L.P.Berkett, IPM Specialist

Stage of Bud Development: Fruit Set at UVM HRC

Apple Scab:

At the three sites in Vermont (i.e., New Haven, Shoreham, UVM HRC) and a site across the Connecticut River in Walpole, NH where we are monitoring DD for apple scab through the AIM project, it is projected that if the warm weather continues, we will reach 900 DD by the end of this week. After reaching 900 DD (base 32, from Green Tip), the next day-time, soaking rain should release the remainder of the ascospores in the leaf litter. It goes without saying that if your site has been cooler, you will reach 900 DD later. Now and over the next 2 weeks it is important to regularly check your orchard for scab lesions. Thorough monitoring must continue until potential lesions from the last primary infection period have had enough time to appear. You should not cut back on your fungicide program until you have fully assessed the effectiveness of your primary scab fungicide program. The following chart can be used as a guideline of when lesions should appear following an infection period:

Approximate Number of Days Required for Lesions to Appear at Different Average Temperatures

* Additional days may be required if conditions are unfavorable for lesion development (a prolonged period above 80 F or very dry weather)

Fire Blight:

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. At the UVM HRC, although the Maryblyt model indicated that infection did not take place, we have been watching the DD accumulation from May 4 which was the earliest date on which there was a "High" risk of infection at our site. As of May 18, we had reached 103 DD from May 4. If you have had similar temperatures, you should start to see blossom blight symptoms in your orchard over the next week if infection did take place during bloom.  

What do the first symptoms of fire blight blossom blight look like? Infected blossoms look water-soaked and darker green. Ooze may be present as milky droplets on the surface of the infected fruit. Eventually, the blossoms turn brown/black. [Note: A picture of blossom blight can be seen on the WV University's Gallery of Disease Images of Tree Fruit Diseases on the web -- which can be accessed through a link on the Vermont Apple IPM Focus web page -- http://orchard.uvm.edu/uvmapple/pest/ ]

The next issue of the Vermont Apple Newsletter will contain information on post-bloom management of fire blight. 

Plum Curculio (PC):

PC damage has been observed on non-sprayed fruit. PC activity should continue until approximately 340 DD (base 50 F) have accumulated since Petal Fall.  

Codling Moth (CM):

CM are being captured in pheromone traps. As mentioned in a previous IPM Alert, a DD model can be used to better time spray applications if this insect is considered a problem in your orchard. As of May 18, we were at 140 DD (base 50 F) from May 6 (=the biofix for the UVM HRC). If CM pressure is not severe, one spray, applied at 360 DD (base 50 F) after the biofix (=1st moth capture in your pheromone traps), 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 .

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

Threshold for Sap-feeding mines at PF:

Agri-mek applied for European red mites will also have activity against LM. As mentioned in a previous IPM Alert, Provado is also effective against sap-feeding LM.

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