Apple Scab -- The Acceleration Phase.

Although the above graph is not clear, it is inserted here to draw attention to the fact that once 300 DD from GT are reached, ascospore maturity is in the accelerated phase (the grayer area in the center of the graph). What does this mean? It means that during warm weather, a high percentage of the season's ascospores accumulate rapidly over dry periods. It is a time of high risk for infection. It is a key time for scab management.

The following are insights on scab management that Dr. David Rosenberger of Cornell's Hudson Valley Lab shared in an article entitled: "Timing Apple Fungicide Sprays Around Bloom" in Scaffolds Fruit Journal, vol. 7, no. 5. The article was written for New York apple growers but has application to Vermont.

SI fungicides (Rubigan, Nova, or Procure) provide a bit more flexibility for timing sprays than do traditional contact fungicides because of the eradicant capabilities of the SI's. Drs. Wilcox and Kovach demonstrated that SI fungicides, when used in combinations with a contact fungicide, will control scab effectively in low-inoculum orchards if the fungicides are applied at tight cluster, pink, petal fall and first cover. This strategy is described on pages 79-80 in the 1998 Pest Management Recommendations for Commercial Tree-Fruit Production. Using this 4-spray program, the back-to-back sprays at petal fall and first cover provide eradicant activity against infections that may have occurred during the latter part of the bloom period when fungicide protection may have been exhausted.

The 4-spray SI fungicide program can only be used in orchards that were virtually scab-free the previous year. Even then, the 4-spray program may be a high-risk strategy in years where the period between pink and petal fall stretches beyond 12 days. In the absence of a short-bloom period, what are the options to consider when fungicide coverage runs out midway through bloom?

Option 1: Protect trees for a short (3-5 day) period prior the anticipated petal fall spray by applying mancozeb or captan on an alternate row basis. An alternate row spray will require only half of the material and application time that would be required for a full spray, but it will usually provide adequate protection for a short interval prior to the full cover spray at petal fall. Where this strategy is used, the alternate row spray of contact fungicide should be applied prior to any mid-bloom infection periods that occur after protectant activity of the pink spray has lapsed. Those using SI fungicides on a 10-day interval should recognize that the protectant activity of the SI-contact fungicide combination spray applied at pink will only last 6 or 7 days. Therefore, the contact fungicide spray applied during bloom should be applied ahead of predicted infection periods that might occur on days 7 to 14 after the pink spray was applied.

Option 2: Growers who traditionally use only contact fungicides could opt to ignore infections periods occurring 3 or 4 days before the anticipated petal fall spray. These late-bloom scab infections could then be controlled by using an SI fungicide (in combination with a contact fungicide) at petal fall and first cover. This strategy saves the costs associated with an extra trip through the orchard during bloom, but it is advisable only if one is certain that the petal fall spray can be applied within the 96 hr window for eradicant activity with the SI fungicides.

Option 3: Growers using SI fungicides may opt to apply a full SI-plus-contact combination spray at mid-bloom if the anticipated petal fall spray is still 7-10 days away. In years with a very extended bloom period, this strategy may be preferable to using alternate row sprays of contact fungicides alone. With this approach, the fourth SI spray of the year would be applied at petal fall. For those seeking mildew control on mildew-sensitive cultivars, a fifth SI spray will probably be needed at first cover. Where mildew is not a concern, the SI fungicide program could be discontinued with the petal fall spray, and contact fungicides could be used for disease control beginning at first cover.

The most important consideration in timing fungicides during bloom is ensuring that trees are adequately protected during this period of peak susceptibility. Ascospores are usually still abundant at pink and early bloom stages, and any primary infections that became established early in the season will begin producing conidia during bloom. Fruit and foliage are extremely susceptible. "Stretching" spray timing just a few days so one can reach petal fall can be a costly mistake if trees are left unprotected during critical bloom-time infection periods."

Page 49: Table 10. Restricted Entry intervals and Preharvest Intervals.

Powdery Mildew - This fungal disease is not as severe a problem in Vermont as it is farther south because the below 0 F temperatures that we usually experience in the winter kill the overwintering mycelium in buds. [Winter temperatures of below -11F negatively impact overwintering inoculum.] However, that is not to say that some cultivars, such as Cortland, Gala, Idared, Jonathan, and Paulared which are considered highly susceptible to mildew, cannot be significantly affected by the disease here in Vermont, particularly when we have a 'warm' winter and a warm spring. Moderately susceptible cultivars, such as McIntosh, are more likely to be affected by mildew if they are planted near susceptible cultivars and environmental conditions favor overwintering inoculum and spring infections.

I would not be surprised if we see more powdery mildew 'primary infection sites' developing in Vermont orchards this spring. 'Primary infection sites' are blossom clusters or vegetative terminals that develop from buds in which the fungus has overwintered. The fungus grows across the surface of the leaves and blossoms forming white, 'felt-like' patches or can cover their whole surface, giving the leaves and blossoms a white, powdery appearance . The powdery appearance is due to the conidia that are formed on the surface. These conidia are the source of secondary infections. Rain or dew are not needed for infection. Wind can blow the conidia to other leaves and infection can take place when temperatures are above 50F. Optimum temperatures for infection are 66-72F.

The most effective fungicides for powdery mildew are the SI fungicides (Bayleton, Nova, Procure and Rubigan). They will provide good control when applied from pink through the time when the apical bud sets on vegetative terminals. Note that all except Bayleton are effective against apple scab, so, if you are applying SIs for scab, you will be getting the added benefit of mildew management. Sulfur is also effective against powdery mildew but applications have to begin earlier and, because of short residual activity, reapplied every 7 days for good results under high disease pressure. Benlate and Topsin-M have been used against powdery mildew but it has been reported in New York that they have provided poor control in orchards in recent years. Mildew will only infect young, immature tissue. Once the leaves harden off, the threat of infection is gone. If you are unsure what the disease looks like and have access to the Internet, the Vermont Apple IPM Focus web page (http://orchard.uvm.edu/ uvmapple/pest/) has a link under "Apple Diseases" to West Virginia University's Index of Apple Disease Photographs and Biologies. There are a number of good pictures at that site that illustrate powdery mildew symptoms.

Fire Blight (FB): In Vermont, it is very difficult to predict when this disease will cause significant damage. This is another disease that is more prevalent in more southern growing regions. The following is a review of the factors that can increase the risk of fire blight:

Two models that you might find helpful for predicting fire blight in your orchard are:

• MaryblytÒ -- which is a commercially available computer program developed by Dr. Paul Steiner at the University of Maryland. The program rates the risk of fire blight blossom blight and predicts the need to treat for the disease. The program assumes the bacterial pathogen is present and identifies an infection period when four requirements are met: (1) flowers are open; (2) at least 198 degree hours greater than 65F have accumulated after first bloom; (3) at least 0.01"rain or dew that day or at least 0.10" of rain fell the day before; and (4) an aver. daily temp. equal to or greater than 60F. When all of these conditions are met in sequence, the first symptoms of blossom blight is predicted to occur when an additional 103 degree days have accumulated (base 55F). The risk of infection is considered ‘low’ when one factor is present; ‘moderate’ when two factors are present; ‘high’ with 3 factors; and infection occurs when all 4 factors are present.

• The Washington Fire Blight Risk Model: (adapted from A risk assessment model for fire blight of apple and pear, T.J Smith, Wash. State University)

You would then refer to the infection risk chart to determine if the risk estimate for the day is very low, low, low-moderate, moderate, high, or extreme (see Table 7c). In most instances, control measures will not be necessary unless the risk level is high or extreme.

Table 7b - Estimated daily fire blight degree hours.

If you need to spray during late pink and bloom -- Apply streptomycin (+ surfactant) just before an anticipated infection event. Reapply the streptomycin in 4 days if infection conditions reoccur. Do not apply on an alternate row middle basis. Avoid high volume foliar sprays for other purposes during bloom when fire blight infection risks are high, since these may trigger an infection. Do not exceed 4 antibiotic applications per year.

Note the following Precaution regarding Agri-Mek:

On the topic of adjuvants, the 20th March Message written by Prokopy, et al. contained the following information: "Several adjuvants were compared in Massachusetts, New York and Pennsylvania in 1997. Among horticultural oil (such as Sunspray Ultrafine Oil), Sylgard 309, SilWet L-77, Regulaid and LI-700, no adjuvant proved better than oil. Silwet was a close second, with the others close behind. Oil is inexpensive but does pose potential phytotoxicity problems if captan is to be used in place of EBDC fungicides after bloom."

Page 50 -- Table 10. Restricted Entry Intervals and Preharvest Intervals

                    Add: "abamectin Agri-Mek 12 hours 28 days"

                    Add: "pyridaben Pyramite 12 hours 25 days"

Page 64 (upper right) --

Page 50 -- Table 10. Restricted Entry Intervals and Preharvest Intervals

carbaryl - Change preharvest interval from "1 day" to "1 or 3 days"

permethrin - Change preharvest interval from "1 day" to "1 or 3 days"

pyrethrin & rotenone - Change preharvest interval from "0 days" to "12 hours"

Leafminers (LM) - It will be important to check the undersurface of cluster leaves for sap-feeding mines at PF to determine the need for treatment. There have been reports of high populations of LM adults in some Massachusetts orchards. The following are the trap captures from the UVM Hort. Research Center:

Aver. # new LM /red rect. trap:

The highest number of LM caught on one trap was 230 ! With a threshold of 9 moths/trap at full pink, you can see we are above threshold. In one orchard I was in last week, traps were not needed to determine high populations -- walking through the orchard on a warm, calm afternoon, one could see about 10 -15 LM moths flying in the canopy of most trees. The following are some facts about the spotted tentiform LM:

• Females can mate and begin egglaying within a day after emergence.

• Fecundity is variable, ranging from 1 - 152 eggs per female but averages about 16 eggs/female for this first brood.

• Oviposition threshold is about 42F; They lay their eggs usually from mid-afternoon to sunset.

• Egg development requires about 172DD above a development threshold of 36F .[Hatch usually occurs within 5-16 days, depending on temp.]

Cumulative first-generation sap-feeding mines per 100 leaves are:

What are the options at PF for LM management? Provado and Agri-Mek are both effective against LM. Provado is also effective against leafhopper nymphs and aphids (except wooly apple aphid). As mentioned earlier in this newsletter, Agri-Mek is also effective against ERM and two-spotted spider mites.

• European Apple Sawfly (EAS) --The pink bud stage is the time to place white, rectangular traps in your orchard to monitor EAS adults. These should be placed at about head height, on the south side of the tree, within 18" of the tree dripline.

• Codling Moth (CM) pheromone traps should be placed in your orchard at bloom. Degree days (DD), calculated from base 50F, are accumulated from the date of first moth catch (the biofix).

Getting the Most Pollination for Your Dollar by Nick Calderone, Entomology, Cornell University Ithaca (from Scaffolds Fruit Journal, vol. 7, no. 4)

"Tree fruits, small fruits, and many vegetable crops, especially the vine crops, all require pollinating insects for a successful harvest. Remember! Not only is pollination important for a high yield, it is just as important to fruit size, shape and sweetness! A number of insects pollinate crops, but, for several reasons, the honey bee is the most versatile, all-around pollinator. Honey bees are available in large numbers throughout the growing season, they pollinate over 90 commercial crops, they are easily transported by truck, and they can be easily distributed throughout large plantings. Compared with other pollinators, honey bees are very cost effective. A single strong, two-story colony provides 15-25 thousand foragers.

Growers are usually concerned about the number of colonies they need to rent. New York growers have traditionally used about one colony of bees per three acres for apple pollination. This number may have been adequate in small orchards visited by feral honey bees and by solitary bees and bumble bees from adjacent hedgerows and woods. However, feral honey bee populations have been greatly reduced in recent years, and modern agricultural practices have eliminated many natural nesting sites for solitary bees and bumble bees. In addition, the flight range of solitary bees is not generally sufficient to ensure coverage of the center portions of large plantings. Growers with large blocks of apples and other tree fruits may wish to increase the number of hives to one per acre. Most other crops are also adequately served by a single strong colony per acre. If your fruit set has been lower than expected in the past, or your fruits are lopsided or misshapen, you probably need to use more bees. Remember, if your fruit set is too high, you can always thin, but if it is too low, you are just out of luck.

Some crops have special requirements. Red Delicious apples have flower structures that are different from most other common varieties such as McIntosh. Their anthers are widespread, and bees learn to insert their mouthparts between the anthers to obtain nectar. In this way, the bees do not contact the flower's sexual parts and no pollination occurs. It takes time for bees to learn to obtain nectar in this way. To counteract this problem, the number of colonies in the orchard must be increased so there are more inexperienced bees present. Up to two colonies per acre may be needed in large stands of red delicious apples. Move bees into apples, regardless of variety, right as the king blossoms open.

Pollination of pears will probably always be a problem because pear nectar contains only about 15% sugar versus 40% for apples, dandelions, and yellow rocket. The answer is to move the bees into the center of the pear block when the pears are at 50% bloom. It will take some time for the bees to discover better sources farther away, and in that time, the pears may be adequately pollinated. An alternative is to use more colonies per acre, which will increase the number of bees foraging within the orchard. Sweet cherries should be pollinated soon after they open. Therefore, bees should be moved in the day before bloom. Since sweet cherries require a high fruit set for a commercially viable crop, and since they bloom early in the season when the weather is often unfavorable for foraging, two colonies per acre may be required. There is growing evidence that strawberries can benefit substantially from having hives of bees in the field during bloom.

Always select good locations for the bees you rent to obtain maximum benefit for your pollination dollar. It's a lot like real estate -- location-location-location. A good location slopes slightly to the east or south, is protected from the wind, and has as much exposure to sunlight as possible. It is important that colonies of honey bees be kept in full sunlight in order to warm the hives rapidly in the morning and entice the workers out of the hives on chilly spring mornings. Entrances should face south to east, whenever possible. Keep colonies on pallets or cinder blocks to keep the bottom boards 3-6 inches above the ground. Hives with wet bottom boards will be cooler and have less foraging activity than dry colonies. A hive stand will also keep colonies above tall grass, which may shade or block the entrance. Place colonies in groups of 4-6 to take advantage of good locations. In large orchards and fields, groups of 10-20 hives can be used to take advantage of prime locations. It is best to locate hives near pollinizer rows where that consideration applies, such as with apples.

Overall, pesticides are less of a problem to bees and beekeepers today than they were 10 and 20 years ago. Nevertheless, serious poisoning incidents still occur, and several reports of bee poisoning from methyl parathion were confirmed last year in New York. It is important to read the pesticide label and to avoid using materials that are especially toxic to bees whenever there is a safer alternative available. Sevin (carbaryl), Guthion (azinphosmethyl) and Penncap-M (micro-encapsulated methyl parathion) are especially toxic to bees.

Honey bees are most often killed by pesticides when they ingest contaminated pollen. However, bees can also be poisoned by pesticides that have contaminated small pools from which foragers collect water to dilute the honey they feed their young. Bees will collect water from the closest available source, including standing water in wheel ruts and old tires in or near your fields. A problem exists if more than 10 dead bees are found in front of a hive in the morning. If too many bees die, your crops will not be adequately pollinated and it may be necessary to rent more bees. You can help the bees by providing them with a source of clean water nearby. A small tub with a few wooden floats or a ridged piece of hardware cloth placed diagonally in the tub will work well. If you don't provide floats or screens, the bees may drown.

You can eliminate almost all damage to bees, both managed and wild, by not spraying when flowers, including weeds, are open and attractive to bees, and by not spraying when there is any risk of drift to non-target crops or flowers. Evening, about an hour before sunset, is usually a good time to spray because there is generally little wind at that time. Always use the largest droplet size possible when spraying, and check out the use of spray stickers to help minimize drift. Keep flowering ground-cover plants mowed if you are going to spray in an orchard during the summer. Clover is a common problem for bees on orchard floors; keep it mowed or use an herbicide.

Bees should be moved onto location at night, and once the hives have been set down for pollination, you should leave them at that spot until the job is done! Moving bees in the daytime and moving them short distances (less than 3 miles as the crow flies) will cause a serious loss of foragers and seriously damage the colony. Always contact the beekeepers if the need arises to move the bees. If you live in an area with known bear problems, use an electric fence to protect the bees. Keep nearby, flowering plants mowed to reduce competition for the bees' attention.

I recommend establishing good working relations with several beekeepers to ensure yourself a ready supply of bees for pollination. Any individual beekeeper's situation may change over time, but if you work with several beekeepers, you should always have ready access to an adequate supply of colonies. Remember! Bees are an essential part of your crop production system, but they are only one part. In many ways, they are like the fertilizers and chemicals that you buy. Each is essential, but none of them, by themselves, can guarantee a crop. Many things influence the quantity and quality of your crop. One is the weather. Bees will visit flowers and pollinate only if they can fly. Cool, rainy, and windy weather will delay, slow, or stop flight, and the beekeeper cannot do anything about the weather. Excessive heat during the summer can cause problems with fruit set in certain crops, like pumpkins. Again, this is beyond the beekeeper's control. Be clear up front about your expectation concerning the strength of the colonies you rent and satisfy yourself that you have received what you expected. This will eliminate misunderstandings down the road.

Look for rental fees in the $35-$60 range, depending on strength. Remember, the best deal may not always be the cheapest deal! What is one major consumer of pollination services doing to ensure a steady supply of the highest grade colonies? Look for the answer in an upcoming issue.

TIP -- Planning a new orchard? Be sure to determine if your main cultivars are self-sterile -- like McIntosh and Red Delicious apples -- or, worse yet, self-sterile and inter-incompatible like many popular cultivars of sweet cherries. If so, be sure to plant an adequate proportion of pollinizer cultivars. Be sure you select pollinizers that bloom at the same time as your main variety. If you do not have pollinizers in your self-sterile stands, you can often purchase compatible pollen and use hive inserts to distribute it to the blossoms."

Where trade names or commercial products are used for identification, no discrimination is intended and no endorsement is implied. Always read the label before using any pesticide. The label is the legal document for the product use. Disregard any information in this newsletter if it is in conflict with the label.