TO: RI Apple Growers
FROM: Heather Faubert, URI Extension
DATE: May 25, 1999
RE: Apple Newsletter
I know I have been doing an especially dreadful job writing newsletters but I justify this fault with having too little time. Also, all the other New England states put out great newsletters and since many of you now have internet access you can easily access all their newsletters through the AIM web site. The AIM web site (Apple Information Manager) has all the New England apple newsletters and much more! You may have heard of the newsletter <Scaffolds>, from New York. Scaffolds can be accessed by clicking on <Library> on The AIM home page. Another great feature of AIM is Orchard Radar. When you click on the Rhode Island site in Orchard Radar, it takes weather data for Greenville, RI and runs numerous models to help time when things are happening in orchards. For example, using temperature data, Orchard Radar runs a degree day model to predict the end of plum curculio season. Another model uses predicts when is the next time to apply another summer fungicide against fly speck and sooty mold. There are models for many insects and diseases as well as models predicting bud stages and ripening. It is worth your time to get familiar with what is on AIM! The address is http://orchard.uvm.edu/aim
I have been good about updating the weekly telephone recorded message - the hot line! Messages are updated Thursday afternoon. You can call and listen to the message daily between 5:00 PM and 8:00 AM. The number is (401) 949-0670.
Primary apple scab season is over for Rhode Island. The last spores were probably released by the rain of May 19-20. Definitely any remaining spores would have been discharged by the rain of May 23. Since it takes about two weeks for lesions to start to appear after an infection period, you need to continue scouting for lesions for another 2 weeks before you know your orchard is free of primary scab lesions. I didn't find scab lesions on unsprayed trees until May 20th. These lesions were not on the small, fruit cluster leaves but on the 5th of 6th leaf. This means the infection period during tight cluster on April 22 & 23 didn't produce many lesions, at least none that I saw.
If you are scab-free and feel fairly confident that you won't find primary scab lesions, it is safe to switch to your summer fungicide program. If you are finding lesions now the best strategy at this time is to apply Rubigan or Nova, in combination with a protectant fungicide at full rate. This protects against the development of new lesions and suppresses further development of spores (conidia) on existing lesions. Read up on scab eradication on page 15 of your New England Apple Pest Management Guide.
Plum curculio have not been very active but I have seen some damage in commercial orchards. My lone Liberty apple tree at home has been bombarded with plum curculio; nearly every fruit has an egg laying scar! So, even if you don't see damage you know they are around. I can't believe there is much pesticide residue after the 4+ inches of rain we received so it would be wise to reapply an insecticide when fresh egg laying scars are found or before expected warm weather. Plum curculio are most active during warm, calm, humid evenings. Fresh scars are ones that have not yet developed any corky tissue and the crescent-shaped slits are often orange colored.. Imidan or Guthion are your best choices for plum curculio control.
Most growers have applied an insecticide against apple blotch leafminer. There is probably still time to apply Agri-Mek against the small, sap feeding mines. I expect to see mines that have advanced to the tissue feeding stage early next week. Once mines advance to the tissue feeding stage and are visible from the upper leaf surface it is too late to use Agri-Mek (and much too late for Provado). Lannate can be applied when the mines first start being visible from the upper leaf surface but I don't know of anyone who is planning on using Lannate this year. Remember, if you use Agri-Mek it must be applied with a penetrant such as oil, LI 700 or Silwet otherwise it will be ineffective!
European red mite numbers are high in a few orchards. Mite injury is most likely to be significant in the weeks following petal fall. It is critical that mites not be allowed to build up during May and June, when trees are most sensitive to even relatively low numbers of mites (2 -5 per leaf). Check leaves now for mites. The new label on Apollo allows it to be used up to 45 days before harvest. The current thinking is to use Apollo when the first generation summer eggs begin to hatch in early June. Agri-Mek is also recommended against early season mites but should not be applied later than two weeks after petal fall. As apple leaves mature, Agri-Mek is not well absorbed into leaves making mite control much less effective. Again, a penetrant must be added to the Agri-Mek. Since we are short on summer miticides I think it is best to reserve Pyramite for summer time. The spray threshold for mites for this time of year is 1 mite/leaf or 30% of fruit cluster leaves infested with mites.
White apple leafhoppers start hatching during pink and complete hatching shortly after petal fall. The pale white nymphs complete their development on the underside of older leaves. Leafhopper feeding removes sap from leaves, causing stippling that may coalesce into silvery patches. I don't expect first generation white apple leafhoppers to be much of a problem this year due to all the spraying for apple blotch leafminer and Sevin used for thinning. Though white apple leafhoppers are resistant to Imidan and Guthion they are controlled by Sevin, Provado, Agri-Mek, and Thiodan.
Rose leafhoppers adults look identical to white apple leafhoppers but don't start out in apple orchards. Rose leafhoppers overwinter as eggs on cultivated and multiflora rose. In June adult rose leafhoppers migrate into apple orchards and complete two generations before returning to rose and laying overwintering eggs. Preliminary research in Massachusetts shows that removal of multiflora rose within 100 yards of an orchard block could substantially reduce the migration of rose leafhoppers into orchards. Like white apple leafhopper control, control of rose leafhoppers should be aimed at young nymphs. Spraying old nymphs or adults is ineffective.