Northern Michigan FruitNet 2003
Weekly Update
NW Michigan Horticultural Research Station

Jim Nugent                   Gary Thornton                       Bill Klein
        District Horticulturist           District Fruit IPM Agent         Farm Mgr, NWMHRS

    Duke Elsner                                                          Jim Bardenhagen
            Agricultural Agent                                              Leelanau Extension Director

May 13, 2003

WEATHER

Rainy, damp conditions have been common during the past week, with the exception of a warm, sunny day on Saturday, May 10. Degree day accumulation, base 42, is very close to a long term historical average, and hence the stage of tree development is "normal" at this time.

GROWTH STAGES at NWMHRS

Apple: Red Delicious—tight cluster
Pear: Bartlett – green cluster
Sweet Cherry: Napoleon – full bloom
Tart Cherry: Montmorency – early white bud
Apricot – full bloom
Plum: European type – green cluster
Grapes: Chardonnay – early bud swell

INSECTS & DISEASES
By Gary Thornton & Jim Nugent

Sweet Cherries: Recent cool weather has been ideal for developing populations of the bacterial canker pathogen, Pseudomonas syringae. Similar conditions in 2002 were followed by a hard frost on May 19, which led to the severe bacterial canker infections. Let's hope this year we do not see any frost conditions in the coming days. Bloom is generally very sparse due to the March 3 winter freeze event. Winter injury in wood is becoming more evident as spring progresses, particularly on young trees. Leaf tissue is exceptionally well developed compared to the stage of flower development in trees with few remaining flowers. Trees with few flowers have more resources than normal for leaf development.

Tart Cherries: Spring frosts have damaged some buds, but at this point substantial bud damage is generally present only in low areas of blocks. The crop potential in NW Michigan appears to remain good. Balaton lost some flower buds to the March 3 winter freeze, and as in sweet cherry, we are seeing plenty of leaf tissue that is susceptible to cherry leaf spot (CLS) infection before the tree reaches bloom. Montmorency in some early sites also have fully expanded leaves, not just bract leaves. These leaves are susceptible to CLS infection. Spore release can occur during early bloom. Considering the early start that leaf spot had last year, growers that have trees with fully expanded leaves should protect for leaf spot from this time forward. Brown rot pressure is light with the cool temperatures.

Apples experienced a moderate scab infection period on Sunday and Monday, May 11 and 12. This occurred at a time when spore release is typically high. With early varieties nearing pink, powdery mildew should be controlled, particularly on susceptible varieties like Ida Red and Cortland. Insect activity remains low. Rosy apple aphids are difficult to find. Spotted tentiform leaf miner trap catches averaged 32 per trap. Populations of European red mite eggs are light, with no hatch reported so far. 

Pear psylla eggs are easy to find on spurs and should be hatching out soon.

Climbing cutworms have not been very active with the cool temperatures, but as the nights warm, they will increase activity on newly planted tree fruit and grapes. Grapes that over wintered may have few live buds above the snow line, so in order to renew trunks, it may be critical to manage this pest this year.

TREE REMOVAL ASSISTANCE NEEDED
By Jim Nugent, Station Coordinator

We need to remove 180 – 15 year old sweet cherries in the next 4 to 6 weeks to free up space for future research. If you are able to provide a loader and operator to assist us in the removal, please let us know. You could get a tax deduction for the charitable donation. Please give Bill Klein or me a call at 946-1510. Thanks!

WATER BILL PASSES MICHIGAN STATE SENATE
By Jim Nugent

On May 8, 2003, the Michigan Senate passed SB-0289, to amend sections of the Natural
Resources and Environmental Protection Act that deal with ground and surface water use. 
The bill that passed the Senate is far different from the Senate bill first introduced last year 
and then reintroduced earlier this year. The original bill required a permit for new agricultural 
wells (above a certain size). The bill that passed the Senate no longer has a permitting
requirement, and instead requires reporting of water use by agriculture. 

For complete text of the bill visit this website: http://www.michiganlegislature.org/  and type 
in the bill number 0289, or contact the NW MI Horticultural Research Station and we'll send
you a copy.

This bill will now go into conference committee with the House bill. The House bill is designed
to help resolve water well conflicts. The Senate version plans to incorporate the House bill into 
the final bill. A synopsis of the bill that passed the Senate is as follows:

--   Require the Department of Environmental Quality (DEQ) to prepare a Statewide 
groundwater inventory and map within two years after the bill’s effective date.

--    Increase water use reporting fees for industrial, processing, and irrigation facilities 
with a capacity to pump over 100,000 gallons per day from $50 to $100.

--    Require farms with a capacity to pump over 100,000 gallons a day, beginning one 
year after the bill’s effective date, either to register with the DEQ, report annually to the 
DEQ, and pay the annual water use reporting fee, or to register with to the Michigan 
Department of Agriculture (MDA) by annually submitting a water use conservation plan 
(no fee). Details below.

--    Require the MDA to use water use conservation plan information to determine an 
estimate of water use and consumptive use data for each township in the State, and 
then forward the data to the DEQ for inclusion in the groundwater inventory and map.

--    Allow the DEQ to use money in the Water Use Protection Fund to prepare the 
groundwater inventory and map.

--    Create the Groundwater Advisory Council within the DEQ to study the sustainability 
of the State’s groundwater use, monitor implementation of the Great Lakes Charter Annex 
2001, make recommendations on statutory conformance with Annex 2001, and, within 
two years after the bill’s effective date, report to the Legislature; and provide for the 
Council to disband six months later.

The bill is tie-barred to House Bill 4087, which would require the DEQ Director or the 
MDA Director to investigate and resolve complaints about groundwater withdrawal 
conflicts.

The water use conservation plan to be submitted annually to MDA shall include all of 
the following information:

a) The amount and rate of water withdrawn on an annual and monthly basis in 
either gallons or acre inches.

b) The type of crop irrigated, if applicable.

c) The acreage of each irrigated crop, if applicable.

d) The source or sources of the water supply.

e) If the water withdrawn is not used entirely for irrigation, the use or uses of the 
water withdrawn.

f) If the source of water withdrawn is groundwater, the static water level of the 
aquifer or aquifers.
 

APPLE SCAB: ARE THE SI FUNGICIDES USED UP, AND HOW DO THE STROBILURINS HELP OUT?
(Bill Turechek & Wolfram Koeller, Plant Pathology, Geneva) 
SCAFFOLDS Fruit Journal, NY, Volume 12, No. 6, April 21, 2003

In the March 31 edition of Scaffolds, Dave Rosenberger covered the basic strategies for managing apple scab in 2003.  His article emphasized the need for early scab protection because of the potential for high disease pressure in orchards that had foliar scab last year and because of poor scab control caused by SI fungicide resistance.

There are several reasons for concern about SI resistance in New York.  Let us go back in history.  The SI fungicides Rubigan and Nova were introduced in 1988; Procure was added later.  It had been noticed early that the SI's had excellent post-infection performance in the control of scab.  These post-infection activities allowed the development of a delayed four-spray program for scab, with applications made at tight cluster, pink, petal fall and first cover.  But it was clearly emphasized from the start that the delayed four-spray program should only be used in orchards with a low potential ascospore dose (PAD), and that the SI's should be mixed with a protectant at least for the last two of the four applications.  The recommendation to mix had two reasons.  One was to provide additional protection of fruits, because the SI's had shown some weaknesses in the control of fruit scab.  The other reason was to add an anti-resistance component to the equation.  The delayed four-spray program worked well for many growers and for many years. 

Over the years, we have kept track of SI resistance through both research in experimental orchards at the Geneva Experiment Station and periodic testing of SI resistance in commercial orchards.  We found that the protectant mixed with an SI did not delay resistance in strict post-infection programs.  SI resistance developed slowly but steadily, putting more and more pressure on the protectant partner.  We also found that SI resistance developed faster in orchards where SI's were used at low doses, a statement deserving of a comment.  Low doses are not only determined by low application rates.  Low doses are also reached when spray intervals are long and when spray coverage is poor to begin with.

Where do we stand in 2003 with regard to SI resistance?  We have monitored the development of SI resistance over the many years growers have used the SI's.  We found that full-blown SI resistance could develop after a total of 30 applications in orchards where the PAD was high and where SI's were not always used in mixture with a protectant.  On the other hand, we found orchards that have seen over 40 SI-plus-protectant sprays without any sign of resistance developing.  Not surprisingly, we found that most of the orchards we tested were in between these two extremes: they were not fully resistant to SI's, but they also were no longer at baseline.  This in-between status prompted us last year to make the statement that the "party for the original four-spray SI program is over" in the majority of our orchards.  This warning does not imply that SI's are used up entirely.  It means that more emphasis needs to be placed on using protectants in mixture with the SI's and on protection early in the season because the "delayed" part of the four-spray SI program is worn out.

In 2002, we were fortunate to have complete spray records as well as assessments of fruit scab at harvest for 17 commercial orchards located throughout the state.  These growers were participants in the so-called "RAMP" project; a large, multi-state, federally funded project looking at the efficacy and economics of reduced-risk programs for insect and mite control.  In NY, the RAMP project involves apple scab.  Participating growers were asked to apply their standard scab programs, and the incidence of fruit scab was evaluated at harvest.  Analyses of the 2002 data provided by Harvey Reissig and Art Agnello were revealing:

1. The 17 apple growers participating applied an average of eight scab fungicides, with a range of five to 11 applications.  The table below summarizes the pattern of fungicide usage by the growers.  The protectant fungicides mancozeb and captan, applied alone or in mixture, were the most widely used.  Apparently, many growers trust the conventional protectants most.  This is not a bad decision, because mancozeb and captan are quite reliable, if they are applied on a protective calendar schedule.  We must remember though that they are quite unforgiving whenever post-infection activities are needed.

2. Three of the seventeen growers applied exclusively mancozeb or captan, with eight to 11 treatments made on a standard schedule.  Three growers continued to apply the reduced-SI spray program.  Scab control was excellent in 2 of these orchards.  In the third, over 20% fruit scab was encountered; a failure most likely attributed to SI resistance.  We will test this orchard in 2003.

3. The benzimidazole Topsin M, dodine and the anilinopyrimidine Vangard were part of the scab management equation.  Avoidance of Topsin M is a good choice, because benzimidazole resistance persists in most of our orchards.  The situation with dodine resistance is not as clear cut, and the value of Vangard is still debatable.

4. Seven growers replaced some or all of their former SI-plus-protectant applications with a strobilurin fungicide.  Three of these seven growers experienced more fruit scab than commercially acceptable (5-20%).

__________________________________________________________________
Fungicide Class                                       % Usage
______________________________________________________________
Mancozeb (Dithane, Penncozeb, Manzate)                  34.6
Captan                                                  29.4
SI's (Nova, Rubigan, Procure) mixed w/ protectant       18.4
SI's alone                                               5.1
Strobilurin (Sovran or Flint)                           11.8
Benzimnidazoles (Topsin M)                               0.7
Dodine (Syllit)                                          0.0*
Anilinopyramidines (Vangard)                             0.0
______________________________________________________________
* Two applications in mixture with a DMI

There are several concerns relating to the use of SI's and the strobilurins.  One concern is that some growers still use SI's alone without a protectant added.  This has become very risky because of SI resistance.  The data also show that the SI's are still very reliable in some of the orchards.  This underscores our results that the level of SI resistance is by now very different from orchard to orchard but almost impossible to predict.  One of our major concerns is that the strobilurins didn't fare too well.  Why was this so?  We should first answer the following question: Can we use the strobilurins in post-infection programs as we used the SI's in their good old days?  We might be able to provide an answer.

The strobilurins are better protectants than the SI's ever were, but their post-infection performance is not as good as that of the SI's when SI's were first introduced.  Just replacing post-infection SI's with a strobilurin is risky, in particular if the decision was made because of declining SI performance.  First, the strobilurins will not have the same reach-back activity the SI's once had.  Secondly, just replacing SI's with a strobilurin in a delayed four-spray SI program will undoubtedly drive strobilurin resistance.  For example, we tested a Michigan orchard in 2001 where the grower had full-blown SI resistance and had used strobilurins instead of SI's without changing the application schedule.  After only two seasons with four applications each season, scab became a problem.  Our tests showed that strobilurin resistance was clearly on the march in that orchard. 

We know by now how strobilurin resistance will develop.  First, the strobilurins will succumb to the gradual emergence of SI-type resistance and a gradual loss of activity.  This aspect of resistance can be managed with higher doses of strobilurins.  Higher doses can be achieved using either higher application rates or shortened spray intervals or both.  But this initial SI-type resistance will then be followed by the "all-or-nothing" benomyl-type of resistance.  At that stage, high doses of strobilurins will have no impact whatsoever and scab will not be affected by strobilurin sprays. 

Are the SI's used up?  The answer is that they are not in many orchards.  Will the strobilurins help out?  Yes, they will.  But we have to keep in mind that they will not provide the same reach-back activity the SI's once had and still have in sensitive orchards.  The strobilurins are very potent protectants, and they provide powdery mildew control in addition.  But if we use them in the same post-infection programs as we used the SI's before resistance was on the rise, we will drive strobilurin resistance and will lose these fungicides.

What are our recommendations?  Most growers will still be able to use the SI's, but in many orchards, the "party" of the delayed four-spray SI program is over.  Early protection and less reliance on post-infection programs will be the key.  The strobilurins will be very effective, but we must keep in mind that they are less active in post-infection programs than the SI's were at the time we started to use them.  We are currently working on an affordable test to determine orchard levels of resistance to all of our modern scab fungicides.  This will help to design scab programs without the risk of being burned by fungicide resistance.  In the meantime, we should play it safe. 

Fruit scab has never been cheap.  In a Cornell Bulletin published in 1946 and entitled: "Apple Quality and Its Effect on Price and Rate of Sales", it said that "In New York, apple scab is probably the most serious defect resulting from disease or insect."  It also said: "These discounts are highly important to growers.  One or two serious defects could reduce the value of marketable fruit by $100 or more per acre.  Such an amount would have amply covered any ordinary costs of spraying."  Although the dollar figures are much higher now for both the potential loss and the fungicides, the basic message has not changed much.  The difference is that resistance was not an issue in 1946.  Now, we have to factor resistance in.

 If the performance of SI's has noticeably declined over the past years, this was most likely caused by resistance.  In many cases, the SI's will not be used up entirely, but it will be risky to continue with their post-infection use.  The strobilurins will help out, but in strict post-infection programs they are just not as good as the SI's once were.  They do have some post-infection activity, but this should be reserved for emergency situations.  Just replacing a SI with a strobilurin without changing spray schedules will be risky, and it will drive strobilurin resistance.  Has good scab control become more expensive?  Perhaps it has, but the above 1946 statement is still true.  If we look at the potential "discount" losses, then this "amount would have amply covered any ordinary costs of spraying".
 
 

Please send any comments or suggestions regarding this site to: 

Bill Klein, kleinw@pilot.msu.edu
Last Revised: 5-13-03