Today’s Topics – Weather, apple scab update, fire blight update, bacterial spot on stone fruit 

Tree Fruit Development -  In most locations, apples and pears are in various stages of bloom depending on variety and location in state; peaches are at bloom to petal fall. 

Weather Highlights:  We had some weather extremes during the past week.  Rainfall amounts from my weather station locations ranged from 2.2 to 2.5 inches during the rains of April 28 and 29.  After this weather front went through, the temperatures dropped dramatically with very low temperatures the morning of May 1.  The low temperatures from my weather station locations ranged from 23 to 29 degrees for that morning.  I have not had any reports yet regarding the amount, if any, of freeze damage. 

Apple Scab status – I have Spectrum Instrument weather stations at 7 orchard locations throughout the state.  See below for the date that data was last downloaded, dates when apple scab infections occurred, percent spore maturity and degree days for apple scab development.  The degree days for apple scab maturity are calculated with a base of 32 degrees and start at 50% McIntosh green tip in each location.  Note that the "accelerated" phase of apple scab occurs between approximately 300 to 700 degree days (DD).  This is the time when most of the apple scab spores mature; therefore; the critical time for apple scab fungicide treatments.  In most locations, we are in this “accelerated” phase.  Note that we do not have spore maturity and apple scab degree days for all locations due to missing weather data. 

Ledyard- May 6, 2008

Green Tip – April 11

Dates of Apple Scab Infection-4/28, 4/29, 5/3, 5/5

Spore Maturity-61%

Apple Scab Degree Days-506

 

Lebanon-May 6, 2008

Green Tip- April 11

Dates of Apple Scab Infection-4/28, 4/29, 5/2, 5/3

Spore Maturity-61%

Apple Scab Degree Days-507

 

East Lyme-May 6, 2008

Green Tip – April 14

Dates of Apple Scab Infection- 4/28, 4/29, 5/2, 5/3

Spore Maturity- 47%

Apple Scab Degree Days- 429

 

Cheshire-May 7, 2008

Green Tip – April 10

Dates of Apple Scab Infection- 4/28, 4/29, 5/2, 5/3

Spore Maturity-76%

Apple Scab Degree Days-590

 

Glastonbury-May 6, 2008

Green Tip – April 12

Dates of Apple Scab Infection-4/28, 4/29, 5/2, 5/3

 

Preston-May 6, 2008

Dates of Apple Scab Infection- 4/28, 4/29, 5/2, 5/3, 5/5*

*(only a light infection indicated on 5/5)

 

Fire Blight – Fire blight was very serious in Connecticut in 2007.  A number of orchards were affected varying in severity from light (a few strikes noticed on several trees) to serious (whole trees needing to be removed).  Those that had fire blight in 2007 should pay special attention to conditions during bloom, especially if it is predicted to be rainy and warm during bloom. 

Factors necessary for fire blight infections on apples and pears include that the disease is present in your area, that there are open flowers, that enough heat has occurred to allow bacterial populations to build up, and that you have a wetting event such as rain or a spray.   I use the Maryblyt model along with my weather data to determine if fire blight infections have occurred.  I can also use a prediction mode by plugging in predicted temperature and rainfall amounts for the upcoming days.   

Up until now (May 7), we have not had conditions conducive to fire blight infections.  Most rain events occurred during cooler temperatures.  However, more rain is predicted during the upcoming week.   

The Maryblyt program indicates infections are possible (assuming other factors are present) once it's Epiphytic Infection Potential (EIP) value reaches or exceeds 100 units.  See below for the predicted EIP values and predicted temperatures (from AccuWeather.com)  for 2 locations in the state through May 14. Cheshire would represent a "warmer" spot and Ledyard would represent a “cooler” spot.  The predictions show fairly cool temperatures for the next week.   

The EIP values for the upcoming week are all less than 100, particularly in the Ledyard location.  The highest predicted EIP value of 83 occurs tomorrow, May 8 in Cheshire and presumably other “warmer” locations of the state.  Growers in these locations may want to pay particular attention to the weather to see if warmer temperatures occur during the upcoming rain events, particularly if you experienced fire blight last year.  See Dan Cooley’s article (below) for more information on assessing fire blight threats.

 

Ledyard 

Date     Min Temp   Max Temp            EIP

5/7              52                    68             11

5/8              50                    70             24

5/9              44                    57             16

5/10           45                     64               8

5/11            46                    62               0

5/12            41                    58               0

5/13            44                    59               0

 

Cheshire-

Date     Min Temp   Max Temp             EIP

5/7               53                   76              73

5/8               49                   72              83

5/9               46                   59              55

5/10             44                   68              51

5/11             47                   67              27

5/12             42                   58              18

5/13             44                   63                6

ADDENDUM - May 8, 2008

Healthy Fruit Disease Elements – UMass Healthy Fruit, May 6, 2008

Fire Blight. Jon Clements and I have run Maryblyt for Cold Spring Orchard, and according to the latest projections the worst case has a moderate risk of infection for the next 3 days. Levels of risk are not near what they were last year, nor are they predicted to be so far at CSO. However, your conditions may differ, and it is best to evaluate risk on individual farms. Maryblyt requires that data be taken from green tip. However, Cougarblight requires data from the previous four days only. Information for using Cougarblight is available at this site: http://www.ncw.wsu.edu/treefruit/fireblight/mdl98f.htm 

For orchards that had fire blight last year, a streptomycin spray at bloom is recommended, particularly if rain is predicted. Given the low to moderate risk in most areas, if there was no history of fire blight last year, and copper was applied this spring, a streptomycin spray is not critical. However, again, risks vary by farm, and evaluate the weather and risk for your orchard.  

Streptomycin may be mixed with a fungicide, though it is most effective is applied alone when drying is slow, to allow maximum absorption. Available formulations of streptomycin all contain 17% streptomycin, and include Firewall and Agri-Strep. 

When streptomycin is applied to open flowers, those flowers generally will be well protected through petal fall. New-formed fruit don’t have an opening to allow bacteria to enter, and are much more resistant to infection. It is critical that streptomycin applications cover flowers well, so avoid poor spray conditions (wind, etc.) and alternate row applications. Adding the nonionic spreader-activator Regulaid will improve coverage and uptake of streptomycin. 

Nectaries at the bases of flowers are where bacteria enter apple trees, so it is critical that streptomycin reach flower interiors. If the streptomycin is not applied to an open flower, the residue inside that flower is greatly reduced or non-existent. It may be necessary to reapply streptomycin within two or three days of an initial application, not because the antibiotic loses efficacy, but because significant numbers of new flowers open. 

Apple Scab. There have been several infection periods over the past week, and this is matched with high levels of inoculum. Do we need to say any more? After the rains, and because tissue is developing rapidly, fungicides should be reapplied to maintain protection. Risk is high – use protectant or postinfection fungicides to maintain control as recommended in last week’s Healthy Fruit. 

Brown Rot. Risk of brown rot infections on peaches remains high from bloom through shuck split. If you feel that you may not have had good coverage during the rains, consider an SI fungicide at this time (Indar, Orbit, Elite). Chlorothalonil (Bravo, Echo, etc.) may be used up to shuck split, but not after. 

Bacterial Spot. With more bacterial spot showing up, remember that petal fall on peaches is an important time to control infections. The recommendations from states further south, such as New Jersey, where bacterial spot is a big problem are to start terramycin sprays (Mycoshield or Flameout) after shuck split, and to continue them weekly. They may be alternated with copper sprays, though many peaches are sensitive to copper to some degree, and it may end up causing as much damage as it does good.   

The recommended rate is 12 oz. per 100 gal. of terramycin. However, Norm Lalancette in NJ stresses that the antibiotic should be put on dilute and when drying is slow. Here are his statements from the NJ management guide:

"The desired concentration [of terramycin] for control is 150 ppm, or 12 oz. of material per 100 gal. of water applied. Since it has a short residual of only 5 to 7 days, terramycin must be applied on a weekly schedule beginning at shuck-split. Furthermore, this bactericide is most effective when it gets inside the plant tissue. Thus, applications are best made when conditions allow slow drying, such as during the evening when relative humidity tends to be higher. This approach greatly improves tissue penetrations and subsequent control.  

"For effective control of bacterial spot using this antibiotic, complete spray coverage is also critical. It is important to use a spray volume that thoroughly wets the foliage and fruit to the point of runoff.  Typical volumes are 3 gal. per tree for planting densities of 80 trees per acre, which translates to 240 gal. of spray per acre. For trees of different sizes and/or densities, adjust the volume to maintain good wetting but maintain the concentration at 150 ppm."

D. Cooley 

Jon Clements and Dan Cooley from UMass provide very useful information on tree fruits that is also pertinent to Connecticut.  If you are interested in subscribing or to see back issues of the UMass Healthy Fruit Newsletter, go to http://www.umass.edu/fruitadvisor/healthy_fruit/index.html