Q. We currently record the daily max. and min. temps. at 8:00 AM (May 2) from data recorded by our weather station for the previous 24 hrs (May 1 and 2). The temperature recorder is also reset at that time. Usually the high occurs during the previous day (May 1) and low just prior to reading the temps.(May 2). Occasionally the low for the next 24 hr period (May2-3) occurs just after the recorder is reset (May 2), so the low for the that period is about the same as for the prior 24 hrs (May 1).

Another method is to select the low that follows the next high in that 24 hr. period. The two selection methods produce different results. The first method tends to produce lower averages and lower EIP which may skip an infection period (EIP=109, ave.temp.= 59.5 F and a wetting event where MaryBlyt shows HIGH) when compared to the second method (EIP=109, ave temp.= 60 F where MaryBlyt shows INFECTION). This is what actually happened on May 1.

Maybe there are other conventions for selecting max/min temps? Please indicate what convention is to be used for selecting temps. This topic has come up at various times at grower meetings and needs to be clarified so we are all on the same page. The same goes for the occasion when a wetting event bridges two 24 hr periods (rain starts in one 24 hr period (May 1) and ends in the next 24 hr period (May 2) but occurs less than 24 total hrs. One or two wetting events?

A. The problems you describe with selecting the most appropriate temperature and rain data for use in MARYBLYT are not uncommon and will persist so long as we try to "quantify" infection events. As a rule, enter the HIGH and LOW temperatures that you record for the last 24 hr period, preferably at about the same time each day (i.e., your 8 AM is fine). The type of "error" you describe with respect to the influence of low temperatures on May 1, 2 and 3 and the average temperature and the risk of infection will occur OCCASIONALLY. About the only place where such a difference is apparent, however, is when EIP is really marginal (100 +\- 10) or where the temperatures are marginal (60F +\- 1 degree). Here is where your subjective judgement and experience comes into play to get the most out of an objective risk assessment and forecasting program such as Maryblyt.

Example: You have had and continue to have a serious problem with fire blight (hence, an abundance of inoculum in the orchard) and your decision to spray\not spray hinges on temperture data that gives you high risk at 59.5F and infection risk at 60F -- prudence and experience would favor making the streptomycin application. If, on the other hand, you have done a good job in the past in managing fire blight and have not had a serious outbreak in the last 2 years, your risk here is marginal and little loss if any is likely to occur if you don't spray. Despite the fact that we assign numbers to certain thresholds (i.e. 198 cumulative degree hours, 60F, 0.01 inch or 0.10 inch of rain) does not mean these are ABSOLUTE LIMITS. Wherever possible, we have chosen our program thresholds on the lowest possible, CONSERVATIVE judgement. Because of this making a decision not to spray when these conditions are just marginal is not likely to result in significant levels of infection.

On the rain issue: If one rain period stretches across the 8AM data time you use, mark it as a rain both days. Using 0.1 inch yesterday and 0.01-0.09 inch today or using 0.01-0.09 for both days will give the same risk. Using 0.01-0.09 inch yesterday and 0.1 or more inches today will give you a risk for yesterday, today and tomorrow even it it does not rain tomorrow. On rainfall, the significant element here is in the thoroughness of wetting. In designing MB, we felt that 0.01 inch of rain or a dew or fog event was sufficient to induce infection if all other conditions for infection were met (flowers open, EIP>100, 60F ave temp). A rain of 0.10 or more, however, might have a "scrubbing" effect in physically moving bacteria from the stigma to the nectarthode and so we consider a rain of 0.10 inch or more to "count" as a wetting event not only for the day it occurs, but for the following day as well, even if no rain occurs on that following day. The same is true if a 0.5 inch rain fell yesterday when the temperature was less than 60F, but if it is greater than 60F today -- we still identify an infection event. (PWS)

Q. What does it mean when EIP reaches 100?

A. I'm getting many inquiries now relevant to HIGH INFECTION RISK when EIP is LOW (12 to 48) to MARGINAL (61 to 85). EIP = 100 means that approx 3-5% of the blossom OPEN that day are colonized. If you have 20% bloom, then 3% of 20% = (0.03 x 0.20)100 = 0.6% of open blossoms could be infected if it rains... etc. Maryblyt was built ON THE ASSUMPTION that there was an abundance of inoculum. A light to moderate amount of fire blight, if not properly and promptly attended to can provide an abundant amount of inoculum. Where an aggressive blight management program has been used and the overall number and distribution of potential overwintering cankers is low, then EIP=100= somewhere less than 3-5% flowers colonized. (PWS)

Q. How much control do I get when I apply streptomycin after infection?

A. What little data we have suggests that streptomycin applied 24 hours AFTER an infection event will provide about 90% control and that 10% infection that does occur can be large enough to fuel an epidemic of shoot blight. (PWS)

Q. What procedure should I use to record my daily high and low temperatures?

A. MaryBlyt was built for use by fruit growers. The program can be run accurately using only a minimum-maximum thermometer and a simple rain gauge. Automatic weather stations are real nice when you'd like a day off or a weekend to go fishing without worrying about missed data. Among these, the least expensive and uncomplicated is a 7-day, wind-up recording hygrothermograph with a leaf wetness recording pen added. Change the paper and rewind the clock once a week and you have a hard copy of your information available on a 24 hour/day x 7 days a week basis. There are more expensive weather stations but none provide MORE accurate information. Yet another option is the new SKYBIT satellite forecasting service. We've heard much about this system and it is being tested now in many locations for its reliability vs ground based monitoring to see how reliably we can depend on such remote sensing information when we need to make critical decisions such as to spray streptomycin BEFORE an anticipated infection event. Note that SKYBIT and most Automatic weather stations (i.e. computer driven) are programmed to report daily data as of 1AM so there is always a possibility that the reported LOW temperature for a given day is derived by selecting the LOWEST of two temperatures before sunset and after sunset. Using the recording hygrothermograph or a minimum-maximum thermometer, temperatures can be read routinely at a given AM time such as 6, 7 or 8 AM. This would make the occurrence of having to select one of two lows less likely (although this would still happen occasionally). (PWS)

At Kearneysville, I always read the data at 7 am and use the low that occurs following the previous day's high. (ARB)

Q. What is the S column for?

A. See p. 30 of MARYBLYT 4.3 Manual. S is for spray. A "?" appears when you need to make a treatment decision by going to the prediction mode (F2 key). If you decide to spray streptomycin, change this "?" to "S" as you would in correcting errors. When an "S" is written in the S column, MARYBLYT assumes you obtained excellent coverage of all blossoms and that no open blossom in the orchard is unprotected. When you need to repeat a spray, therefore, will depend upon when the first flowers to open AFTER your treatment become colonized by the pathogen. For this reason the EIP value is reset to "zero" everytime you write "S" in the S column. (PWS)

Q. What is the T column for?

A. The "T" column stands for trauma. A trauma blight situation develops when epiphytic populations of the bacteria are presumed to be high enough AND damage due to hail, high winds or a late frost occurs. MARYBLYT will automatically write FRST in the NOTE column and trigger a prediction for trauma blight symptoms (TBS column) when the temperature is 28F or lower, but you need to tell the program when you have visible damage from either hail or wind (type H or W in the T column, and the word HAIL or WIND will automatically appear in the NOTE column). If hail or wind did not occur, leave the T column space blank by simply pressing ENTER and continue. (PWS)

Q. How do I enter DEW into Maryblyt?

A. When your data entry window gets to the WET column, type the word DEW, or the letter D. If, in your opinion, fog in the orchard is producing wet leaves, then type the word FOG or the letter F in the WET column. In either case, when you complete the data line entry you will see 0.01 inch of rain recorded in the wet column and the word DEW (or FOG) in the NOTE column. (PWS)

Q. Do I have to measure rain or can I just estimate the numbers?

A. MARYBLYT operates using 2 rain triggers. A rain greater than 0.01 inch but less than 0.10 inch affects the infection risk of that day. A rain greater than 0.10 inch affects the infection risk of that day AND the next even though no rain might actually occur on the second day. As noted above DEW is recorded by simply typing in DEW in the wet column which will then be converted automatically to 0.01 inch rain, but the fact that it was a dew is automatically written in the NOTE column. Tipping bucket recording raingauges are relatively inexpensive and easy to install with a manual counter (no battery power) for daily reading\resetting or with electrical connections to record the amount of rain. These are generally available to record rain in 0.01 or 0.1 inch increments. With respect to rainfall and wetness, the thoroughness of wetting is more important than how long or how much rain occurred. Thus, a heavy wetting dew can actually encourage more infections than a scattered shower of less than 0.10 inch. Having the actual amount of measured rainfall allows you to make some subjective assessment of how severe an infection event might have been based on the degree of wetting. (PWS)

Avoid using this subjective assessment on potential severity as a factor in decision making about whether or not to apply streptomycin. (ARB)

Q. What is the "notes" column for?

A. The note column will be used to maintain a visible record of certain data entries you make: thus, HAIL or WIND will appear when you enter H or W in the T column or FRST for "frost" if a late frost occurs that might trigger a trauma blight prediction. The word SPRY appears in this column automatically when you change the "?" in the S column to "S" to indicate that you applied streptomycin. The above automatic entries are the only ones to appear and have an affect on the program's function. You can enter any four letter word or signal you want in this column as a note on variety bloom or variety petal fall, or even BDAY for your birthday, and the program will not be affected. (PWS)

Note: Answers to frequently asked questions were provided by Paul Steiner (PWS, deceased), University of Maryland, and Alan Biggs (ARB), West Virginia University.

Fire Blight Links

• Fire blight "fact sheets" for apple and pear from the Mid-Atlantic Orchard Monitoring Guide (West Virginia University)
• Fire blight "fact sheet" from Cornell University
• Fire blight "fact sheet" from Penn State University
• Fire blight "fact sheet" from Michigan State University