Here it is March 21 and today will mark the 7th day in March 2012 with record-setting high temperatures. As I write this it is a balmy 82 degrees outside. Amazingly, the average high temperature for this month so far is a warm 61 degrees. The normal high temperature for this month is usually around 47 – 50 degrees! And these temperatures are playing havoc with fruit trees all over the Midwest. Last Friday our apple trees were at silver tip and by noon today, our southern most trees were beginning to show tight cluster. That growth process would normally take several weeks at our normal average temperatures for this time of the year!
This weather pattern is greatly effecting our fungal disease sprays applied during the dormant period and up to fruit set. These sprays are critically important. Usually, these sprays are applied when the trees reach their specific developmental stages during this period or on an extended spray program of every seven to ten days. An additional timing consideration is the actual or projected occurrence of infection periods, the wetting periods of sufficient duration for the various fungus diseases. This factor helps determine when a treatment may be most advantageously applied during the range of a given key growth stage. Additionally, in cool wet springs, it may be necessary to apply one or more "additional" or "in-between-growth stage" fungicide treatments. This action is most generally taken for us in coping with apple scab.
The number, timing, and the type of disease treatments applied between the dormant and the fruit set period varies from year to year. These differences are dictated by the pest complex present and by the amount of precipitation falling during this growing season. The amount of precipitation will directly determine the prevalence and extent of fungal diseases such as apple scab in the orchard and thereby the extent to which fungicides are needed in the spraying program. But when we have the type of spring temperatures we are having this spring, it is going to be necessary to adjust the normal growth stage sprays to compensate for the accelerated growth the trees are experiencing.
We did our normal dormant/green tip copper spray for fire blight control today with the trees being at 1/2” green. That being the case, we adjusted the rate of copper from 6 pints/acre to 2/3 pint/acre per the Champ label to avoid the potential for phytotoxicity on the trees or russeting on apples. The copper rate should be reduced for any applications made after green-tip, and no copper sprays should be applied to apples after half-inch green. We were cutting it pretty close!!
This is the earliest we have ever had to apply our copper spray to the orchard. We normally apply copper the last week of March to the first week of April and we had to drop our dormant/green tip oil spray for fear of the oil adding too much efficacy to the copper causing it to stay on the leaves too long and creating a phytotoxicity issue for us.
We will be adjusting our scab sprays to reflect the accelerated growth stages of the trees by jumping to our tight cluster stage spray and dropping the 1/4” green and 1/2” green sprays. This will allow us to maintain our fungicide rotation in our resistance management program.