June 6, 1997 

Plum curculio (P.C.) have been active, marking some, but not yet a lot of apples in my Tolland orchard. The warmer temperatures expected for much of next week will probably bring most of the remainder of P.C.=s out of their overwintering sites and into the orchards. Check for new fruit injury every day, once you have been 7 days past an insecticide treatment. If little or no injury is seen by 14 or 15 days after the previous spray, immigration into the orchard may be finished.

New York fruit entomologists believe a population of fewer than one WAL per leaf, average, does not justify a treatment. Monitor spur leaves, rather than shoot leaves, during this first generation. Damage produced by the first generation is from removal of chlorophyl from foliage, producing a speckling with small white spots, almost invariably described as Astippling@ by entomologists. WAL also drop dark honeydew spots that are visible on the fruit, but this is typically washed off by rains before the second generation appears. It is the second generation, combined with second generation Rose Leafhopper that deserves more attention. The second generation merges ultimately with a 3rd generation WAL. At that time fruit spotting can be serious, requiring washing of harvested fruit. Whether the current first generation is treated or not, it will be necessary to monitor in July for the second generation, which can be controlled with several insecticides if treatment is begun before nymphal development has progressed very far. At that time it may also be possible to achieve control of potato leafhopper and leafminer species with the same one or two treatments.

The first new generation of crawlers will begin to emerge from under its mothers= scale coverings in about 2-3 weeks. If scale was found on apples last fall, it is important that insecticide sprays (Guthion, Imidan, Penncap M, or Lorsban 50W) be timed for the crawler stage. Two or 3 sprays, at 2 week intervals, may be needed if a thorough oil spray was not applied before Tight Cluster.

Crawlers can be seen with a 10X mangifying glass on bark that shows overwintered scale. They are bright yellow, and active movers. Monitoring problem blocks at 5-7 day intervals, beginning June 30, continuing to July 1, or until activity is seen. If inspection of infested bark does not reveal crawlers, you can conclude your prebloom oil or Lorsban or Supracide treatment prevented further development.

Spores of this disease are expected to be dissiminated during rainy periods until about the middle of June. Very brief showers are not enough to release spores. If you have juniper trees nearby with cedar galls present, you can test them to see whether they are still capable of producing spores. Cut a gall immediately before each test. Soak it with water, then leave it in a high humiidty environment, such as in a plastic bag for a few hours. If gelatinous orange-colored spore-horns appear on the gall, it is still capable of releasing spores. If the gall is allowed to dry, no spore horns will be produced.

Control of CAR requires inclusion of a sterol-inhibitor fungicide (Rubigan, Nova, Procure, or Bayleton) within 3-4 days before or after wet periods that are sufficieint to release spores, or, on a protective basis, a mancozeb or Polyram, ferbam, ziram, or thiram.

At this time of the year apple leaves may begin to show small round brown dots on some leaves, particulalry those very near attached fruit mummies or dead wood that has remained in the tree since last year. The dots are symptoms of the foliar stage of black rot, a disease that can also produce fruit rots as harvest time approaches.

Leaf infections may cause a few leaves to drop off the tree, but they do not produce a lot of spores. Appearance of these spots should alert you to the major spore sources (the mummies or dead wood in the tree). If these are not removed, fruit infections are a possibility. Even though fruit rots are not obvious until much later, most fruit infections begin between petal fall and late June, according to Dr. David Rosenberger (Cornell, Highland). He observes that mancozeb fungicides used at half-rate (one pound per 100 gallons) are not particularly effective against fruit infection, and that Captan, Topsin M and Benlate are the most effective fungicides for black rot at this time.

Some apple scab workers now believe the best indicator of primary spore maturation is the number of degree days accumulated for the growing season. The first rainfall (0.1 inch or more) that follows maturity of Aall@ (95%) of the ascospores in overwintered scabby leaves will discharge those mature spores. A method for determining accumulated degree days is explained in the New England Apple Pest Managmeent Guide, pages 9 and 10.

900 degree days is the value currently being used to indicate 95% ascospore maturity. Temperatues have certainly not been the same across the state, so degree days will vary considerably from place to place. If you do not have a daily record of temperatures (maximum and minimum), you might wonder whether fruit size could serve as an indicator of 900 degree days. Possibly it could, but because temperature of the fruit may be considerably different than temperature of leaf litter on the ground (ascospores), standard air temperature measurements may not be appropriate indicators for both conditions. Fruit size may also respond to sunlight (foliar photosynthesis) differently than do ascospores in dead leaves in the ground.

Dr. Don Aylor (Connecticut Agricultural Experiment Station) reports trap capture of significant numbers of airborne ascospores during the rain of June 2, when McIntosh fruit was 3/4 to one inch diamter. That is larger fruit size than normal for the end of the ascospore season, I think, and it seems further past Petal Fall than normal for end of scab season. Nine hundred degree days had accumulated May 19 in Hamden, meaning 95% of ascospores had matured, according to the degree day model. Rain on May 19 was heavy, and would be expected to have ended the primary scab season; but significant additional airborne ascospores were caught in two subsequent rains (May 25 and June 2).

I conclude from all of this that there is much fine-tuning yet to be done in the methods for identifying the end of primary scab season. My recommendation for Connecticut growers who could easily find scab spots last year is this: Maintain a primary scab fungicide program to cover a 2 week post infection period following the last rainfall of 0.1 inch or more since June 1. If that last rainfall was not wet long enough to permit infection, then maintain the primary fungicide program for 2 weeks beyond the previous infection period. After the 2 weeks look for scab spots. If none, or almost none, stop treating for scab.

If scab spots appear on leaves or fruits, the spores they produce can produce new infection under the same conditions of temperatue and wetness that permit primary infection. There are two differences worth noting: (1) the spores produced on current season=s growth, called conidia, are heavier than ascopores, and do not carry long distances in wind. They are thought to be carried primrily in raindrops, to positions below (or within wind-blow distance from) their source, (2) current season infections continue to produce new spores as long as temperatures do not go too high (somewhere in the upper 80's?), but this process can be impaired by application of certain fungicides. Dodine, sterol inhibitors, captan, Benlate, and Topsin M have been effective at inhibiting conidia production. At least two applications about 10 days apart, are needed to shut off most of the spore production. Spore production may resume after a couple of weeks or more.

If you can find scab spots in many trees, it is important to maintain fungicide residue on the fruits (10-14 day intervals if there is rain) at least through the month of June, when fruits are most easily infected.

Heavy bloom and heavy set indicated this would be a year for aggressive chemical thinning, but winds and below-70 degree temperatures have frequently interfered. By the time fruits reach 20mm diameter, thinning chemicals may be ineffective. If you need thinning, and king fruit is nearing 20 mm, do not wait for warmer weather.

From Pennsylvania State University pomologist, Rob Crassweller comes this nomination for AThe single most important task in young orchards@: clothespinning of nascent scaffold branches. Place them as soon as possible, preferably before July. Toothpicks can be used in July, but they are subject to coming out in winds.

Another task that may be important in young orchards is application of copper spray at Green Tip, and again at Bloom time, in the first two years in the orchard. The purpose is to prevent introduction of streptomycin-resistant fireblight from those out-of-state nurseries where streptomycin resistance is common. See Fruit Growers Newsletter, April 4, 1997, last page, for more information.

As of today, formal approval of this new miticide has not been made for Connecticut, though it is expected, probably next week. Label information will be announced when I see the approved label.

_______________________________

David A. Kollas

Extension Pomologist

Phone: 486-1944

FAX: 486-0682

email: dkollas@canr1.cag.uconn.edu