied at the higher rate for Botrytis control. Endura will also provide powdery mildew control, whereas Scala is strictly a Botrytis material (although we saw activity against powdery mildew, Phomopsis, and black rot in a field trial in Aurore grapes in 2004). Luckily, all these materials have different modes of action, so they can be used in alternation as a fungicide resistance management strategy. Pristine, which shares one of its active ingredients with Endura, is not as effective against Botrytis in grapes because of the relatively low application rates on this crop. If you do use it to control other diseases, applying it at the high rate can help suppress Botrytis. |
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| Control of fruit rots in blueberries after bloom | As blueberries are now in various stages of development and ripening, the main diseases of concern are fruit rots such as anthracnose (orange spore masses) and Alternaria fruit rot (green velvety mold). Botrytis fruit rot (gray mold) is not as common in Michigan. Anthracnose tends to be a problem in cultivars such as Bluecrop, Jersey, Blueray and Rubel, while Alternaria fruit rot may be visible before harvest in Bluecrop. Cultivars Duke and Elliott are moderately resistant to anthracnose. Fruit rots are generally separated into two types: field rot and post-harvest rot. The former can be seen on berries in the field before harvest and is especially common when berries are left on the bushes too long. So timely harvesting is an important control measure. Post-harvest rot can develop on sound-looking berries, as spores from infected berries can infect them before or during harvest or during processing. 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. These infections can also contribute to high microbial counts in frozen berries, leading to rejection of fruit lots by some buyers. Rapid cooling of harvested fruit is important in reducing post-harvest fruit rot incidence, particularly at the later harvests when disease pressure is generally high. While fruit rot is often not visible until the berries ripen or even after harvest, it is prudent to assume that you will have a fruit rot problem if you had problems in past years. The warm, wet conditions of the past week are particularly conducive to anthracnose fruit rot. If the first blueberries are starting to show rot, fungicide sprays can still limit new infections of neighboring healthy berries. Applications within one to two weeks of the first harvest can still be beneficial in preventing these late infections. In fact, an additional fungicide application between the first and second harvest may be beneficial under high disease pressure. Following are examples of fungicides that can be used during fruit development and ripening. 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 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 are supposed to 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. Captevate (captan and fenhexamid) at the high rate will provide good control of anthracnose as well as Botrytis fruit rot, but this disease tends to be less common in Michigan. Captevate is also fairly expensive. Aliette (fosetyl-Al) is a highly systemic fungicide that provides good control of anthracnose, Alternaria fruit rot and Phomopsis. Of course Topsin M + Captan can still be used, provided the 7-day PHI of Topsin M is taken into consideration. While Topsin M is a systemic material and is more active against Phomopsis, Captan as a protectant will do much of the work against anthracnose. Therefore, if anthracnose is the disease you wish to control and the weather is relatively dry, a Captan or Captec spray alone may suffice. Do take note of the pre-harvest intervals for the various fungicides. |
| Reminder: June 15 blueberry insect control meetings | Two meetings for Michigan blueberry growers will be held on June 15. The topic of the meetings will be a four-year MSU research project at commercial blueberry farms that aims to identify the opportunities and challenges of transition to new insecticides. Results from the first two years of this project will be highlighted at two meetings at grower-cooperator farms on June 15. The meetings are open to anyone interested in blueberry insect management. A morning meeting from 10:00 AM to noon will be hosted by Larry Bodtke of Cornerstone Ag Enterprises. His farm is on the left side of 57th Street, a quarter mile north of CR 388 (Phoenix Road). 57th Street crosses Phoenix Road a few miles west of Grand Junction. Afternoon meeting This meeting will run from 2:00 to 4:00 PM and will be hosted by Al Ochoa of A&L Blueberries at his farm on the left side of 144th Ave about 1 mile north of M-45 in Grand Haven. Restricted Use Pesticide Applicator credits have been applied for, and refreshments will be provided at both meetings. Contact Rufus Isaacs at (517) 355-6619 or isaacsr@msu.edu for more information. |
Regional reports 1 – Southwest |
Weather
Tree fruit Apricot trees in sandy sites show drought stress and wilting. Peach June drop continues and pit hardening has begun. Rose chafers are out and often attack young peach fruit. Oriental fruit moth egg laying has ended. Flagging of peach shoot tips from Oriental fruit moth larvae were reported last week. Tarnished plant bug feeding scars have been found on young fruit. Bacterial spot symptoms continue to appear. We are catching peach tree borer adults and growers should be thinking about trunk sprays. Sweet cherries are coloring and birds are eating the fruit. Tart cherry fruit are yellowing. Sunday’s rain was a cherry leaf spot infection period. Apple fruit are an inch in diameter. Fruit are differentiating into several size classes and still dropping. Fire blight appeared in more orchards last week. The storm Sunday was a trauma infection period for fire blight, especially wjere there was hail. Green apple aphids are out and can spread the infection to healthy trees. New apple scab symptoms were found from the May 22 infection. If scab lesions are found in the orchard, growers should continue to apply protectant materials to suppress fruit scab. The first generation of Oriental fruit moth is ending. Obliquebanded leafroller adults were caught in good numbers. Moth catches were reported Friday, June 3 (870 GDD42) and Monday, June 6 (935 GDD42). We are setting obliquebanded leafroller biofix at June 6 at 935 GDD. We are now at 1178 GDD42. Egg hatch begins at 400-450 GDD past biofix. This would be about 1350 GDD42. See the article in the June 7, 2005 Fruit CAT Alert. Codling moth trap catches are high. We biofixed for codling moth on May 20 at 334 GDD50. We are now at 709 GDDs, almost 375 GDD past biofix. Activity for the first generation of codling moth should end at about 1000 GDD after biofix. Small fruitBlueberry fruit are sizing well. Cherry fruitworm and cranberry fruitworm egg hatch and feeding continues. Tussock moth larvae are out and causing severe damage in some fields. Blueberry aphids are becoming more numerous. There are a series of upcoming blueberry meetings on June 15 and June 27. Grape bloom is ending. Botrytis rot (brown shriveled flowers) showed up in some vineyards during bloom. Vinifera grapes are blooming. Rose chafers and rose chafer feeding damage are easy to find. Grape berry moth adults are being trapped, and egg laying has begun. Sunday’s rain was a black rot infection. Phomopsis, black rot and downy mildew symptoms can be found. Growers should be protecting the flower clusters from diseases with bloom sprays or post bloom sprays before our next rain. Strawberry harvest is moving quickly. Fruit bronzing due to flower thrips feeding was reported. Verticillium wilt symptoms were also reported. MiscellaneousThe next Monday Update meeting will be Monday, June 20 at Fruit Acres Farm near Coloma in Berrien County at 5:00 PM. There will be one MDA restricted use pesticide recertification credit available at this meeting. |
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| 3 – Grand Rapids Area | Weather According to 30-year averages from the Sparta weather station, degree day totals are running about five to six days ahead of average for both GDD42 and GDD50. There was some rain that moved through the Grand Rapids area over the weekend, but actual rainfall totals were quite variable. Most areas received at least a half-inch, but some areas have had close to two inches – it seems that the farther east you’re located, the more rain has reached those areas. GDD accumulated in West Central Michigan
Tree fruit Most apple varieties are around the 20 to 25 mm size. Chemical thinning seems to have worked pretty well this year and there is a nice set. Some blocks and varieties such as Goldens and Galas might still be too heavy and need some hand thinning. Blossom blight strikes from rain events back in mid-May started to show up last week. Growers should still be aware of the danger for fire blight to explode if there are any trauma situations such as hail or high winds. There is a high risk with all the oozing cankers and blossom blight strikes that are currently present – add in the high temperatures and some trauma from hail or high winds and fire blight could become a big problem in a hurry. Up until Monday, June 13, there had been little rainfall at the spore monitoring site on the Ridge, but as of June 13 I have caught no additional spores. I’ll look at the rods once or twice more, just to be sure, but it looks like primary scab is over for 2005 on the Ridge. Close scouting for any primary apple scab lesions should be done – you don’t want to get caught with secondary scab on fruits once fungicide rates are lowered for the summer. A bit more activity from plum curculio egg laying can be found in apples over the weekend, but numbers are still light and sporadic. They should be Blueberries in West Central Michigan are in green fruit stage. With the daily temperatures above 80 degrees, we are observing an increase in plant health problems. The past week we reported the outbreak of Phomopsis twig blight and canker in most of the region. Drought conditions and high temperatures affecting the region have exacerbated the Phomopsis outbreak. We have sampled about 100 acres in Ottawa County and we found that at least in one case, Phomopsis has caused extensive damage equivalent to more than $500,000 just in lost plants. Fields that looked healthy two weeks ago are now blighted. In those fields, a large number of shoots that look green when cut open show the xylem with a brown coloration symptomatic of Phomopsis infection (see Picture 1). The outbreak has also affected small plants, but we believe that in this case the infection originated in the greenhouse during the process of plant propagation. Fields with history of Phomopsis and fruit rots should be closely monitored for symptoms of wilt and poor growth. Initiate preventive measures as soon as the first symptoms of Phomopsis appear. We recommend continuing with fungicide treatments according to the program outlined in the 2005 Michigan Fruit Management Guide. When possible, collapsed canes and dead plants should be pruned and infected wood removed from the field and burned to prevent further infections. Regarding insect problems, berry damage by the fruitworm complex is progressing. However, most of the damage has been caused by cherry fruitworm (less than 1% fruit damage). Only a few cranberry fruitworm ovipositions have been observed in most sampled fields in both Ottawa and Allegan counties but in some localized areas ovipositions are on the rise. Another problem is the presence of the rose chafer, Macrodactylus subspinosus (F.), a serious pest of ornamental and fruit crops in Michigan. A number of fruit crops are among the hosts for rose chafer, including peach, grape, apple, cherry, pear and plum. This summer the rose chafer has been very active in blueberries, mainly in Allegan County. At least in one case, the rose chafer has damaged very seriously a newly planted blueberry field. Young plants are more susceptible to rose chafer damage than older plants. However, in bearing plants the beetle damages fruits and new growth (Pictures 2 and 3). Control alternatives for this beetle are similar to those for Japanese beetle. These include applications of Sevin, Imidan or Guthion. Please, consult the 2005 Michigan Fruit Management Guide for further information. |
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| 4 – West Central | Weather Forecasters kept calling for possible rains just about every day this past week. Unfortunately, all the threatening clouds would just dissipate and disappear before reaching our shores. A few widely scattered and very short showers did pass through leaving behind barely measurable precipitation. Manistee was the “wet” spot with 0.15 inches of rain that skimmed the area on Saturday. Drought symptoms are evident all over but particularly in non-irrigated blocks. Extreme heat and high winds are maintaining high evapotranspiration index. Seasonal precipitation continues to be more than three inches behind normal. Heat unit accumulation has been very rapid. Average daily GDD accumulation for GDD50 has been around 22-25.
Tree fruit Fruit thinning of apples produced very good results overall. In all the blocks that I frequent on a regular basis and use the information as my reference points, there has never been better thinned apples in the last 13 years. It appears that everything came together to insure very good outcome of the thinning applications. It took about two weeks to fully realize the effect and appreciate the results of thinning intervention. Many small fruit that appeared to be still “hanging on” firmly a week after the spray, eventually dropped off leaving behind just one and, occasionally, two apples in a cluster. Pears are looking good. Fruit is about an inch in diameter. It appears that the fruit is self- thinning. There is still a prospect of a good pear crop. In both apples and pears, a few scattered wetting events did not produce any scab infection periods. At the same time, they were neither long enough nor strong enough to induce any spore release. At best, I can say that the statement from last week still stands… though we are very near the end of the primary that could not be confirmed at this time! There are a few scab leaf lesions from the previous infections widely spread throughout the area. This is in line with the findings over the years that in “dry” years we might have a bit more scab lesions than in the “wet” years. Inevitably, there is tendency for an oversight when using only protectant fungicides in disease management. People often fail to take in consideration the rate of new growth since the last cover leaving a significant percentage of the newly developed and unprotected foliage exposed to the infections. Often, under the given circumstances that requires tightening up the spray program or incorporating different chemistries with a “kick back” action. No fire blight infections according to the Maryblight model. High humidity has been perpetuating powdery mildew development. Disease symptoms are present in apple blocks throughout the district. Codling moth numbers are still very high. All scouted blocks have been assigned a biofix date and approximate first generation spray control date. The optimum window for the best control of the first generation codling moth is rapidly closing. Though many blocks have been sprayed already, the ones that still haven’t ought to be covered in a day or two. Scouts are finding increased numbers of European red mites, twospotted mites and their eggs. Looking at the mid- and long-term weather forecast that calls for above normal temperatures and below normal precipitation, it seems like perfect conditions for rapid and forceful mite population build up. Plum curculio stings have been found on apples. White apple leafhoppers and potato leafhoppers are present and already doing significant damage. First spotted tentiform leafminers mines and larvae have been reported. Sweet cherries are coloring fruit but not increasing in size. It appears to be “rubbery” and “chewy.” June fruit drop is underway. Some stressed trees are loosing both fruit and leaves and some are even dying. Tart cherries are starting to change color from green to straw color. It looks like the fruit has “lost weight” and “slimmed down” due to the drought. Young trees are dropping a lot of fruit. The irony is that we have a very good fruit set and a significant crop load on the trees but if the rain does not come soon, we might get cheated out of good yields and premium quality fruit. Peaches are an inch in diameter. The crop load is very good. Bacterial leaf spot is found quite readily in cherry, apricot, plum and peach blocks. Oceana County had a little bit of rain yesterday morning that resulted in a light cherry leaf spot infection. So far, cherry leaf spot symptoms have been found in a very few blocks. With the cherry fruit coloring, brown rot is coming back into focus. In the abandoned block of sweet cherries, the fungus is actively sporulating and infecting developing fruit. Conditions are favorable for disease development and protection measures must be in place. Plum curculio larvae found in the abandoned block are big and ready to drop out of the fruit. It is important to maintain good plum curculio coverage so we do not have any surprises at harvest time. No cherry fruit fly catch has been reported yet. |
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| 5 – Northwest | GDD accumulations at NWMHRS GDD42 1037 GDD50 597 Tree fruit Isolated apple scab symptoms have been reported in northwest Michigan, but due to extremely little rainfall, there have been very few lesions detected. We are predicted to be near the end of primary scab, but again with the small amount of moisture, there may be spores yet to be discharged with the next rain event. On Saturday, June 11, we reported a wetting event, which resulted in an apple scab infection in Eastport, Kewadin, Elk Rapids and Bear Lake. Codling moth catches are still on the high side with over 30 moths per trap. Oriental fruit moth has declined to half the population of last week: 30 moths per trap. Spotted tentiform leaf miners catches were very low this week. We are still finding isolated pockets of cherry leaf spot around northwest Michigan, although Saturday’s wetting event resulted in a light cherry leaf spot infection in many areas. Powdery mildew has also been reported in a few sites on cherry but less than we expected with this hot, dry weather. European brown rot has been reported in high quantities in both Balaton and Montmorency cherry blocks this season. The first adult cherry fruit fly was caught in the unsprayed Entomology block at the NWMHRS on June 13. Plum curculio oviposition scars have been detected in multiple stone fruit orchards, and many of our organic blocks have been hard hit. To control plum curculio using the postponed insect treatment strategy (PITS), sprays should be applied at 375DD after full bloom. We are still seeing green fruitworm leaf and fruit feeding. American plum borers and lesser peachtree borers are on the decline this week. Rose chafers have started to emerge; we have seen them on cherry and grape. Shoot growth and development of grapes was rapid during the past week with most cultivars now in the immediate pre-bloom stage. Powdery mildew remains very light, but it should be of significant concern during bloom if humid weather persists. The first rose chafers, hornworm larvae and adult potato leafhoppers were found in vineyards this week. Growers should be removing suckers and tucking shoots at this time. |
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| Weather news | Cooler weather on the way A cool front will move across the Great Lakes region Tuesday (June 14), setting off showers and thunderstorms across most of Michigan and bringing an end to the warm, humid conditions that have persisted for more than one week. Some thunderstorms could reach severe limits Tuesday afternoon and evening with the primary threat being high winds and hail. Cooler, less humid air will move into the state by Wednesday, although a series of upper air disturbances will bring a continuing chance for mainly afternoon or early evening showers both Wednesday and Thursday. Precipitation amounts with the thunderstorms Tuesday will generally range from the 0.25 to 0.50 inches with some higher totals and best areal coverage in northern sections of the Lower Peninsula and across the Upper Peninsula. Strong southerly winds are expected Tuesday ahead of the front, shifting to the north or northwest at 10 to 20 with higher gusts during the day on Wednesday and Thursday. Fair and drier weather is expected Friday continuing through the upcoming weekend. Temperatures will fall from highs ranging from the 70s to upper 80s Tuesday to the upper 60s to mid 70s Wednesday and continue at those levels through Saturday. Low temperatures will range from the upper 50s to low 60s Wednesday falling back to the upper 40s to mid 50s Thursday through Saturday. A warming trend will begin on Sunday as an upper air ridge currently over the Great Plains moves eastward into the Midwest. This ridge is expected to become the primary weather story in the medium range time frame with both the 6-10 day (for June 19-23) and the 8-14 day time frame (covering June 21-27) outlooks calling for above normal temperatures and for below normal precipitation. |