L.P.Berkett, IPM Specialist

May 7, 1998

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Stage of Bud Development: Late Bloom - Early Petal Fall at UVM HRC

Apple Scab:

Until 700 DD (base 32F from Green Tip) are reached, we are still in the accelerated phase of ascospore maturity. As of this morning, we had reached 608 DD at the UVM Hort Res. Center (HRC) (GT = March 31). I would not be surprised if most orchards around the state have had an infection period every day since last Saturday if those orchards had the numerous showers and warm temperatures similar to what we have had here in Burlington. If you do not think your trees were adequately protected this past week, you should apply a material such as Nova, Rubigan or Procure in combination with a protectant within 72-96 hours of the beginning of the "non-protected" infection period. Note that the hours of post-infection activity given are accurate at average temperatures of 50-60 F. If scab lesions are already present from an earlier infection period(s), you should consider 2-3 applications of an SI fungicide in combination with a full rate of a protectant to protect against the development of new lesions and suppress further development of secondary inoculum (conidia) on existing lesions.

According to the Maryblyt model, if infection took place in your orchard, blossom blight symptoms should start to appear when 103 DD have accumulated (base 55F) from the time of infection. We have been tracking conditions at the UVM HRC this past week and although we had 3 of the 4 criteria for infection for at least two days [i.e., we had (1) open blossoms, (2) rain, and (3) aver. daily temps. of 60+F], we did not reach the "Epiphytic Infection Potential" (EIP) threshold of 100. In other words, 100 degree hours had not accumulated since first bloom (base 65F). Temperature (measured in degree hours) affects the rate at which blossoms are colonized by the bacteria on the surface (=epiphytic bacteria) of the flower. It must be noted that the Maryblyt model assumes that inoculum is present in the orchard. Hopefully, the criteria for infection were also not met in orchards around the state.

Plum Curculio (PC): With the warm, humid, wet weather we have been experiencing lately, special attention should be given the following excerpt from the 1998-1999 New England Apple Pest Management Guide:

Guthion and Imidan remain the standard materials for PC.

• cumulative average of 6 to 9 EAS per trap if block received prebloom insecticide
• cumulative average of 4 to 5 EAS per trap if block did not receive prebloom insecticide

Pheromone trap captures in combination with a DD model developed in Michigan can be used to time sprays. Traps should be placed in the orchard at bloom. They should be checked daily until first moth capture. If CM pressure is not severe, one spray, applied at 360 DD (base 50 F) after the biofix, should be sufficient. If you have had a problem with CM, then the first spray for CM should be applied once 250 DD have accumulated from the biofix, with a second spray applied 10-14 days later. A spray for the second generation should be applied 1260 DD after the original biofix date. If CM pressure is severe, that application should be followed by another spray 10-14 days .

Older leaves on interior fruit clusters should be checked for sap-feeding mines. These appear as lightened areas on the undersurface of the leaf.

Cumulative first-generation sap-feeding mines per 100 leaves are:

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