May 23, 2006
In this issue
Tree fruit news
§ Early season obliquebanded leafroller monitoring and control
§ Trauma blight control in Michigan
§ Gem fungicide for stone fruit
Small fruit news
§ Cool, wet weather conducive to angular leaf spot of strawberries
§ Bloom is a good time to start control of fruit rots in blueberries
§ Grape IPM meeting this week
Other news
§ Regional reports
§ Weather news
Obliquebanded leafroller (OBLR) overwinter in the orchard as immature larvae and begin feeding inside bud clusters prior to bloom and on young fruit in May and June. (see photo) Fruit that do not abort can be deeply scarred and deformed by OBLR feeding. Scouts can monitor overwintering survivors in terminals after petal fall, but signs of leafroller activity often are more readily visible than the actual larva. The name leafroller comes from the larva’s habit of rolling leaves to form a shelter. These feeding sites are most often found at the tips of growing shoots. Larvae also will use silk webbing to attach two leaves or a leaf and fruit together to form a shelter. The presence of webbing is a good clue that leafrollers are around.
Controlling the overwintering larvae has proved to be the best strategy for preventing OBLR populations from reaching damaging levels. This is especially true if early scouting indicated high levels of OBLR larval activity, or if an orchard experienced high levels of OBLR injury the previous summer. The incidence of leafroller damage appears to be on the rise in Michigan. It was not uncommon to record 5 to 10% fruit injury caused by this pest in the pre-harvest damage assessments we conducted on over 2,000 acres of apples in 2005. Past failures to control OBLR have in part been attributed to a reduction in susceptibility to insecticides that had proved effective for many years. Indeed, bioassays conducted by our labs from 1998-2000 revealed a reduced susceptibility to many of the compounds used for leafroller control. The major exception was spinosad (SpinTor, or Entrust for organic growers). Spintor, as well as Intrepid and a few other materials, have proved effective for leafroller control over the past several years. However, growers have relied heavily on these insecticides, and it would not be unreasonable to see some decline in their efficacy. Washington State researchers have documented a reduction in OBLR susceptibility to spinosad in recent years.
A good long-term strategy for OBLR control is to rotate among several controls. Bt is a good option, especially as the late afternoon temperatures climb above 70°F. Two new insecticides targeting early codling moth control (Rimon and Proclaim) also provide good to excellent control of overwintering OBLR larvae. Both pests are targeted by an early application of Rimon at biofix plus 100 GDD. The label allows for a wide rate range. In our trials the lower rate of 20 oz acre has proven effective against first generation OBLR and codling moth. A higher rate of 30 oz per acre may be warranted where pest pressure is high. Proclaim will control OBLR, but not codling moth, at this early timing. Either material is a good option for OBLR and codling moth control at the typical first cover timing of biofix plus 250 GDD. Proclaim is registered at a label rate of 3.2 to 4.8 oz per acre. Stick to the higher end of the label rate if codling moth and OBLR are being targeted. Proclaim’s activity is aided by the addition of a horticultural spray oil (1 qt/100 gallons) or non-ionic surfactant (0.25% v/v). Refer to last week’s Fruit CAT Alert article (Vol. 21, No. 6, May 16, 2006) on codling moth, as well as Table 1 in this article, for additional information on these materials.
|
Compound Trade Name |
Chemical Class |
Life-stage Activity |
Optimal Spray Timing for CM |
Mite Flaring Potential |
|
Rimon |
IGR (chitin inhibitor) |
Eggs, Larvae |
Biofix + 100 DD Residue under eggs |
M* |
|
Proclaim |
Avermectin |
Larvae |
Biofix + 250 DD |
L |
|
* May cause mite flaring in
combination with carbaryl or pythrethroids that kill predacious mites. |
||||
Monitoring of summertime OBLR activity begins at the start of the month of June, when growers should have their pheromone-baited traps for the OBLR placed in their orchards to monitor adult activity. One pheromone-baited trap for every 10 acres of orchard is sufficient for monitoring OBLR. In most orchards, traps should be placed in the middle third of the tree canopy. As with codling moth traps, the key considerations for effective trap placement within a block are historical “hot spots,” and location relative to the block perimeter. An area where moth catches or injury to fruit was high the previous season, is a good place to locate a trap. Traps should also be placed in other locations throughout the orchard to represent pest pressure for the whole orchard.
There are two periods of adult activity. In Michigan, the first adult flight typically begins in early June and lasts about six weeks. A second flight takes place from early August to mid-September.
Moth capture in pheromone traps is not a good indicator of leafroller abundance or potential damage, but is essential for tracking biological development with the OBLR degree day model for proper timing of control measures.
|
GDD42 (Post biofix) |
Event |
Action |
|
Tight cluster |
Majority of larvae have emerged from shelters |
Examine fruit buds for larval activity |
|
0 DD° = biofix (~900 DD° after Jan 1) |
1st sustained moth captures |
Set DD° = 0 |
|
220-250 DD° |
Peak moth flight - overwintering generation |
|
|
400-450 DD° |
Start of egg hatch |
Timing for treatment |
|
1000 DD° |
End of egg hatch |
|
|
2300 DD° |
Peak moth flight - 2nd generation |
|
|
2750 DD° |
Start of 2nd generation egg hatch |
Timing for treatment |
Damage occurs at three periods during the growing season. Larvae of the overwintering generation will feed on young fruit in May and June. Fruit that do not abort will be deeply scarred and deformed (Photo 1). Young, summer generation larvae will feed on fruit before moving to growing shoots. Several shallow feeding sites within a small area characterize fruit damaged by young summer generation larvae. Late in the summer, young larvae will feed on the fruit prior to seeking overwintering sites. The pinhole size feeding sites are difficult to detect at harvest, but become noticeable as the fruit ripens in storage.
As the summer progresses, sampling for larvae is a good way to determine if OBLR controls are warranted. If overwintering larvae were found in more than 1 to 2% of the shoots inspected, summer controls likely will be needed. Insecticides may also be required to prevent fruit injury if summer larvae or visuals signs of their presence are detected in fruit clusters or shoots.
Degree day models can aid in timing insecticide sprays by predicting key events in the leafroller’s life, such as the start of egg hatch. Using these models relies on the establishment of a biofix and daily temperature records. Biofix is the date when the scout records the date of the first sustained moth capture in pheromone traps, provided that moths are trapped on two successive trapping dates. The model is set to zero, and degree days are accumulated from this date forward based on daily temperatures. The obliquebanded leafroller model calculates degree days based on a minimum developmental threshold of 42°F.
We will provide an article updating summer leafroller management control materials as timing for treatment approaches.
It appears that most areas of the state did not experience weather during bloom conducive to blossom blight infection by the fire blight pathogen. However, temperatures will eventually warm and fire blight cankers will begin to ooze. Thus, inoculum will be present throughout the state.
Weather events leading to potential trauma events in apple orchards are inevitable. Strong storms accompanied by high winds and/or hail can injure trees and deliver inoculum that can colonize and cause shoot blight infections. Shoots are susceptible to infection any time that they are actively growing.
The only effective control measure for trauma blight available currently is streptomycin. Streptomycin is best applied as early as possible after the trauma event has occurred to maximize control. This is especially important if there are active fire blight cankers or strikes in the orchard or if the trauma event resulted in extensive foliage damage. We used to think that there was up to a 24 hour window of time after the trauma event to get a spray on. New data coming out suggests that the timing should be much sooner, within 4 to 12 hours. The sooner the material can be applied after the event enables targeting of bacteria prior to their internalization and establishment of infection.
Streptomycin should not be sprayed as a preventive measure for shoot blight. This is not an effective use of this material and only promotes the development of streptomycin-resistant strains.
Unfortunately, in areas where streptomycin resistance occurs, Mycoshield will not be a useful substitute for trauma blight control. Mycoshield is bacteriostatic and inhibits the growth of the fire blight pathogen, but does not kill the pathogen. This works as a control for blossom blight because blossoms are only susceptible to infection for a short time period. Inhibiting the growth of the pathogen during this time period will enable blossoms to escape infection. This strategy doesn't work on shoots because the growth inhibition is not permanent. As the material becomes naturally degraded, the pathogen will begin growing again and cause shoot infection. The reason that streptomycin works is that the material kills the pathogen which will prevent shoot infection.
Gem is a new fungicide from Bayer available in 2006 for the stone fruit market in Michigan. The active ingredient of Gem is trifloxystrobin, the same active ingredient as in Flint. The concentration of trifloxystrobin in Gem is 25%, which is lower than the concentration of trifloxystrobin in Flint (50%). Gem is a replacement product in the stone fruit market for Flint and is only labeled for use on stone fruit.
The use of Gem fungicide should be targeted towards control of cherry leaf spot and powdery mildew. Label rates of Gem are 4.0 to 8.0 oz per acre with recommended rates of 4 to 5 oz per acre under conditions of low infection severity and 6 oz per acre under conditions of higher infection pressure. Disease control ratings in the 2006 Michigan Fruit Management Guide for Flint (2 to 4 oz acre) at the cover spray timings for leaf spot and powdery mildew control are excellent for both diseases, and we would expect similar results with Gem.
As with other strobilurin fungicides, there is a risk of fungicide resistance developing. Therefore, Gem should not be used more than twice consecutively or more than four times per season. My recommendation is that Gem not be used more than twice per season.
Think "protectant mode" when applying Gem or any other fungicide for stone fruit disease control. We do not have data on after-infection activity of fungicides for leaf spot control. Resistance management strategies focus on killing pathogen inoculum and preventing spore germination. Fungicides applied preventively at the correct rates and with good coverage will accomplish the goal of killing pathogen inoculum and preventing spore germination.
In the Midwest, angular leaf spot (also called bacterial blight) is the only reported strawberry disease caused by a bacterium, namely Xanthomonas fragariae. This bacterium has been hitchhiking around the United States on strawberry planting material, since it was first reported in Minnesota in 1960. Although the disease has not been a major problem, it can occasionally become serious. Economic damage is mainly due to blackening of berry stem caps, which mars the appearance of berries. However, severe leaf spotting can also result in premature leaf drop which may affect plant vigor and yield. Among strawberry cultivars, Allstar, Redchief, Glooscap, Kent, Lester and Lateglow are known to be fairly susceptible.
Typical symptoms of angular leaf spot are small, angular water-soaked spots on the lower leaf surface. Spots may coalesce resulting in larger lesions and necrotic areas. On the upper leaf surface, the lesions look like irregular reddish-brown spots and could easily be mistaken for scorch. It is important, therefore, to inspect both the upper and lower leaf surface. Angular leaf spot lesions are distinctly angular and translucent when the leaf is held up against the light, whereas scorch lesions are more rounded and not translucent. Under humid conditions, a shiny or slimy bacterial exudate can be seen on the lesions on the lower leaf surface. The exudate eventually dries out into a scaly, whitish film. Heavily infected leaves may die, especially if major veins are infected, and the infection may even become systemic. The pathogen can infect all plant parts, except berries and roots. However, berry stem cap infections can be serious, resulting in blackened caps and unattractive fruit.
The bacteria overwinter in old infected leaves and crowns. Primary infection of new growth in the spring occurs by rain or irrigation water splash. The bacteria enter plants through wounds or by actively swimming into natural plant openings (such as stomata, the plant’s breathing pores) aided by dew, rain or irrigation water. Development of the disease is favored by moderate to low daytime temperatures (around 68ºF), low nighttime temperatures (near or below freezing), and high relative humidity. Long periods of leaf wetness due to heavy dew, irrigation, or prolonged rains also favor disease. Young, vigorous leaf tissues are more susceptible to the disease than older leaves.
Angular leaf spot can be managed by using clean planting material, adequate plant and row spacing, and removal of infected plant debris after harvest. If leaf spots are common during fruit development and the weather is conducive, there is a risk of berry stem cap infection. It is therefore important to protect the berry stem caps from infection by applying protective sprays. Copper products, such as Kocide and Cuprofix, applied on a regular basis are the most effective products for control, but care has to be taken to avoid phytotoxicity, which manifests itself by purplish discoloration on leaves. Adding lime as a safener is recommended, particularly since the cool, slow-drying conditions that promote the disease also promote copper uptake by the plant.
Fungal fruit rots, especially anthracnose caused by Colletotrichum acutatum, continue to be of economic concern in blueberries. Losses can occur before as well as after harvest. The cultivars Jersey, Bluecrop, Rubel and Blueray are very susceptible to anthracnose fruit rot, whereas Elliott is quite resistant. Alternaria fruit rot is sometimes found on Bluecrop berries before harvest and affects most varieties after harvest. Botrytis fruit rot is not as common in Michigan, but may be a problem in years when cool, wet weather prevails during the flowering and fruit development period. These rots can be distinguished to some extent with the naked eye: anthracnose is characterized by wet, pink to orange spore masses; Alternaria fruit rot by a dark green velvety mold and Botrytis by fluffy, tan to gray fuzzy mold on the berry surface. See the blueberry web site (www.blueberries.msu.edu) for pictures of symptoms.
The anthracnose fungus overwinters in dead fruiting twigs, but has also been found to overwinter in live, dormant buds. The infected buds typically die in the spring and support sporulation of the fungus. A twig blight, which is difficult to distinguish from Phomopsis twig blight, can also result from bud infection. With anthracnose there are two important periods when the infection risk is high because of peak spore release:
1) From pre-bloom to about pea-size berry (due to overwintering inoculum), and
2) From first blue fruit until the end of harvest (due to sporulating berries that infect surrounding berries). Fungicide spray programs should focus on these periods.
There are several fungicide options for control of blueberry fruit rots. The strobilurin fungicides Abound (azoxystrobin), Cabrio (pyraclostrobin) and Pristine (pyraclostrobin + boscalid) are excellent for controlling anthracnose fruit rot. They are (locally) systemic and considered “reduced risk.” Since Pristine has two active ingredients, it tends to have a broader spectrum of activity than Abound and Cabrio. However, at the rates recommended for blueberries, Pristine is rather expensive. Applications can also be made between harvests, since the pre-harvest interval is 0 days.
Switch (cyprodinil and fludioxonil) is a systemic fungicide with a unique mode of action. Switch has activity against anthracnose, Alternaria fruit rot and Botrytis fruit rot and would be a great option if you are trying to control multiple fruit rots at once.
Elevate (fenhexamid) is primarily a Botryticide with suppressive activity against mummy berry.
Captevate (a pre-mix of Elevate and Captan) has efficacy against anthracnose also.
Topsin M (thiophanate methyl) + Captan (captan) or Ziram (ziram) are also good options for anthracnose fruit rot control.
Topsin M received a Section 18 emergency exemption for use in blueberries this year. Fungicides should be applied around bloom and early fruit development (to prevent the primary infections) and at first blue fruit or pre-harvest (to prevent secondary infections).
This Thursday, May 25, there will be a grape IPM meeting focused on bloom and post bloom grape IPM issues with presentations by Rufus Isaacs and Annemiek Schilder from MSU and Terry Holloway from National Grape Cooperative. This meeting will also address the freeze injury and IPM programs in vineyards with different levels of freeze injury.
The morning meeting will be at 10:00 AM to noon at the Cronenwett Farm Shop at 70123 28th Street east of Lawton.
Afternoon meeting will be at the Berrien County MSU Extension Office at the Southwest Michigan Research & Extension Center, 2:00 to 4:00 PM. These meetings are co-sponsored by National Grape Cooperative and MSU Extension and are open to all.
Last week was cool with highs in the 50s and 60s and lows
above 40 at night. GDD accumulations have slowed, and we are near normal. Rain
fell Monday and Wednesday, 0.3 inches of rain. This long, cold period slowed
plant growth and insect and disease activity. Soils are moist. Soil
temperatures are in the low 50s. Scattered frosts Monday morning (May 22)
caused little damage. The windy conditions over the last several weeks have
caused a fair amount of wind damage to fruit and leaves. This week’s forecast
is for much warmer weather with highs into the 80s by the weekend.
GDD totals: March 1 through May 21
|
Grapes, from April 1
|
|||
|
Location |
GDD 42 |
GDD 45 |
GDD 50 |
GDD 50 |
|
666 |
511 |
309 |
277 |
|
|
701 |
546 |
340 |
314 |
|
|
597 |
453 |
269 |
241 |
|
The warm temperatures should bring on a lot of
insect activity. Tarnished
plant bug and plum
curculio will be a problem when it warms up and controls should be applied
before Thursday. Growers report large numbers of ladybug adults, larvae and
eggs in orchards. San
Jose scale has become a problem in the area, and growers should be aware
that the first flight should begin soon.
Peaches are at 10
mm. Foliage is off-color and growing slowly due to recent cool weather. A few
orchards have been hand-thinned but most will be done when fruit are larger. A
lot of fruit have self-thinned, but the crop is still decent in many orchards. Oriental fruit moth trap
catches are low. We should be at peak adult emergence, but cool temperatures
have kept the flight down. We set biofix Oriental fruit moth as
April 16 with a GDD of 180 GDD45 at SWMREC. Chemical controls are focused on
egg hatch, which continues to about 650 GDD after biofix. We are about 331 GDD
past biofix. Tarnished
plant bugs have been found in peach orchards and growers are mowing
orchards. This can drive the bugs into the tree canopy to feed on the fruit. We
are starting to catch lesser
peach tree borer.
Sweet cherries
are 14 mm fruit and nearing the end of pit hardening. Plum curculio will be
a problem when it warms up.
Tart cherries are at 10 mm fruit and relatively uniform in size. The crop looks a little heavier than average. Growers need to protect against plum curculio and cherry leaf spot. No cherry leaf spot symptoms have been found yet. In general, the weather has been too cool for this disease. There is some shot-holing of the leaves, probably from bacterial canker, but not other symptoms have been found.
Plums are at 10 mm fruit and the fruit is starting to sort out by size. We will not have a good estimate of the crop for several weeks. Growers need to protect against plum curculio and maintain protection for black knot.
Apple fruit set
is good. The fruit are about 10 mm in diameter. The warm temperatures forecast
for later this week are an ideal thinning window with temperatures rising from
the 50s into the 80s by the weekend, apply thinners when daytime highs are
forecast to be above 70. Growers need to protect against plum curculio. Wednesday’s
rain was an apple scab infection in some areas. Scab symptoms from earlier
rains have been found. Scab symptoms from infection periods in early May should
be appearing now. Scab spore release has continued at low levels. We have not
reached the end of primary scab. You
can monitor scab spore maturity using the Enviro-weather
web site. Growers need to maintain scab protection. Growers also need to
protect against powdery mildew. Fire blight canker
margin symptoms should appear this week as wilted shoots near old cankers. Fire blight could be a
problem if we get severe weather in orchards with oozing cankers and shoots. Cool weather kept Oriental fruit moth and codling moths trap
counts low last week. A regional biofix for codling moth has not
been set. We expect the flight to begin again with warm dry weather this week. See
the article on pesticides
for codling moth in last week’s Fruit CAT Alert. Leafroller larvae about
20 mm long can be found in apples. Obliquebanded leafroller
traps should be out. Other regions are report high numbers of European red mites in
some areas so growers should scout their hot spots.
Pear fruit are at 10 mm. Growers need to protect against pear scab. Pear psylla nymphs are common in some orchards. Pear blister mite was reported for several small growers.
Blueberries are blooming. Growers should be protecting against mummy berry and anthracnose fruit rots. Few mummy berry shoot strikes have been found. Cherry fruitworm are being caught in pheromone traps. We expect to see cranberry fruit worm emergence this week with the warm temperatures. See the article on these fruitworms in last week’s Fruit CAT Alert. Growers should be ready to treat for these pests at the end of bloom. Post bloom sprays also control blueberry gall midge and blueberry tip borer.
In grapes, primary shoots are almost a foot long and secondary and tertiary buds are opening. New growth is off-color and growing slowly due to the cool weather. There are few live secondary buds. In areas showing little growth from a distance both primary and secondary buds are dead. An accurate estimate can be made when flower clusters in new replacement shoots are visible. Growers should continue their disease control programs in areas that show fair growth and may have a marketable crop. Grape flea beetle larvae have been found feeding on the leaves.
Strawberries are blooming. The cool, wet conditions have been favorable for Botrytis grey mold disease development.
Raspberries flower clusters are emerging. Growers should be scouting for leafrollers.
Cranberry buds are beginning to burst.
There will be no Monday Fruit IPM meeting on May 29. The
next Monday Fruit
Update meeting will be, Monday June
5, at the Fruit Acres Farm in
Berrien County, at 5:00 PM.
The Grape IPM meetings
in Berrien and Van Buren Counties on Thursday, May 25 will discuss management
options for freeze-damaged vineyards. The morning meeting will be from
10:00 AM to noon at the Cronenwett Farm Shop at 70123 28th Street east of
Lawton. The afternoon meeting will be at the Southwest Michigan Research &
Extension Center from 2:00 to 4:00 PM.
Last week brought
more rain showers through Friday (May 19), and then finally a break on Saturday
that will last through midweek. With these cooler temperatures, apples and all
of our other fruit crops have not grown very much. Also, insect pressure has
been at a low level. Over the past weekend, growers finally had a chance to
apply much-needed fungicides and insecticides to tree and small fruits. Growers
are now looking for a window for applying thinner, which may occur late this
week as warmer temperatures approach. We had rooftop and light field frost on
Monday and this morning. Temperatures were not cool enough to effect tree
fruits. Most strawberry growers needed to frost protect.
Our current degree day
totals have dropped back with the cool temperatures, to a point where we are
just a few days ahead of normal in terms of degree days and about normal in
terms of growth stages.
Our soils remain wet
with little warming. There is little to no field work taking place as growers
are waiting for soils to dry out. Soil temperatures have remained cool in the
mid- to high 50s.
|
GDD totals for March 1 to May 22 |
|||
|
Location |
GDD42 |
GDD45 |
GDD50 |
|
Flint |
620 |
482 |
291 |
|
Lapeer |
687 |
534 |
336 |
|
Petersburg |
682 |
530 |
337 |
|
Romeo |
642 |
499 |
315 |
Apples in the Flint/Romeo area are mostly at 7 to 9 mm. Idas and some of the
earlier flowering apples are around 10 mm for king bloom and side bloom is 6 to
7 mm. Apples to the south are 10 to 12 mm. It has been reported that apples
along the shore of Lake Huron have an abnormal flowering sequence this year. Macintosh
there are at petal fall, and Paulared’s, Northern Spy and Idareds are in full
bloom. Most apple varieties have not grown very much over the last week. Apple
thinning is now foremost in grower’s minds for the next week. It appears that
we are looking at a good thinning window possibly starting today in areas to
the south where more warming will most likely take place, and tomorrow and over
the weekend in areas in the north. Many apple varieties also appear to be
thinning on their own possibly due to the extended cold temperatures and cloudy
weather. Thinning decisions are always difficult to make, and this week it will
be tougher than most years.
We are just starting
to catch adult codling moth in traps. I am aware of only one farm that has
reached codling moth biofix, but with warmer nighttime temperatures expected on
Wednesday and Thursday, I would expect to see a strong catch of codling moth
and many more growers biofixing at that time. A new pest to report this week is
mullen bug caught at three farms. Potato leafhoppers were seen this week after
being reported in last week’s Fruit CAT
Alert. White apple leafhopper has been seen for the first time, however,
they are very small. Rosy apple aphid numbers seem to be growing. Plum curculio
numbers have been very low. European red mite numbers are building, as are
two-spotted spider mites. Only a few blocks have now reached threshold levels. With
cool temperatures, I have not seen a great expansion of predators in apples,
however they are present and with warmer temperatures expected, I hope to see
them continue to develop.
Apple scab spore
discharge continues with each rain event. Over the last week many growers had
between 2 to 3 wetting events. While there may
be an early end to primary apple scab season this year, I am not ready to state
that we are out of primary apple scab season. Stay tuned for details in next
week’s report as we are expecting a slight chance of rain showers on Thursday. I
expect to see apple scab symptoms from last week’s major rain event start to
show up on Thursday (May 25). We have a few ragtag apple blossoms still out
there in some varieties; therefore, with warmer temperatures expected, fire blight
may be an issue, particularly with newly planted apples.
Pears are at fruit set and continue to size slowly with most being in the
range of 8 to 13 mm. There is quite a wide spread of fruit sizes in pears this
year. There is also some ragtag bloom in pears, and therefore fire blight
remains a threat.
Peaches still are at shuck split to fruit set, about the same stage of growth
that they have been at for over two weeks now. Hopefully with warmer
temperatures expected at the end of the week, I would hope to see peach fruit
to begin to size more than it has. I am not seeing any damage from Oriental
fruit moth. I am starting to see some early signs of peach leaf curl. The
leaves on many peaches look tattered and have poor vigor. This is due to the
extended cool temperatures and in many cases the strong wind.
Sweet cherries are currently at 9 to 13 mm. We continue to
see slow growth in sweet cherries this season. There continues to be a certain
amount of drop of fruit. Pit hardening has not begun. I am beginning to see some
black cherry aphids developing in sweet and tart cherries. Perennial cankers
continue to ooze quite heavily. Some systems of bacterial spot are also
starting to show up on foliage.
Tart cherries are currently at 7 to 13 mm with most being
10 to 11 mm. As is the case in sweet cherries, tarts also have not sized very
much over the last week. There is currently a good crop of tart cherries.
Plums are mostly at 6 to 7 mm. I have seen a fair amount of drop in plums
over the last two weeks. No plum curculio stings have been seen in plum or any
other tree fruit crop.
Strawberries are at 70% to nearly full bloom. I continue
to see a few scattered thimble size fruit in several varieties of strawberries.
Many growers frost-protected on Monday and this morning with temperatures being
in the range of 27 to 31 degrees. I continue to see light amounts of early
strawberry clipper damage to the flower blossoms. However this week I’ve seen a
couple of fields that actually had flower trusses clipped. I continue to see
light amounts of tarnished plant bug. Many growers have now applied fungicides
to control gray mold.
Raspberries have also continued to produce new flower buds. I am not seeing any
open bloom in summer red raspberries. Fall raspberries are now about 6 to 8
inches. There are no major problems.
Blueberries are in full bloom. We have a normal to above average crop of blossoms.
Grapes are mostly at 6 to 7 inches with flower blossoms now plainly visible
on most varieties.
Most apple varieties are in the petalfall
stage with some fruits beginning to grow. Late varieties (Romes) have quite a
bit of bloom on them yet. Sweet cherries
and peaches are starting to show
significant fruit growth. There appears to be excellent fruit set in sweet
cherries and peaches.
According to 30-year
averages from the Sparta weather station, degree day totals have fallen off a
bit from the cool weather over the last week. GDD42 totals are about five days
ahead of average and GDD50 totals are about three days ahead.
Fire blight: There was very little risk for blossom blight infections from the rains over the weekend because of the cooler temperatures. Looking ahead, MaryBlyt is calling for a very high risk for blossom blight for any blocks with bloom left. There will also be the threat of trauma blight if storms on Thursday (May 25) bring any high winds or hail that rips foliage. For those with known Streptomycin resistance, you’ll have to watch the weather closely so that you can be covered ahead of a trauma event.
Apple scab: There have been two rain events over the past
week that did not result in infection periods. Spore numbers appear to be
lessening, but these rains did occur at night. We should reach the necessary
degree day totals for GDD32 to satisfy the model used to track apple scab
ascospore maturity to a level of 100% mature spores. We will need to have a few
good rains to discharge all spores. Primary scab is not over.
Apple insects: A regional biofix for codling moth was set for May 10, and we’ve accumulated 40 GDD50 since then. It’s anticipated that we’ll reach the 100 GDD50 post biofix for early egg materials late probably this Thursday or Friday. It is best to set a biofix based on traps in individual blocks. A regional biofix is just a guide.
Oriental fruit moth
adult numbers have been about the same for the last two weeks with numbers
variable block by block. A regional biofix was set for May 1, and we’ve
accumulated 166 GDD45 since. This indicates that egg hatch is beginning, and
cover sprays need to begin in stone fruits to prevent shoot flagging. Spotted tentiform
leafminer continue to fly and sap feeders should be present. Rosy apple aphids
continue to be found and numbers are building. European red mites continue to
hatch. Some blocks have rather high numbers already. Plum curculio damage still
has not been seen, but the warmer weather this week will most likely get them
moving.
Last week was still under the influence of the cool weather
pattern. There were two frost events on May 22 and 23 with the temperatures
recorded by the automated weather stations dropping to 27°F. Growers reported
temperatures as low as 25°F. These
frost events did cause various degree of damage mainly in apples and cherries.
Peaches and cherries, still in shuck, seem to be unharmed by these frost
events. This past week we had several rainfalls. Precipitation totals across
the area range from 0.33 inches in Hart to 0.43 in Bear Lake.
|
Location |
GDD42 |
GDD45 |
GDD50 |
|
Hart |
537 |
408 |
244 |
|
Ludington |
528 |
401 |
238 |
|
Manistee |
555 |
430 |
267 |
Insect activity has significantly been impaired for more than a week now. Aphid colonies have exploded with all this new flush growth induced by the rains. A few single codling moths have been trapped on the forefront of this cool down, but it appears that they are picking up the pace. There has been an increase in trap catches significant enough to set a biofix for May 21 at 238 GDD50. This will be used as a benchmark for the blocks that do not have high codling moth pressure. The blocks that have a history of high codling moth pressure will need to be sprayed early next week. Oriental fruit moth biofix date was on May 1 at 252 GDD45. There has been 153 GDD45 accumulation since biofix.
There were two rain events this week, but only one (May 17) developed into low infection period for apple scab. Both wetting events produced spore discharge. Currently, there are 99% mature spores and it would take a few more rains to flush them out. The end is near, but not here yet. Scab lesions have not been found in the commercial blocks yet, but they are easily visible in the abandoned blocks. I would expect to see the first leaf lesion from the prolonged wetting period that started on May 9 in the next couple of days. There is a lot of new growth and foliage that need to be kept covered.
Apples are mostly in full petalfall, though there are still a fair number of varieties that have secondary blossoms open and some late-blooming varieties that are still in full bloom. Keeping in mind the forecasted rise of temperatures in the next few days and potential rain called for Thursday and Friday, the danger of blossom fire blight infection potential is going to be high where there are open flowers. Canker blight symptoms have not been reported yet. I would expect to see some canker oozing shortly, possibly early next week.
No lesions from previous infections have been found yet for cherry leaf spot.
Symptoms of bacterial leaf spot could be found readily throughout the area.
|
GDD42 |
574 |
|
GDD50 |
265 |
During the past week
weather remained very cool with some continued moisture. Scattered frost
occurred on May 21, 22 and 23.
Over the past two weeks conditions for apple pollination have been very poor. It will be particularly
important this year to assess crop potential prior to application of thinners. Even with all the rain, we have seen very
little scab in managed orchards. Fire blight has not been an issue in most
blocks so far this year, but as temperatures warm and secondary bloom opens, we
need to be aware of fire blight infection for the coming days. Growers should
check blocks for late bloom and use the fire blight model on Enviro-weather to
determine infection potential. Oriental fruit moth numbers are down to zero for
the week, probably due to cold temperatures. We have been catching codling
moth, but only an average of one per trap here at the NWMHRS and five per trap
in an unmanaged block. Blocks that do not have exceptionally high overwintering
codling moth populations have not yet had enough flight to establish a biofix. Our
adult spotted tentiform leafminers counts are down to an average of 30 per
trap.
Sweet cherry fruit are exhibiting a lot of frost scars. The major problem with frost scars is that they lead to cracks during the preharvest fruit swell. This in turn increases the potential for brown rot and Alternaria fruit rot. We have not observed cherry leaf spot so far this season, but European brown rot has shown up in most Balaton blocks and a few Montmorency orchards. No plum curculio have been evident in cherry, but with warming temperatures, we expect them to be in sweet and tart cherries in the next few days. Green fruitworm is present in tart blocks, and we have seen black cherry aphids in higher numbers than is typical.
In grapes, cold temperatures resulted in very slow shoot growth during the last week. Chardonnay shoots are still only at 2 to 4 inches in length with clusters now showing. There has been no sign of significant cold injury at the NWMHRS and, so far, only limited reports of injury from growers. The predicted warm temperatures should result in rapid shoot growth over the next week, so growers need to get ready for early powdery mildew sprays. Insect activity has been minimal over the last week.
Deer have already begun feeding on young fruit trees. Growers in Benzie County are reporting the highest deer population in years. Repellents are generally most effective if applied prior to first damage, or at least as soon as possible after first damage, to try to alter behavior before they think you are providing a banquet!
Following a series of frosty mornings, a significant warming trend will begin Tuesday (May 23) across the Great Lakes region with gradual formation of a large upper air ridging pattern over the eastern half of the United States. Sunny and dry conditions are expected Tuesday and most of Wednesday. An area of low pressure is expected to drift eastward across the region Wednesday evening through early Friday, bringing the next chance for rainfall in the form of showers and thundershowers. Best chances for rainfall will be in extreme western and southern sections of the state Wednesday and Thursday evenings, where 0.25- to 0.50-inch totals are possible. Rainfall totals elsewhere will generally remain less than 0.25 inches.
Temperatures will increase from highs in the 60s to near 70 on Tuesday and lows in the 40s to highs in the 70s and lows in the 50s Wednesday through Friday. For the upcoming holiday weekend, mostly fair and warmer than normal weather is expected with highs in many areas of the state reaching or exceeding 80°F. Dew point temperatures will also be on the increase with muggy conditions possible by Sunday and Monday, and low temperatures falling only into the 60s in some parts of the state. Some scattered showers and thunderstorms will be a possibility once again by Memorial Day (May 29), but areal coverage is expected to be limited at best with most locations remaining dry. Mean temperatures for the next week will likely average 4 to 8 degrees above normal, so a flush of new crop and insect growth and development is likely.
Medium‑range forecast guidance for at least the next one to two weeks is suggesting that the upper air ridging pattern across the eastern United States will continue to be a dominant weather feature with some weakening possible during the 8-14 day time frame.
NOAA 6-10 day and 8-14 day outlooks (covering May 28 through June 1 and May 30 through June 5) both call for above normal below normal temperatures state- and region-wide. Precipitation totals during both time frames are forecast to remain at near normal levels over most of the state with the exception of western sections of Upper Michigan during the 8-14 day time frame, when above normal totals are predicted.
With near neutral ENSO conditions in the equatorial Pacific and little or no direction from other major forecast “tools,” the new NOAA ensemble of long lead outlooks for the next few months are highly vague. Officially, the outlooks for Michigan and the entire Great Lakes region call for near equal odds of below-, near-, and above-normal temperatures and precipitation during the month of June and the 3-month June-August period (the “climatology” scenario).
Nationally, warmer than normal temperatures are expected across much of the southern and western United States during these periods, and possibly for above normal precipitation totals across the extreme southeastern United States associated with what is expected to be a busier than normal tropical storm season in the western Atlantic Basin.
Further ahead, the outlooks suggest warmer than normal temperatures for at least parts of the Great Lakes region for the late summer and fall.