FRUIT IPM UPDATE #5. What s New? July 18, 2017

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FRUIT IPM UPDATE #5 July 18, 2017 What s New? Apple Scab Infections...1-4 SWD and Japanese Beetle...4-5 Apple Pest Counts.5 Apple Scab Infections.

this year. In a few cases, apple scab on the fruit is primarily cosmetic (Figure 1), but this year apple scab is causing major crop losses.

1 FRUIT IPM UPDATE #5 July 18, 2017 What s New? Apple Scab Infections SWD and Japanese Beetle Apple Pest Counts.5 Apple Scab Infections... 6 Secondary Apple Scab Infections Thaddeus McCamant, Specialty Crops Management Specialist, Central Lakes College Many growers are reporting a high incidence of apple scab in susceptible cultivars this year. In a few cases, apple scab on the fruit is primarily cosmetic (Figure 1), but this year apple scab is causing major crop losses. In some cultivars, infected fruit fell off, resulting in extremely poor fruit sets. In many cases, there are multiple lesions that severely stunt the fruit, or the lesions have started cracking (Figure 2). Figure 2. Zestar! apple with multiple apple scab lesions. Apple scab on the fruit is frequently misdiagnosed. Russetting can also cause the apples to crack, but russetting typically covers a larger part of the apple, is always a brown color, and has lines (Figure 3). Damage from leafroller feeding can only be distinguished from apple scab with close inspection. Leafroller damage is frequently irregular, has a brown color, and rarely cracks. Apple scab is gray to black, the lesions are usually round, and a high percentage of apples will have multiple lesions, whereas leafroller damage is typically one damaged area per apple. Figure 1. Minor apple scab injury in Zestar! Apple Pest Update #6, July 18,

Figure 3. Russetting on Haralson and leafroller feeding injury (bottom) are often mistaken for apple scab.

The tops of the leaves often have small chlorotic spots (Figure 4), and with severe infections, leaves develop bumpy areas (Figure 5).

In most varieties, the scab forms irregular spots, while in a few varieties, the scab will grow in creases formed by the leaf veins.

Like most fungal diseases, apple scab is dispersed through the air. Fungal structures in the leaves eject spores which move through the air.

2 Figure 3. Russetting on Haralson and leafroller feeding injury (bottom) are often mistaken for apple scab. Apple scab also infects leaves, but the symptoms vary somewhat from variety to variety. The tops of the leaves often have small chlorotic spots (Figure 4), and with severe infections, leaves develop bumpy areas (Figure 5). The most distinctive part of apple scab are the brown areas that grow to give the leaves a moldy appearance. In most varieties, the scab forms irregular spots, while in a few varieties, the scab will grow in creases formed by the leaf veins. The brown spots are the spore producing structures of the fungi. Figure 4. Top and bottom of heavily infected Minnieska leaf. Like most fungal diseases, apple scab is dispersed through the air. Fungal structures in the leaves eject spores which move through the air. Infection only occurs when the leaves remain wet for a specified period of time. If the temperature is 75 F, the leaves only need to wet for 8 hours for an infection to occur. The leaves must be wet for a longer period of time at cooler temperatures. In May, some growers had several days of leaf wetness, but the weather was cool. Even at 50 F, a heavy infection can form after 26 hours of leaf wetness. Apple scab has a long latent period, and in some cases, the infections did not show up until June, catching many people by surprise. Apple Pest Update #6, July 18,

Secondary infections occur in orchards where infections started during the primary infection period, and then growers have to be concerned about the disease spreading for the duration of the summer.

3 infection period, the orchard will have no apple scab for the duration of the summer. Many apple growers either reduce or eliminate fungicide sprays in late summer if they achieve complete control during the primary infection period. Secondary infections occur in orchards where infections started during the primary infection period, and then growers have to be concerned about the disease spreading for the duration of the summer. The apple scab fungi continue to produce spores that can then infect other leaves. Secondary infections primarily spread from leaf to leaf. Infections on apple fruit are rare during much of the secondary infection period, and then the scab primarily forms small lesions or pinpoint scab. At this point, we don t know exactly why many growers have apple scab in spite of spraying fungicides through the primary infection period. Some growers struggled to find times when the ground was dry enough to drive through the fields. There is also the real possibility that the apple scab fungus is becoming resistant to some fungicides. Apple scab has shown an incredible ability to develop resistance to many fungicides. Generally, resistance to specific fungicides has shown up in other apple districts before Minnesota. In other states, resistance has been documented for sterol inhibitors (myclobutanil or Rally) and benzimidazoles (thiophanate methyl or Topsin M). Figure 5. Top and bottom of a Zestar! leaf infected with apple scab. Apple scab has two phases during the growing season. During the primary infection period, the fungi that overwintered on fallen leaves send out spores which start new infections for the year. The period of primary infection lasts a little over one month. Most apple fruit are infected during the primary infection period. If no leaves are infected during the primary There is little consensus about how aggressive growers should treat secondary apple scab infections. In some cases, the fungi die after a long, hot, dry spell. When the weather stays wet, many producers continue to spray fungicides on a 7 to 10 day schedule until harvest. The best fungicides to use now is the multisite protectant fungicide Captan, which shows a potential for resistance development. The broad spectrum protectant fungicides that belong to the dithiocarbamate group (mancozeb and others) have long pre-harvest intervals and cannot be sprayed at this time. In late July, sooty blotch and flyspeck start to grow on the fruit, and Captan will help protect the apples from those fungi as well. Apple Pest Update #6, July 18,

Growers with secondary infections will have a large number of overwintering sites for the apple scab fungus and will need to develop aggressive means to control the fungus and protect next year s

Spotted Wing Drosophila (SWD) and Japanese Beetle (JB) Update Bill Hutchison, Eric Burkness, Dominique Ebbenga, Suzanne Wold-Burkness MN Extension IPM Program, Dept.

4 Growers with secondary infections will have a large number of overwintering sites for the apple scab fungus and will need to develop aggressive means to control the fungus and protect next year s crop. Late season apple scab control measures will be discussed in a later newsletter. Spotted Wing Drosophila (SWD) and Japanese Beetle (JB) Update Bill Hutchison, Eric Burkness, Dominique Ebbenga, Suzanne Wold-Burkness MN Extension IPM Program, Dept. of Entomology, University of Minnesota Spotted Wing Drosophila Update Harvest of June bearing strawberries should be complete across the state and in southern Minnesota, and the harvest of summer bearing raspberries and most blueberry varieties should be coming to end. However, any thin skinned soft fruit that is ripening or ripe at this point (day neutral strawberry, raspberry, blackberry, blueberry, cherry) is susceptible and now at high risk for SWD infestation. Numbers of SWD in traps continue to increase across the state. All traps were positive this week with the highest single trap catch at ~5,000 flies per trap in one week in southern Minnesota. Traps in the Twin Cities Metro are generally between flies per trap. Unfortunately, fly numbers could go even higher than 5,000 per trap and management strategies will have to remain in place to protect fruit until the end of harvest. In addition to trying to maintain shorter spray intervals of 5 days and trying to practice clean harvests and sanitation to eliminate excess fruit remaining on plants or the ground, we remind growers to store fruit under refrigerated conditions prior to sale, if possible. Cooling the fruit can cause mortality to SWD eggs and larvae and will slow development as well. For updated SWD trap catch (sorted by location and berry type) and reference materials on management options, please visit: If you plan to make insecticide applications to manage SWD, please make sure to carefully read and follow the directions on the label of the insecticide. SWD adult male, with characteristics spots on wings and SWD trap in row of raspberries. Japanese Beetle Update The first Japanese beetles of the season were observed on raspberry during the last week of June in Rosemount, MN. Populations have been relatively low until the past week. They have increased rapidly and winter survival was likely high, which has contributed to higher populations this summer compared with Japanese beetle has a wide host range that includes many types of fruits, including: raspberries, apples, grapes, and ornamental plants and trees. Adults are typically active in late June and throughout July. Egg lay occurs in July in weedy grass areas or turf, and after egg hatch larvae (white grubs) that feeds on developing roots in the soil. To view the current distribution of Japanese beetle in Minnesota visit: nesebeetle.aspx If you ve had issues with Japanese beetle in the past, you will likely have issues this year as well. Spot spraying (only treating areas where the beetles are present) with an insecticide (for example products containing the active Apple Pest Update #6, July 18,

So an infestation should continue to be monitored until about mid-august when adults begin to die and populations decline.

5 ingredient carbaryl) will typically work well. However, as populations increase, treating an entire crop or planting may be necessary. Because the beetle population can be high in an area this year, re-infestation is likely as the insecticide residues degrade. So an infestation should continue to be monitored until about mid-august when adults begin to die and populations decline. If Japanese beetle traps are used, it is typically a good idea to locate the traps away from the crop to draw them off of the plants you are trying to protect. For information regarding management of Japanese beetle populations please visit: If you plan to make insecticide applications to manage Japanese beetle, please make sure to carefully read and follow the directions on the label of the insecticide. Japanese beetle adult on raspberry fruit and leaves, with characteristic white tufts of hairs on the side of the abdomen, and metallic bronze and green coloration. Apple Pest Update #6, July 18,

6 County Location 2017 Degree Days (Dates)* Apple Insect Pests: Weekly Trap Counts for 2017 Dates Traps were Out in Orchard CM DWB LAW OBLR RBLR STLM AM Dakota Lakeville (04-05 to 07-18) to , Houston La Crescent (04-01 to 07-18) to , 5, 3 Morrison Little Falls to , 7, 1 Nobles Worthington (04-01 to 07-18) to , 0, 0 Rice Faribault (04-21 to 07-17) to ~ Scott Veseli (04-01 to to , 3, 2 St. Louis City of Duluth to St. Louis Duluth (03-29 to 07-19) to Wabasha Elgin (04-01 to 07-19) to , 1, 0 Wabasha Lake City - Site (04-01 to 07-19) to , 0, 0 Washington Afton (04-01 to 07-11) to Washington Washington Hastings Site 1 Hastings Site (04-01 to 07-17) to , 0, , 0, (04-01 to 07-18) to , 2, Washington Hugo to , 1, 2 Washington White Bear Lake (04-01 to 07-18) to , 1, 1 Wright Buffalo (04-01 to 07-18) to >1000 0, 2, 6 Wright Delano (04-01 to 07-17) to , 7, 5 KEY: AM = apple maggot, CM = codling moth, DWB = dogwood borer, LAW = lesser apple worm, OBLR = obliquebanded leafroller, RBLR = redbanded leafroller, STLM = spotted tentiform leafminer, AM = apple maggot --- = no data provided. * Degree days using Spec 7 Pro or Spec 8 Pro = cumulative or integral degree days (uses hourly temperatures), with calculation parameters of Base Temp = 50 o F and Upper Limit = 86 o F. Apple Pest Update #6, July 18,

7 2017 Apple Scab Infections (Cornell Model) Produced using Spec 7 Pro or Spec 8 Pro (Spectrum Technologies, Inc.) (Parameters: Base temp. = 33 degrees F, Upper limit temp. = 78 degrees F, Wetness threshold = 6) Orchard # of Infection Periods Infection Period Dates Overall Hours of Wetness 2017 Dates Duluth , thru Faribault thru Hastings Site , 07-13, 07-14, 07-15, thru Lakeville thru Veseli thru DISCLAIMER References to products in this Newsletter are not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current manufacturer directions. 625 Robert Street North St. Paul, MN In accordance with the Americans with Disabilities Act, this information is available in alternative forms of communication upon request by calling TTY users can call the Minnesota Relay Service at 711. The MDA is an equal opportunity employer and provider. Apple Pest Update #6, July 18,

CROP PROTECTANTS: Science K-5

CROP PROTECTANTS: Science K-5 Meets North Carolina Standard Course of Study Apple Pest, Disease, and Predators Apple Disease Pests Photos Monitoring Apple Orchards for Pest, Disease, and Predators Most