Fruit Pest News

April 16, 2001

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 Crop Status

2. Apple: Fire Blight Status

3. Apple: Disease Control During Bloom and at Petal Fall

4. Tree Fruit: Insect Update

5. Blackberries: Watch For Rosette Disease

1. CURRENT CROP STATUS

Crops developed rapidly with last week's unseasonably warm weather. Peaches at the Plant and Pest Diagnostic Center are now at shuck fall, apples are nearing the end of bloom, and blackberries are approaching white tip. The accelerated development of peaches and apples will be beneficial this week, when light frost is predicted on April 18. Frost protection may be needed on strawberries and blueberries, as most varieties are still in bloom. (SB)

2. FIRE BLIGHT STATUS

Last week's hot weather resulted in fire blight infections on days on which moisture was available. The MaryBlyt model indicated infection each day from April 12 through 15. Three of those days saw showers or storms, and a heavy dew occurred on one day. Light dews occurred earlier in the week, probably too light to cause infection. The risk of infection is now medium and should remain low to medium for the remainder of the week because of the cool temperatures. The epiphytic inoculum potential (the amount of bacteria on blossom surface) is now low, and the temperatures for the next few days should be too low for infection (daily average less than 60 F). When high-risk conditions continue for several days after an application of streptomycin, re-apply in 4 days. (SB)

3. APPLE: DISEASE CONTROL DURING BLOOM AND AT PETAL FALL

Most apple trees in Tennessee are now in bloom, and some may be at petal fall. The upcoming cool weather will extend the bloom period for those trees at that stage of growth. A fungicide application may be needed during bloom when this stage is extended by cool weather. It is unwise to allow more than 10 days between fungicide applications at this time of year. Scab and powdery mildew operate well under cool conditions, and 10 days is as long as control can be expected by the fungicides we use for these diseases.

A contact fungicide such as mancozeb or ziram may be sufficient for the bloom-time spray, if the spray is applied only 6 or 7 days after the pink tip spray. Fungicides with lengthy kick-back activity should not be necessary in such case. Consider tank-mixing the fungicide with streptomycin in fire blight-susceptible blocks.

Petal fall and first cover is a peak risk period for powdery mildew, cedar-apple rust, and fruit infection by scab. Use a sterol inhibitor (Nova, Rubigan, or Procure) with a contact fungicide at each of these growth stages. (SB)

4. TREE FRUIT: INSECT UPDATE

Redbanded leafrollers have been found feeding and curling up leaves on apple at our Nashville (Davidson Co.) location. The moths were found when I first checked last years pheromone traps on March 26. One larva found today was 9 mm long (almost 2/5 inch long).

Oriental fruit moth (OFM) and codling moth (CM) adults are being caught in our traps but not signs of larvae yet. The biofix for Oriental fruit moth (trap catches exceed 5 moths per trap per week) has occurred April 9 for Putnam Co., April 12 for Bradley Co., and probably around April 9 (caught 23 moths between April 6 and 12) for Davidson Co. The Obion Co. traps were just recently put out so we do not know if Oriental fruit moths have been active at that location yet. Since we have caught them in our other locations, there is reason to expect that the moths have been active although none were caught in Obion Co. the week of April 9.

In general, Oriental fruit moth eggs hatch by Petal Fall for apples. Oriental fruit moth DD models use a base temperature of 45F. First generation egg laying is usually low on apple, and only one insecticide application 500 to 600 DD after biofix is necessary. As of April 15 there are 170.8 DD accumulated since the April 9 biofix. This weeks cool daytime and cold night temperatures should slow development down.

In peaches the biofix for Oriental fruit moth (OFM) begins with the first sustained catch of 2 or more moths in the spring. The biofix was April 6 for the Putnam Co. orchard and the estimated biofix was April 9 (0 caught on April 6 and 23 found in trap when checked on April 12; I should have checked trap more often) for Davidson Co. Low OFM density orchards are those with less than 0.5 percent of fruit damaged the previous year and pheromone trap catches not exceeding 10 moths/trap/week anytime before the accumulation of 500 DD after biofix. There were 23 OFM in trap on April 12 in Davidson Co. so this would be a moderate to high OFM density orchard which would require two insecticide applications applied 14 days apart, the first at 500 DD after biofix for first generation OFM. As of April 15 there were 170.8 DD accumulated since the April 9 biofix so we have some time before the first spray, especially considering the expected cold weather. For your information, a low density OFM density orchard would require a single insecticide application at 600 DD after biofix.

The biofix for codling moth (the first sustained catch of 2 or more moths in the spring) was April 13 (possibly earlier) for Obion Co. and April 4 for Davidson Co. A biofix was not determined yet for the other sites. Codling moth DD models use a base temperature of 50F. As of April 15 there were 232 DD accumulated at the Davidson Co. location. At low density orchards (less than 0.5 percent of fruit damaged the previous year and pheromone traps that do not exceed 10 moths per trap anytime before the accumulation of 200 DD after biofix) a single insecticide application can be made at 350 DD after biofix. Moderate to high density orchards will have had higher fruit damage the previous year or higher pheromone trap catches than with low density orchards. In the Davidson Co. trap we had a catch of 12 codling moths on April 4 and one on April 6 so we are in the moderate density orchard category. In moderate to high density orchards, two insecticide applications are applied 14 days apart, the first at 150 to 250 DD after biofix. Treat beginning at 150 DD if using a product which is primarily ovicidal (i.e., Confirm or Intrepid), and begin treatments at 250 DD if using a product which has contact activity against larvae (i.e., organophosphate or pyrethroid). Since we plan to use an organophosphate and we already have 232 DD, we are very near the 250 DD where we will begin treatments. If we had not caught so many codling moths on April 4 (12 caught) and instead not exceeded 10 moths per trap per week we would call this a low density orchard and could get by with a single insecticide application at 350 DD after biofix. (FH)

                            Obion Co.(traps put out April 9)

                            Bradley Co.

                            Putnam Co.(traps put out 4-4-01)

Davidson Co. (OFM and RBLR traps put out 3-26, The 8 RBLR on 3-26

were found in last year's trap. The OBLR and CM traps put out 4-2)

5. BLACKBERRY GROWERS: WATCH FOR ROSETTE DISEASE

Blackberries are preparing to bloom already. Growers need to be prepared to look for evidence of rosette, also known as double blossom. This fungal disease can be very destructive, and indeed has been known to drive growers out of the blackberry business. The fungus can drastically reduce yields by causing sterility of the blossoms and through its debilitating effect on the plant.

The key to managing rosette is to remove the infected blossom clusters before the blossoms open. That is because all of the spores that cause new infections come from infected blossoms. The infected blossom clusters should now be apparent. They are recognized as bunchy growths consisting of multiple shoots, rather than the normal single shoot. Such growths are known as rosettes or witch's brooms. The sepals (the green, leaf-like structures that enclose blossoms) are abnormally long and pointed. When the blossoms open, they will be pinkish and ruffled.

Fungicide applications will help to control infections that result from spores that enter the planting from nearby wild blackberries. Benlate alternated with copper fungicides can be applied at 10-14 day intervals, beginning about 6 weeks before harvest. Do not expect the applications to control rosette in this year's crop. Fungicides applied this year control rosette in next year's crop by protecting the new primocanes. Any rosettes you see this year arose from infections that occurred on last year's primocanes.

Fungicidal control also has a place if you do not currently have rosette, but are growing a susceptible variety. Shawnee is particularly susceptible. Cherokee, Comanche, and Black Satin are also quite susceptible. Chester, Hull, Lock Ness, Arapaho, and Navaho have good tolerance, and the recent variety Triple Crown has not had any serious problems to my knowledge. (SB)

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