L.P.Berkett, IPM Specialist

June 17, 1998

Apple scab is present in a number of orchards around the state. Why is it present? Reasons range from: being caught off-guard with the early bud development and not being ready to spray for the first infection period of the season and subsequently, not using an effective material post-infection; not being able to put on a fungicide during bloom because of all the rain and then having to contend with wind, thus getting out of the effective post-infection activity range of available fungicides; not waiting enough time to see if a fungicide program was effective against primary scab -- extending intervals before realizing that lesions had developed; spraying alternate middles and, with all the rain, not having enough residue to protect against scab infection; etc.

If you do have scab, it is important to try to determine why. It is important to regularly monitor your orchard so that you can note when scab first appears and then try to trace it back to a recent infection period (and also take quick action against it). The May 18th Vermont Apple IPM Alert included a table with the number of days required for lesions to develop based on average daily temperatures. If you don't know exactly when the lesions first appeared, you should note where the oldest lesions are located. Are they on the oldest cluster or terminal leaves? Middle-age cluster or terminal leaves? Answers to these questions will indicate when infection took place.

If you can determine the likely infection period from which the lesions originated, then it is on to your spray records. Were you "covered" for that infection period either with a protectant or a post-infection material? What were the conditions when you sprayed -- were there conditions that could have impeded good coverage ? How much rain fell from your last spray prior to the suspected infection period and the suspected infection period? There may not have been enough protective residue on the tree, particularly if this occurred during a period of active vegetative growth.

Every year brings its challenges -- including the challenge to learn and gain insights that can be applied in future years. Hopefully, during the VTFGA tour next month we can discuss the scab situation and exchange our insights and learn from each other's experience this year.

Flyspeck and Sooty Blotch:

Warm temperatures and high humidity favor development of these diseases. Cultural practices that increase air flow can significantly reduce these disease problems. Please see Table 14 of the 1998-1999 New England Apple Pest Management Guide (page 64) for fungicide options.

Leafminers (LM):

So far in my travels visiting apple orchards around the state, most orchards did not have high numbers of first generation mines. However, it is important to monitor the 2nd generation mines in your orchard since populations can greatly increase from one generation to the next.

When is the most optimal time to sample for second generation sap-feeding mines? Based on information from Cornell, it is predicted that most of the second generation will be in the sap-feeding stage at about 500-700 DD (base 43F) after the start of the second moth flight for the spotted tentiform leafminer. The second flight has started at the UVM Hort. Research Center and we will be keeping track of DD and posting them at our Website on the Internet: http://orchard.uvm.edu/uvmapple/ . We will also send out an Alert when we approach the DD.

As noted in the 1998-1999 New England Apple Pest Management Guide (page 29), three different Leafhoppers can attack apple trees -- the White Apple Leafhopper (WALH), the Rose Leafhopper (RLH), and the Potato Leafhopper (PLH). It is difficult to distinguish between the WALH and the RLH. With a magnifying lens, you can see a row of small dark spots on the back of the RLH; the WALH does not have these spots. PLH can be distinguished from WALH and RLH by its movement -- when the PLH is disturbed, nymphs move rapidly and often in a sideways fashion. Nymphs of both WALH and RLH nymphs move slowly and straight ahead. Another difference is that PLH feed primarily on immature leaves of actively growing shoots causing a yellowing of the edges which eventually turn brown and look "scorched". WALH and RLH feeding causes stippling (small, yellow/white "dots") on the leaf.

Pictures of the these insects and the damage they cause can be viewed on the Internet at:

WALH and RLH -      http://www.ento.vt.edu/Fruitfiles/walh.html

PLH -     http://www.ento.vt.edu/Fruitfiles/PLH.html

Some orchards in the state already have significant "stippling" from leafhopper feeding. Populations should be monitored. Second and third generations of the WALH/RLH are more difficult to manage than the first generation. Sprays should be targeted at nymphs. Threshold in July/August: 50 nymphs/100 leaves.

European Red Mites:

ERM populations are variable in orchards around the state. Please see the June 4, 1998 issue of the Vermont Apple Newsletter for thresholds and miticide options. (This can be viewed on the Internet at: http://orchard.uvm.edu/uvmapple/pest/disease/IPMNews60498g.html#EuropeanRedMites).

**Incompatibility Alert**

A potential incompatibility problem with Pyramite and NuFilm, a spreader-sticker manufactured by Miller Chemical was reported in recent issues (May 26 and June 16) of Scaffolds, which is an extension publication of Cornell University. One pint of NuFilm/100 gal plus 13.2 oz Pyramite (probably on pears) resulted in a "white-grey cottage cheese-like" sticky residue". Upon further investigation, it appears that the problem arose from incomplete breakdown of the water-soluble bag in which the product is packaged. It was further noted that if the Pyramite bag is completely dissolved first before adding the NuFilm, the incompatibility problem should not occur.

Codling Moth (CM):

As mentioned in previous IPM Alerts, a DD model can be used to better time spray applications if this insect is considered a problem in your orchard. As of June 17, we were at 437 DD (base 50 F) from May 6 (=the biofix for the UVM HRC) which is beyond the most effective time to treat this generation of CM. If you do have a problem with CM in your orchard, a spray for the second generation should be applied 1260 DD after the original biofix date. In situations where CM pressure is severe, that application should be followed by another spray 10-14 days .

More information about CM, including pictures of damage to fruit, can be viewed on the Internet at:

http://www.nysaes.cornell.edu:80/ipmnet/ny/fruits/FruitFS/codmoth.html

Please note: Do not confuse CM tunneling with that caused by European Apple Sawfly larvae when EAS larvae migrate from their original tunnel just under the apple 'skin' to another fruit where they tunnel to the core. The damage looks similar but occurs at different times in the growing season.

Apple Maggot:

Because the growing season started early does that mean that Apple Maggot traps should be placed in the orchard earlier than "normal"? Based on information in the 1998 Cornell Pest Management Recommendations for Commercial Tree-Fruit Production, first trap capture of apple maggot flies should occur around 867 DD, base 50 F, from Jan 1 (give or take 128 DD = from 739 - 995 DD). We have been accumulating degree days from Jan 1 at the UVM HRC and, as of June 17, we have accumulated 618 DD. We will continue to post DD at our Website (http://orchard.uvm.edu/uvmapple/) and also send the information out in Alerts. Information on monitoring will appear in the next issue of the Vermont Apple Newsletter.

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