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Fruit Pest News Volume 15, No. 2 August 6, 2014

Entomology and Plant Pathology Department, University of Tennessee

In This Issue: 1. Downy Mildew Creeps In 2. Spotted Wing Drosophila Update 3. Stink Bugs 4. Basil Downy Mildew 5. Tomato Early Blight Sprays 6. Late Blight Status 7. Scenes from the Plant and Pest Diagnostic Center

1. Downy Mildew Creeps In Cucurbit downy mildew has been reported recently along the eastern and northern borders of the state, in garden cucumbers. The only TN county reporting it has been Unicoi, but I suspect it may be in other areas. In western NC, Henderson and Haywood Counties have reported downy mildew in the last week. Allen County, KY reported it two weeks ago. Last year’s experience reminds us of the need to remain vigilant and be prepared, as many fields were wrecked by this disease. All cucurbit crops should be protect-ed with sprays of chlorothalonil or mancozeb, applied every 7 to 10 days. It is diffi-cult to play catch-up using the site-specific fungicides (Ranman, Presidio, etc.) after a spore shower arrives on an air current, and the disease is suddenly upon you. Dry weather has to assist you, in order for these “curative” fungicides to be effec-tive. You can find the full map of reported cases at http://cdm.ipmpipe.org/. Given the location of the sites, I would consider the whole state to be under alert. Keep pro-tectant sprays of chlorothalonil or mancozeb on your cucurbit crops and, if downy mildew appears in your field, add site-specific fungicides. (SB)

2. Spotted Wing Drosophila Update At least 23 Tennessee Counties are currently positive for spotted wing drosophila (SWD). If a grower has not put out traps for this pest, insecticide sprays should be made to protect the small fruit or cherry crops just in case the pest is already there. Traps should then be put out and checked regularly for SWD. This pest has spread quickly across the country since it was found in central California in 2008. It could potentially be in any part of the country where fruit is grown or where wild fruit are found. This pest tends to start out at relatively low numbers in the spring and builds throughout the summer into the fall. Thus, pest pressure is lower for early crops such as strawberries and sour cherries in the spring and builds for blueberry and bramble crops in the summer and continues to build for grapes and fall bearing raspberries. SWD are being caught in traps in Kentucky and North Carolina although we have not caught any yet at our single trap in Nashville. They should be active and we expect to catch some soon. If you are running traps, please let us know the date of your first catch. (FH) 3. Stink Bugs Stink bugs are one of those pests that can sneak up on you. Depending on the crop, the damage might not show up until well after the feeding has occurred. For this reason, chemical control needs to be proactive. Scouting of fruit and vegetable crops is an important part of controlling stink bugs and the damage they cause. Many insects including stink bugs move into vegetable fields and orchard blocks from surrounding areas where they overwinter. The new invasive pest, the

Figure 1. Downy mildew on cucumber (top) and pumpkin (bottom) leaves .

Figure 2. Blueberry showing egg-laying scars of spotted wing drosophila.

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brown marmorated stink bug overwinters inside buildings, under tree bark and in hollow trees. Once they move into the field and start feeding, they release an aggregation pheromone that attracts both males and females. Thus, it is beneficial to visually inspect around the edge of fields to deter-mine when they are moving toward and into the field. Inspect trees and weeds around field edges for stink bugs or use a beat tray or sweep net. If stink bugs are detected on the field edge, an insecticide spray can be made around the edge and several rows into the field. Continue to inspect in the field to determine if the whole field needs to be

treated. Pay particular attention to inspecting the fruit or marketable part of

the plant for stink bugs and other direct feeders. Sample fields twice a week

by making a zigzag pattern across the field. Make 6 stops for a 1-5 acre

field and 1 stop per acre for a 6-10 acre field with 8 stops maximum. At

each stop, sample 6 feet of row. Count the number of live stink bugs in each

6 foot sample. The threshold level for live stink bugs is an average of 0.5

stink bug per 6 foot sample. The other count is made by checking 10 fruit

per 6 feet of row for stink bug injury (the same 10 fruit examined for corn

earworm (tomato fruitworm) injury). The economic threshold for fruit dam-

age from stink bugs is an average of ½ % fruit damage (one damage fruit

out of 200 checked). (FH)

4. Basil Downy Mildew This disease is widespread this year, largely due to the sale of infected plants at garden centers. You may have downy mildew in your basil and not know it, as the symptoms are subtle. The plants may just appear to have a nutrient deficiency, as in Figure 4. What appears to be a poor-quality leaf becomes much poorer after harvest. What to do? An infected leaf is unsalable. And quite often, all leaves are infected, if the basil type is very susceptible, such as certain sweet basil varieties. For less susceptible varieties, grown in full sun with good plant spacing, fungicide sprays will help protect uninfected leaves. Ranman, Quadris, and phosphorous acid products are some of the best perform-ing fungicides that are labeled for use on basil. Revus and potassium bicarbonates are also labeled. For the organic grower, Actinovate, Dou-ble Nickel, Milstop, Regalia, Trilogy, and Oxidate are NOP approved. Note: Before using any of these products in greenhouses, check the label to make sure this use is not prohibited. (SB) 5. Tomato Early Blight Sprays

Tomato growers should remember to use alternatives to the Group 11 fungicides (Quadris, Cabrio, Tanos), as resistance to this group appears to be widespread in the early blight fungus. Programs that alternate a Group M (chlorothalonil or mancozeb), Inspire Super, and Fontelis have worked well. If you spray frequently, you will need this three-way rotation, as Inspire Super and Fontelis have strict limitations on the number of applications. Additional information on the tomato spray program is available at https://ag.tennessee.edu/EPP/Documents/tomato%20spray%20program.pdf . (SB) 6. Late Blight Status Given the unexpected outbreaks of late blight last year, it appears that this disease has re-entered our consciousness. It was reported in a garden in Henderson County, North Carolina in late June. However, the hot, dry weather appears to have stamped it out. There have been no other reports nearby. (SB)

Figure 3. Brown marmorated stink bug.

Figure 5. Early blight of tomato.

Figure 4. These basil plants appear to have a nutrient deficiency, but these symptoms are caused by downy mildew in this case.

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Scenes from the Plant and Pest Diagnostic Center

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

Copyright 2014 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. Programs in agriculture and natural resources, 4-H youth development, family and consumer sciences, and re-

source development. University of Tennessee Institute of Agriculture, U.S. Department of Agriculture and county governments cooperating. UT Extension provides

equal opportunities in programs and employment.

615-832-6802

fax 615-781-2568

Soil, Plant and Pest Center

5201 Marchant Drive

Nashville, TN 37211

Fig. 9. Coulure is a physiological condition thought to be caused by alternating conditions of dry/wet or hot/cold during bud break. The grapevine begins to move sap past the embryonic grape clusters to the shoot-tips, depriving the cluster of the nutrients that it needs to develop. The berries at the distal end of the cluster only partially develop and the rachis dries.

Fig. 6. Aminopyralid herbicide injury can occur when hay or animal manure from sprayed pas-tures is used in vegetable plantings. In this gar-den, horse manure was aged 6 months before incorporation, and still caused this damage.

Fig. 7. Two-spotted spi-der mite-affected tomato leaflets (three on left) and a non-infested leaf-let (right). The dull leaf appearance and the chlorotic stippling along the midrib are the first clues of mite presence. Check the undersides with a hand lens. Treat before damage pro-gresses any farther.

Fig. 8. Genetic silver-ing of pumpkin leaves, also occurs on squash. Those who are not familiar with this symptom can be thrown for a loop, because it does not occur on all leaves, giving it the appear-ance of a disease. It is a perfectly normal condition.

Fig. 10. When this condi-tion occurs on apple trees, it can be confused with fire blight. Howev-er, the terminal leaves remain green, and the shoots (one- and two-year old) do not die. Botryosphaeria has been isolated from the spurs, but it is not clear whether that fungus is the cause of the dead leaves and spurs or is just second-ary. This condition has an uncertain cause.

Photo credits: Figures 1a,1b,4,5,7,9,10 by Steve Bost; 2,3 by Frank Hale; 6 was submitted; 8 by Becky Muller.