Fruit Pest News

Volume 8, No. 20  August 23, 2007

An online newsletter whose goal is to provide all interested persons with timely information on diseases and insects of commercial fruit and vegetable crops 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. Fungicide Use on Plasticulture Strawberries in the Fall

    2. Fusarium Crown and Root Rot of Pumpkin and Squash

    3. Using Sulfur on Cucurbit Crops

    4. Current Status of Cucurbit Powdery Mildew

    5. Imported Fire Ants in Fruit and Vegetable Crops

    6. Grape Root Borer and Squash Vine Borer

    7. Pheromone Trap Catches

1. Fungicide Use on Plasticulture Strawberries in the Fall

Many growers have received their tips and begun the rooting process. Disease control is a primary concern at this time. It is natural to want to spare no expense in protecting such an expensive crop. However, we should try to direct our efforts where we know they should be most effective. If we followed an intensive spray program from the time the tips are stuck until winter, and then resumed it in the early spring and continued through harvest, we would have a tremendous bill for chemicals. Plus, we would be setting ourselves up for poorer disease control and wasted spray applications in the future due to the development of resistant strains of the pathogens!

There are three main diseases with which to be concerned: Botrytis, Phytophthora crown rot, and anthracnose.

Botrytis: With the frequent misting needed to root the tips, Botrytis can get started in the plug bed. Occasional spraying with a Botryticide in the plug bed is justified. Care must be taken not to deplete your allotted number of applications per year. Many fungicides have only 4 allotted sprays per season (year). Keep in mind that crunch time for Botrytis is in the spring, during bloom. Try to include some chemistries that you may not normally use for Botrytis control, such as Rovral or Topsin M. Rovral can be used one time per year. Topsin M can be used several times, but is often good for only one application before resistance becomes a factor. Allow the spray to dry thoroughly before turning the mist system back on.

It has been speculated that a Botryticide application in the field during the fall will help reduce fruit rot the following spring. I am not aware of any research that indicates that to be true. The idea has merit in theory, since the fungus gets a foothold at that time. However, Botrytis infects young, emerging leaves throughout the fall during favorable weather conditions. To reduce this activity, fungicides would have to be applied regularly. This would be another recipe for excessive fungicide use.

Phytophthora: If you know your ground is infested with the Phytophthora crown rot fungus, make one application of Ridomil after planting and another one in the early spring. If the ground has not been known to be infested and your plants are Phytophthora-free, you do not need to make this application.

Anthracnose: Your guide for fungicide use here should be whether anthracnose was found on the plants either before or after transplanting to the field. If it was not, and the plants did not come from an infested lot, fungicides would not be needed during the fall. For anthracnose-infested fields, a minimal fungicide spray program can be followed, but keep in mind the allotted number of applications for each product. I am not aware of any research that indicates that fall applications of fungicides are beneficial in anthracnose control. I do know, from my research efforts, that anthracnose fungicides do not work well when applied during the summer for control of anthracnose runner rot in matted row strawberries.

In summary, usage of fungicides in the fall on plasticulture strawberries is faced with two main problems: (1) a lack of proof that they are beneficial and, if so, how best to use them; and (2) consumption of valuable allotted fungicide applications, and associated increased risk of resistance development. Don't feel guilty about not spraying your crop..... Sometimes, it's the best thing you can do! (SB)

2. Fusarium Crown and Root Rot of Pumpkin and Squash

Despite the dry weather, there have been a couple of cases of Fusarium crown and root rot of pumpkin. This disease is caused by a soil-borne fungus, Fusarium solani f. sp. cucurbitae, that can also cause Fusarium fruit rot. This disease is particularly problematic in Prizewinner, a popular giant pumpkin.  Usually, the first symptom noticed in the field is wilting of the leaves. Within several days, the entire plant wilts and dies. The crown area, that is, the part of the stem at the soil line is soft to the touch. Infected plants break off easily when pulled, due to the rot at the crown area. The stem rot, which extends from a couple of inches above the soil line to a couple of inches below it, is often orange in color. The rot can extend into the tap root. It begins in the cortex of the crown, causes cortex tissue to slough off, and eventually destroys all of the stem tissue except the fibrous vascular strands. The end result is a dry, fibrous, orange rot.

The causal organism is thought to live only 2 - 3 years in the soil, so a 4-year crop rotation should be effective in control. Seed transmission is possible, so fungicide seed treatments are recommended. Good soil drainage is very important, as Fusarium crown and root rot is more severe in wet soils. When the disease occurs, there is no remedial treatment for that crop. (SB)

3. Using Sulfur on Cucurbit Crops

With the resistance problems that have occurred with fungicides for control of powdery mildew of cucurbits, sulfur should be getting increased attention. Not all sulfurs are created equal, especially with regard to crop clearances, as shown in the table below. Some crops may not have clearances, not because of phytotoxicity problems, but because of company decisions not to pursue those markets. Follow the product label for crop clearances and rates to use.

There is an extra incentive to use sulfur products this year due to the increased spider mite pressure brought on by the hot, dry weather, as sulfur will provide some suppression of those pests. The high temps may cause some growers to hesitate to use sulfur because of the frequent warnings regarding possible phytotoxicity in weather over 90 degrees. These warnings are directed at cucumber and muskmelon. Pumpkin and squash should not be at risk of sulfur injury. I have sprayed summer squash at upper 90's to low 100's with 5 lb per acre and have not seen any injury. Sulfur tolerant varieties of cucumber and muskmelon are available and may warrant consideration for planting until we get more powdery mildew products labeled.

See the following article regarding the current status of cucurbit powdery mildew. (SB)

4. Current Status of Cucurbit Powdery Mildew

It has been so hot and dry that not even powdery mildew can stand it, and that is saying something! There has been very little of this disease. Some things to remember in your management efforts: (1) Powdery mildew is one of the few diseases in which you can wait until you see the disease before you begin your control program, and still get good control. You would need to begin immediately upon seeing the first colonies form, and your action would be to use a specialized fungicide (something other than mancozeb or chlorothalonil). However, until the weather changes, powdery mildew pressure should not be too severe. (2) Of the specialized powdery mildew fungicides, those that are no longer effective because of the development of resistance include the strobilurins (Quadris, Cabrio, Flint) -- Even the sterol inhibitors (Nova, Procure) have experienced a reduced effectiveness. Substitutes include sulfur (see article above) and Pristine. Also, for melons, Quintec can be used and is highly recommended. (SB)

5. Imported Fire Ants in Fruit and Vegetable Crops

Imported fire ants are definitely on the move in Tennessee. Mild winter temperatures in Tennessee have allowed these pests to greatly expand their range. They can sting in mass and some people are allergic to the sting. Workers or customers need to be protected on the farm from imported fire ants. Remember, most people have not been around imported fire ants and may not understand the potential danger. It is the responsibility of the landowner to control these pests and to provide a safe environment for both workers and customers.

The use of insecticide baits is one of the preferred methods of controlling these pests. There are a number of baits that can be used. Some are for use in residential areas, some can be used where animals graze and some can even be used in fruit and vegetable plantings. Just be sure that you read the insecticide bait label so that you pick a product that is labeled for use on the intended crop or site.

Methoprene is an insect regulator and it is the active ingredient of Extinguish Professional Fire Ant Bait. It is labeled for many outdoor site usages including cropland. I take this to mean that you can use it on any cropland. It can be applied as an individual mound treatment, a broadcast treatment, or as a hopper blend with another product. Note that when blending products, the more restrictive label will apply. Extinguish can also be used in refillable bait stations that would be placed along the perimeter of a structure or fence row every 15 to 30 linear feet. Affix a sticker to bait stations indicating the contents. In areas of heavy infestation, repeat applications may be necessary 10 to 12 weeks following the initial application.

Esteem Ant Bait utilizes the insect growth regulator active ingredient, pyriproxyfen. The worker ants take the bait back to the colony and feed it to both the ant queen and the immature ants. This causes degeneration of the reproductive organs of the queen so that she can not reproduce and the immature ants do not mature and become adults. The existing worker ants age and die. Within 3 to 4 weeks there is substantial colony mortality and within 8 weeks the majority of the colony population has been eliminated. It is labeled for use on brassica leafy vegetables, bushberries (blueberry, huckleberry, gooseberry and others), cucurbits, figs, fruiting vegetables, grape, legume vegetables (except soybean), onion (dry bulb only), pome fruits, strawberry, stone fruits, tree nuts, and other listed crops. Do not apply within 24 hours of harvest.

Esteem Ant Bait should be applied in the early spring or summer at the first sign of ant activity. In general, fire ant baits should not be applied when the grass or soil is wet. It should be put out when the ants are actively foraging, usually when the soil temperature is above 60 F. Also, avoid application if rain is expected within 4 to 6 hours and do not water the treated area within 24 hours after application. A second application may be advisable after 12 to 16 weeks in areas of heavy infestations, or when a reinfestation occurs.

Clinch Ant Bait has abamectin as the active ingredient. It is only labeled for use in potatoes and a few other crops or sites. Apply when soil temperatures are greater than 60 F. When reinfestation occurs or when large mounds remain active, retreatments may be desirable after 3 to 4 months. (FH)

6. Grape Root Borer and Squash Vine Borer

The squash vine borer pheromone trap will also catch grape root borers. On July 23, I saw two grape root borers flying around the Davidson County trap during the day. On July 26, there were 4 grape root borers in the trap and 2 more were found on July 30. On August 10, 2 squash vine bores were caught along with 14 grape root borers. Both these clearwing borers can be very destructive. The squash vine borer is more of a home garden pest than a commercial squash pest. The grape root borer can severely damage both home and commercial vineyards if preventative measures are not taken. (FH)

7. Pheromone Trap Catches for 2007

Nashville (Davidson County)
Oriental fruit moth (OFM), redbanded leafroller (RBLR), obliquebanded leafroller (OBLR), codling moth (CM), grape berry moth (GBM), variegated leafroller (VLR), black cutworm (BCW), diamondback moth (DBM), armyworm (AW), cabbage looper (CL)

* Biofix for RBLR in Davidson County was February 28.
** Biofix for OFM in Davidson County was March 26.
*** Biofix for GBM in Davidson County was April 10.
**** Biofix for OBLR in Davidson County was April 25.
^ Biofix for DBM in Davidson County was April 25.
+ Pheromone lure missing

Bradley County

Putnam County

*Biofix for RBLR in Putnam County estimated as March 2 (trap not out early enough).
**Biofix for OFM in Putnam County March 21.
***Waiting to verify biofix for CM, many unknown moths being caught in these traps that can easily be mistaken for CM.
**** Biofix for OBLR in Putnam County for OBLR was April 25.

Obion County

* Biofix for RBLR in Obion County estimated to be on March 2 (trap not out early enough).
** Biofix for OFM in Obion County on March 26.
*** Biofix for OBLR in Obion County on April 30.
**** Biofix for VLR in Obion County on April 30.

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 2007 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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