Fruit Pest News

Fruit Pest News

Volume 7, No. 3 March 28, 2006

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. Methyl Bromide Critical Use Exemptions

3. Phytophthora Root Rot of Apple

4. MaryBlyt Program for Fire Blight Management

5. Spray Water pH

6. Mating Disruption Products and Timing

7. Pheromone Trap Catches

1. Current Conditions

Two weeks worth of cold weather has definitely slowed things down. Things are about at a normal stage of development now. This interlude in temperatures may spread out the harvest dates of some strawberry and blueberry plantings. The early-blooming varieties bloomed earlier than usual, while the later-blooming varieties were delayed by the cold spell. The brown, pencil-sized strands on cedar-apple rust galls are poised for the transition to orange, gelatinous tendrils and spore production upon the next rain. Time to apply the first rust spray.

Tomato growers, watch the rainfall during the month of March. Thrips, which spread tomato spotted wilt virus, proliferate in summers following dry weather in spring. The severity of the virus can be predicted by rainfall in March through mid-April. So far, the 2.59 inches we have received in Nashville is 1.69 inches below the normal of 4.28 inches. If you consider TSWV a threat, you should consider planting a resistant variety. (SB)

2. Methyl Bromide Critical Use Exemption

The 2006 Critical Use Exemption (CUE) final rule has been announced by the EPA. The Final Rule authorizes 32 percent of the 1991 baseline for U.S. use. The U.S. had requested 35 percent of the baseline. Methyl bromide can now be produced, sold, and used for those critical uses defined in the 2006 final rule. Among the crops included on the exemption requests were tomatoes, pepper, strawberries, cucurbits, orchard replants, and post-harvest uses.

Methyl bromide use in developed nations was scheduled to be phased out completely by January 1, 2005. However, the Montreal Protocol allows for exemptions from the phase out in critical use situations for as long as they are needed. A committee meets each year to consider nominations for the exemptions. The members determine whether there are adequate alternatives to methyl bromide for each nominated use. It is not known how long these exemptions will continue, but usage is expected to decline each year.

Nutsedge control is the main justification for a continued need for methyl bromide. Semi-suitable alternatives are available for most other soil-borne pests. None are as broad-spectrum as methyl bromide, most require a longer waiting period between application and planting, and they tend to be not as consistent as methyl bromide. The virtually-impermeable plastic films increase the effectiveness of all the fumigants, but add to costs. (SB)

3. Phytophthora Root Rot of Apple

Mefanoxam (Ridomil Gold EC) and will aid in the management of crown, collar, and other root rots caused by Phytophthora spp. on both bearing and non-bearing apple trees. Applications should be made on a preventive schedule before symptoms appear, especially in orchards where conditions are favorable for disease development. For best results, make one application at the time of planting or in the spring before growth starts. Make another application in the fall after harvest.

Dipping the roots of nursery-grown trees into a solution of the fungicide Aliette prior to planting may reduce inoculum on infested rootstocks. To use, thoroughly mix Aliette at a rate of 3.0 lbs./100 gallons of water, in the desired volume of water and dip the entire root system for 30 to 60 minutes in the mixture prior to planting in the field.

Phytophthora root rot control is also aided by improvement of drainage conditions and the use of tolerant rootstocks. (SB)

4. MaryBlyt Program for Fire Blight Management: What to Do Now

The MaryBlyt 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. Spray Water pH

In order for your pesticide sprays to perform their best, your spray water pH should be between 4.5 and 6.0. Above that, alkaline hydrolysis can cause breakdown of the active ingredients. The high cost of so many pesticides today makes good performance all the more important.

There are several commercial products available for reducing the pH of spray water, and some producers use vinegar. However, the rate to use depends on the existing pH of the water. So there are two reasons to have the pH of your spray water tested: To determine whether you need to reduce the pH, and to determine how much of the buffer (acidifying agent) you need. (SB)

6. Mating Disruption Products and Timing

Mating disruption saturates the orchard with pheromone to prevent mating and subsequent laying of fertile eggs. This reduces the populations to below economically damaging levels. Mating disruption of Oriental fruit moth (OFM) is effective only in stone fruit blocks in excess of 5 acres with low OFM populations. A one-year transition from insecticide only to a combination of insecticide and mating disruption may be required in situations with moderate to high OFM pressure. Accurately time insecticide sprays targeted at larval populations in April and May. Then, before moth flight begins in mid- to late May, place in the upper third of trees 100 of the Isomate-M100/acre for OFM (gives 90 days of control). A second application of Isomate-M100 may be needed by early August. Monitor for fruit damage weekly, especially around the edge of orchards where migrant females may lay fertile eggs. Apply insecticides to areas or blocks with damage.

The disruption of mating of codling moth in apples using Isomate CTT or CheckMate CM-XL 1000 should be initiated in the orchard before moths emerge (bloom), with hanging of the pheromone dispensers completed by petal fall. Also, supplemental sprays with an insecticide may be necessary under moderate to high population densities. Do not use mating disruption in blocks of less than 5 acres. (FH)

7. Pheromone Trap Catches

In Nashville, we have caught plenty of redbanded leafrollers (RBLR) but none of the Oriental fruit moth (OFM) and variegated leafroller (VLR). RBLR are always out in early March while many of the other key pests tend to become active in April. There have been some small unknown gray moths caught in the OFM and VLR traps starting on March 13 and March 15, respectively. They are twice the size of the actual OFM and do not look at all like the VLR. Do not count these unknown tortricid moths. It is very important that you correctly identify the first pest moths that you catch because these catches will be used to set the biofix so that future moth flights can be predicted.

The cold nights slowed down insect activity last week. None were in the trap on March 24, while recent warming temperatures have increased activity and 15 were found in the trap on March 28. (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, Professor and Extension Entomologist

fahale@utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211

Copyright 2006 The University of Tennessee. All rights reserved. This document may be reproduced and distributed for nonprofit educational purposes provided that credit is given to University of Tennessee Extension.

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