May 10, 2005
In this issue
Tree fruit news
§ Current fire blight risk assessment
§ 2005 TNRC trapline data – Oriental fruit moth
Small fruit news
§ Blueberry fruitworms: Deploy monitoring traps now
§ Phosphorous acid fungicides
§ Spartan 4F label approved for strawberry
Other news
§ Regional reports
§ Weather news
We have experienced relatively warm temperatures during apple bloom throughout the state – warmer temperatures than we've had during bloom for a few years. A quick rule of thumb for fire blight risk is that days with high temperatures between 70°F and 80°F present a moderate blossom blight infection risk if the rainfall is less than 0.1 inch and a high blossom blight infection risk if the rainfall is greater than 0.1 inch. Days with high temperatures greater than 80°F present a high blossom blight infection risk regardless of rainfall.
High temperatures for the last five days have been conducive to growth of the fire blight pathogen in several areas with trees in various stages of apple bloom (see accompanying table).
|
Location |
May 5 |
May 6 |
May 7 |
May 8 |
May 9 |
May 10 (predicted) |
|
Sparta |
66 |
67 |
72 |
81 |
81 |
76 |
|
Hart |
65 |
68 |
66 |
79 |
74 |
69 |
|
NWMHRS |
68 |
64 |
63 |
81 |
79 |
63 |
Although temperatures are predicted to be cooler over the next few days, the risk is present now. Low amounts of rainfall have kept the fire blight infection risk as determined by the MaryBlyt model from climbing off the charts. However, we must remember the extended period of warm temperatures from earlier in the season (April 4-20). These temperatures would have activated growth of the fire blight pathogen in cankers on trees to likely high internal populations. The long cold period that followed probably shut down growth, but the internal populations would remain at higher levels than normal.
Thus, I believe that fire blight risk may be even greater than predicted by the MaryBlyt model because of the prolonged early season activation of the pathogen. Orchard blocks with fire blight symptoms from prior years would be particularly at risk. Growers should keep trees protected during bloom (see articles in the April 26, 2005 Fruit CAT Alert) and also use Apogee (prohexadione calcium) for shoot blight control where possible applied at petal fall of the king bloom.
There are two species of fruitworms that can infest blueberries in Michigan: the cherry fruitworm and the cranberry fruitworm (see images here). The larvae can be found inside young blueberry fruit during and after bloom, but their presence is often not evident until the premature ripening of infested berries, or the webbing of berries together by cranberry fruitworm are noticed. However, an Integrated Pest Management approach using monitoring for moths, scouting and appropriate application of effective controls can prevent fruit contamination by these pests.
Regular weekly scouting in blueberry fields across west Michigan as part of our RAMP Project indicates that the flight of cherry fruitworm moths has just started. All our monitoring traps were empty one week ago, and yesterday male cherry fruitworm moths were trapped at a farm in Grand Junction. So, if not already deployed, monitoring traps for cherry fruitworm and cranberry fruitworm should be placed in fields this week. In recent years, some fields have experienced high pressure from cherry fruitworm, and it is worth monitoring for both moth species if this has been your experience. Cherry fruitworm emergence usually precedes cranberry fruitworm by up to a week.
To monitor for these pests, hang traps baited with a pheromone lure in the top third of the bush. Deploy one trap for each species per five acres of field with traps placed on bushes along wooded borders or areas where fruitworms were a problem last year. Traps should be checked weekly and the moths counted and removed. Writing the number trapped on the bottom of the trap is one way to keep track of the developing population.
Pheromone traps are very specific, but it is important to know what the species you are monitoring looks like. See the photos in this article for the correct species to identify. Contaminant moths have been caught in cherry fruitworm traps at most of the farms we are scouting in Van Buren County, but these should not be confused with cherry fruitworm. These contaminants are Pseudexentra vaccinii, which are longer and lighter-colored than cherry fruitworm with a distinctive pattern (see photo).
The monitoring traps catch male moths, but because females lay the eggs, controls should be delayed until egglaying starts. This is usually soon after petal fall begins, so in high-pressure fields an insecticide may be warranted during bloom, limiting grower’s choices of what to apply. If pressure is lighter or if bush development is faster than the moths, growers may be able to wait until the immediate post-bloom timing to control fruitworms.
In next week’s Fruit CAT Alert, John Wise and I will review the control options for fruitworms in blueberry.
Recently, a number of new fungicides that have phosphorous acid as the active ingredient have come on the market. Other names that you might hear for this group are “phosphonates” or “phosphates.” Examples are ProPhyt, Phostrol and Agri-Fos. Aliette (fosetyl-Al), an older fungicide, is the prototype for this group of fungicides. However, the long-standing patent on Aliette had prevented similar fungicides from being developed up to recently. In Australia, where the patent did not apply, growers have been using these types of fungicides for over a decade.
This term “phosphorous acid” should not be confused with
phosphoric acid or phosphorus (P), a fertilizer component. In fertilizers, P is
normally found in the form of phosphoric acid (H3PO4),
which readily disassociates to release hydrogen phosphate (HPO42)
and dihydrogen phosphate (H2PO4-). Both of
these ions may be taken up by the plant and are mobile once inside the plant.
Phosphorous acid is H3PO3. A single letter difference in
the name of a chemical compound can make a make major difference in its
properties. Phosphorous acid releases the phosphonate ion (HPO32-;
also called phosphite) upon disassociation. Phosphonate is easily taken up and
translocated inside the plant. Phosphorous acid does not get converted
into phosphate, which is the primary source of P for plants.
Because phosphorous acid and its derivatives do not get
metabolized in plants, they are fairly stable and probably contribute little or
nothing to P nutritional needs of the plants. Some researchers have
investigated the ability of phosphorous acid to act as a nutrient source for
plant growth and found that P-deficiency symptoms developed with phosphorous
acid as the sole source of P. This means that although phosphorous acid can
control diseases it is not a substitute for P fertilization. The inverse is
also true: phosphate is an excellent source of P for plant growth, but is
unable to control diseases other than improving the general health of the crop.
So applying high amounts of P fertilizer will not work as a disease control
measure.
Researchers have found that phosphorous acid fungicides are especially effective against Oomycete pathogens, such as Phytophthora, Pythium and downy mildews in a number of crops. Phosphorous acid has both a direct and an indirect effect on these pathogens. It inhibits a particular process (oxidative phosphorylation). In addition, some evidence suggests that phosphorous acid has an indirect effect by stimulating the plant’s natural defense response against pathogen attack. This probably explains the much broader spectrum of activity observed in fungicide efficacy trials in small fruit crops in Michigan. We’ve found, for instance, that ProPhyt had efficacy against downy mildew, Phomopsis and black rot (but not much against powdery mildew) in grapes. We also have evidence of activity of these compounds against anthracnose in blueberries.
The phosponate ion is highly systemic and fairly stable in plants. The systemic activity allows them to be applied as foliar fungicides for prevention of Phytophthora and Pythium root rots. They also display curative activity. In general, applications every 14 days seem to be effective in grapes, but follow label directions. These fungicides are sold as solutions of potassium and/or sodium salts of phosphorous acid. To compare them, one should look at the “phosphorous acid equivalent,” which should be listed on the label. Prices range from about $25 to $35 per gallon, and the application rate ranges from 2 to 5 pt/acre (~$6.25 to $22 per acre, depending on the product and rate). Under high disease pressure, higher rates may need to be used and spray intervals tightened. Since these fungicides are actually in salt form, care must be taken not to exceed a certain concentration as crop injury may result. In addition, if the concentration is too high, the pH may become so low that in tank mixes with copper products (particularly copper hydroxide, such as Kocide), too much copper will become available and result in crop injury.
EPA has approved a Section 18 label for Michigan for use of Spartan 4F herbicide on strawberry. The label is in effect from June 25 to December 15, 2005. Spartan has both preemergence and postemergence activity on several broadleaf weeds. Spartan should be applied after renovation or during dormancy in late fall.
Apply 4 to 8 fl. oz. of Spartan 4L per application. A total of 12 fl. oz. may be used per acre per year. Spartan should not be used on soils with less than one percent organic matter, because it may injure strawberry plants.
Normally, Spartan is not sufficient for complete weed control in strawberry. Growers should use it along with Sinbar, Poast, Select, 2,4-D or Stinger, depending on the weed problem for a balanced season-long weed control program.
A copy of the label may be downloaded from: www.msue.msu.edu/vegetable/
On May 4 a radiation frost hit southwest Michigan after ten days of cool, cloudy but dry weather. Low temperatures varied widely. The lowest temperatures reported were just above 20°F in frost pockets and low areas. Warmer temperatures, about 28°F, were common in higher well-drained sites. At the time of the frost grapes, had one- to two- inch shoots, stone fruits were in the shuck, apples were in bloom and blueberries at pink bud. Under these conditions temperatures below 29°F should have caused damage to all fruit. Only apples suffered severe damage. Damage was minor close to Lake Michigan. Damaged increased to the east away from the lake where temperatures in the mid-20s were common. Warmer temperatures returned on Thursday with highs into the 80s since Friday. Precipitation totals for last week were less than a tenth of an inch. Most soils are dry. Soil temperatures are about 50. This week is forecast to cool through the weekend with little chance of rain.
GDD totals: March 1 through May 8, 2005
|
Grapes April 1
|
|||
|
Location |
GDD42 |
GDD45 |
GDD50 |
GDD50 |
|
462 |
354 |
256 |
234 |
|
|
485 |
374 |
256 |
233 |
|
|
Lawton: |
466 |
365 |
250 |
228 |
|
435 |
350 |
223 |
203 |
|
|
506 |
400 |
270 |
245 |
|
|
410 |
304 |
205 |
182 |
|
Plant development
has taken off with the return of warm weather. Leaves in apples, pears and
plums look tattered and color has improved with the warm temperatures.
These warm conditions could bring out plum curculio, which
likes warm humid conditions for egg laying. We have the temperature but not the
humidity and we have had strong winds. See
the notes on plum curculio monitoring in last week’s Fruit CAT
Alert. At this time only apricots, sweet cherries and Japanese plums
are out of the shuck.
Apricot fruit set looks good.
Peach fruit are in the shuck. Last week we said we were going to ignore the first flight of Oriental fruit moth and Biofix on the adult emergence after the weather warmed up. Southern and central Berrien County had a significant flight before the cool weather arrived. Biofix for the first flight was April 15 at 175 GDD45, we are now at 354 GDD and have picked up 180 GDD and Oriental fruit moth egg hatch has begun in Berrien County. For the rest of the region, warm weather and Oriental fruit moth returned on May 6 at 320 GDD45. Growers treating bearing orchards for tarnished plant bug and plum curculio should check the insecticide efficacy table on page 56 of the Fruit Management Guide, E-154.
Sweet cherries are out of the shuck and show good growth. The largest fruit are almost 12 mm in diameter. Most fruit are about 9 mm. Tart cherries are still blooming. Leaves are out and growers need to protect against cherry leaf spot. Newly opened tart cherry flowers appear white, while older flowers from before the frost have lost their petals. Older fruit is in the shuck. We should have a good handle on fruit set next week. Sweet cherry growers should be monitoring for plum curculio.
Japanese plums are out of the shuck and about 8 mm in diameter. These fruit will be a target for plum curculio. European plums are in the shuck. Fruit set looks light. Growers need to protect against black knot if it rains.
Apples are at petal fall. There is severe damage to apples in eastern Van Buren and Kalamazoo counties. Some growers report that they have no apple crop. Areas within ten miles of the lakeshore show little damage. Very warm conditions mean that a rain will cause a fire blight blossom infection at this time. Temperatures and the bacterial population rose into the danger level Sunday. The risk of fire blight remains high as long as the daily high temperatures are above 65°F. Friday’s rain was an apple scab infection period in some areas, but most areas reported little rain, not enough leaf wetting to begin an infection. European red mites have hatched. Redbanded leafroller trap catches are declining signaling the end of the first flight. There are no reports of leafroller larvae feeding. Next week may be our best apple thinning window, when the temperatures rise again. We biofixed codling moth on May 8 and 256 GDD50. Check the article on using new insecticide materials in the May 11, 2004 issue of the Fruit CAT Alert.
Pear bloom is ending. Wind burn and freeze damage is easy to find in pears. Pear psylla eggs have hatched; we can expect a heavy hatch with warmer weather this week.
Blueberry bloom has begun. Growers should apply fungicides to control mummy berry if they get a freeze, rain or irrigate with leaf wetness for more than four hours. Redbanded leafroller trap catches are declining signaling the end of the first flight. There are reports of leafroller larvae feeding, but this is probably due to overwintering obliquebanded leafroller. Cherry and cranberry fruitworm adults are now being caught. During bloom growers should apply only fungicides not insecticides to protect the bees. Insecticide sprays can wait until after bloom.
In grapes, Concord shoots are about three inches long, have three leaves out and the flower clusters are well exposed. Chardonnay primary shoots are about two inches long and have three leaves out and the flower clusters are emerging. The secondary buds in Chardonnay are at first swell. There are few reports of flea beetle feeding, but some growers report that cutworms have been feeding on the flower clusters. Grape berry moth adults were trapped last week. The frost on Wednesday caused surprisingly little damage to grapes. Perhaps the dry conditions allowed the grape shoots to withstand colder temperatures than we expected them to.
Strawberries are blooming and early varieties have small green fruit. Many growers irrigating and protected against frost so there was little damage Wednesday. Growers are finishing spreading straw. Growers should apply fungicides during bloom to control fruit rots.
Summer raspberry flower buds are plainly visible and early varieties have begun to bloom. Fall raspberries have emerged from the ground.
Cranberries buds are swelling and some varieties have begun to green up.
Growers have been busy watering new plantings. The next Monday Update meeting will be May 16 at the Overhiser Fruit Stand in Allegan County at 5:00 PM. Apple thinning will be a main topic of this meeting. There will be one MDA restricted use pesticide recertification credit available at this meeting.
Warm temperatures
over the last few days have kicked the flowering process back into high gear,
resulting in a great deal of activity in most of our tree fruits. We are again
picking up degree days fairly rapidly over the last few days. It was
interesting to see apples come into bloom so quickly over the weekend and on
Monday.
It now appears that
we had some frost and freeze damage from cold temperatures on Tuesday and
Wednesday morning (May 3-4) last week. Low temperatures that were reported
included 25 and 26 degrees at many orchards. Most orchards report temperatures
at 27 to 28 degrees. Some areas were a bit luckier and only had temperatures as
low as 30 degrees. Most of the cold damage on apples has occurred in low frost
pockets of orchards. In these areas varieties such as Gingergold and Crispin
have been hurt fairly significantly. In most of the orchards I sampled for
frost damage on Monday, apples were still in great shape with little to no
damage. Damage was reported this morning on sweet cherries with about 90
percent injury to small fruit. Two great differences in these more recent cold
events were the fact that cold temperatures had preceded the cold events and
therefore flower buds were fairly tight (the positive side). On the negative
side, our flower buds were exposed to cold temperatures on one or two of those
nights starting at about midnight or 1:00 AM and running all the way through
7:00 AM. This is a bit unusual to have such an extended cold period. The more
typical cold period that we run into is flower buds being exposed to just a few
hours of cold close to sunrise. The foliage on most tree fruits still appears
to be “tattered” from cold and wind injury.
Our season is now
running about normal in terms of degree days and flowering stage. The flowering
date for many people for McIntosh is May 8-10. So Mac’s and other apple
varieties are back to normal. One rather unusual thing in apples is that most
of our apple varieties are flowering at about the same time. There seems to be
very little spread this year in apple blossom times. Another unusual factor in
blossom this year has been the length of time that sweet cherry blooms have
been on many trees. I’ve now seen blossom for two to two and a half weeks on
some varieties of sweet cherries.
Soil moisture is now
adequate to below adequate in the north, which would include the Flint/Romeo
areas. Most areas only had a trace of rain last evening. For many people to the
south soil moisture supplies are much below normal and below adequate. Many
growers have already turned on irrigation systems and are particularly paying
attention to newly planted fruit and small fruits. Soil temperatures at the
four-inch depth have moved back toward the low 60s.
|
Location |
GDD42 |
GDD45 |
GDD50 |
|
Flint |
361 |
279 |
175 |
|
Romeo |
350 |
270 |
160 |
|
Petersburg |
365 |
282 |
179 |
Apples are flowering at about their normal time period. Mac’s and Red
Delicious are at full bloom. Due to cold weather last week there are very few
new pest problems to report over the last week or so, except European red mite
egg hatch has occurred. Tarnished plant bugs continue to be seen in low
numbers. Redbanded leafroller trap catches remain about the same at 20 to 30
per trap. A few trap catches have been as high as at 60 per trap. Oriental
fruit moth trap catches are mostly at 0 with one or two apple blocks at 25 to
30 per trap, however these high trap catches are unusual. However, I expect to
see trap catch jump quickly as a result of recent warm temperatures, even at
biofix levels later in the week. Spotted tentiform leafminer trap catches
continue to rise with each warm event that we have. I have not seen any egg
laying and peak first generation adult flight should be here in the next few
days. I continue to see a few rosy apple aphids, however numbers are fairly
low. Plum curculio was not detected last week, mostly due to cold temperatures.
No codling moth adults have been caught yet. European red mite egg hatch has
occurred at just two or three farms. This early egg hatch is an indication that
over the next few days I expect to see widespread European red mite egg hatch.
Apple rust mites continue to be seen, however in fairly low numbers. One
incidental pest this year is mealy bugs seen in one apple block. It is curious
to see this pest in apples and with numbers this high. Dogwood borer larvae
continue to be seen in crotches of apples and in burr knots of rootstocks. The
number of predators continues to rise each week with fairly good numbers of
ladybugs, increasing numbers of Amblyseius fallacies and Stethorus
punctum. Lacewings eggs continue to be seen as well.
Most apple growers
have not had a fire blight infection yet, however conditions were very close in
the Flint area with a rain event last night. Temperatures were just a bit lower
than was required for an infection period. Most growers will be covering for
fire blight sometime this week. Several growers had another apple scab wetting
event mid- to late week last week. This was very site-specific depending on
rain showers and temperature. There are a few lucky apple growers this year
that have not experienced any apple scab wetting periods. This is a rather
unusual event. Apple scab spore discharge continues at a normal pace this
season. I am concerned about powdery mildew infections in these situations
however.
Pears are mostly at full bloom with a good crop of pears coming along. Pear
psylla adults have been seen flying for about four weeks now, and egg laying
was reported for the first time last week. Eggs are numerous at most farms.
Peaches are mostly at full to late bloom or in the shuck. There is a
widespread of peach flowering. With the exception of the Romeo area, which has
a fantastic crop of flower buds, most people’s peach crop is average to below
average.
Sweet cherries are in the shuck. As reported earlier there
was some damage from cold injury to sweet cherries last week.
Tart cherries are mostly at full bloom to early petal
fall. Brown rot control sprays are being applied now on tart cherries. Again, I
reported last week that there was a fairly significant amount of winterkill on
young twigs of tart cherries.
Strawberry flowers have emerged from the crowns. There is little to no bloom. Most
growers have frost protected two to three times this year. However there is
quite a spread where some growers have frost protected as many as five or six
times and a few only needing to frost protect once. There was a good layer of
ice at most strawberry farms last Wednesday morning. Strawberries have picked
up in terms of vigor over the last week with plantings looking a bit better. I
continue to see very light numbers of strawberry clipper and tarnished plant
bug in strawberries.
Raspberries are a couple weeks past bud break and continue to look weak due to
winter injury. Fall red raspberries have been slow to emerge from the ground
with canes being about two to three inches in length right now. There are no
major pest problems to report on raspberries.
Blueberries continue to be at late pink bud. I expect to see flowering over the next few days on some early varieties.
|
Weather Station |
GDD42 |
GDD50 |
|
West Olive |
444 |
228 |
|
Holland |
437 |
222 |
Most apple
varieties are in the full bloom to beginning petal fall stage. According to
30-year averages from the Sparta weather station, degree day totals are running
about four days ahead for GDD42 and six days ahead for GDD50.
The frosts last
week didn’t cause too much damage to the flower buds in general. Red Delicious
seemed to be affected the most, but right now it only looks like the Red crop
will be down in the Grand Rapids area by 5 percent or so.
Fire blight is of
great concern over the next week on any fire blight susceptible varieties with
open bloom. Fire blight bacterial populations should be at high enough levels
with the warmer weather that growers should protect open bloom.
So far this season,
there has still only been one light apple scab infection recorded on April 20.
Most growing areas have had four or five wetting periods, but only one has
resulted in a light apple scab infection. Lesions from this infection should
show up at any time in abandoned blocks. According to GDD32 accumulations,
about 70 to 75 percent of the ascospores mature at this time.
Most trap numbers
have been low or even at zero over the past week, but an increase should be
expected this week with warmer nighttime temperatures. Codling moth should
start to fly at any time. Oriental fruitmoth adult numbers should increase.
Spotted tentiform leafminer are flying again. Rosey apple aphids are being
found – numbers seem to be increasing even in the cooler weather of last week.
Plum curculio damage has not been seen yet, but they should start being active
at any time in early fruiting tree fruits such as plum and apricots.
Petalfall
applications should be carefully timed this year – it’s been a long time since
pink sprays went out and the warmer weather will push insect development along
quickly.
Blueberries in West Central Michigan are in the early stages of the bloom period. The variety Bluecrop is in the late pink bud-early bloom stage while the variety Jersey is in early pink bud. There was a freeze/frost event that occurred on May 3-4. The event started at 11:00 PM on May 3 and concluded at 8:00 AM on May 4. The lower temperature registered in West Central Michigan was about 26ºF. In Ottawa County, growers with overhead irrigation initiated frost protection measures during the evening of May 3 when the temperature dropped below 36ºF. However, by midnight the irrigation was turned off since the temperatures were above the critical temperature that may cause significant frost damage to blueberry early varieties such as Bluecrop. An evaluation conducted on May 4 and two days later showed little or no damage in Ottawa and less than 5 percent in Allegan County early varieties.
Regarding pest problems, the redbanded leafroller is the only active pest in blueberries but leaf bud damage is minimal. The cherry fruitworm (CFW) initiated its emergence in the southern portion of Allegan County but the cranberry fruitworm (CBFW) has not emerged yet. As in the past, pheromone traps for the CFW that were installed early are trapping a contaminant moth, Pseudexentra vaccinii Miller. This insect is occurring in low numbers (less that 8 per trap) and it is recommended to take a close look at it to avoid misidentification of the adult CFW. In the picture from the article by Rufus Isaacs, you can see the difference between the true CFW and the contaminant moth. Although both moths are almost the same size, be aware of the band pattern and peppered color in the adult CFW versus the silver color observed in the contaminant moth.
With respect to our educational programs, this year’s Blueberry Integrated Pest Management (IPM) Scout training program has been possible thanks to the collaboration and funding of the USDA Risk Management Agency, MSU Extension West Central Region, Ottawa County Extension and MAES through the Trevor Nichols Research Complex. Our program began on February 17 and we have completed the classroom modules corresponding to the training curriculum. On May 12, we will initiate the field “hands-on” portion of the training program. The class meets from 1:00 to 5:00 PM at the MSU Trevor Nichols Research Complex in Fennville, Michigan. The 2005 enrollment includes part and full-time workers and growers. We have 12 African-American, 5 Hispanics, and 13 Caucasian blueberry growers and farm workers.
Instructors participating in this educational initiative are Dr. Annemiek Shilder (MSU Plant Pathology), Dr. Rufus Isaacs (MSU Entomology Small fruit Specialist), Dr. Eric Hanson (MSU Horticulture, Weed Specialist), Dr. Anamaria Gomez-Rodas (MSU Entomology Research Associate), Carlos Garcia-Salazar (MSU Extension Small Fruit Educator), Mark Longstroth (MSU Extension District Educator), Dr. John C. Wise (MSU Entomology Fruit Specialist, TNRC), Dr. Trent Wakenight and Dr. Lillian Occena-Po (MSU Food and Toxicology Center).
Temperatures are finally rising and it is starting to look like and feel like spring. Last week we had a little bit of rain, nearly enough to offset the droughty soil conditions. The Friday/Saturday morning rain (May 6-7) was a strange one. A short but very intense storm brought rain and pea-sized hail. The radar was tracking the storm stretching from the southwest to northeast corridor and covering much of our district. Some of the purple echoes appeared to have covered Mason and parts of Manistee Counties. The most recent wetting event from yesterday and last night did not result in any significant precipitation. Our weather stations were showing the amounts less than 0.1 inches. Currently, we are under the ongoing wetting event in northern parts of the district that are likely to result in infections.
|
Location |
GDD42 |
GDD45 |
GDD50 |
|
Hart |
371 |
287 |
179 |
|
Ludington |
334 |
257 |
157 |
|
Manistee |
368 |
289 |
183 |
Apples are into bloom. In the Hart area, McIntosh is in full bloom and other varieties are not too far behind. A couple of days in high 70s and even 80s have speeded up bud development. No scab infections have occurred from the recent rains. The ongoing wetting event may result in infection periods. As of May 8, there are 71 percent mature spores in Manistee/Bear Lake area, 68 percent in Hart and 56.7 percent in Ludington. With predicted rains for the next several days, there is a potential for major spore discharge. Pay attention to powdery mildew. In dry years, when we have reduced spray program for scab, powdery mildew becomes a problem. With most varieties getting into bloom, there is a major concern with the possibility for fire blight infections. Maryblight is indicating that there is a high potential for infection for the next three days. The epiphytic infection potential (EIP) throughout the area is over 100 or above the threshold, so a wetting event and the temperatures in low 70s will result in infection. Mind you, the wetting event does not necessarily mean rain; it could also be high humidity or spray. It is strongly recommended that the blocks be protected ahead of the wetting event. Insect activity is relatively low given the phenological development. There is an increased number of spotted tentiform leafminers in posted traps. Oriental fruit moth catches are below the levels noted prior to the cold spell. First catch of codling moth in the region has been reported for May 9. Scouts are reporting finding tarnished plant bugs, rosy apple aphids and European red mite young instars.
Pears are in full bloom and subject to fire blight infections.
Sweet cherries are in petal fall. More reports regarding frost damage from April 29-30 are coming in. It appears that Ulsters and Lapins have suffered the most damage. I would expect to see some symptoms indicating the presence of bacterial canker – blossom blight.
Tart cherries are in full bloom. We have had some excellent pollination weather and fruit set over the last few days. Under these optimum conditions, pollen tube penetrates the style within 24 hours after the pollination resulting in a fruit set.
European plums are in full bloom. Excellent pollination conditions since last Friday.
Peaches are in full bloom. It appears that the fruit set will be very good. It looks like a very good crop.
In stone fruit, besides the bacterial cancer and leaf spot, brown rot is of concern as well. The optimum temperature for brown rot blossom blight development is 68-75 degrees. Under these conditions, presence of water film on the blossoms of only five hours will result in infection. Currently, we are having ongoing infection of brown rot and cherry leaf spot under optimum conditions. Blocks need to be fully covered. There are several very good materials that we have been relaying upon for a number of years (Nova, Elite, Orbit). In order to postpone resistance development it is recommended to use different chemistries – protectants like Bravo, Captan, Ferbam, Ziram, Thiram, Wettable Sulfur, strobilurins like Elevate. In any case, it would make sense to use something that would provide protection from leaf spot as well. At this point one (somewhat costly) possibility would be Elite +Bravo. Currently, we are having low cherry leaf spot infection in progress in Manistee/Bemzie area. Oriental fruit moth has not been seen since before the cold snap. Plum curculio has been very active in Manistee/Bear Lake area. That area received a bit more rain that accounts for their early arrival on the orchard scene. Growers brought some samples to the meeting indicating the damage to the buds by the plum curculio’s early feeding.
GDD42 361
GDD50 164
Warm weather finally returned this week, but not until another frost event on the morning of May 4. Rain occurred a couple of days, but amounts were generally very low. Precipitation for April and May is well below normal. Degree day accumulations remain ahead of normal despite below normal temperatures from April 20 through May 4.
Apple crop potential looks good this time. A
wetting event was reported for Monday, May 9 that resulted in a light scab
infection period in the Northport and Eastport areas. There is fire blight
potential in warmer areas with the increased heat and moisture on May 9. Pest
insects are still in low numbers, but we have spotted a few different bugs in
the past week. European red mite nymphs just showed up in Leelanau County, but
they have been bopping around the Elk Rapids area for four or five days.
Twospotted spider mite eggs have been laid, and a few nymphs are noticeable. We
are still seeing low levels of apple rust mites. Tarnished plant bugs have made
their debut this week. Spotted tentiform leafminer eggs were detected
yesterday, but the eggs numbers seem lower than normal. A few OBLR have been
recorded in Antrim County. On a good note, predator mites were noticed for the
first time this week.
Spring frost events have caused enough bud damage to reduce crop size in tart cherries in low pockets, but most sites are looking good at this time. Warmer areas of northwest Michigan have reached full bloom as of this writing. Pollination conditions have been excellent to date for tarts. Cooler areas are not yet in bloom or are in partial bloom. The May 9 wetting event has also resulted in light cherry leaf spot infection across the northwest; however, minimal leaf surface is present. No insects to report for cherries.
Sweet cherries began blooming during the recent very cold period in the more advanced areas. Expect pollination problems in these areas to significantly reduce crop. Sweet acreage in cooler areas did not bloom until the recent warm period when pollination conditions were good. Frost damage appears quite limited in sweets. The wetting event on May 9 provided conditions for brown rot blossom blight and a light infection period for cherry leaf spot. At this time, no plum curculio egg laying has been observed. Insecticide sprays should be avoided during the pollination period and bees have been removed from the area.
Peaches are currently in bloom.
Grape flea beetle and climbing cutworm activity
have been low this year.
Trees and vines have not pulled much moisture from the soil to date, but they are now entering the period when foliage will be rapidly developing. The demand for water increases as the foliage develops, so given the dry start for this growing season. We suggest getting irrigation systems ready for use. The need will occur first in plants with smaller root systems, i.e., young trees/vines and apple and cherry trees on dwarfing rootstocks.
If no irrigation is available, try to mulch newly planted trees as soon as possible. Mulching early will reduce evaporative soil moisture loss and suppress weed growth, both of which will help conserve existing moisture.
Despite widespread snow and rain during the last week of April, precipitation totals across Michigan have consistently remained below normal since early March. The extended dryness has resulted in depleted topsoil moisture levels in many areas of the state, especially given recent warm temperatures and accelerated potential evapotranspiration rates. Some rainfall is in the forecast during the next several days, although amounts and areal coverage remain somewhat uncertain due to inconsistencies in numerical forecast guidance. A cold front marking the edge of a large Canadian-origin air mass will move from northwest to southeast across Michigan late Tuesday into Wednesday (May 10-11). Some showers will be possible in northern sections of the state overnight Tuesday with dry conditions elsewhere. Winds behind the front will shift from the west and southwest to north or northeast and continue for much of the rest of the workweek.
The greatest forecast challenge of the week will be what happens to the frontal boundary after it passes Michigan. Computer guidance suggests that it will return northward late Wednesday, setting off rain and some embedded thunderstorms possibly as far north as the Lower Peninsula. Should the boundary remain well south of the state, dry conditions will continue, while widespread rainfall will be more likely if the boundary actually moves back into Michigan (current expectations are that it will not). With a reinforcement of high pressure on Thursday, fair and dry weather is expected across the state.
On Friday and Saturday another weather disturbance will approach from the southwest, bringing a better chance for showers and thunderstorms to nearly all of the state. Drier weather is expected by Sunday. Temperatures will vary widely across the state during the next few days following the frontal passage. High temperatures will fall back to the 50s in northern sections of the state (with some upper 40s possible in northern lakeshore areas) to the 60s in the far south. Some nighttime freezing temperatures will be possible in interior sections of the Upper Peninsula on Thursday and Friday morning with above freezing temperatures (upper 30s to mid 40s) elsewhere.
The combination of cool temperatures and steady northeasterly winds is expected to lead to generally unfavorable pollination conditions across much of the state through the end of the week. In the medium range time frame, latest forecast guidance calls for a general westward shift of the major upper air features of the past week, which would put Michigan under the influence of northwesterly flow. The NOAA Climate Prediction Center 6-10 day and 8-14 day outlooks (for May 15-19 and 17-23) both call for near normal temperatures and below normal precipitation totals state- and region-wide.
In the newest set of long lead outlooks, the NOAA Climate Prediction Center officially puts all of Michigan outlook into the equal odds or “climatology” scenario of equal odds of below-, near-, and above normal values for temperatures and precipitation during the month of May. The outlook suggests increased odds of warmer than normal temperatures across large sections of the central and western Corn Belt region, and greater than normal rainfall for parts of the Upper Midwest.
For the 3-month May through July period, the outlook
suggests wetter than normal conditions across western sections of Michigan with
the climatology scenario in the east. Temperatures statewide are officially
forecast to remain in the equal odds category, although cooler than normal
temperatures are expected just west of the state across areas of the Upper
Mississippi Valley.