Fruit Pest News

Volume 4, No. 2   March 24, 2003

A weekly, online newsletter whose goal is to update Extension agents and growers of commercial tree fruit and small fruit crops

on diseases and insects in Tennessee.

Text appearing in blue or red can be clicked to link to other web sites. Be aware that much of the linked information is produced in other states and may not be applicable to Tennessee.

In This Issue:

    1. Current Conditions

    2. Tree Fruit: Pest Monitoring and Spray Timing

    3. Fruit Spray Guides: Where to Find

    4. Apple: MaryBlyt Program for Fire Blight Management

    5. Strawberry: Should You Remove Old Leaves?

    6. Strawberry: What Fungicides Should I Use?

    7. Tree Fruit: Redbanded Leafroller

1. Current Conditions

Things are moving fast! The cold winter may have caused a late daffodil display, but a warm March has fruit trees on the move.  Peaches are in bloom, apples are at green tip to tight cluster, early blueberry varieties such as O'Neal are in bloom, and blackberry buds are about 1 inch long and expanding. For many apple plantings, it is already too late to apply copper sprays for fire blight control, since application of copper after the green tip stage can cause fruit russetting. The forecast is for continuing warm weather. (SB)

2. Tree Fruit Pest Monitoring and Spray Timing

The last few years we have used pheromone traps at the Ellington Agricultural Center and had cooperators at several orchards across the state using the traps. This year we would like to continue this trapping so please let me know if you want to participate. I will provide the pheromone and traps for those of you who participated last year (and plan to participate this year) please make a count of any left over fresh stick traps so I will know how many additional traps to send. I have ordered pheromone and will ship it to cooperators as soon as I receive it. If you have some left-over pheromone, I would put out the traps now since recent warm weather could bring on a flight for some of the earlier of these tortricid moths.

In order to better time pest sprays we will be using Degree-Day Models along with our trapping. This will require the use of a minimum-maximum thermometer that should be checked each day or a recordable thermometer that does most of the work for you. The minimum-maximum thermometers are fairly inexpensive (in the $25.00 range) while the recordable ones are significantly more expensive. I may have some funds to buy a few minimum-maximum thermometers for those that do not have one. Let me know if you do not have a thermometer and need for me to provide one.

It is important that we get our pheromone traps out early so that the first flight of the pests can be detected. This first flight of the season sets the biofix date (first sustained catch of moths in a pheromone trap) for a particular pest. We know that insect development is temperature dependent. By keeping track of the temperature starting at the biofix date we can determine when the following generations of the pest will be occurring so that properly timed protective sprays can be made.

There are many types of recordable thermometers that can be used to determine Degree-Day values. A study by Dr. James F. Walgenbach entitled "Comparison of Degree-Day Recording Methods for Insect Phenology Models" can be found in the Arthropod Management Studies on Fruit and Vegetable Crops in Western North Carolina, 2000 Annual Report. In this report, he concluded that there was a enough Degree-Day variation in the instruments so that this could potentially lead to large differences in the timing of insecticide applications. In one case there was a difference in 28 days (one instrument reached 2600 Degree-Day for tufted apple bud moth at August 8 while another brand instrument had it on September 5). This differences seem to be greater later in the season. Dr. Walgenbach's suggestion was "To minimize the effect of instrument DD variation, pheromone trapping and monitoring of orchards must be used together with egg hatch models to help determine the need for and timing of applications." (FAH)

3. Fruit Spray Guides: Where to Find

All of the commercial fruit and vegetable spray guides that we commonly use in Tennessee have been revised and are now available.

• Commercial Vegetable Disease, Insect and Weed Control (University of Tennessee PB 1282). Printed, bound copies are available at county Extension offices. It is also available for downloading from our web site at http://web.utk.edu/~extepp/pubs/PB1282-2003.pdf

• 2003 Commercial Small Fruit Spray Schedules (University of Tennessee PB1197). Printed, bound copies are available at county Extension offices. It is also available for downloading from our web site at http://web.utk.edu/~extepp/pubs/PB1197-2003.pdf

• 2003 Integrated Orchard Management Guide for Commercial Apples in the Southeast (regional publication). Printed, bound copies are available at county Extension offices.  

• 2003 Southeastern Peach, Nectarine, and Plum Pest Management and Culture Guide (regional publication). Printed, bound copies are available at county Extension offices. (SB)

4. MaryBlyt Program for Fire Blight Management: Plans for the Year and What to Do Now

One of the priorities for this newsletter is to provide training and updates for the MaryBlyt program. Fire blight will require increasing attention as time goes by, with the changes that are taking place in apple production.

I have a limited number of MaryBlyt programs (software and manual) available for free. Please let me know if you would like one. I only ask that the cooperator use it diligently and report to me when the program indicates that an infection period has occurred and when you see your first fire blight symptoms. The program is not difficult to operate, and can help tremendously in managing fire blight.

What it does: The program use temperature and rainfall amounts to tell you when you need to spray with streptomycin and to tell you when to expect fire blight symptoms to appear. The program will improve control efficiency, resulting in better control with fewer sprays than would be obtained by spraying on a fixed schedule. Fewer sprays mean less chance of resistance to streptomycin developing.

For those of you who have begun to use MaryBlyt, here are some points to keep in mind:

• Begin monitoring temperature and rainfall when 50% of the buds show green tissue. This is the "biofix," when the program begins calculating pathogen and plant development. In judging when to begin measurements, consider only blossom buds (those at terminals and spurs). Don't consider the leaf buds (those at the nodes).

• You don't need to enter the data into the computer until the blooms begin to open, but you do need to record the measurements every day, and reset the max-min thermometer and empty the rain gauge after the reading. When the first blossom bud opens, the data must be entered into the computer each day.

• The thermometer should be located in the shade, away from the ground. The rain gauge should be located in the open.

• Time of day to take measurements: Can be taken any time, but you should choose a time and be consistent with it each day. I think the most desirable time is late afternoon, because it would allow all of the measurements for that day to be kept together . . . and a spray decision based on that day's data to be made that night (streptomycin applications work well under the slow drying conditions of night). Remember to take note of whether a dew occurred in the morning, since dewfalls are also recorded. (SB)

5. Should You Remove Old Strawberry Leaves?

You have probably already finished your leaf sanitation job, but it is good to think about this while it is still fresh on your mind. Late winter removal of winter-damaged strawberry leaves is often practiced in the belief that Botrytis losses will be reduced. The reasoning is that this dead tissue serves as a staging area for the Botrytis fungus to attack the blossoms when they open. Some Canadian research with matted row strawberries indicated that such sanitation did indeed reduce the amount of Botrytis fruit rot, which results from infections of the blossoms by Botrytis. But does it work for plasticulture strawberries?

Research in Florida indicated that sanitation reduces Botrytis if no fungicides are used, but not if a fungicide program is followed. Sanitation also tended to decrease yields (probably because of damage to buds). Incidentally, the Florida work also demonstrated that there was no advantage in removing berries with Botrytis from the field.

Keep in mind that Botrytis spores are readily wind-borne and travel some distance on the wind. For this reason, small plot research may not accurately depict how effective a control practice is, since spores produce by the check or less effective practices are such a short distance away.

Research in North Carolina also has not demonstrated a benefit from sanitation in four years of work. Yields were not consistently affected by sanitation. Furthermore, the sanitation job served to spread the anthracnose fungus, which was present in one of the sites. In the sanitation plots where workers hand-removed leaves, anthracnose affected 14% of the fruit; only 3.7% were affected in the undisturbed plots.

In summary, sanitation may still have a place in matted-row fields, where the amount of dead leaf matter can accumulate over the years and beds tend to be more densely populated with plants. Sanitation can also have a place in fields in which fungicide programs are not rigorously followed, such as organic production. If anthracnose is known to be present in the field, it may be advisable to forego sanitation. (SB)

6. Strawberries: What Fungicides Should I Use?

The strawberry fungicide arsenal has changed much in recent years. Since last growing season, two new registrations (Cabrio, Procure) have been granted (see the March 10, 2003 issue of Fruit Pest News). Benlate is less available, since it has been discontinued by the manufacturer, and resistance to the related benzimidazole fungicide Topsin M is becoming widespread. Also in recent years, Elevate, Quadris, and Switch have been registered, the strawberry label for Ronilan was discontinued, and the strawberry label for the related fungicide Rovral was severely restricted. With so many changes, what strategy should you follow in designing a fungicide spray program?

Bloom sprays. The focus of the bloom sprays is on Botrytis control. Bloom time is the key time to prevent this fruit disease, and other fungal disease activity is low at that time (However, the bacterial disease angular leaf spot may require copper sprays). Use either Elevate or Switch as your primary Botrytis material. If anthracnose is known to be or suspected of being present, Switch would be the preferred material. Follow a 7 to 10-day schedule through bloom. Both labels limit the number of applications, so alternate after one or two sprays with a tank mix of Topsin M with either captan or thiram. I recommend that the strobilurin fungicides, Quadris and Cabrio, not be used during the bloom period. They are rather weak against Botrytis. Furthermore, the labels only allow 4 applications of strobilurins per year, so reserve those applications for the harvest period, in case anthracnose appears.

Harvest sprays. In severe anthracnose cases, the strobilurin products Quadris or Cabrio should be applied once per week for 4 weeks during harvest. To comply with the alternation requirement, make a captan or Switch application between each application of a strobilurin. The strobilurins can be tank-mixed with captan, but the requirement of alternating to a non-strobilurin fungicide for 1 application after the second application of the tank mix must still be satisfied. (SB)

7. Tree Fruit: Redbanded leafrollers

Redbanded leafrollers (RBLR) have been active since traps have been put out. A trap in Bradley County, caught 22 in 2 traps (green tip on Gala and Empire) when checked on March 10. There were 69 RBLR in the two traps for March 17. The Nashville trap was put out March 17 had caught 3 moths on 3-18, 9 on 3-19, 9 on 3-20, 7 on 3-21 and 20 on 3-24. I have not caught any Oriental fruit moths (OFM) in Nashville. I caught several unknown tortricid moths in the codling moth trap. They look similar to codling moth but they are probably not. This is probably too early for codling moth anyway. I will try to identify them to species this week.  (FH)

The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm

Contacts:

Steve Bost, Professor and Extension Plant Pathologist

scbost@utk.edu

Frank Hale, Associate Professor and Extension Entomologist

fahale@ext1.ag.utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211