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nafex - Re: [NAFEX] Spraying for scab with bagged apples

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  • From: "Dennis Norton" <dmnorton@royaloakfarmorchard.com>
  • To: "North American Fruit Explorers" <nafex@lists.ibiblio.org>
  • Subject: Re: [NAFEX] Spraying for scab with bagged apples
  • Date: Sat, 3 Jun 2006 23:42:56 -0500

Copper is to be used only from dormancy to silver tip and is for fire blight, rarely for scab. Copper should be applied every spring and if fire blight was severe the previous year, a Bordeaux mixture or fixed copper spray at silver tip is best. To remain organic, use the following program for apple scab:

Controlling Scab and Mildew early in the season will insure little or no problem later in the year unless your neighbor's trees are heavily infected. Better yet, plant scab resistant apples. Begin your control program as soon as you see green in the apple buds. For the rains occurring prior to when the green tissue is ½ inch long copper or lime sulfur can be used either just ahead of the rain or within 48 hours of the start of the rain. Copper should be discontinued at ½ inch green tip or russeting of the fruit will result. Sulfur is applied every 3 to 5 days or prior to every rain from ½ inch green tip until 4 weeks after petal fall. If you cannot spray prior to a rain, use lime sulfur within 48 hours of the start of the rain. For summer disease control and if you have Scab infected leaves 4 weeks after petal fall you should continue sulfur sprays on a 2 week interval until harvest or the end of August whichever comes first. Spray until leaves are dripping. Leaves which fall from the tree should be mowed or removed and composted since the scab fungus overwinters in fallen leaves. Powdery Mildew overwinters in infected buds.

RATES

1 Gallon of Water Per 10 Gallon Per 100 Gallon
Copper Sulfate 1 Tablespoon 1. 6 oz. Dry 1 lb.
Lime Sulfur .65 oz. liquid 6.4 oz. liquid ½ Gallon
Sprayable Sulfur 3.4 oz. 1.2 lb. 5 lb.




In a typical year in most locations, the first mature ascospores are capable of causing infections at about the time of bud break or soon thereafter. Ascospores continue to mature and are discharged over a period of five to nine weeks, with peak discharge during the pink to petal fall phenological stages. The length of time required for infection to occur depends on the number of hours of continuous wetness and the temperature during the wet period. Young leaves remain susceptible for five to eight days, but their lower surfaces may become infected in late summer. For fruit, the duration of the wet period required for infection increases with the age of the fruit, which remains susceptible until harvest. Once the fungus is established in the leaf or fruit, conidia form on the surface of the lesion and become the source of secondary inoculum for the remainder of the season. Conidia are disseminated to developing leaves and fruit by splashing rain and wind. Several secondary cycles of conidial infection may occur during the growing season depending upon the frequency of infection periods and the susceptibility of host tissue. Scab should be continuously monitored during the growing season. During the prebloom period, for both fresh and processing apples, determine apple scab infection periods by observing duration of leaf wetness and average temperatures during the wet period. Use the Mill's table for the indicator of time required for lesion expression. Begin monitoring for first leaf symptoms (photo 2-5) on early-developing cultivars such as Delicious by examining the upper and lower leaf surfaces on a minimum of ten leaf clusters on each sample tree. In monitoring, walk around the perimeter of the tree and examine at least two leaf clusters at each of the four compass directions. Record the total number of clusters with scab lesions. For fresh market production, more than one infected leaf cluster per tree represents potentially damaging levels of apple scab. For processing apples, one to ten infected clusters represents a moderate risk, and more than ten infected clusters represents a high risk. During mid-season and the preharvest period, no monitoring is required for processing apples at this time. For fresh market production, continue monitoring for lesions on leaves of vegetative terminal shoots and on fruit. Walk around the perimeter of each sample tree and examine at least two terminals at each of the four compass directions and 25 fruit per tree. Record the total number of terminals and fruit with scab lesions. More than one infected fruit per tree is a potentially damaging level for the fresh market. After harvest, for both fresh and processing apples, determine the percent of leaves infected and number of lesions per infected leaf on six terminal shoots from each sample tree after harvest and before natural defoliation begins. Greater than 0.5 percent leaves infected with an average of one lesion per leaf represents significant risk of early scab infection next season.

Approximate wetting period required for primary apple scab infection at different air temperatures, and time required for development of conidia. (a)
Average temperature Average temperature Wetting period (hr)(b) Wetting period (hr)(b) Wetting period (hr)(b)
Farenheit Celsius Light Infection Moderate Infection Heavy Infection Incubation period (days)(c)
78 25.6 13.0 17 26 -
77 25.0 11.0 14 21 -
76 24.4 9.5 12 19 -
63 - 75 172. - 23.9 9.0 12 18 9
62 16.7 9.0 12 19 10
61 16.1 9.0 13 20 10
60 15.6 9.5 13 20 10
59 15.0 10.0 13 21 12
58 14.4 10.0 14 21 12
57 13.9 10.0 14 22 13
56 13.3 11.0 15 22 13
55 12.8 11.0 16 24 14
54 12.2 11.5 16 24 14
53 11.7 12.0 17 25 15
52 11.1 12.0 18 26 15
51 10.6 13.0 18 27 16
50 10.0 14.0 19 29 16
49 9.4 14.5 20 30 17
48 8.9 15.0 20 30 17
46 8.3 15.0 23 35 -
45 7.8 16.0 24 37 -
44 7.2 17.0 26 40 -
43 6.7 19.0 28 43 -
42 6.1 21.0 30 47 -
41 5.6 23.0 33 50 -
40 5.0 26.0 37 53 -
39 4.4 29.0 41 56 -
38 3.9 33.0 45 60 -
37 3.3 37.0 50 64 -
36 2.8 41.0 55 68 -
33 - 36 0.6 - 2.2 48.0 72 96 -


If anyone would like further information on apple scab or the management of scab, let me know and i will be happy to help. I hope the above information is useful and will clear up some possible confusion, especailly for those who want to remain organic.


Dennis Norton
Royal Oak Farm Orchard
http://www.royaloakfarmorchard.com
http://www.theorchardkeeper.blogspot.com
----- Original Message ----- From: "Jason MacArthur" <rotread@localnet.com>
To: <nafex@lists.ibiblio.org>
Sent: Saturday, June 03, 2006 6:03 AM
Subject: [NAFEX] Spraying for scab with bagged apples


Nathan Torgerson wrote:
Dennis,
I have no experience with copper sprays, but from the little that I've read, copper applications aren't used after silver tip because it causes the fruit to russet if it's done later. I was guessing the russeting is caused because the copper is applied on the apples, but maybe that's a bad assumption, Do you know if there other reasons not to use copper applications throughout the summer?

Nathan, as I see it spraying copper now would be the wrong medicine applied at the wrong time. To be dealt with effectively, especially under an organic regime, scab has to be dealt with before it becomes established on your leaves, when less toxic materials than copper( i.e. Sulfur) can be used. Copper is a toxic and persistent material which will have effects on earthworms and soil life for many years after it is sprayed. I would think long and hard before using copper on a season long basis. Beyond that, I am not even sure how effective it is against secondary scab infections, and whether it is legal to use for this purpose.
My advice: keep your trees as heathy as you can this year by mulching, fertilizing, etc., and be prepared for apple scab in the spring when it is at it's weakest.

Jason MacArthur
Marlboro, Vt.








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