September 10, 1997

CORE Values Northeast Tour:

Enclosed please find an invitation to attend an apple harvest celebration on September 22 and 23, sponsored by the CORE Values Northeast program. As you may be aware, a number of VT growers are participating in this program. This would be an excellent opportunity to learn more about this program which has the goal of raising consumer awareness and market support for apples grown in the Northeast.

Although everyone is focused on harvesting, it is also an important time to assess the leaves in your orchard for scab to determine if your blocks are candidates for the 'delayed-spray' strategy in 1998. Ideally, this should be done as close to leaf fall as possible but still at a point when the leaves are in relatively good condition. The 'delayed-spray' strategy is described on pages 12 and 13 of the 1996-1997 New England Apple Pest Management Guide. The technique for assessing your orchard, as outlined in the Guide, is as follows

• Select a sampling scheme that will allow you to sample every 10 to 30 trees, making sure that trees are selected from throughout the block. The total number of shoots examined should equal 600 per block. Three sampling schemes are presented below:

• On each selected tree, examine shoots at random from the top, bottom, inside, and outside. It is particularly important to include shoots as near to the tree top as you can reach, because that is where scab is more likely to occur due to poor spray deposition. If sucker shoots are common, include one sucker shoot per tree.
• On each selected shoot, scan the upper and lower surfaces of the leaves and record the number of leaves with one or more scab lesions.
• Total the number of scabbed leaves.

If the number of scabbed leaves is 50 or less, the first fungicide spray can be delayed in 1998 until Pink or until after three infection periods (but before the fourth infection period), whichever comes first * [*Begin determining infection periods at green tip.]

If the number of scabbed leaves totals 51-100, then a sanitation program would be helpful in reducing your potential overwintering inoculum. Please see page 12 of the Guide for details.

If the number of scabbed leaves is greater than 100, you should not follow the delayed-spray strategy.

Note: Based on the results of the 'Whole Farm' Apple Scab IPM Project which were reported in our last newsletter, we also do not recommend the delayed-spray strategy if you were on an SI fungicide program this year regardless of the number of scabbed leaves that are counted.

Again, in assessing your orchard, it is important to look closely at both sides of the leaves for scab lesions. One type of lesion that you may not be too familiar in observing is 'late season' scab lesions that can appear as smoky gray areas on the underside of the leaves. Please visit the UVM APPLE ORCHARD WEBSITE at http://orchard.uvm.edu/uvmapple/ for pictures that illustrate late season scab lesions on the undersurface of leaves.

The following is an article written by Dr. Dave Rosenberger, who is a plant pathologist at Cornell's Hudson Valley Lab. The article appeared in SCAFFOLDS Fruit Journal , vol. 6, September 8, 1997, and provides an update on the issue of postharvest decay, particularly on Empire.

"Most of the postharvest decays of apples are caused by Penicillium expansum or Botrytis cinerea. These fungal pathogens usually invade fruit at wounds, but they can also invade through the stem or through bruises. Penicillium and Botrytis have traditionally been controlled by applying postharvest fungicide drenches to apples before they are moved into controlled atmosphere (CA) storage."

"In recent years, the most serious postharvest decay problems in New York apple storages have involved Empire fruit held in CA storage for six months or longer. Significant postharvest losses are occasionally noted with other varieties as well, but decay problems with Empire have been more persistent and more baffling."

"Varieties such as Delicious and Cortland are highly susceptible to the physiological disorder known as storage scald. These varieties must be treated with diphenylamine (DPA) to prevent scald during CA storage. A fungicide is always included with the DPA treatment to control infections that would otherwise develop as a result of inoculum that accumulates in the postharvest treatment solutions. Some varieties, including Empire, do not develop scald and therefore can be moved into storage without any postharvest treatment. Many storage operators stopped applying postharvest treatments to Empire fruit in the early 1990's, but some of them have resumed applying postharvest treatments because they found the incidence of decay was unacceptable in fruit that were moved directly into CA storage without treatment. Unfortunately, application of a postharvest fungicide has not resolved all of the problems with decay in Empire fruit."

"Over the past several years, we collected decayed Empire fruit from apple storages throughout New York State to determine which pathogens are involved causing decays. We found that Penicillium predominated in fruit that had received a postharvest treatment, whereas Botrytis predominated in fruit that were moved to storage with no postharvest treatment. Thus, postharvest fungicide treatments have been reasonably effective for controlling Botrytis, but the fungicides have not been as effective against Penicillium."

"There are two possible reasons that postharvest treatments are failing to control Penicillium in Empire fruit. The first possibility, and the one with the easiest solution, is that fungicide concentrations in the postharvest drench may be too low. This can occur if the fungicide is not replenished according to label instructions as apples are processed through the drencher. It also occurs when the fungicides settles to the bottom of drencher holding tanks due to the lack of adequate agitation systems. Mertect 340F (thiabendazole, or TBZ) is the most commonly used post harvest fungicide. This fungicide appears to settle out of suspensions much more quickly and completely than did Topsin M or Benlate, fungicides that were used in the 1970's and 1980's. As a result, Mertect 340F may settle to the bottom of the holding tank and remains there in the absence of good agitation. This problem can be rectified by installing a grid of PVC pipes with outlet jets in the bottom of the holding tank so that the postharvest solution can be pumped under pressure through the grid, thereby creating turbulence that will resuspend the fungicide that has settled to the bottom of the tank."

"A second reason that postharvest fungicide treatments are failing involves resistance to the fungicides. Fungicide resistant strains of Penicillium and Botrytis are resistant to all the benzimidazole fungicides including TBZ. In the mid-1980's, we discovered that most of the fungicide-resistant strains of Penicillium and Botrytis were unusually sensitive to DPA. Thus, the combination of DPA plus a benzimidazole fungicide continued to provide good control of Penicillium and Botrytis through the late 1980's. Even in the mid-1980's, however, about 2% of the P. expansum strains recovered from apple storages were resistant to both DPA and TBZ. It appears that these strains have gradually increased in importance and are at least partially responsible for declining effectiveness of postharvest treatments." 

"There are no easy solutions for controlling resistant strains of Penicillium. Sanitation measures that reduce the amount of inoculum harbored on bins and storage walls may help to reduce the incidence of decay, but the benefits of sanitation have not been studied or documented in apple storages."

"One approach for controlling TBZ-resistant strains of Penicillium would be to add captan to the postharvest treatment solution. Captan is registered for postharvest use on apples and can be combined with DPA and TBZ in postharvest treatments. Researchers in Israel have reported that captan is reasonably effective against Penicillium when used at the full label rate of 2.5 lb Captan 50W per 100 gallons. In the US, where captan has usually been tested at lower rates and in combinations with one of the benzimidazole fungicides, captan has provided no benefits compared with using the benzimidazole fungicide alone. As the 1996 Food Quality Protection Act is implemented, captan may once again come under close regulatory scrutiny. Thus, the label of captan will very likely be revised sometime in the next 3-5 years and some currently labeled uses might be eliminated."

"Several new biocontrol fungicides have been registered for postharvest use on apples and may eventually prove useful for controlling strains of Penicillium that are resistant to TBZ. Biocontrol fungicides are formulations of bacteria or yeast -- living organisms that actually grow on the fruit after they are applied. Biocontrols do not act by killing pathogen spores or inhibiting spore germination. Instead, they stop decays by colonizing the wounds on apple fruit where decays are usually initiated. The biocontrol organisms apparently utilize all of the available nutrients in the wounds, leaving nothing to support initial growth of the decay fungi. The decay fungi utilize the apple juice and damaged cells in wounds as a source of nutrients for initial growth of spores. When this "start-up fuel" is consumed by the biocontrol fungi, the pathogens are left without the nutrients needed to initiate growth. This mode of action for biocontrols dictates that biocontrol fungicides will have good protectant activity but virtually no eradicant activity. If Botrytis or Penicillium become established before the biocontrol is present, then the decay fungi will usually predominate and continue to invade and decay the fruit flesh. "

"One biocontrol product, Decco I-182, is now registered in N.Y. State and should be available for use this fall. Decco I-182 is a formulation of the yeast Candida oleophila that was formerly marketed as 'Aspire'. The limited test data available for apples suggests that this product will provide only modest improvements in decay control when applied in combinations with TBZ. Storage operators may wish to experiment with Decco I-182 this fall, but we do not yet have enough information to recommend this expensive product."

"Decco I-182 can be ordered through agrichemical suppliers but will not be warehoused with other agrichemicals. Because Decco I-182 contains a living organism, it must be kept refrigerated until it is used. When this product is ordered, it will be shipped directly from the manufacturing plant to the purchasers in insulated containers. Drench solutions that include Decco I-182 will have a characteristic yeasty odor that some individuals may find offensive, but the odor apparently is not retained on treated fruit."

The larvae of this beetle tunnel for 2-4 years inside the lower part of the trunk of young apple trees causing extensive damage or death of the tree. September is an excellent time to check the trunks of your trees near their base for small holes that have reddish sawdust. Larvae that are close to the surface can be dug out with a knife; larvae that have already tunneled deeper into the tree, can be killed by probing with a wire. If your time is limited (and whose isn't !!), you may want to focus on 3-10 year old trees first, especially if they are near wooded areas that contain alternative hosts of this insect. The roundheaded apple tree borer also attacks wild and crab apples, choke cherry, hawthorn, mountain ash, and shadbush. Also, you should particularly check trees that have had weeds growing high around their base or have had white plastic mouse guards wrapped around them during the growing season. These act as barriers to sprays, providing a haven for the adult beetle during the early summer when egg-laying occurs.

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